WO2018010030A1 - Machine électrique et procédé d'alignement - Google Patents

Machine électrique et procédé d'alignement Download PDF

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Publication number
WO2018010030A1
WO2018010030A1 PCT/CA2017/050856 CA2017050856W WO2018010030A1 WO 2018010030 A1 WO2018010030 A1 WO 2018010030A1 CA 2017050856 W CA2017050856 W CA 2017050856W WO 2018010030 A1 WO2018010030 A1 WO 2018010030A1
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WO
WIPO (PCT)
Prior art keywords
carrier
stator
rotor
posts
post
Prior art date
Application number
PCT/CA2017/050856
Other languages
English (en)
Inventor
James Brent Klassen
Damian SPASOV
Original Assignee
Genesis Robotics Llp
Priority date (The priority date is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the date listed.)
Filing date
Publication date
Priority claimed from US15/235,088 external-priority patent/US10476323B2/en
Application filed by Genesis Robotics Llp filed Critical Genesis Robotics Llp
Publication of WO2018010030A1 publication Critical patent/WO2018010030A1/fr

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Classifications

    • H—ELECTRICITY
    • H02—GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
    • H02K—DYNAMO-ELECTRIC MACHINES
    • H02K7/00—Arrangements for handling mechanical energy structurally associated with dynamo-electric machines, e.g. structural association with mechanical driving motors or auxiliary dynamo-electric machines
    • H02K7/08—Structural association with bearings
    • H02K7/086—Structural association with bearings radially supporting the rotor around a fixed spindle; radially supporting the rotor directly
    • H02K7/088—Structural association with bearings radially supporting the rotor around a fixed spindle; radially supporting the rotor directly radially supporting the rotor directly
    • H—ELECTRICITY
    • H02—GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
    • H02K—DYNAMO-ELECTRIC MACHINES
    • H02K16/00—Machines with more than one rotor or stator
    • H02K16/04—Machines with one rotor and two stators
    • H—ELECTRICITY
    • H02—GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
    • H02K—DYNAMO-ELECTRIC MACHINES
    • H02K1/00—Details of the magnetic circuit
    • H02K1/06—Details of the magnetic circuit characterised by the shape, form or construction
    • H02K1/22—Rotating parts of the magnetic circuit
    • H02K1/27—Rotor cores with permanent magnets
    • H02K1/2793—Rotors axially facing stators
    • H02K1/2795—Rotors axially facing stators the rotor consisting of two or more circumferentially positioned magnets
    • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F16—ENGINEERING ELEMENTS AND UNITS; GENERAL MEASURES FOR PRODUCING AND MAINTAINING EFFECTIVE FUNCTIONING OF MACHINES OR INSTALLATIONS; THERMAL INSULATION IN GENERAL
    • F16C—SHAFTS; FLEXIBLE SHAFTS; ELEMENTS OR CRANKSHAFT MECHANISMS; ROTARY BODIES OTHER THAN GEARING ELEMENTS; BEARINGS
    • F16C19/00—Bearings with rolling contact, for exclusively rotary movement
    • F16C19/02—Bearings with rolling contact, for exclusively rotary movement with bearing balls essentially of the same size in one or more circular rows
    • F16C19/14—Bearings with rolling contact, for exclusively rotary movement with bearing balls essentially of the same size in one or more circular rows for both radial and axial load
    • F16C19/18—Bearings with rolling contact, for exclusively rotary movement with bearing balls essentially of the same size in one or more circular rows for both radial and axial load with two or more rows of balls
    • F16C19/188—Bearings with rolling contact, for exclusively rotary movement with bearing balls essentially of the same size in one or more circular rows for both radial and axial load with two or more rows of balls with at least one row for radial load in combination with at least one row for axial load
    • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F16—ENGINEERING ELEMENTS AND UNITS; GENERAL MEASURES FOR PRODUCING AND MAINTAINING EFFECTIVE FUNCTIONING OF MACHINES OR INSTALLATIONS; THERMAL INSULATION IN GENERAL
    • F16C—SHAFTS; FLEXIBLE SHAFTS; ELEMENTS OR CRANKSHAFT MECHANISMS; ROTARY BODIES OTHER THAN GEARING ELEMENTS; BEARINGS
    • F16C19/00—Bearings with rolling contact, for exclusively rotary movement
    • F16C19/54—Systems consisting of a plurality of bearings with rolling friction
    • F16C19/545—Systems comprising at least one rolling bearing for radial load in combination with at least one rolling bearing for axial load
    • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F16—ENGINEERING ELEMENTS AND UNITS; GENERAL MEASURES FOR PRODUCING AND MAINTAINING EFFECTIVE FUNCTIONING OF MACHINES OR INSTALLATIONS; THERMAL INSULATION IN GENERAL
    • F16C—SHAFTS; FLEXIBLE SHAFTS; ELEMENTS OR CRANKSHAFT MECHANISMS; ROTARY BODIES OTHER THAN GEARING ELEMENTS; BEARINGS
    • F16C35/00—Rigid support of bearing units; Housings, e.g. caps, covers
    • F16C35/04—Rigid support of bearing units; Housings, e.g. caps, covers in the case of ball or roller bearings
    • F16C35/06—Mounting or dismounting of ball or roller bearings; Fixing them onto shaft or in housing
    • F16C35/067—Fixing them in a housing
    • H—ELECTRICITY
    • H02—GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
    • H02K—DYNAMO-ELECTRIC MACHINES
    • H02K1/00—Details of the magnetic circuit
    • H02K1/06—Details of the magnetic circuit characterised by the shape, form or construction
    • H02K1/12—Stationary parts of the magnetic circuit
    • H02K1/14—Stator cores with salient poles
    • H02K1/146—Stator cores with salient poles consisting of a generally annular yoke with salient poles
    • H—ELECTRICITY
    • H02—GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
    • H02K—DYNAMO-ELECTRIC MACHINES
    • H02K15/00—Methods or apparatus specially adapted for manufacturing, assembling, maintaining or repairing of dynamo-electric machines
    • H02K15/16—Centering rotors within the stator; Balancing rotors
    • H—ELECTRICITY
    • H02—GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
    • H02K—DYNAMO-ELECTRIC MACHINES
    • H02K21/00—Synchronous motors having permanent magnets; Synchronous generators having permanent magnets
    • H02K21/12—Synchronous motors having permanent magnets; Synchronous generators having permanent magnets with stationary armatures and rotating magnets
    • H02K21/24—Synchronous motors having permanent magnets; Synchronous generators having permanent magnets with stationary armatures and rotating magnets with magnets axially facing the armatures, e.g. hub-type cycle dynamos
    • H—ELECTRICITY
    • H02—GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
    • H02K—DYNAMO-ELECTRIC MACHINES
    • H02K7/00—Arrangements for handling mechanical energy structurally associated with dynamo-electric machines, e.g. structural association with mechanical driving motors or auxiliary dynamo-electric machines
    • H02K7/08—Structural association with bearings
    • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F16—ENGINEERING ELEMENTS AND UNITS; GENERAL MEASURES FOR PRODUCING AND MAINTAINING EFFECTIVE FUNCTIONING OF MACHINES OR INSTALLATIONS; THERMAL INSULATION IN GENERAL
    • F16C—SHAFTS; FLEXIBLE SHAFTS; ELEMENTS OR CRANKSHAFT MECHANISMS; ROTARY BODIES OTHER THAN GEARING ELEMENTS; BEARINGS
    • F16C19/00—Bearings with rolling contact, for exclusively rotary movement
    • F16C19/02—Bearings with rolling contact, for exclusively rotary movement with bearing balls essentially of the same size in one or more circular rows
    • F16C19/10—Bearings with rolling contact, for exclusively rotary movement with bearing balls essentially of the same size in one or more circular rows for axial load mainly
    • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F16—ENGINEERING ELEMENTS AND UNITS; GENERAL MEASURES FOR PRODUCING AND MAINTAINING EFFECTIVE FUNCTIONING OF MACHINES OR INSTALLATIONS; THERMAL INSULATION IN GENERAL
    • F16C—SHAFTS; FLEXIBLE SHAFTS; ELEMENTS OR CRANKSHAFT MECHANISMS; ROTARY BODIES OTHER THAN GEARING ELEMENTS; BEARINGS
    • F16C19/00—Bearings with rolling contact, for exclusively rotary movement
    • F16C19/49—Bearings with both balls and rollers
    • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F16—ENGINEERING ELEMENTS AND UNITS; GENERAL MEASURES FOR PRODUCING AND MAINTAINING EFFECTIVE FUNCTIONING OF MACHINES OR INSTALLATIONS; THERMAL INSULATION IN GENERAL
    • F16C—SHAFTS; FLEXIBLE SHAFTS; ELEMENTS OR CRANKSHAFT MECHANISMS; ROTARY BODIES OTHER THAN GEARING ELEMENTS; BEARINGS
    • F16C2322/00—Apparatus used in shaping articles
    • F16C2322/50—Hand tools, workshop equipment or manipulators
    • F16C2322/59—Manipulators, e.g. robot arms
    • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F16—ENGINEERING ELEMENTS AND UNITS; GENERAL MEASURES FOR PRODUCING AND MAINTAINING EFFECTIVE FUNCTIONING OF MACHINES OR INSTALLATIONS; THERMAL INSULATION IN GENERAL
    • F16C—SHAFTS; FLEXIBLE SHAFTS; ELEMENTS OR CRANKSHAFT MECHANISMS; ROTARY BODIES OTHER THAN GEARING ELEMENTS; BEARINGS
    • F16C2380/00—Electrical apparatus
    • F16C2380/26—Dynamo-electric machines or combinations therewith, e.g. electro-motors and generators
    • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F16—ENGINEERING ELEMENTS AND UNITS; GENERAL MEASURES FOR PRODUCING AND MAINTAINING EFFECTIVE FUNCTIONING OF MACHINES OR INSTALLATIONS; THERMAL INSULATION IN GENERAL
    • F16C—SHAFTS; FLEXIBLE SHAFTS; ELEMENTS OR CRANKSHAFT MECHANISMS; ROTARY BODIES OTHER THAN GEARING ELEMENTS; BEARINGS
    • F16C35/00—Rigid support of bearing units; Housings, e.g. caps, covers
    • F16C35/04—Rigid support of bearing units; Housings, e.g. caps, covers in the case of ball or roller bearings
    • F16C35/06—Mounting or dismounting of ball or roller bearings; Fixing them onto shaft or in housing
    • F16C35/061—Mounting or dismounting of ball or roller bearings; Fixing them onto shaft or in housing mounting a plurality of bearings side by side

Definitions

  • Electric machines typically use electrically conductive wire turns wrapped around soft magnetic stator posts (teeth) to generate flux.
  • the manufacturing process for this type of motor construction can be time consuming and expensive.
  • such motors typically have a torque to mass ratio that makes them relatively heavy for mobile actuator applications such as in robotics where the weight of a downstream actuator must be supported and accelerated by an upstream actuator.
  • the inventor has proposed an electric machine with a novel range of structural parameters particularly suited for robotics, along with additional novel features of an electric machine.
  • a method of aligning a plurality of electromagnetic elements in an electric machine comprises a first carrier having an array of electromagnetic elements and a second carrier having an array of posts defining slots between each post.
  • the second carrier is arranged to move relative to the first carrier.
  • the first carrier and the second carrier are placed in axial alignment.
  • the first carrier and second carrier are arranged so that an airgap is formed between the first carrier and the second carrier.
  • a plurality of permanent magnets is provided, each having a pair of magnetic poles.
  • the plurality of permanent magnets is placed one at a time in an alternating polarity arrangement in the slots so that for each post in the array of posts the two permanent magnets placed adjacent to the post are oriented so that the magnetic poles of each permanent magnet face towards the post.
  • the plurality of posts may further comprise at least one tab at each of the slots. Placing the plurality of permanent magnets in the slots may further comprise sliding each magnet into each slot so that each permanent magnet is positionally stabilized within the slots by the tabs.
  • the first carrier and second carrier may be separated by a bearing connecting the first carrier and the second carrier.
  • Placing the first carrier and second carriers in axial alignment may further comprise aligning the bearing between the first and second carriers.
  • the first carrier and second carrier may be separated by an inner thrust bearing and an outer thrust bearing.
  • Placing the first carrier and second carrier in axial alignment may further comprise aligning the inner and outer thrust bearings between the first and second carriers.
