GB2351121A

GB2351121A - A rotatable joint

Info

Publication number: GB2351121A
Application number: GB0020284A
Authority: GB
Inventors: Nicholas John Peter Wirth
Original assignee: Roboscience Ltd
Current assignee: Roboscience Ltd
Priority date: 2000-08-18
Filing date: 2000-08-18
Publication date: 2000-12-20
Anticipated expiration: 2020-08-18
Also published as: GB0020284D0; GB2351121B

Abstract

A rotatable joint between external members comprises a stator incorporating a stator gear 1 and a rotor incorporating a rotor gear 2, these gears being engaged by pinion gears 3 and 4 which are coupled in a unitary structure. The arrangement is such that rotation of gear 3 around the gear 1 leads to a small movement of the gear 2 about axis O and so provides a gear arrangement of high reduction ratio. The stator and rotor are each provided with a connector structure 30, 31, to which external members 33, 34 may be connected. The gear 3 may be driven by a sun gear which, in turn, is driven by an electric motor. A potentiometer may measure the rotation between the external members which may be the arms of a robot.

Description

1 2351121

SPECIFICATION

ROTATABLE JOINT Descriptio

Technical Field and Backgound Art

The invention relates to a rotatable joint.

It is known to provide rotatable joints for connecting together two members between which relative rotation is required. A known form of rotatable joint is the simple door hinge. In such a hinge a pin rotates within a cylinder, and each of these parts is provided with a connector structure in the form of an apertured plate. These plates may be connected, one to the door, the other to the doorjamb, so as to provide relative rotation between these two.

The present invention contemplates a rotatable joint in which a gearing arrangement is interposed between the two connector structures.

Disclosure of the Invention

According to the invention a rotatable joint comprises a stator incorporating a circular stator gear and a rotor incorporating a circular rotor gear, the gears being of different radii but having a common axis and the rotor being rotatable about that axis relative to the stator, first and second pinion gears of different radii having a further common axis and being disposed to rotate together about that axis, the first and second pinion gears being arranged to engage the stator gear and the rotor gear respectively as planet 2 gears, the arrangement being such that upon rotation of the first pinion gear around the stator gear the second pinion gear, in rotating round the rotor gear causes the latter to rotate about said common axis, and the stator and the rotor each being provided with a connector structure whose purpose is to provide for the connection of an external member.

Brief Description of the Drawings

Figure 1 represents diagrammatically a known epicyclic gear arrangement.. Figure 2 represents a cross-section on the line C - C' of the arrangement of Figure 1. Figure 3 represents diagrammatically a rotatable joint according to the invention. Figure 4 represents a cross-sectiori of the arrangement of Figure 3 taken on the line A-B. Figure 5 represents a modification of part of Figure 4. Figure 6 and 7 represent cross-sections of further modifications of the embodiment of Figure 3. Figure 8 shows a perspective view of a fimlher embodiment of the invention. Figures 9, 10 and 11 show respectively side, top and end views of the embodiment of Figure 8. Figure 12 shows a sectional view of part of the embodiment of Figure 8 Figure 13 shows a sectional view of the embodiment of Figure 8 taken perpendicular to the rotational axis. Figures 14 shows the embodiment of figure 8 as an exploded diagram.

Modes for cgying out the Invention Figures 1 and 2 represent a known epicyclic gear arrangement comprising pinion gears 3, 4 disposed to rotate together about an axis Y - V. As shown these are formed as an integral structure. The gears respectively engage internal gears 1, 2 centred on an axis 0, the gear 1 being stationary and the gear 2 being rotatable. A sun gear 5 drives the pinion gear 3 causing this to rotate round the gear 1 in the direction Mp. As the pinion gear 3 makes one revolution around the gearl, the pinion gear 4 makes the same number of revolutions because the two are integrally formed and constrained to move together. But the distance unrolled by the periphery of the gear 4 is slightly different from the circumference of gear 2, and the latter is caused to rotate in the direction MR to accommodate this small difference. Hence there is a small rotation of the rotor gear 2 for each rotation of the sun gear 5.

It can be shown that the reduction gear ratio G.R. between the sun gear 5 and the rotor gear 2 is given by:

G.R. =(2 + ?R35 R2 R4) R) W,-RA --!Z -R3 2 - R3 where R,, R2, etc., are the radii of the gears indicated by the suffixes, and the tooth size (module) is the same for all gears.

3 Since, in these circumstances, the gear radius is proportional to the number of teeth, it can be shown that with gears having teeth as follows: Gear 1: 72 teeth, Gear 2: 73 teeth, Gear 3: 30 teeth, Gear 4: 31 teeth, Gear 5: 12 teeth, a reduction gear ratio of I: 365 is achieved, i.e., a reduction of 365 times.