  • the plurality of permanent magnets may be removed one at a time following operation of the machine.
  • a bonding agent may be applied to secure each permanent magnet positionally within the slots.
  • the bonding agent may be a glue.
  • an electric machine having an axial flux configuration.
  • a first carrier has an array of electromagnetic elements.
  • a second carrier has electromagnetic elements including permanent magnets. The second carrier is arranged to move relative to the first carrier.
  • An airgap lies between the first carrier and the second carrier.
  • the electromagnetic elements of the first carrier comprise posts, with slots between the posts, the slots having one or more electric conductors in each slot.
  • the second carrier comprises a homogenous rigid element and posts, in which the posts comprise homogenous extensions of the rigid element.
  • the posts of the second carrier may further comprise a stop.
  • the stop may be formed by the cooperation of tapered shapes on each of the posts and each of the permanent magnets.
  • the posts may each be tapered to narrow in a direction away from the first carrier and the permanent magnets may be tapered to narrow in a direction toward the first carrier.
  • the posts of the second carrier may prevent the electromagnetic elements of the second carrier from moving in a direction towards the first carrier.
  • the stop may further comprise a tab on each post adjacent to the airgap.
  • the permanent magnets may be held in place in the corresponding slots by magnetic force when the first and second carriers are in the operational position.
  • the permanent magnets may be configured so that they are not held in place in the corresponding slots by the magnetic force when the second carrier is separated from the first carrier.
  • the second carrier may further comprise a plurality of inner flux restrictors on the homogenous rigid element radially inward from the posts in which the plurality of inner flux restrictors further comprises a plurality of holes within the rigid element.
  • the plurality of inner flux restrictors may further comprise a plurality of blind holes.
  • the plurality of inner flux restrictors may further comprise a plurality of through holes.
  • the second carrier may further comprise a plurality of outer flux restrictors on the homogenous rigid element radially outward from the posts, in which the plurality of outer flux restrictors comprises a plurality of holes within the rigid elements.
  • the plurality of outer flux restrictors may further comprise a plurality of blind holes or a plurality of through holes.
  • the second carrier may further comprise a plurality of inner flux restrictors on the homogenous rigid element radially inward from the posts and the plurality of inner flux restrictors may further comprise a plurality of holes within the rigid element.
  • the second carrier may further comprise a plurality of outer flux restrictors on the homogenous rigid element radially outward from the posts and the plurality of outer flux restrictors may further comprise a plurality of holes within the rigid elements.
  • Each of the inner and outer flux restrictors may be radially aligned in an alternating pattern with the posts on the second carrier so that the inner and outer flux restrictors are adjacent to every second post on the second carrier.
  • Each of the inner and outer flux restrictors may be radially aligned with the posts on the second carrier so that the inner and outer flux restrictors are adjacent to each post on the second carrier.
  • the plurality of inner flux restrictors and the plurality of outer flux restrictors may further comprise a plurality of holes having the same geometry.
  • the plurality of holes having the same geometry may further comprise a plurality of holes having a circular shape.
  • Fig. 1 is an isometric view of an exemplary actuator
  • Fig. 2 is an exploded view of the exemplary actuator of Fig. 1;
  • Fig. 3 is an isometric view of a rotor of the exemplary actuator of Fig. 1 ;
  • Fig. 4 is an isometric view of a stator of the exemplary actuator of Fig. 1;
  • Fig. 5 is an isometric view of a section of the exemplary actuator of Fig. 1 ;
  • Fig. 6 is a view of the body of the exemplary actuator along the section A-A in Fig. 1;
  • Fig. 7 is an enlarged detail view of an outer bearing and thermal interference fit showing the detail CI in Fig. 6;
  • Fig. 8 is an enlarged detail view of an inner bearing and safety ring showing the detail El in Fig. 6;
  • Fig. 9 is an isometric view of a section of an exemplary actuator having an alternative thermal interference fit
  • Fig. 10 is an section view of the exemplary actuator in Fig. 9;
  • Fig. 11 is an enlarged detail view of an outer bearing and an thermal interference fit showing the detail C2 in Fig. 10;
  • Fig. 12 is an enlarged detail view of an inner bearing and safety ring showing the detail E2 in Fig. 10;
  • Fig. 13 is an isometric view of a section of an exemplary stator plate with integrated bearing races;
  • Fig. 14 is an isometric view of a section of an exemplary rotor plate with integrated bearing races
  • Fig. 15 is an isometric view of a section of exemplary actuator with integrated bearing races
  • Fig. 16 is a section view of a rotor and stator including representations of magnetic flux and forces along the section B-B in Fig. 6;
  • Fig. 17 is a view of the body of an exemplary actuator with a safety ring
  • Fig. 18 is a detail view of a safety ring with a plain bearing
  • Fig. 19 is a detail view of a safety ring with a thrust bearing
  • Fig. 20 is a close up view of a rotor during installation and removal of the magnets
  • Fig. 21 is a partial cross section of a rotor plate section
  • Fig. 22A is a partial view of a rotor plate section having flux restricting holes
  • Fig. 22B is a partial view of a rotor plate section having another arrangement of flux restriction holes
  • Fig. 23 is a FEMM simulation result on a rotor plate without flux restricting holes
  • Fig. 24 is a FEMM simulation result on rotor plate with flux restricting holes
  • Fig. 25 is a cross section of a stator plate section with uninterrupted path between ID bearing and OD bearing;
  • Fig. 26 is an exploded view of an exemplary actuator
  • Fig. 27 is a cross section of an embodiment showing an exemplary actuator connected to an upper and lower housing
  • Fig. 28 is an exploded isometric view of the exemplary actuator in Fig. 27;
  • Fig. 29 is an isometric cut away view of the exemplary actuator in Fig. 27;
  • Fig. 30 is a cross-section through a segment of an axial flux concentrated flux rotor with tapered magnets and flux path restrictions;
  • Fig. 31 is a close-up section view of a portion of an axial flux concentrated flux rotor with extended length magnets;
  • Fig. 32 is a simplified exploded section view of an embodiment of an axial flux stator- rotor-stator configuration of a concentrated flux rotor with end iron;
  • Fig. 33 is a simplified exploded section view of an embodiment of an axial flux stator- rotor-stator configuration of a concentrated flux rotor with back iron, end iron and flux path restrictions;
  • Fig. 34 is a simplified exploded section view of an embodiment of an axial flux rotor- stator-rotor configuration of a concentrated flux rotor with end irons and flux path restrictions;
  • Fig. 35 is a simplified exploded section view of an embodiment of an axial flux rotor- stator-rotor configuration of a concentrated flux rotor with end irons, flux path restrictions and back irons;
  • Fig. 36 is a simplified perspective view of a linear flux machine with back irons and flux restrictors
  • Fig. 37 is a simplified perspective view of a linear flux machine without back irons and with flux restrictors
  • Fig. 38 is a simplified perspective view of a linear flux machine with an alternating pattern of flux restrictors
  • Fig. 39A shows a graph of torque at constant current density for a simulated series of motors differing in slot pitch and post height
  • Fig. 39B shows the highest stator current density possible at a given temperature for a simulated series of motors differing in slot pitch and post height
  • Fig. 39C shows constant temperature torque as a function of slot pitch and post height for a series of electric machines
  • Fig. 39D shows the value of a weighting function for at the highest stator current density possible at a given temperature for a simulated series of motors differing in slot pitch and post height;
  • Fig. 39E shows Km" for a simulated series of motors differing in slot pitch and post height, for a fixed current density
  • Fig. 39F shows KR" for a simulated series of motors differing in slot pitch and post height, for a fixed current density
  • Fig. 40 shows the region of benefit for KR", with respect to the rest of the geometries in the domain, for a machine with 200 mm size and a boundary line for KR" > 1.3;
  • Fig. 41 shows the region of benefit for KR", with respect to the rest of the geometries in the domain, for a machine with 200 mm size and a boundary line for KR" > 1.5;
  • Fig. 42 shows the region of benefit for KR", with respect to the rest of the geometries in the domain, for a machine with 200 mm size and a boundary line for KR" > 1.8;
  • Fig. 40 shows the region of benefit for KR", with respect to the rest of the geometries in the domain, for a machine with 200 mm size and a boundary line for KR" > 1.3;
  • Fig. 41 shows the region of benefit for KR", with respect to the rest of the geometries in the domain, for a machine with 200 mm size and a boundary line for KR" >
  • FIG. 43 shows the region of benefit for KR", with respect to the rest of the geometries in the domain, for a machine with 100 mm size and a boundary line for KR" > 1.5;
  • Fig. 44 shows the region of benefit for KR", with respect to the rest of the geometries in the domain, for a machine with 100 mm size and a boundary line for KR" > 1.7;
  • Fig. 45 shows the region of benefit for KR", with respect to the rest of the geometries in the domain, for a machine with 100 mm size and a boundary line for KR" > 1.9;
  • Fig. 44 shows the region of benefit for KR", with respect to the rest of the geometries in the domain, for a machine with 100 mm size and a boundary line for KR" > 1.9;
  • Fig. 45 shows the region of benefit for KR", with respect to the rest of the geometries in the domain, for a machine with 100 mm size and a boundary line for KR" >
  • Fig. 46 shows the region of benefit for KR", with respect to the rest of the geometries in the domain, for a machine with 50 mm size and a boundary line for KR" > 2.2;
  • Fig. 47 shows the region of benefit for KR", with respect to the rest of the geometries in the domain, for a machine with 50 mm size and a boundary line for KR" > 2.5;
  • Fig. 48 shows the region of benefit for KR", with respect to the rest of the geometries in the domain, for a machine with 50 mm size and a boundary line for KR" > 2.9;
  • Fig. 49 shows the region of benefit for KR", with respect to the rest of the geometries in the domain, for a machine with 25 mm size and a boundary line for KR" > 3.3;
  • Fig. 50 shows the region of benefit for KR", with respect to the rest of the geometries in the domain, for a machine with 25 mm size and a boundary line for KR" > 3.4;
  • Fig. 51 shows the region of benefit for KR", with respect to the rest of the geometries in the domain, for a machine with 25 mm size and a boundary line for KR" > 3.6;
  • Fig. 52 shows the joint of a robot arm using a frameless motor/actuator;
  • Fig. 53 displays a cross-sectional view of the frameless motor/actuator and robot arm
  • Fig. 54 shows a close up of the section view of the frameless motor/actuator stator, rotor and housing assembly
  • Fig. 55 shows an exploded view of the frameless motor/actuator robot arm assembly
  • Fig. 56 displays a section view through the housing to view the stator and tab features on the rotor;
  • Fig. 57 shows a representation of an up, over and down assembly motion used with the tab features in Fig. 56 to secure the rotor;
  • Fig. 58 shows a close up of the section view displaying the tab feature used to secure the rotor
  • Fig. 59 shows a section view through the housing to display the tab features used on the stator to secure the stator.
  • a carrier as used here in the context of electric machines, may comprise a stator or a rotor when referring to rotary machines.
  • a rotor as used herein may be circular.
  • a rotor may also refer the armature or reaction rail of a linear motor.
  • a stator may be circular. It may also refer to the armature or reaction rail of a linear motor.
  • Teeth may be referred to as posts.
  • either a stator or rotor may have a commutated electromagnet array defined by coils wrapped around posts, while the other of the stator or rotor may have magnetic poles defined by permanent magnets or coils or both coils and permanent magnets.
  • An electric machine may be configured as a motor or generator.
  • Permanent magnets may be used in combinations with electromagnets on the rotor and/or stator to add flux to the system.
  • PM means permanent magnet.
  • EM means electromagnet.
  • ID means inner diameter.
  • OD means outer diameter.
  • Electromagnetic elements may comprise permanent magnets, posts, slots defined by magnetic posts, which may be soft magnetic posts, and electrical conductors.
  • the other may have permanent magnets for the electromagnetic elements, and for any such embodiment, the term electromagnetic element may be replaced by the term permanent magnet.
  • Magnetic poles in some cases, for example in a concentrated flux rotor embodiment, may be defined by permanent magnets in conjunction with adjacent posts in which a magnetic field is established by the permanent magnets.
  • flux refers to magnetic flux.
  • Soft Magnetic Material is a material that is magnetically susceptible and that can be temporarily magnetised such as but not limited to iron or steel or a cobalt or nickel alloy.
  • a fractional slot motor is a motor with a fractional number of slots per pole per phase. If the number of slots is divided by the number of magnets, and divided again by the number of phases and the result is not an integer, then the motor is a fractional slot motor.
  • Thrust bearings include any bearing arranged to support a substantial axial thrust, including angular contact bearings and four-point contact bearings as well as pure thrust bearings.
  • a radially locating bearing is a bearing that, in use, prevents relative displacement of the axes of the elements connected by the bearing.
  • a bearing can be radial and thrust locating (such as a cross roller bearing) or it can be just radial or just thrust locating.
  • a carrier may be supported for motion relative to another carrier by a frame or bearings, and the bearings may be sliding, roller, fluid, air or magnetic bearings.
  • An axial electric machine is an electric machine in which magnetic flux linkage occurs across an axial airgap, and the carriers are in the form of discs mounted coaxially side by side.
  • a first carrier can be arranged to move relative to another carrier by either carrier being supported by a frame, housing or other element, while the other carrier moves relative the first carrier.
  • a radial electric machine is an electric machine where the airgap is oriented such that magnetic flux is radially oriented, and the carriers are mounted concentrically, one outside the other.
  • a linear actuator is comparable in construction to a section of an axial flux or radial flux rotary motor where the direction of motion is a straight line rather than a curved path.
  • a trapezoidal electric machine is an electric machine that is a combination of both an axial and radial flux machines, where the plane of the airgap lies at an angle partway between the planes formed by the airgaps in the axial and radial configurations.
  • the airgap diameter for a rotary machine is defined as the diameter perpendicular to the axis of rotation at the centre of the airgap surface. In radial flux motors, all of the airgap resides at the same diameter. If the airgap surface is a disc-shaped slice as in axial flux motors, the average airgap diameter is the average of the inner and outer diameter. For other airgap surfaces such as a diagonal or curved surfaces, the average airgap diameter can be found as the average airgap diameter of the cross-sectional airgap view.
  • the airgap diameter refers to the average of the rotor inner diameter and stator outer diameter for an outer rotor radial flux motor or the average of the rotor airgap outer diameter and stator airgap inner diameter for an inner rotor radial flux motor. Analogues of the airgap diameter of a radial flux motor may be used for other types of rotary motors.
  • the airgap diameter is defined as the average of the PM inner diameter and PM outer diameter and EM inner diameter and EM outer diameter.
  • the back surface of the stator is defined as the surface on the opposite side of the stator to the surface which is at the magnetically active airgap. In a radial flux motor, this would correspond to either the inner surface of the stator for an outer rotor configuration, or the outer diameter surface of the stator for an inner rotor configuration. In an axial flux motor, the back surface of the stator is the axially outer surface of the stator.
  • the number of slots will be N x the number of poles where N is a multiple of the number of phases. So for a 3 phase machine N could be 3, 6, 9, 12, etc.
  • the number of slots can vary but must be a multiple of the number of phases. It does not depend on the number of poles, except that certain combinations of slots and poles will yield higher torque and better noise-reduction or cogging-reduction characteristics. The minimum number of slots for a given number of poles should not be below 50% to obtain adequate torque.
  • Conductor volume may be used to refer to the slot area per length of a single stator.
  • the slot area is the area of a cross-section of a slot in the plane which is orthogonal to the teeth but not parallel to the plane of relative motion of the carriers. In an axial motor, this plane would be perpendicular to a radius passing through the slot.
  • the slot area effectively defines the maximum conductor volume that can be incorporated into a stator design, and it is usually a goal of motor designers to have as high a fill factor as possible to utilize all the available space for conductors.
  • maximum conductor volume in a stator is defined in terms of slot area, any stator referred to as having a maximum conductor volume or slot area must have slots and teeth to define the slots. This parameter is defined for rotary motors as:
  • As is the cross-sectional area of a single slot, or the average area of a single slot for stator designs that have varying slot areas.
  • Slot depth or post height may also be used as a proxy for the conductor volume.
  • the post height also known as the tooth height or slot depth, is a proxy for the amount of cross- sectional area in a slot available for conductors to occupy.
  • the slots may have a variety of shapes such as curved or tapered profiles, the slot height is based upon the closest rectangular approximation which best represents the total area of the slot which may be occupied by conductors. This dimension does not include features such as pole shoes which add to the height of the tooth without adding substantially to the slot area.
  • the post height is defined as the portion of the post which is directly adjacent to the conductor coil, perpendicular to the direction of the coil windings.
  • a concentrated winding comprises individually wound posts or any winding configuration that results in the alternating polarity of adjacent posts when energized. It is understood that not all posts will be the opposite polarity of both adjacent posts at all times. However, a concentrated winding configuration will result in the majority of the posts being the opposite polarity to one or both adjacent posts for the majority of the time when the motor is energized.
  • a concentrated winding is a form of fractional slot winding where the ratio of slots per poles per phase is less than one.
  • the terms one-piece, unitary, homogenous, solid, isotropic and monolithic are used interchangeably when referencing a stator or rotor herein.
  • Each of the terms excludes laminates and powdered materials that include significant electrical insulative materials. However, small insulating particles may be present that do not significantly interfere with the electrically conducting properties of the material, for example where the bulk isotropic resistivity of the material does not exceed 200 microohm-cm.
  • a one-piece, unitary, homogenous, solid, isotropic or monolithic material may comprise iron, including ductile iron, metal alloys including steel, and may comprise metal alloys formed of electrically conducting atoms in solid solution, either single phase or multi-phase, or alloys formed of mixtures of metals with other materials that improve the strength or conductivity of the material, for example where the bulk isotropic resistivity of the material does not exceed 200 microohm- cm.
  • Embodiments of the present device use an integrated bearing race that is preferably machined into the stator and/or rotor where the bearing races and at least the axial surfaces of the stator and rotor posts can be machined in the same set-up. This can provide for very high tolerance manufacturing of the critical geometry relationship between the bearing race axial and radial positions relative to the stator and rotor posts. Consistency of these geometric relationships is important for consistent cogging and other performance characteristics of the device.
  • Embodiments of the present device can allow for streamlined manufacturing with a rotor configuration that allows the permanent magnets to be installed into the rotor individually after the stator and rotor have been assembled.
  • Embodiments of the device can provide high torque density, ease of manufacturability, ease of assembly and serviceability due to a very simple assembly with a minimal number of components, and excellent operational safety as a result of high torque-to-inertia which allows very fast emergency stopping.
  • a non-limiting exemplary embodiment of an axial flux motor 110 is housed in an upper arm member 100 and a lower arm member 200.
  • the upper and lower arm members 100, 200 rotate around a rotational axis 300.
  • the upper arm member 100 includes a support housing 101.
  • the lower arm member 200 includes an arm housing 201.
  • the support housing 101 and the arm housing 201 are preferably made of a light weight material such as, but not limited to, aluminum, magnesium or carbon fiber composite.
  • stator 102 is attached to the upper arm 100 such as with bolts and/or adhesive and/or thermal fit or by being formed integrally with the arm.
  • the stator 102 is connected to the upper arm 100 using a press fit with a ring 101 A.
  • An outer bearing 302 and an inner bearing 301 allow relative rotation of the stator 102 and rotor 202 and provide precise relative axial location of the stator 102 and rotor 202 to maintain an airgap between stator posts 105 (Fig. 4) and rotor posts 205 (Fig. 3).
  • the rotor may have flux restriction holes 206 and permanent magnets 204. The permanent magnets are seated in slots 208.
  • the placement of the inner bearing 301 inside the ID of the airgap and the outer bearing 302 outside the OD of the airgap distributes the attractive forces between the stator 102 and rotor 202 between two bearings 301, 302 for longer service life and/or lighter bearings.
  • the use of ID and OD bearings also reduces the mechanical stress on the stator 102 and rotor 202 to allow a thinner cross section and lighter weight, for example as is possible with the high pole count of embodiments of the device.
  • the rotor 202 includes a rotor plate 203 (Fig. 3) and the stator 102 includes a stator plate 103 (Fig. 4).
  • the stator plate 103, as shown in Figure 4, and the rotor plate 203, as shown in Figure 3, can be made of ductile iron.
  • the permanent magnets 204 can be Neodymium - N52H. Many other materials can be used for the various components. These materials are given by way of example.
  • the rotor 202 is housed in the lower arm 200 and attached such as with bolts and/or adhesive and/or thermal fit or by being formed integrally with the arm. As shown in Fig. 2, the rotor 202 is connected to the lower arm 200 using a press fit with a ring 201A.
  • the axial magnetic attraction between the stator 102 and rotor 202 which results from the permanent magnet flux in the rotor 202 provides axial preload on the bearings 301 and 302.
  • This axial force is adequate to keep the bearings 301, 302 preloaded in the stator 102 and rotor 202 and to provide adequate axial force to allow the lower arm 200 to support useful loads in all directions.
  • This load may be a combination of the arm weight and acceleration forces and payload in any direction.
  • the use of the magnetic forces to provide the bearing seating force and axial preload on the bearings allows for the use of thrust load and/or angular contact bearings which can be preloaded by the magnetic attraction of the stator and rotor to remove bearing play in the axial direction.
  • the stator includes a stator plate 103.
  • the stator plate 103 includes an inner bearing race 111 that defines an inner bearing groove and an outer bearing race 112 that defines an outer bearing groove.
  • the rotor includes a rotor plate 203.
  • the rotor plate 203 includes an inner bearing race 211 that defines an inner bearing groove and an outer bearing race 212 that defines an outer bearing groove.
  • the rotor plate 203 may be connected to a rotor housing 201 using a press fit between cooperating pieces 231 and 232.
  • stator plate 103 may be connected to a stator housing 101 using a press fit between cooperating pieces 131 and 132.
  • An outer bearing element 322 (in this non- limiting example, a cross roller bearing) is sandwiched between the two outer bearing grooves 112, 212 such that the axial magnetic attraction between the stator 102 and rotor 202 eliminates axial and radial play in the bearing 301.
  • An inner bearing element 321 (Fig. 6) is sandwiched between the two inner bearing grooves 111, 211.
  • the bearing 301 is, in this non-limiting exemplary embodiment, a cross roller bearing with axial and radial locating stiffness.
  • the axial preloading of the rotor and stator provided by the magnets 204 in the rotor 202 results in a precise relative location of the stator 102 and rotor 202 in the axial and radial directions. This precise location is accomplished without the need for mechanical or adhesive bearing race retention in the opposite axial direction of the magnetic attraction force between the stator and rotor.
  • the axial flux motor 110 may have the design shown.
  • An outer bearing 302 and an inner bearing 301 allow relative rotation of the stator and rotor and provide precise relative axial location of the stator and rotor to maintain the desired airgap between the stator posts 105 and the rotor posts that hold magnets 204 and that provide a flux path for the magnetic fields provided by the magnets.
  • the rotor may have flux restriction holes 206 and magnets 204.
  • the use of a bearing inside the ID of the airgap and a second bearing outside the OD of the airgap distributes the attractive forces between the stator and rotor between two bearings for longer service life and/or lighter bearings.
  • the use of ID and OD bearings can reduce the mechanical stress on the stator and rotor to allow a thinner cross section and lighter weight, for example as is possible with the high pole count of embodiments of the device.
  • the outer bearing 302 can also be a bushing, with for example one of the rotor or that stator incorporating bronze or another bushing material, with the other of the rotor or the stator being steel or other suitable material.
  • bronze some of the metal of the material may migrate over to the other bushing part and lubricates it.
  • Other materials such as nickel or copper may also be used instead of bronze.
  • the bushing surface could also be another suitable material, such as TeflonTM or other low friction material.
  • stator posts corresponding to 96 slots
  • 92 rotor posts with three phase wiring and each phase on the stator being divided into 4 equally array sections of eight posts each.
  • the number of rotor posts in this example is 92 resulting in four equally arrayed angular positions where the rotor and stator posts are aligned. This, in-turn, results in a peak axial attraction force between the stator and rotor in four positions.
  • stator post numbers and rotor post numbers may be used.
  • Other numbers of phases may also be used.
  • the examples here have been found to provide beneficial performance but do not limit the various construction principles to these exemplary geometries.
  • features of embodiments of the device such as, but not limited to, the magnetically preloaded bearings or the wiring constructions can be used with rotors and stators with much lower or much higher numbers of poles.