Figures 3 and 4 represent an embodiment of a rotatable joint according to the invention, this embodiment incorporating an epicyclic, gear arrangement as previously described. but not restricted to any particular size of gears.

In this embodiment three sets of pinion gears 3, 4, are disposed at 120 'to one another for rotation within internal gears I and 2, and a sun gear 5 drives the gears 3. The gear I (the stator gear) is provided externally of its outer periphery with a connector structure 30 which is provided to pen-nit an external member (e.g. a robot arm) to be connected thereto. As shown the connector structure is formed integrally with the stator gear I, though it may be formed separately and attached thereto. As shown the connector structure is planar, extending in the plane of the gear, and is provided with holes 32 to permif the attachment of the external member, shown in phantom under reference 33. Similarly the gear 2 (the rotor gear) is provided with a similar connector structure 31 externally of its periphery for acceptance of a second external member 34. The rotatable joint of the invention may therefore provide a connection between the two members 33, 34 between which relative rotation is required.

Whilst the connector structure as shown is planar, other forms are possible, for example the connector structure may comprise a threaded stud or rod upstanding from the periphery of the of the gear. It is also clear that the connector structure may be attached to the side of the gear, rather than being disposed externaHy of the periphery.

Figure 5 shows a modification in which a connector structure 35 external to the outer periphery of the of the gear 2 is disposed normally to a radius of the gear 2 and receives an external member 36.

It is sometimes advantageous to sandwich a single rotor gear 2 between a pair of stator gears I as shown in Figure 6, or a single stator gear between a pair of rotor gears as shown in Figure 7.

A preferred embodiment of the invention will now be described with reference to Figure 8 to 14.

Figure 8 shows a perspective view of this embodiment which provides a pair of stators 41 sandwiching a central rotor 42. Essentially each stator 41 comprises a stator block 8 in which is bonded a stator gear 1, and the rotor 42 comprises a rotor block 9 in which is bonded a rotor gear 2. The rotor block has a bottom portion 44 which comprises a connector structure for connecting to an external member, e.g. a robot arm, and screw holes 43 are provided to this end. The connector structure 44 has an essentially planar bottom surface normal to a radius of the rotor. However, as shown in Figure 13 this may be partially cut away to reduce weight.

The stator blocks 8 are provided with flanges 45 which support a stator mounting block 12 which comprises another connector structure for connection to another 4 external member, e.g. another robot arm or part of a robot. Again the surface of the stator mounting block is essentially perpendicular to a radius of the rotor, though it may depart from being strictly planar.

Considering particularly Figures 8 and 12, which show the assembled construction, it will be seen that end pivot bearing plates I I are secured to the rotor 42 by screws 26 and pins 17. An electric motor 18 whose casing is secured to the stator has a spindle 18a (Figure 12) which carries the sun gear 5 which engages a stator planet pinion gear 3. This is secured to a shaft 6, and engages the internal stator gear 1. Also secured to the shaft 6 is a rotor planet pinion gear 4 which engages the internal rotor gear 2. Rotation of the sun gear 5 causes the pinion gear 3 to rotate around the gear 1. The corresponding rotation of the pinion gear 4 effects a small arcuate rotation of the rotor gear 2 as previously explained.

Considering particularly the exploded diagram of Figure 14 and the list of parts at the end of this description, it will be noted that there is symmetry about the centre of the rotor block 9 between two end pivot bearing plates 11. Starting at the right-hand end of the system shown in Figure 14 an end pivot bearing plate I I has secured within it a bearing 21. Rotatable within this bearing is a bearing cap 10 which is secured within a stator block 8. Hence the stator block 8 and the end pivot bearing plate 11 are relatively rotatable. The bearing cap 10 has a hollow boss I Oa on one side and a circular flange 48 on the other side (see the bearing cap 10 on the left-hand side). A potentiometer 22 has a body which is secured by a potentiometer holder14 to the end pivot bearing plate I I by screw 28. The potentiometer spindle, which has two flat surfaces, is fitted into a potentiometer adapter 13 with a central hole 29 of corresponding shape, the adaptor being press-fitted into boss I Oa (see Figure 13) By these means relative movement between the stator 8 and the end pivot bearing plate I I is reflected by the potentiometer reading.