  • the total axial preload between the stator and rotor remains relatively constant such as within 10% in a multiphase wiring configuration such as, but not limited to, a three phase configuration, regardless of the current supplied to the windings and the torque developed by the motor. This is because the electromagnetic forces are reasonably equally in repelling and attraction. But although the total axial force on the stator and rotor remains reasonably constant, the axial attraction force on an individual post on the stator or rotor will vary quite a bit more (such as 14% or more).
  • the peak axial load from the permanent magnets occurs at more than one angular position (for example, at four equally arrayed angular positions).
  • This can be beneficial to provide a more consistent axial preload on the bearings around the circumference of especially the OD bearing so any cantilevered external loads that would pull the stator from the rotor (such as a cantilevered load on a SCARA arm that is pulling the stator and rotor apart primarily at one angular position) are opposed by one or more peak axial force areas at all times, regardless of angular position of the arm.
  • peak axial force positions (as a result of four sections per phase) is considered a good balance of manufacturability and peak axial force consistency.
  • Four peak axial force positions can be accomplished with many different numbers of stator and rotor posts with the important characteristics being that there is a four post difference between the number of posts on the rotor and the number of posts on the stator.
  • the number of posts on the stator be a multiple of three sections such as 3, 6, 9, 12, 14, 16 etc with each section having an even number of posts such as 2, 4, 6, 8, 10, 12 etc on the stator.
  • a high number of cogging steps is beneficial to reduce cogging (because a higher number of steps generally results in a lower force variation between the maximum and minimum torque of each cogging step) so a two post difference (corresponding with two sections per phase) between the stator and rotor would seem to be preferable to reduce cogging because, in a non- limiting exemplary embodiment of 96 stator posts and 94 rotor posts, the number of cogging steps is 4512, which is a very high, resulting in a theoretical cogging torque that is very low.
  • stator and rotor results in only two peak axial attraction force position at any given time resulting in a less stable support of a cantilevered load on the output of the actuator such as in a SCARA arm configuration when lifting a payload.
  • a rotor/stator post difference of four is considered to be a good choice in terms of payload lifting stability even though it has a lower number of cogging steps and theoretically higher cogging forces.
  • a 96 stator-post to 92 rotor-post configuration results in only 2208 cogging steps which would be expected to result in about two times greater cogging force variation.
  • a post difference of four would, therefore, not seem to be beneficial in terms of cogging reduction because the cogging steps would be fewer and, as a result, larger in magnitude.
  • there can be another benefit of fewer cogging steps (which results from a larger post number difference between the stator and the rotor - such as, for example, a four post difference as shown in Figure 3 and Figure 4 of four, as opposed to a one or two post difference).
  • This advantage is related to a correlation between the size of the cogging steps and the required accuracy of the stator and rotor axis alignment during manufacturing/assembly and in operation under various loads.
  • the stator and rotor will not be aligned sufficiently to achieve consistent cogging steps. This will result in inconsistent cogging forces during rotation. Any radial displacement of the rotor relative to the stator will have a misaligning effect, in the same radial direction, on posts that are diametrically opposed, resulting in less than ideal cogging cancellation.
  • Some combinations of rotor/stator axis misalignment and relative angular position of the stator with very high cogging step embodiments may even result in greater cogging force variation in some conditions than if a larger rotor/stator post difference is used (assuming similar radial misalignment in each exemplary case).
  • bearing stiffness in the radial direction can be an important consideration because the cogging forces or the payload forces will, at times, displace the rotor more, radially, relative to the stator, with bearings which are less radially stiff.
  • a four (4) post difference between the rotor and stator has the advantage of providing at least two peak axial attraction force positions on the load side of the actuator in a robotics application (such as when supporting a cantilevered load) at all times.
  • the allowable radial displacement of the rotor relative to the stator can be higher because the cogging steps are larger. This is expected to allow for consistent cogging torque to be achieved with lower manufacturing tolerances and bearing stiffness than if a higher number of cogging steps is used.
  • the number of each of N and M may be selected so that N and M have the property that the greatest common divisor of N and M is four or more.
  • Embodiments of the present device use a wiring configuration where two or more adjacent slots in a row contain conductors from only one phase. Many different winding methods may be used with this device but the advantages of a winding configuration 104 as shown in Figs. 4 and 5 includes the ability to use axially aligned (circumferentially layered in each slot) non-overlapping flat wire (overlapping the wire - as is typically done in three phase distributed winding machines, is problematic with flat wire).
  • the number of rotor posts for this winding configuration is preferably equal to the number of stator slots plus or minus the number of sections per phase EG 94 or 98 rotor posts for a 96 stator slots having two equally arrayed sections per phase.
  • Figure 5 to Figure 8 shows the exemplary actuator with a safety ring 121 that attached to the stator housing 101 and Figure 9 to Figure 12 shows an alternative exemplary actuator with the safety ring 121 attached to stator plate 103.
  • the safety ring 121 is installed on the stator 102 to keep the stator and rotor from separating in the case of a force being applied to the end of an arm attached to the rotor, along the rotational axis of the actuator, which is greater than the axial attracting force from the PM magnetic attraction across the airgap.
  • a section of the actuator in Figure 8 shows that the safety ring 121 is located at the inner diameter of the stator.
  • Section view in Figure 8 shows that a lip (first shoulder) 122 A of the safety ring overlaps the lip (second shoulder 122B) of the arm housing.
  • a thin plain bearing ring 124 is in place to provide low resistance gliding contact in event of rotor and stator separation.
  • the first shoulder 122A protrudes in a first radial direction
  • the second shoulder protrudes 122B in a second radial direction opposed to the first radial direction
  • the first shoulder 122A is configured to cooperate with the second shoulder 122B to prevent separation of the rotor and the stator beyond a pre-determined distance.
  • the safety ring 121 is attached to the stator housing 101 using a press fit between cooperating pieces 123A and 123B.
  • an overlapping feature forming a first shoulder 122A which has a larger OD than the ID of the rotor housing, in this example, is located around the ID of the stator and rotor.
  • the safety ring and first shoulder 122 A do not need to contact the rotor during normal operation, and serve to prevent complete separation of the rotor and stator in the axial direction if the separating load on the rotor 202 and stator 102 exceeds the axial preload on the bearings provided by the permanent magnets.
  • a counter bearing or bushing 124 is attached to the stator or rotor or other member, after assembly of the stator and rotor.
  • the material combination of the first shoulder 122A and the bushing 124 and the rotor is preferably suitable for sliding contact.
  • a plain bushing material 124 can also be used between these two surfaces as shown in Figure 18.
  • a thin section thrust bearing 124 is used to allow rotation without damage if the magnetic preload is exceeded during actuator rotation.
  • the first shoulder can also be used on the OD of the actuator with similar effects.
  • a rolling element bearing is used as a counter bearing, and if it is desired to have a small amount of separation of the stator and rotor in case of an emergency to reduce the force of the robot arm on an unintended object, it may be desirable to use a preload spring to keep the counter bearing lightly preloaded in order to prevent the bearing balls from spinning.
  • a wave washer could, as a non-limiting example, be used for this purpose.
  • the rotor housing 201 and the rotor plate 203 are connected by a press fit using cooperating pieces 23 IB and 232B.
  • the stator housing 101 and stator plate 103 are connected by a press fit using cooperating pieces 13 IB and 132B.
  • a monolithic material from post to post on the stator and/or rotor can used to provide a housing structure.
  • the rotor and/or stator have the structural rigidity to eliminate the need for an additional housing on one or both members. Integrating the stator and rotor as a homogenous plate may reduce weight, as well as manufacturing cost and complexity.
  • An integrated bearing race that is formed as part of each homogenous plate may allow the structural load path from the stator posts to the bearing race in contact with the rolling elements to be formed from a single piece of magnetic metal such as shown in Figures 13 to 15.
  • ID and OD bearings are used to reduce rotor and stator material stress with axially thin components and to maintain a small airgap.
  • An uninterrupted soft magnetic homogeneous material may be used such as, but not limited to iron or steel alloy between two or more of: a stator or rotor post and a bearing, a stator or rotor post and an adjacent post, a stator or rotor post and an OD bearing or bearing seat, a stator or rotor post and an ID bearing or bearing seat, and a stator or rotor post and a structural member in the load path between the post and a bearing.
  • the homogenous material for the stator and/or rotor could include ductile iron or other type of iron construction.
  • the homogenous material for the stator and/or rotor could also include from one of iron, ductile iron and steel alloy and may also include an electrical conductivity inhibitor, such as silicone.
  • the stator plate 103 has a bearing groove 11 IB at the inner diameter and a bearing groove 112B at the outer diameter.
  • the stator may be formed as a homogenous plate having both the inner bearing groove 11 IB and the outer bearing groove 112B as homogenous extensions of the homogenous plate.
  • the rotor plate 203 also has a groove 21 IB at the inner diameter and a groove 212B at the outer diameter.
  • the rotor may be formed from a homogenous plate having both the inner bearing groove 21 IB and the outer bearing groove 212B as homogenous extensions of the homogenous plate.
  • these grooves are for the steel balls 304 and the steel rollers 303.
  • Materials of the rotor plate and the stator plate may be of many materials such as but not limited to a high strength metallic material that has soft magnetic properties to provide electromagnetic functionality as well as high enough structural strength to provide the strength to maintain a small and consistent airgap between the stator and rotor posts, and high enough mechanical hardness to provide bearing race functionality.
  • Ductile iron has been found to possess these and other qualities for certain applications and especially when combined with the claimed range.
  • the bearing grooves 11 IB, 112B, 21 IB, and 212B may also be hardened for increased load capacity and service life.
  • Ductile iron or other cast iron products are not usually used for bearing races, but iron is used in railway car wheels and rails so it is expected that this integrated bearing can be configured for adequate service life for robotics and other motion control applications if made of ductile iron or other suitable materials preferably with high magnetic saturation density so the bearing races on the stator can be of the same monolithic material as the stator posts (on the stator) and the rotor bearing races can be of the same monolithic material as the rotor posts (on the rotor).
  • the advantages of an integrated bearing race may include lower cost, and the potential for increased precision due to the elimination of tolerance stack up of the bearing races and bearing race seats in the rotor and/or stator.
  • the use of an integrated bearing race can also reduce the volume and mass of the stator and rotor because the bearing race becomes an integral part of the load bearing structure, thus eliminating the need for additional material to support separate component bearing races.
  • ductile iron for the stator and/or rotor allows a combination of characteristics that may be uniquely suited to the unusual requirements of embodiments of the device.
  • Some of the features of ductile iron that may be beneficial in some embodiments include poor electrical conductivity due to the high carbon content which results in reduced eddy current losses, excellent machinability for low cost manufacturing, excellent castibility for net or near-net shape casting of stator and/or rotor, high fatigue strength for long service life, self lubricating properties which may allow an integrated bearing to operate with minimal or no additional lubricant, excellent wear properties between certain seal materials in the dry condition to provide bearing and actuator sealing with no need for lubricant in some applications, and good damping qualities to reduce noise and vibration from cogging and other high frequency effects
  • embodiments of the device include a set of bearing elements at or near the inner diameter (ID) and a set of bearing elements at or near the outer diameter (OD).
  • This combination of bearings provide axial and radial support between the rotor and stator when combined with the claimed geometry range may allow the rotor and stator to be light weight.
  • the ID and OD bearings also maintain a fixed air gap distance.
  • Air gap distance between the rotor and stator can be limited by machining tolerance and deflection of the rotor during operation due to permanent magnet (PM) attraction.
  • PM permanent magnet
  • the rotor and stator in an ID-only actuator deflect significantly more than the rotor in the ID/OD bearing actuator.
  • the reduction in deflection in the ID/OD actuator may allow a smaller air gap distance to be maintained which result in greater torque for a given input power. It has been shown by analysis and experimentation that the torque gained by air gap distance reduction may be larger than the drag induced by the OD bearing in some embodiments. It has also been shown that the increase in torque-to-weight that results from the use of an OD bearing, due to the reduction of structural material needed to maintain the airgap, may be more significant than the weight of the additional bearing and material needed to support the additional bearing.
  • the outer diameter of the stator is 200mm and the axial air gap is approximately .010".
  • a non-limiting exemplary embodiment of the device has one stator and one rotor as shown in Figures 7 to 9.
  • the single stator / single rotor setup enables the rotor to preload the ID and OD bearings by constantly attracting the stator in the axial direction.
  • permanent magnets 204 generate magnetic flux represented by the arrow 401.
  • an adjacent magnet also generates the same polarity magnetic flux 402 into the pole 205.
  • Both flux 401 and 402 travel through the rotor pole 205, pass through the airgap 400, into stator post 105, and generate magnetic attractive forces 403 on both the stator 102 and the rotor 202.
  • the magnetic forces 403 are so strong that they are able to hold the stator and the rotor together during passive and active operation under usable operating conditions for many applications.
  • the posts are connected to a back iron 106.
  • FIGs 17 to 19 shows an example of the operation of the safety ring 121.
  • the rotor including the rotor plate 203 will start separating from the stator including the stator plate 103.
  • the lip of the safety ring will contact the arm housing 201 of the rotor and keep the arm assembly 200 from separating.
  • the bearing ring 124 (Fig. 18) will be free spinning in the gap between the lip 122A and arm housing 201 and does not create drag and friction.
  • the coils When the coils are engaged or powered, the coils generate attracting and repelling forces which are very similar resulting in primarily tangential forces along the rotational plane. Any axial repelling force under power is, therefore, very small relative to the permanent magnet attractive forces, so the permanent magnet attractive forces are available at all times to prevent separation of the stator and rotor and to maintain adequate preload on the bearings under predetermined maximum load conditions.
  • the bearing 124 may form a shoulder by being or having some part of the bearing secured to or integral with the rotor plate 203.
  • This design provides room for the rotor joint to provide a limited break-away effect for a small displacement before the safety ring contacts.
  • This break-away effect would be beneficial, for example, if a robot arm makes unwanted contact with a human, pinning them between the arm and an immovable object. In this case, the arm may have a very short stopping time, but there may still be a small amount of movement before the actuator comes to a full stop.
  • the partial separation of the rotor from the stator of one or more actuators in the arm, before the safety ring comes into contact can be used to provide a maximum axial load on one or more actuators in the arm which are loaded from the impact, in such a way as to cause the rotor and stator of these actuators to partially separate. With a small amount of separation and very fast acting and fast decelerating actuators, such as embodiments of the present device, this partial separation is believed to provide a level of increased safety by reducing the impact or pinning force of a robot arm.
  • the rotor plate shown in Figure 3 has no back iron immediately axially outward from the permanent magnets (corresponding to radially outward from the permanent magnets in a radial flux embodiment of the device etc.).
  • magnet slots 208 are open on the back face of the rotor so magnets can be assembled into the slots after the stator and rotor are assembled.
  • Figure 20 shows that the magnets 204 can be accessed from the back of the rotor which allows each of those magnets to be removed or installed individually without removing the rotor from the stator.
  • the magnets 204 may be installed into the slots as follows. Align the magnet to the slot with the same polarity magnetic flux contacting the rotor post as the adjacent magnet contacting the same post. Every second magnet will be in the same circumferential polarity alignment. Every first magnet will be the opposite of every second magnet so the posts are alternating polarity. Slide the magnet into the slot until it is secured against the tabs (if parallel sided) or, if tapered magnets are used, until the tapered magnet seats into the tapered slot. Repeat the above steps until all the magnets are installed. Apply bonding agent (eg, wax, epoxy, glue) to fill the clearance gap. This step may not be necessary in all cases, such as with a precision tapered magnet in a precision tapered slot.
  • bonding agent eg, wax, epoxy, glue
  • the rotor can be easily demagnetized by removing the magnets individually.
  • each of the permanent magnets 204 in the rotor generates the same polarity flux as its immediately adjacent permanent magnet which means every magnet will be repelling the adjacent magnets on both sides of it. This would cause the magnets to repel each other, except it has been shown that certain geometries are able to prevent these repelling forces from causing the magnets to dislodge themselves form the slots.
  • tapered magnets are also beneficial in this sense, because a tapered magnet, with the large dimension of the taper toward the back face of the rotor, will generally be more apt to pull itself axially toward the rotor posts and therefore toward the airgap.
  • a physical stop is used to stop the magnet from moving into the airgap.
  • the stops are tabs 210 on each side of the slot generate attractive forces as the magnet slides into the slot. Their combined force pull the magnet into the slot. Since the repelling forces partially or completely cancelled out, the combined force from the poles and tabs becomes the resultant force acting on the magnet. The magnets sit on the tabs and the magnetic attractive forces secure the magnets to the poles.
  • the net force on the magnets can be tailored to use the magnetic forces to magnetically retain the magnets in the slots. Adhesive or mechanical mechanism is not required in this case except to prevent side-to-side movement of a magnet in a slot.
  • FIG. 22A A non-limiting exemplary embodiment of the actuator is shown in Figure 22A with flux restriction holes 206 placed between magnet slots 208, and along the outside and inside radius of the magnet slots 208 on the rotor to reduce flux leakage between the opposite polarity faces of a magnet and between adjacent rotor poles. Magnetic simulation was done to verify if those holes reduce flux leakage and it has been shown that the flux leakage between rotor poles can be substantially reduced while still maintaining the necessary structural strength and stiffness to achieve a small and consistent airgap.
  • the flux restriction holes can, alternatively, be located between every second post on the OD and between every second post on the ID as shown in Figure 22B.
  • the inner and outer flux restriction holes are staggered so that each post is adjacent to only one of the inner or outer flux restriction holes. This provides an unrestricted flux linkage between only the N posts around the OD and only the S posts around the ID as well as increased structural integrity for every first post around the OD and every second post around the ID.
  • These holes can be thru-holes or blind holes, as long as they provide the necessary structural strength and stiffness as well as the desired flux path reluctance.
  • Figure 23 shows the flux path from the magnetic simulations without flux restriction holes and Figure 24 shows the flux path from the magnetic simulations with flux restriction holes. From the figures, it is shown that flux restriction holes reduce flux leakage between adjacent rotor poles. For example, when flux restriction holes are used, the flux density increased at the air gap surfaces of the rotor poles and more flux is directed to pass through the stator. As a result, electromagnetic force increases when the coils are engaged and torque generated by the stator and rotor increases.
  • the stator is formed of unitary material (instead of a common laminated structure) and comprises a stator post 105, a stator back iron 106, inner bearing race 11 IB, and outer bearing race 112B. Looking at the cross section of the stator in Figure 25, there is no interruption along the stator material path 500 between the tip of a stator post and the inner bearing race, the tip of said stator post and the outer bearing race.
  • stator plate which is held inside the integrated housing, is machined from a solid piece of material.
  • a typical stator is often made using laminated steel layers.
  • material path between the inner bearing race 11 IB, stator post 105 and outer bearing race 112B is uninterrupted and comprises a homogeneous material such as, but not limited to, ductile iron or magnetic steel such as Ml 9.
  • the stator core can be cast or machined from a solid piece of steel. The benefit of this construction may include lower cost and complexity due to a single part rather than an assembly of many small laminated parts, and much higher strength, stiffness and creep resistance because there is no adhesives in the load path as there would be in typical laminated stator constructions. This allows the use of much thinner stator cross sections which is beneficial for reduced weight.
  • the uninterrupted radial flux path corresponds to an uninterrupted axial path in a radial flux device.
  • the flux path 500 in Fig. 25 terminates at the ID and OD at an integrated bearing race.
  • the uninterrupted path may also terminate at a bearing race seat if a separate bearing race is used. It may also terminate at an intermediate component or layer between the stator and the bearing race seat.
  • the uninterrupted radial path need not extend purely radially, but connects inner and outer diameters of the carrier (here, a stator). That is, the path follows a three dimensional path from ID to OD that is not interrupted. Thus, holes may be drilled in the cross section shown in Fig. 25, but there would still be an uninterrupted monolithic material path from ID to OD.
  • FIG. 26 an exploded view of exemplary rotor and stator is shown that is connected to a pair of robot arms using bolts.
  • a first arm 700 is connected to a rotor housing 702 using bolts 718.
  • the rotor housing 702 is connected to a rotor 708 using bolts 720.
  • a first bearing element 706 connects between the rotor 708 and a stator 712 and is connected by a press fit ring 704.
  • a second bearing element 710 also connects between the rotor 708 and the stator 712 using bolts 722.
  • the stator 712 is connected to a stator housing 714 using bolts 724.
  • a second arm 716 is connected to the stator housing 714 using bolts 726.
  • a rotor 606 is made from a ferrous material, such as Ductile Iron, and holds an equi-spaced array of magnets 605 that are polarised in a circumferential direction. The polarity of the magnets 605 is alternated in order to generate alternating north and south poles in the radial webs of the rotor 606.
  • the stator 609 is made from a ferrous material, such as Ductile Iron, and includes an equi-spaced array of axial posts around which a set of stator windings 610 are wrapped.
  • stator windings 610 polarises the posts of the stator 609 such that circumferential attraction and repulsion forces are generated between the posts of the stator 609 and the radial webs of the rotor 606, thereby generating torque.
  • the stator windings 610 are encapsulated by the stator potting compound 611, which serves to prevent movement of the wires and helps to transfer heat from the wires to the stator 609.
  • a stator cap 612 may be placed over the stator 609 and hold the wires 610 in place.
  • the magnets 605 also cause attraction between the stator 609 and the rotor 606.
  • the bearings 603 and 604 counteract the attraction force between the stator 609 and the rotor 606 via the housings 601, 602, 607 & 608 and act to accurately control the gap between them.
  • the axial attraction force between the stator 609 and the rotor 606 is adequate, in most applications, to prevent the upper housing 601 from separating from the lower housing 602, thereby eliminating the need for additional retention between them.
  • Diametral fits at the interfaces between the housings 601, 602, 607 & 608 and the rotor 606 and the stator 609 carry radial loads between the two assemblies via the inner 4-point contact bearing 604. External moments applied to the assembly are carried primarily through the outer thrust bearing 603.
  • the flow of current through the stator windings 610 tends to increase the temperature of the stator 609 relative to the other components. Conduction of the generated heat to the adjacent housings helps to reduce the increase to its temperature.
  • the example shown includes light alloy housings which have a higher coefficient of thermal expansion than the stator 609. To maintain an interference fit at the interface between the outer diameter of the stator 609 and the inner diameter of the lower housing 602 as the temperature increases the primary diametral location occurs at the inner diameter of the locating hook of the stator 609.
  • Magnets which taper tangentially such that they are thinner toward the air gap, can provide high performance in a concentrated flux rotor configuration.
  • a rotor 3300 in an axial flux configuration with magnets 3302 having tapered ends 3316 and rotor posts 3304 with tapered ends 3318.
  • the magnets and rotor posts taper in opposite directions to form an interlocking arrangement.
  • Permanent magnets taper in the direction of the stator 3330 while rotor posts 3304 taper away from the stator.
  • two substantially mirrored rotors 3300 can be assembled between a pair of stators, with tapered posts of each rotor meeting back to back and tapered magnets of each rotor meeting back to back.
  • tapering the magnets 3302 in this way allows for greater rotor post width at the air gap. It also allows for greater magnet width at the wide end of the magnet taper to provide more flux to the rotor post 3304 away from the air gap, where if the sides were parallel the posts 3304 would tend to be less saturated. In this way, the active permanent magnet 3302 and soft magnetic materials are used more effectively to provide more flux at the airgap.
  • the two rotors parts can be secured together for example by an adhesive, but in some preferred variations a mechanical feature such as bolts (not shown) or a securing ring (not shown) may be used.
  • tapered posts 3304 and magnets 3302 operate as stops that prevent the permanent magnets from dislodging, which reduces the need for magnetic force to retain the magnets in the rotor, and therefore reduces the need for magnetic flux to leak through the end iron 3314.
  • an array of flux path restrictions 3328 can be formed in the end iron 3314, for example, as holes in the end iron 3314 at the base of each rotor posts 3304 where they connect with the end iron 3314. These flux path restrictions 3328 reduce the available flux path between rotors posts 3304 and end iron 3314.
  • Fig. 30 shows an axial flux configuration of a tapered slot rotor, but the tapered slot rotor can be equivalently constructed in a radial flux configuration. Tapered magnets may narrow towards or away from the opposing carrier.
  • a second effect of tapering the magnets in this way is to bias a high percentage of the flux from a permanent magnet toward the air gap.
  • This is beneficial in at least two ways.
  • a first is that the tapered permanent magnet will be drawn toward the air gap where they will close the airgap between the permanent and the rotor slot wall for lower reluctance flux linkage and where they will be mechanically prevented from further movement and therefore securely retained by the tapered rotor posts.
  • the narrower rotor posts at the back surface results in a greater distance from post to post along the center plane of the rotor. This reduces the amount of leakage through the air from post to post along the center plane of the rotor.