Press-fitted on to the outside of the boss I Oa isa planet carrier bearing 20 on which a planet carrier 7 rotates. The planet carrier 7 has three holes at 120' to each other in which three planet bearings 19 are fixed, and a stator gear I (not separately shown on the right-hand side) is bonded within the stator block 8. Three sets of planet gears are provided. Each set comprises a gear shaft 6, having a spindle 6a, on which are secured a rotor planet pinion gear 4 with stator planet pinion gears 3 on either side, the gears, shaft and spindle being fixed to rotate together. The right-hand ends of the spindles 6a rotate within the planet bearings 19 in carrier 7. Similarly the left-hand ends rotate within planet bearings 19 in a second planet carrier 7. The stator block 8 carrying the stator gear 1, the bearing cap 10 carrying the planet carrier bearing 20, and the end pivot bearing plate I I carrying the bearing 21 are all duplicated on the left-hand side of the system. The two stator blocks are secured to the stator mounting block 12, which constitutes a connector structure, by screws 17 A rotor gear I is bonded within the rotor block 9. Screws 26 and pins 17 fix the end pivot bearing plates I I to the rotor block 9 through the intermediary of O-rings 23 which seal against the egress of grease but do not prevent relative rotation of the two parts.

The motor 18, whose spindle 18a carries the sun gear 5 which drives one of the sets of planet pinion gears 3, is located on the circular flange 48 of the bearing cap 10.

Screws 25 passing through holes 47 in the bearing cap secure the motor thereto. (A similar flange and similar holes in the other bearing cap 10 serve no purpose.) The casing of the motor 18 therefore forms part of the stator side of the system The sun gear 5 engages the three pinion gears 3 nearest to it. Each of these is constrained to cause the other pinion gears in its set to rotate with it. and hence the planet carrier 7 rotates about the axis 0, with the pinion gears 3 engaging the stator gears I and the pinion gears 4 engaging the rotor gear 2. In consequence the rotor 2 is caused to rotate about the axis 0.

The output from the potentiometer is fed to an external electrical position control system whose output is fed to the motor to control the relative rotation.

Figures 9, 10 and I I show external views of the assembled arrangement. It will be clear from the drawings that in this embodiment the stator and rotor blocks will interfere with one another and prevent full 360' rotation. Figure I I shows the limiting positions of the stator relative to the rotor in this embodiment, indicating a rotation restricted to 2 100.

In this specification where gears have been shown as simple circles it is to be understood that these represent the pitch circles of toothed gears or the circumferences of friction gears.

Although reference is made to spur gears in the list of parts, it is clear that the invention is not necessarily limited to such toothed gears. For example other gears such as spiral or helical gears may be used.

Reference is made to the fact that the pinion gears 3 and 4 must be disposed to rotate together, indeed, without this the gearing would not work. Hence normally these gears may be formed integrally or secured together or secured to a common shaft. However, a further possibility is that the gears are slidably located on a common shaft between two endplates, there being a spring between an endplate and the gears to urge these into frictional engagement Under normal conditions of operation the gears would rotate together, but under extreme overload conditions the spring-urged friction between the gears would be overcome so that slippage could take place.

6 ITEM NO. QTY. PART NO. DESCRIPTION

1 2 RS01-01-031-01 INO.5-72 INTERNAL GEAR 2 1 RS01-01-032-01 INO.5-73 INTERNAL GEAR 3 6 RS01-01-033-01 0.5-30, 3.5 mm WIDE PLANET SPUR GEAR 4 3 RS01-01-034-01 0.5-31, 6MM WIDE PLANET SPUR GEAR 1 RS01-01-035-01 0.5-12,3MM WIDE MOTOR PINION 6 3 RS01-01-036-01 PLANET GEAR SHAFT 7 2 RS01-01-037-01 PLANET CARRIER 8 2 RS01-01-038-01 STATOR BLOCK 9 1 RS01-01-039-02 MAIN ROTOR BLOCK 2 RS01-01-040-02 BEARING CAP 11 2 RSOI-01-041-01 PIVOT BEARING PLATE 12 1 RS01-01 042-02 STATOR MOUNTING BLOCK 13 1 RSOI-01-043-01 POTENTIOMETER ADAPTER 14 1 RS01-01-044-01 POTENTIOMETER HOLDER 3 RSOI-01-045-01 PIN DIA lx2LG 16 4 RS01-01-046-02 RING DOWEL 17 4 RS01-01-047-01 PIN DIA 3x7LG 18 1 RSOI-10-001-01 MOTOR RS-380 19 6 RS01-10-002-01 BEARING DDLF-730 SEALED 2 RSOI-10-003-01 BEARING DDLF-l 170 SEALED 21 2 RS01-10-006-01 BEARING F6706-2RS 22 1 RS01-10-015-01 POTENTIOMETER 23 2 RS01-10-014-01 O-RING 1.5x481D 24 4 RS01-10-016-01 WASHER PLAIN M3 FORM A 2 RS01-10-020-01 SOCKET HEAD CAPSCREW M2.5-0.45xO5 26 4 RS01-10-053-01 SOCKET HEAD BUTTON SCREW M4xlO 27 4 RS01-10-051-01 SOCKET HEAD BUTTON SCREW M3xl 0 -050-01 SOCKET HEAD BUTTON SCREW M3x5 7