  • a cost effective way to manufacture a tapered rotor post rotor is to use two symmetrical rotors 3300 back to back. This construction does not allow for the use of a back iron to stiffen the rotor, so a soft magnetic end iron 3314 is used instead.
  • the end iron 3314 has sections that are preferably as thin as possible to create a high reluctance flux path between rotor posts through the end iron, and as thick as necessary to provide the mechanical strength and rigidity to maintain a small and consistent air gap.
  • an embodiment uses permanent magnets 3302 that are longer than the soft magnetic stator posts 3332 at the air gap. This is shown in Fig. 31 where the permanent magnet 3302 are longer than rotor posts 3304 which would have the same or nearly the same length as the stator posts 3332. As shown in Fig. 32, a winding configuration 3334 extends around the stator post 3332. By increasing the permanent magnet depth compared to the stator radial length, the permanent magnets 3302 will be adequate to saturate the end iron 3314 while still maintaining high flux density in the rotor posts at the airgap. As shown in Fig.
  • the rotor posts 3304 have a larger width at the axial outer end of the rotor.
  • the flux restrictors 3328 are larger adjacent to the outer end of the rotor posts and smaller at the inner end of the rotor posts.
  • the flux restriction holes described for example in the embodiments disclosed in Fig. 3, Fig. 14, Fig. 22A, Fig. 22B, and Figs. 34-38 are designed to meet an acceptable trade-off between power and structural strength.
  • the cross-sectional area above the magnets provides the strength to maintain the airgap and the flux restrictors prevent flux from excessively extending between the magnets.
  • the flux restrictors can be placed with holes adjacent to every second post, rather than adjacent to every post, which will provide for a stronger structure but does not have a significant impact on the flux.
  • the flux restrictors could be blind or through- holes, so long as there is a cross-sectional area reduction in the flux path and the structural load path.
  • the flux restrictors will lie on either end of the posts, between the array of posts and each set of bearings.
  • the flux restrictors will preferably lie parallel with the length of each post.
  • the flux restrictors can be designed so that there is a greater cross-sectional area in a structural load path than in a magnetic flux path.
  • the flux restrictors could also be used in a radial flux machine in an equivalent manner as those described for the axial and linear flux machines described herein.
  • An embodiment of the machines described herein with flux restrictors may have a solid material made for example with ductile iron which is strong enough to support magnetic forces, but thin enough to be lightweight.
  • the flux restrictors may be placed adjacent to every post on the rotor or stator or adjacent to every second post on the rotor or stator.
  • the flux restrictors will generally be placed on both ends of each post, or each second post.
  • the flux restrictors may be placed adjacent to every post on one end of each post and adj acent to every second post on the other end of each post.
  • the flux restrictors may be placed in an alternating pattern so that each post is adjacent to only one flux restrictor, and for each adjacent post, the corresponding flux restrictor is adjacent to an opposite end of the adjacent posts.
  • the flux restrictors may have different sizes while maintaining the same geometry.
  • the cross-sectional flux path may be consistent between every second post, but the cross-sectional flux path may be selected so that it alternates between adjacent posts so that each post has a different cross-section flux path than the post directly adjacent to it.
  • the cross-section of each post that is adjacent to the flux restrictors may be smaller than the cross-section of each post that is not adjacent to the flux restrictors.
  • every second post will have a larger cross-section than each of the adjacent posts that are adjacent to the flux restrictors.
  • flux restrictors will generally be more effective to reduce cogging when placed on the rotor, rather than the stator, the flux restrictors can be placed on both rotor and stator, or only on the rotor. As shown in Fig. 31, there may be multiple flux restrictors adjacent to each end of the posts.
  • Manufacturing methods for the rotor can include casting or forming or powdered metal construction, additive manufacturing, machining etc. Manufacturing of the magnets can be done by forming or additive or subtractive manufacturing. Magnets can also be magnetised after insertion into slots. It may be possible with present or future processes to press powdered hard magnetic material into the rotor slots and then magnetizing the PM material after pressing, or a slurry of PM magnet material in an epoxy or other polymer can be used to fill the slots and then magnetized after hardening. Magnetizing of the hard magnetic material can be done by applying very high flux density to two or more posts at a time.
  • Back irons, side irons and end irons serve as retaining elements and form a rigid connection with the rotor posts.
  • Features of one embodiment may be combined with features of other embodiments.
  • FIG. 32 there is shown a stator-rotor-stator configuration with an end iron 3314.
  • the end iron 3314 and rotor posts 3304 can be formed from a single piece of isometric soft metallic material, with a single array of permanent magnets 3302 fitting between rotor posts 3304.
  • End iron 3314 is formed at both ends of the rotors 3300.
  • flux path restrictions 3328 can be included as shown in Fig. 33.
  • FIG. 33 shows an embodiment of a stator-rotor-stator configuration with a back iron 3310, end iron 3314 and flux path restrictions 3328.
  • the two array of permanent magnets 3302 are separated by back iron 3310.
  • Flux path restrictions 3328 are formed as bores at the ends of the permanent magnets 3302 to reduce the flux leakage in the end iron 3314.
  • Fig. 34 shows an embodiment of a rotor-stator-rotor configuration.
  • Two concentrated flux rotors 3300 engage a central stator 3330.
  • the rotors 3300 each include end iron 3314 and flux path restriction 3328. In many applications end iron only or back iron only will be sufficient to provide adequate rigidity to the concentrated flux rotor 3300.
  • Fig. 35 shows an embodiment of a rotor-stator-rotor configuration. The embodiment is essentially the same as that shown in Fig. 34 with the addition of a think back iron 3310 on each rotor 3300.
  • Fig. 36 shows an embodiment of a rotor-stator-rotor configuration of a linear flux machine.
  • the stator 3330 has an array of posts 3332.
  • the rotor surrounds the stator and is made of one or more pieces of material, for example, a soft magnetic isotropic material.
  • Receiving slots for the permanent magnets 3302 on the internal structure of the rotor 3300 act as rotor posts 3304, rotor back iron 3310 and rotor end iron 3314.
  • Many constructions of a linear motor are contemplated herein.
  • the side section of the rotor for example, may be of a different material than the upper and lower rotor portions.
  • FIG. 37 shows an embodiment of the rotor-stator-rotor configuration of a linear flux machine without a back iron 3310 on the rotor 3300 and having a number of flux restrictors 3306 adjacent to each of the permanent magnets 3302 on either side of the slots.
  • Fig. 38 shows a rotor-stator-rotor configuration with an alternating pattern of flux restrictors 3306 that are adjacent to every second permanent magnet.
  • any of the disclosed structures may be used with an electric machine that has electromagnetic elements including posts and slots between the posts, where the posts are wound to create poles, at least on either of a stator or rotor, where the pole density is within a range of pole density defined by the equations specified in this patent document and the post height is within a range of post height defined by the equations specified in this patent document.
  • These equations each define a bounded area.
  • the bounded areas are dependent on the size of the electric machine, where the size is defined by the radius of the machine.
  • the bounded areas together define a bounded surface in a space defined by pole density, post height and size of machine. This bounded region is disclosed in copending WO2017024409 published February 16, 2017, and repeated here.
  • An electric machine with increased torque to mass ratio is particularly useful when several of the electric machines are spaced along an arm, such as a robotic arm, since efficiency is less important relative to the need for one electric machine to lift or accelerate one or more other electric machines. It is believed that improved performance of an electric machine having pole density and conductor volume or post height as disclosed results at least in part from 1) a narrower slot having a shorter heat flow path from the hottest conductor to a post and 2) a shorter heat flow path from the top of a post to a heat dissipation surface.
  • each electric machine embodiment disclosed is shown as having a pole density and post height that is within the definition of pole density and post height that is believed to provide a benefit in terms of KR.
  • tooth width can be in the order of 1 mm for a 25 mm wide machine.
  • Narrower teeth can be used.
  • An advantage of thinner teeth is that solid materials such as, but not limited to steel or iron or a magnetic metal alloy, may can be used with minimal eddy currents due to the teeth being closer to the thickness of normal motor laminations.
  • a common motor lamination for this size of motor can be in the range of 0.015" to 0.025".
  • the proposed pole density and tooth geometry also helps avoid eddy currents in the first carrier (stator).
  • Embodiments of the disclosed machines may use fractional windings. Some embodiments may use distributed windings; others may use concentrated windings. Distributed windings are heavier due to more copper in the end turns and lower power (requiring a bigger motor). They also require thicker backiron because the flux has to travel at least three posts, rather than to the next post as with a fractional winding. Distributed windings produce more heat because of the longer conductors (the result of longer distance the end turns have to connect between).
  • An embodiment of an electric machine with the proposed pole density may have any suitable number of posts.
  • a minimum number of posts may be 100 posts.
  • a high number of posts allows fewer windings per post.
  • the windings on each posts are only one layer thick (measured circumferentially, outward from the post). This reduces the number of airgaps and/or potting compound gaps and/or wire insulation layers that heat from the conductors conduct through for the conductors to dissipate heat conductively to the stator posts. This has benefits for heat capacity (for momentary high current events) and for continuous operation cooling.
  • This is beneficial for cooling the conductors and is one of many exemplary ways to take advantage of the low conductor volume as disclosed.
  • a single row (or low number of rows) of coils per posts also reduces manufacturing complexity allowing for lower cost production.
  • the windings of each post are two layers thick.
  • the number of slots may be 60 or more, or 100 or more for an axial flux electric machine, for example 108 slots in an exemplary 175 mm diameter embodiment.
  • the average radial length-to-circumferential width of the posts may be above 4: 1, such as about 8: 1 but may go to 10: 1 and higher.
  • the ratio is about 8: 1.
  • a reduced rigidity requirement by coating the airgap with a low friction surface that maintains the airgap.
  • a low friction surface is applied in the airgap which maintains a 0.008" airgap. Coatings, such as DLC (diamond-like coating), can be deposited at 0.0025" on both the rotor and the stator and the gap will be maintained.
  • Ranges of pole pitch (or density) and conductor volume have been found which give a significant benefit either in terms of KR, or in terms of a weighting function combining torque, torque-to-weight, and Km (as described further).
  • the amount of benefit in terms of the weighting function is dependent on the amount of cooling and other factors, but the equations define novel structures of electric machines that provide benefits as indicated. Equations are given which define bounded regions determined by the ranges of pole density and conductor volume which yield these benefits.
  • advantages are obtained by operating within a region of a phase space defined by machine size, pole density and post height.
  • a series of graphs shown in Fig. 39A to Fig. 39F, show torque density (z axis) v slot density (x axis) and post height (y axis) for an exemplary series of linear motor section geometries, created and analysed using FEMM software using an automated solver generated in OCTAVETM(which is a program for solving numerical computations). Slot density was used in this example because it is the same as pole density.
  • the program yielded values for coil temperature, rotor temperature and stator temperature.
  • a set cooling rate was applied to the stator inner surface using water as the coolant and a convection coefficient of 700 W/m 2 K.
  • the temperature of the water was set at 15°C and it had a flow rate between 6-20 mm/s. Steady state conditions were assumed.
  • High torque-to-weight is of benefit in some applications, but a minimum level of torque may be necessary for applications such as robotics where the arm, no matter how light it may be as a result of high torque-to-weight actuators, must still have enough torque to lift and move a payload.
  • Electric machines having a pole density and conductor volume within the ranges disclosed in this patent document provide high torque and torque-to-weight at acceptable power consumption levels.
  • the force per area at a constant current density 2320 is plotted in Fig. 39A as a function of slot pitch and post height.
  • the same current applied to all motors in the virtual series results in dramatically lower force per area in the disclosed ranges 2322 (indicated schematically by the dashed lines).
  • the dashed lines correspond to the middle boundary from each size (25 mm, 50 m, 100 mm and 200 mm as discussed in relation to the equations below) projected onto the 3D surface.
  • the middle boundaries correspond to the sets of equations A2, B2, C2 and D2.
  • Fig. 39B the same series of motors is used as in Fig. 39A, but instead of constant current density applied to each motor, the current density was varied until the steady state temperature of the conductors was ⁇ 70°C.
  • a reasonable representation of a typical water cooling effect was applied to the outer axial surface of the stators at a convection coefficient of 700 W/m 2 K. The temperature of the water was set at 15°C. Ambient temperature was set at 15°C. No air convective cooling was applied to the rotor for simplicity because the water cooled surface was highly dominant in terms of cooling and because the rotor was not producing heat of its own. Steady state conditions were assumed. For each point on the 3D graph, the current density of the motor was increased from zero until the temperature of the coils reached -70 deg C.
  • Fig 39C is the same as Fig. 39D except that it has constant current at 6 A/mm2 as apposed to constant temperature of 70 deg C.
  • Torque - weighting 1
  • Torque-to-weight 3
  • Power consumption 2
  • Torque-to-weight was the most highly weighted because the weight of the arm is determined by the weight of the actuator and because the weight of the arm will typically be significantly higher than the weight of the payload.
  • Torque was weighted at 1 to include it as an important consideration but recognizing that the payload may be quite a bit lower than the weight of the arm.
  • Power consumption was given a moderate weighting because it is an important consideration, but power consumption is known to benefit from lower arm weight, as is accomplished by a higher weighting on torque-to-weight, so a higher weighting on power consumption was deemed to be potentially counter-productive.
  • Fig. 39D shows a trend toward lower overall performance toward and continuing through the disclosed ranges 2322 of slot (or pole) density and conductor volume.
  • Fig. 39D shows a benefit in the disclosed range when the constant temperature current density is applied from Fig. 39B.
  • KM An industry standard metric for motor capability is the KM which is basically torque- to-power consumption. KM assumes sufficient cooling for a given electrical power. It only considers the amount of power required to produce a certain level of torque.
  • the surface 2330 as a function of slot pitch and post height is plotted in Fig. 39E.
  • the torque to weight to power consumption shows the most unexpected and dramatic benefit in the disclosed ranges 2322 as seen from the graph of the KR surface 2332 as a function of slot pitch and post height in Fig. 39F.
  • High KR may not be of great benefit in stationary applications, but in applications such as robotics, KR indicates that power consumption benefits can be achieved by reducing the weight of the entire system.
  • a method of producing a graph showing how KR varies with pole density and post height is as follows. Consider a motor section with geometry A having low conductor volume (low post height) and low pole density. The motor section with geometry A is simulated; a set cooling rate is applied to the stator inner surface using water as the coolant and a convection coefficient of 700 W/m 2 K.
  • the temperature of the water is set at 15°C and it has a flow rate between 6-20 mm/s. Steady state conditions are assumed.
  • the current passing through the conductor of geometry A is then increased until the maximum temperature of the conductors reaches 70 °C.
  • the torque density of geometry A at this point is then recorded and plotted in the graph for the corresponding values of post height and pole density.
  • the process is repeated for other geometries, obtained, by example, through varying the post height and pole density and scaling the remaining parameters as described above.
  • a geometry B may be is obtained from geometry A by increasing the post height, with all other parameters scaled as described above.
  • a geometry C may have the same post height as geometry A but greater pole density.
  • a geometry D may have increased post height and increased pole density as compared to geometry A. Plotting the torque densities results in a surface in a graph.
  • an electric machine comprising a rotor with tangentially oriented permanent magnets and an analogous electric machine comprising a rotor with surface-mounted permanent magnets may possess somewhat different KR surfaces; nonetheless, the principles described above will still apply and a benefit would still be predicted within the region of geometries of low post height and high pole density described previously. As currently understood, the principles apply only to electric machines with posts, such as axial flux and radial flux machines.
  • the parameter KR is size-independent and has been converted from a conventional KR to use force instead of torque, and to be independent of both circumferential length and axial length. Therefore, the conventional KR of any size motor can be found from the K R value. And for two motors of identical size (diameter at the airgap and axial length) but different geometry (i.e. pole density and/or post height), the multiplying factor will be the same, so the motor with higher KR will have a higher conventional KR.
  • K R as a function of pole density and post height greatly resembles the surface of a graph showing conventional KR.
  • this particular surface corresponding to the torque density, may change considerably when different temperatures are used as the constraint in the analysis.
  • KR does not change substantially (provided the current doesn't get sufficiently high for the motors in the series start to saturate; then the 3D curve shape will change.) It is the K R , therefore, that is used to define the specific range of pole density and post height which result in the previously-discussed benefits.
  • the ranges of benefit disclosed depend on the resultant motor diameter at the airgap. Smaller motors are more constrained because the physical size of the motor prevents lower slot densities from being used.
  • a 50:50 ratio of pos slot width was chosen for these simulations, as analysis had shown that highest benefits are obtained when the ratio is between 40:60 and 60:40.
  • a 50:50 ratio represents a typical best-case scenario; at fixed post height, using a 10:90 slot:post width ratio will have a significantly degraded performance by comparison.
  • Analysis shows that at constant post height, an embodiment exhibits the maximum of torque and torque density at a 50% slot width, and the maximum of Km and Kr at 40% slot width. However, the maximum values of Km and Kr are within 5% of the values given at a 50:50 geometry; consequently a 50:50 ratio was viewed as a reasonable choice of scaling parameter for the simulations.
  • Other ratios of post: slot width would give a portion of the benefits disclosed.
  • Equations and graphs are discussed below which show the ranges of pole density and conductor volume which give a significant benefit either in terms of KR, or in terms of a weighting function combining torque, torque-to-weight, and Km, for different embodiments. As with the previously-described equations, the region of benefit in terms of the weighting function is dependent on the amount of cooling.
  • Size of an electric machine means the airgap diameter of an axial flux machine or radial flux machine as defined herein or the length in the direction of translation of the carriers of a linear machine.
  • the first bounded region corresponds to regions where a significant KR benefit is found with respect to the rest of the geometries in the domain.
  • KR has a higher value in the disclosed range of geometry than anywhere outside of the range, indicating potential benefits to overall system efficiency for certain applications using devices of these geometries.
  • the graph of KR is used to define the boundary by placing a horizontal plane through at a specified KR value.
  • Four values of KR are used to define areas of benefit for four different actuator size ranges corresponding to sizes of 200mm and larger, 100mm and larger, 50mm and larger, and 25mm and larger.
  • pole pitch is represented by the variable S, in mm.
  • Post height is also represented in millimetres.
  • each boundary line is defined for a given K" value, such that for each machine size there is a set of K" values and a corresponding set of boundary lines.
  • Pairs of boundary lines can be chosen, in which one boundary line is chosen from each of two consecutive sizes of device, i.e. 25mm and 50mm, 50mm and 100mm, or 100mm and 200mm.
  • the boundary lines occupy a space or volume defined by size, pole pitch and post height.
  • a boundary surface may be defined as the two-dimensional uninterrupted surface in the space that is the exterior surface of the union of all lines that connect an arbitrary point in the first boundary line and an arbitrary point in the second boundary line.
  • the boundary surface encloses a benefit space.
  • the boundary surface defines a benefit space.
  • An electric machine with a size, pole pitch and post height that is within a given benefit space is considered to fall within the embodiment defined by the corresponding boundary lines for that size of machine.
  • the boundary lines calculated for the largest calculated size are used.
  • the benefit space beyond the largest calculated size is thus simply the surface defined by the calculated boundary lines for that size and the volume of points corresponding to greater size but with pole pitch and post height equal to a point on the surface.
  • the main components of an electric machine comprise a first carrier (rotor, stator, or part of linear machine) having an array of electromagnetic elements and a second carrier having electromagnetic elements defining magnetic poles, the second carrier being arranged to move relative to the first carrier for example by bearings, which could be magnetic bearings.
  • the movement may be caused by interaction of magnetic flux produced by electromagnetic elements of the first carrier and of the second carrier (motor embodiment) or by an external source, in which case the movement causes electromotive force to be produced in windings of the electric machine (generator embodiment).
  • An airgap is provided between the first carrier and the second carrier.
  • the electromagnetic elements of the first carrier include posts, with slots between the posts, one or more electric conductors in each slot, the posts of the first carrier having a post height in mm.
  • the first carrier and the second carrier together define a size of the electric machine.
  • the magnetic poles having a pole pitch in mm.
  • the size of the motor, pole pitch and post height are selected to fall within a region in a space defined by size, pole pitch and post height.
  • the region is defined by 1) a union of a) a first surface defined by a first set of inequalities for a first size of electric machine, b) a second surface defined by a second set of inequalities for a second size of electric machine; and c) a set defined as containing all points lying on line segments having a first end point on the first surface and a second end point on the second surface, or 2) a surface defined by a set of inequalities and all points corresponding to greater size but with pole pitch and post height corresponding to points on the surface.
  • the first set of inequalities and the second set of inequalities are respectively sets of inequalities A and B, or B and C, or C and D
  • A is selected from the group of sets of inequalities consisting of the equations set forward in Tables 1, 2 and 3 (respectively sets of equalities Al, A2 and A3)
  • B is selected from the group of sets of inequalities consisting of the equations set forward in Tables 4, 5 and 6 (respectively sets of equalities Bl, B2 and B3)
  • C is selected from the group of sets of inequalities consisting of the equations set forward in Tables 7, 8 and 9 (respectively sets of inequalities CI, C2, C3)
  • D is selected from the group of sets of inequalities consisting of the inequalities set forward in Tables 10, 11 and 12 (respectively sets of inequalities Dl, D2 and D3).
  • the space in which the electric machine is characterized may be formed by any pair of inequalities that are defined by sets of inequalities for adjacent sizes, for example: Al Bl, Al B2, Al B3, A2 Bl, A2 B2, A2 B3, A3 Bl, A3 B2, A3 B3, Bl CI, Bl C2, Bl C3, B2 CI, B2 C2, B2 C3, B3 CI, B3 C2, B3 C3, CI Dl, CI D2, CI D3, C2 Dl, C2 D2, C2 D3, C3 Dl, C3 D2, C3 D3. It may also be formed by any set of inequalities and all points corresponding greater size but having post height and pole pitch within the region defined by the set of inequalities.
  • All of the devices described in this application may have sizes, pole pitches and post heights falling within the regions and spaces defined by these equations.
  • the range of geometry may provide unusually high torque-to-weight for a given electrical power input. This efficiency is independent of temperature. For example, at a given torque-to-weight, an actuator inside the disclosed range, may run cooler, for a given method of cooling, than a similar actuator outside of the disclosed range, because device device in the disclosed range will use less power.
  • the low conductor volume in this case has the benefit of lower thermal resistance due to the shorter conductors.
  • the need to power these conductors at higher current densities is more than compensated for by the heat dissipation benefits of the device to achieve a given torque-to-weight.
  • the reduction in weight which results, in part, from the low conductor volume
  • the extra power required which results from the higher current densities
  • net benefit can be produced in terms of KR.
  • cooling is still needed to achieve the KR benefit, but it is assumed for the KR calculation that adequate cooling is used.
  • radiative cooling is sufficient.
  • a fan and cooling fins is needed.
  • water cooling is needed.
  • the KR is the same at low to high power output (until the stator saturates at which time the KR will be reduced) so different levels of cooling will be needed depending on the power output but the torque-to-wei ght-to-power consumption remains reasonably constant.
  • the disclosed range of pole density and conductor volume may provide unusually high torque-to-weight for a given rate of heat dissipation with a given method of cooling.
  • the disclosed range of pole density and conductor volume may produce higher torque-to-weight for a given cooling method applied to the back surface of the stator and a given conductor temperature.
  • the primary form of electrical conductor cooling for the disclosed range of pole density and electrical conductor volume is thermal conductive heat transfer from the electrical conductors to the back surface of the stator.
  • Heat can be extracted from the back surface of the stator though direct contact with a cooling fluid or through conduction to another member such as a housing, or through radiation, for example.
  • Other surfaces of the stator or conductors can also be cooled by various means. Cooling the back surface of the stator is shown to be a cost effective and simple option for many motor types.
  • a sample analysis (not shown here) indicates that geometry in the disclosed range which shows better heat dissipation from the back surface of the stator (as compared to motors outside of the disclosed range) will also generally show improved heat dissipation than motors outside of the disclosed range when other surfaces of the stator or conductors are cooled.
  • the back surface of the stator is, therefore, viewed as a useful cooling surface, as well as an indicator of the effectiveness of each motor in the series to the application of cooling to other surfaces of the stator and conductors.
  • the back surface of the stator has been chosen for the main cooling surface for the motor series analysis which is used to identify the disclosed range.
  • Stator back iron may have an axial depth that is 50% of the width (circumferential or tangential width) of the posts.
  • the posts may each have a tangential width and the stator may comprise a backiron portion, the backiron portion having a thickness equal to or less than half of the tangential width of the posts, or may be less than the tangential width of the posts.