Claims

I. A rotatable joint comprising a stator incorporating a circular stator gear and a rotor incorporating a circular rotor gear, the gears being of different radii but having a common axis and the rotor being rotatable about that axis relative to the stator, first and second pinion gears of different radii having a fin-ther common axis and being disposed to rotate together about that axis, the first and second pinion gears being arranged to engage the stator gear and the rotor gear respectively as planet gears, the arrangement being such that upon rotation of the first pinion gear around the stator gear the second pinion gear, in rotating round the rotor gear causes the latter to rotate about said common axis, and the stator and the rotor each being provided with a connector structure whose purpose is to provide for the connection of an external member.
2. A rotatable joint according to Claim I in which the stator or rotor is provided with a connector structure which is disposed externally of the outer periphery of its gear.
3 A rotatable joint according to Claim I in which the connector structures of both stator and rotor are disposed externally of the outer peripheries of their respective gears.
4 A rotatable joint according to Claim I in which the stator and rotor gears are external gears around which the pinion gears rotate
5. A rotatable joint according to Claims 1, 2 or 3 in which the stator and rotor gears are internal gears within which the pinion gears rotate.
6. A rotatable joint according to Claim 5 in which a plurality of sets of pinion gears are disposed symmetrically in a planet carrier to rotate within the stator and rotor gears
7. A rotatable joint according to any preceding claim wherein a single stator is sandwiched between two rotors on a common axis of relative rotation.
8. A rotatable joint according to any of Claims I to 6 in which a single rotor is sandwiched between two stators on a common axis of rotation.
9. A rotatable joint according to Claim 7 in which a common connector structure interconnects the two rotors.
10. A rotatable joint according to Claim 8 in which a common connector structure interconnects the two stators.
11. A rotatable joint according to Claim 9 or Claim 10 in which the common connector structure associated with the stator or rotor is substantially normal to a radius of the rotor.
12. A rotatablejoint substantially as described with reference to the accompanying drawings.

12. A rotatable joint according to any preceding claim in which a sun gear rotatable about said common axis drives the first pinion gear.

8
13. A rotatable joint according to Claim 12 in which the sun gear is driven by an electric motor.

14. A rotatable joint according to any preceding claim in which the stator and rotor are connected with the spindle and body of a potentiometer so that the potentiometer output is a measure of the relative rotation between the stator and rotor.

15. A rotatable joint according to Claim 14 in which the potentiometer output is fed to an electrical position control system to control the relative rotation of the stator and rotor.

16. A rotatable joint substantially as described with reference to the accompanying drawings.

Amendments to the claims have been riled as follows CLAIMS 1. A rotatable joint comprising a stator incorporating a circular stator gear and a rotor incorporating a circular rotor gear, the gears being of different radii but having a common axis and the rotor being rotatable about that axis relative to the stator, first and second pinion gears of different radii having a further common axis and being disposed to rotate together about that axis, the first and second pinion gears being arranged to engage the stator gear and the rotor gear respectively as planet gears, the arrangement being such that upon rotation of the first pinion gear around the stator gear the second pinion gear, in rotating round the rotor gear causes the latter to rotate about said common axis, and the stator and the rotor each being provided with a connector structure whose purpose is to provide for the connection of an external member, at least one of the connector structures being disposed externally of its gear and being transverse to a radius of that gear.

2. A rotatable joint according to Claim I in which each connector structure is disposed externally of its gear and is substantially normal to a radius of that gear.

3 A rotatable joint according to Claim 1 or Claim 2 in which a single stator is sandwiched between two rotors on a common axis of rotation.

4 A rotatable joint according to Claim I or Claim 2 in which a single rotor is sandwiched between two stators on a common axis of rotation.

A rotatable joint according to Claim 4 in which a common connector structure interconnects the two stators.

6 A rotatable joint according to any preceding claim in which the stator and rotor gears are internal gears within which the pinion gears rotate..

7. A rotatable joint according to any preceding claim in which a plurality of pinion gears are disposed symmetrically in a planet carrier to rotate within the stator and rotor gears 8 A rotatable joint according to any preceding claim in which a sun gear rotatable about said common axis drives the first pinion gear.

9. A rotatable joint according to Claim 8 in which the sun gear is driven by an electric motor.

10. A rotatable joint according to any preceding claim in which the stator and rotor are connected with the spindle and body of a potentiometer so that the potentiometer output is a measure of the relative rotation between the stator and rotor, 11. A rotatable joint according to Claim 10 in which the potentiometer output is fed to an electrical position control system to control the relative rotation of the stator and rotor.