  • Thicker back iron adds weight with minimal benefit. Thinner backiron helps with cooling but the effect of back iron thickness on cooling is not very significant.
  • the backiron surface may be in physical contact with the housing to conduct heat physically from the stator to the housing, and/or the back surface of the stator can be exposed to an actively circulated cooling fluid and/or the back surface of the stator can be configured for radiative heat dissipation to the atmosphere or to the housing or other components, and/or the back surface of the stator can be configured for convective or passive cooling through movement of air or liquid over the surface of the stator and or housing. Gas or liquid moving past the back surface of the stator may be contained or not contained.
  • the back surface of the stator may be sealed from the atmosphere or exposed to the atmosphere.
  • the atmosphere may be air or water or other fluid surrounding the actuator.
  • the environment may also be a vacuum, such as is necessary for some manufacturing processes or the vacuum of space.
  • the back surface of the stator may be configured with cooling fins which increase the surface area. These cooling fins may be exposed to a cooling fluid and/or in contact with a heat sink such as the housing or other solid member.
  • the cooling fins on a stator may have a height greater than 50% of the post width in the circumferential direction.
  • heat dissipating surfaces may include the surface of a post which may be exposed to a cooling fluid such as air or liquid which is circulated through a slot such as between a conductor and the post.
  • Other methods of cooling the stator and/or the conductors may include cooling channels on or below the surface of the stator and/or on or below the surface of the conductors. These and other forms of cooling are seen as supplementary to the primary thermally conductive cooling from the conductors to the back surface of the stator. In some cases the supplementary cooling methods may even draw more heat away from the stator than the primary conductive cooling effect, but active cooling methods require energy and additional cost and complexity, so the conductive cooling path from the conductors to the back surface of the stator is disclosed here as the primary mode of cooling.
  • a pole carrier of the electric machine includes slots and posts, the slots having a slot or pole pitch s and the posts having a height h, in which s is related to h according to the disclosed equations
  • electric excitation may be applied to conductors in the slots with a current density of at least 70 A/mm2. Electric excitations in excess of 70 A/mm 2 are generally considered suitable for the operation of the disclosed device.
  • the cooling effect of having the disclosed slot and conductor structure provides cooling to offset some or all of the heat generated by the current in the conductors. Any remaining heat generated may be dissipated using one or more of the disclosed cooling structures or channels.
  • Motors inside the disclosed range show a reduction of the average flux density in the magnetic flux path for a given electrical input power. This is due, in part, to the reduced flux path length of the shorter posts and reduced distance from post to adjacent post through the backiron, as well as the reduced flux leakage between posts. The result is the ability to run higher current density in motors in the disclosed range without reaching saturation.
  • the combination of increased cooling capability and lower flux density at a given current density as compared to motors outside of the disclosed range creates a combination of conditions where higher continuous torque-to-weight can be achieved for a given temperature at a given cooling rate, and where the peak momentary torque-to-weight of motors in the disclosed range can be significantly higher due to operating at a lower flux density for a given torque-to-weight in the disclosed range.
  • Embodiments of the disclosed rotor can achieve unusually high flux density in the airgap leading to high attraction forces on the stator posts.
  • achieving the high torque-to-weight of an embodiment of the disclosed electric machine requires the use of a backiron that has an axial thickness that, in an embodiment, is less than the circumferential thickness of the posts (and, in an embodiment, is about half of the thickness of the posts).
  • the axial flux motor configuration disclosed and the relatively short stator posts of the disclosed range results in an inherently thin stator structure.
  • a radial flux motor circular laminates with integrated posts can be used. This has an inherent rigidity and naturally provides a desirable flux path along the circumferential and radial orientation of the laminates.
  • the axial flux function of an embodiment of the present device requires an assembly of individual laminated parts. The result is the need to manufacture up to hundreds of post components for each actuator, which increases manufacturing complexity, time and cost.
  • the relatively thin backiron does not provide an adequate surface area for many potting compounds or adhesives to reliably fix the posts to the backiron, especially at the high frequency force variation and elevated temperatures that are common to electrical machines.
  • a typical aerospace adhesive that might be used to fix a stator post into a receiving slot in the stator, might have a heat deflection temperature of under 80 deg C for a stress on the epoxy of less than 300 psi.
  • the back-iron disk of an embodiment can be made of laminates, powdered metal, or solid metal.
  • laminates has certain advantages, including the possibility of stamped material construction; however; if laminates are used, they must be attached through means capable of withstanding the forces and temperatures of operation of the device. Common methods such as glue may not be sufficient for certain regimes of operation where the forces and/or temperatures are high. Nonetheless, laminations may be a good choice for other regimes, and are expected to work well for many high-speed applications.
  • a stator manufactured of solid steel typically has high eddy current losses.
  • geometric features of motors in the disclosed range have an eddy current and hysteresis reducing effect that, in some regimes of operation of embodiments of the present device, for instance when operating at speeds which are suitable for robotics, the eddy current losses may be sufficiently low to enable the use of a solid stator.
  • Using solid material is advantageous for strength, rigidity, heat resistance, and fatigue strength. Since embodiments of the present device can often generate sufficient torque to be used without a gearbox in certain applications, the resulting operational speeds may be sufficiently low that the eddy current losses be acceptable even with a solid steel stator.
  • Solid cast iron has been found to give sufficiently low eddy current losses to be practical with some configurations and regimes of operation.
  • Stators may be constructed of either laminated stacks or a sintered powdered metal.
  • An objective of these constructions, as compared to the use of solid materials, is to reduce the cross sectional area of electrically insulated soft magnetic material perpendicular to the flux path and thus reduce the generation of eddy currents. Eddy currents reduce the efficiency by requiring additional input power; they produce extra heat which must be dissipated by the system; and they reduce the output torque by creating a damping effect
  • a single-piece stator fabricated from a solid electrically conductive material may be used with embodiments of the disclosed device, particularly within the disclosed ranges of pole density and post height.
  • the application should be sufficiently low speed, for example a duty cycle that consists of 50% (60%, 70%, 80%, 90%) of the operation at 200 rpm or less for a 175mm average airgap diameter motor having the disclosed range of geometry.
  • Speeds of less than 200 rpm are generally considered suitable for the operation of the device.
  • Speeds of less than 100 rpm, less than 50 rpm and less than 25 rpm are also considered suitable for the operation of the device.
  • the continuous flux path may be provided by a stator made of isotropic materials such as ductile iron, steel alloy such as cobalt or silicon steel, pressed or sintered powdered metal, for example.
  • the metal may be isotropic from post to adjacent post and non-isotropic from a post to a bearing race or a post to a member or assembly that connects to a bearing, including variable material alloy from backiron to cooling fins and/or to bearings. This can be done by explosion welding or fused deposition additive manufacturing, or stir welding or other forms of combining dissimilar materials.
  • the stator may be one piece or unitary from a post to an adjacent post and from a post to a bearing race seat (or bushing seat or contact).
  • the stator may be unitary from a post to a post and from one of these posts to a member or assembly that is in compression so-as to preload a bearing or bushing.
  • the stator may be unitary from a post to a post and from one of these posts to a member or assembly that is in compression so-as to pre-load a bearing or bushing and all or part of the compressive load is a result of magnetic attraction between the stator and a rotor.
  • the housing assembly may be flexible enough to displace the bearing race seat in the direction of bearing preload past the bearing seat position if the bearing is present, by more than .002" if the bearing is not present.
  • the housing assembly may be flexible enough to displace the bearing race seat in the direction of bearing preload, past the bearing seat position if the bearing is present, by more than .002" if the bearing is not present and the force exerted on the stator to cause this deformation of the housing is provided at least in part, by the magnetic attraction of a stator to a rotor.
  • Fig. 52 to Fig. 59 show an overview and simplified section views of an exemplary stator 3802 and rotor 3801 of a device within the disclosed range of pole density and post height inserted into a robot arm 3800 as a frameless motor/actuator. Note that conductors and wiring are not shown in these figures for simplicity.
  • An outer bearing 3804 that is used for the arm pivot support is also used to define an airgap 3809. This allows the frameless actuator to be used in the system without the mass and complexity of a separate actuator housing.
  • An additional bearing 3808 may be used on the ID of the frameless actuator assembly in conjunction with a spacer ring 3803 to maintain the desired airgap dimension with a longer radial post length.
  • Interlocking features 3812 (Fig.
  • the spacer element 3803 can be made of a low density materials such as aluminum or magnesium. This exemplary embodiment has a 175mm average airgap diameter and 25 mm radial post length.
  • the isotropic steel alloy or iron alloy stator 3802 and isotropic steel alloy or iron alloy rotor 3801 with backiron are sufficiently rigid to maintain a 0.005" airgap when supported at the ID and OD with a bearing.
  • the magnetic attraction between the rotor 3801 and stator 3802 can be used to provide preload on the bearings 3804, 3808 and may be used to reduce or eliminate the need for fasteners to keep the bearings seated in upper and lower arm housings 3805, 3806, respectively.
  • This construction is considered to be beneficial in terms of simplicity and light weight to the point of allowing the entire arm assembly to be lighter than if it used a motor outside of the disclosed range.
  • this exemplary embodiment provides a way to assemble the arm and magnetic components from the airgap axial end of the actuator. This is accomplished by the use of an array of tabs 3812, 3814 on the OD of the stator 3802 and rotor 3801 which allow the stator and rotor to be inserted in to the housings 3805, 3806 and then turned to engage with the matching array of tabs 3816, 3813 on the housings 3805, 3806. Threaded engagements would be another option.
  • a 10 OD actuator of the present device can have a passive PM preload of up to 1500 lbs or more between the stator or rotor. This makes it very challenging and even dangerous to assemble.
  • Embodiments of the present device allow PM's to be inserted after the stator and rotor are assembled together. This allows precision and low risk alignment of the stator and rotor and bearings and connections before any PM's and their magnetic force is added to the assembly.

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  • Engineering & Computer Science (AREA)
  • General Engineering & Computer Science (AREA)
  • Power Engineering (AREA)
  • Mechanical Engineering (AREA)
  • Manufacturing & Machinery (AREA)
  • Iron Core Of Rotating Electric Machines (AREA)
  • Motor Or Generator Frames (AREA)
  • Rolling Contact Bearings (AREA)
  • Permanent Magnet Type Synchronous Machine (AREA)
  • Permanent Field Magnets Of Synchronous Machinery (AREA)

Abstract

La présente invention concerne un procédé d'alignement d'une pluralité d'éléments électromagnétiques dans une machine électrique. La machine électrique comporte un premier support ayant un réseau d'éléments électromagnétiques et un second support ayant un réseau de montants définissant des fentes entre chaque montant. Les supports sont agencés de sorte à se déplacer les uns par rapport aux autres. Les supports sont placés en alignement axial et de telle sorte qu'un entrefer soit formé entre eux. Une pluralité d'aimants permanents sont prévus, chacun ayant une paire de pôles magnétiques. La pluralité d'aimants permanents est placée une à la fois selon un agencement de polarité alternée dans les fentes de telle sorte que, pour chaque montant du réseau de montants, les deux aimants permanents placés à proximité du montant soient orientés de telle sorte que les pôles magnétiques de chaque aimant permanent soient orientés vers le montant.
PCT/CA2017/050856 2016-07-15 2017-07-14 Machine électrique et procédé d'alignement WO2018010030A1 (fr)

Applications Claiming Priority (6)

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US201662363202P 2016-07-15 2016-07-15
US62/363,202 2016-07-15
US15/235,088 US10476323B2 (en) 2015-08-11 2016-08-11 Electric machine
US15/235,088 2016-08-11
US201762460086P 2017-02-16 2017-02-16
US62/460,086 2017-02-16

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PCT/CA2017/050856 WO2018010030A1 (fr) 2016-07-15 2017-07-14 Machine électrique et procédé d'alignement

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JP (1) JP6823174B2 (fr)
KR (1) KR102208324B1 (fr)
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KR102208324B1 (ko) 2021-01-28
CN109565188B (zh) 2022-12-06
KR20190029668A (ko) 2019-03-20
EP3485556A1 (fr) 2019-05-22
CA3030311A1 (fr) 2018-01-18
EP3485556A4 (fr) 2020-07-29
JP6823174B2 (ja) 2021-01-27
JP2019525720A (ja) 2019-09-05
CN109565188A (zh) 2019-04-02
WO2018010031A1 (fr) 2018-01-18

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