GB2315371A

GB2315371A - Electomagnetic linear actuator with air pressure assistance

Info

Publication number: GB2315371A
Application number: GB9714311A
Authority: GB
Inventors: Susumu Takada; Kazuya Tamura; Kunihisa Kaneko; Nobuhiro Fujiwara
Original assignee: SMC Corp
Current assignee: SMC Corp
Priority date: 1996-07-12
Filing date: 1997-07-07
Publication date: 1998-01-28
Anticipated expiration: 2017-07-07
Also published as: GB2315371B; GB9714311D0; KR980012827A; DE19727344C2; DE19727344A1; KR100270901B1; JPH1030611A; JP3728023B2

Abstract

An operating rod 7, arranged to be movable axially by an electromagnetic servo drive 5, may be initially accelerated by an air piston 11,52 actuated auxiliary rod 6 having limited travel Figs 1,6. The action may be confined to outward movement of the rod 7 Fig 1, the single acting air piston being returned by drive 5 or lost motion link 72-74 and double acting piston Fig 6 may allow additional initial acceleration of the return stroke. A further embodiment Fig 4 has combined electromagnetic and air action permitting the air piston to balance the load, retraction of the rod 7 being performed by the air piston. Position signals are fed to the control module 45 from sensor 36,37.

Description

2315371 LINEAR ACTUATOR The present invention relates to linear actuator

apparatus that employs a direct current servo motor.

Linear actuator apparatuses employing a direct-current servo motor are known in the prior art and comprise an axially movable operating r(:d and an electromagnetic servo drive designed to move the operating rod by dint of thrusts generated when current is directed into a coil in a magnetic field, and are designed so that a servo controller is employed to control current inputs to the coil of the foregoing electromagnetic drive to operate the operating rod. A linear actuator of this kind has the advantage that operating rod operations can be controlled precisely by controlling the magnitude and direction of a direct current directed into the coil.

However, such linear actuator apparatuses have problems with activation response under the influence of counter electromagnetic forces generated in the coil and some other I factors, which causes delays in the startup of the operating rod and hence precludes the quick movement of the workpiece involved. Delays in activation create an impediment to achieving an increase in the speed at which the operating rod can work.

When this linear actuator is vertically installed and is employed to hold or adsorb a workpiece for lifting with some equipment on the operating rod, an (added) load on the operating rod requires more current inputs to the coil, thereby contributing to increased power dissipation. When a heavy workpiece is handled, electric power supplies to the coil increase, resulting in an increase in coil heating, and thus requiring the addition of a coil cooling means to the whole assembly.

It is accordingly a first object of the presentinvention to provide a linear actuator apparatus that has the improved activation response of the operating rod.

A second object of this invention is to provide a linear actuator apparatus that dissipates less electric power- A linear actuator apparatus in accordance with the invention includes an air-cylinder mechanism adapted to increase the activation speed of an 2 operating rod. This air-cylinder mechanism comprises a piston which operates according to the supply and exhaust of compressed air, and an auxiliary rod which, in combination with the piston, moves between an extended position and a retracted position, said air-cylinder mechanism being configured so that the operation rod may be activated with greater speed under pressure from the auxiliary rod when it is started by the servo drive.

The resultant improvement in activation response of the operating rod may achieve an increase in the speed.at which the rod can operate.

In one embodiment, there is provided a linear actuator apparatus which is arranged and configured so that the stroke of the auxiliary rod is shorter than that of the operating rod, the rods not being coupled to each other.

In another embodiment, an engaging portion is provided in the operating rod and an engaging portion is provided in the operating rod and the auxiliary rod, said engaging portions designed so that they engage each other when the rods are in the return mode, thereby enabling the return action of the operating rod to be assisted by the air cylinder mechanism via the auxiliary rod.

In still another embodiment, the auxiliary rod and the operating rod are arranged and :11 configured so that they operate in substantially the same number of strokes, and so that they are connected with each other, thereby ensuring that the efforts to support a load on the operating rod and the return movement thereof are assisted by the air cylinder mechanism via the auxiliary rod.

The foregoing embodiments eliminate the need for high current inputs to the coil of the servo drive to bear a load, leading to lower power consumption and, hence, less coil heating.

Preferably the piston and auxiliary rod of the air cylinder mechanism are supported so that they can slide on an air bearing. This arrangement essentially reduces to zero all the sliding resistances of the sliding portions, ensuring quicker and smoother operation of the auxiliary rod, and thereby contributing to an improvement of the activation response of the operating rod.

The invention will now be further described by way of example with reference to the accompanying drawings in which:

FIG. 1 is a longitudinal sectional front view showing the first embodiment of the present invention.

FIG. 2 is a sectional view along line II-Il of FIG. 1.

FIGS. 3 (A) through (C) are graphs showing the relationship between the displacement of the operating rod 4 and time.

FIG. 4 is a longitudinal sectional front view showing the second embodiment of this invention.

FIG. 5 is a longitudinal sectional front view showing the major portions of a modified form of the second embodiment.

FIG. 6 is a longitudinal sectional front view showing the third embodiment of the present invention.

FIGS. 1 and 2 show a first embodiment of a linear actuator apparatus 1 disposed vertically so that the operating rod 7 can move up and down.

The linear actuator apparatus 1 comprises a box-shaped case assembly 2 with a front opening, a cover 3 adapted to cover the front side of the case assembly, an air-cylinder mechanism 4 formed on top of the case assembly 2, and a voice coil-type actuator 5, an example of DC servo motors, which is disposed on the lower part of said case. The auxiliary rod 6 of the air-cylinder mechanism 4 and the operating rod 7 of the voice coil-type actuator 5 are all axially aligned.

The air-cylinder mechanism 4 includes a cylinder bore 9 formed in the case assembly 2, an end plate 10 designed to close the opening of the cylinder bore so that it is kept airtight, a piston 11 reciprocating in the airtight cylinder 9, an auxiliary rod 6 coupled to the piston, a cylinder chamber 12 and a breathing chamber 13 divided by the piston 11, and a supply and exhaust port 14 designed to supply or exhaust compressed air into and out of the cylinder chamber 12, said supply and exhaust port 14 being connected to a solenoid valve 16 and a breathing port 15 with an opening to the breathing chamber 13. Accordingly, the air-cylinder mechanism 4 in this embodiment works in a single-action mode of operation.

The solenoid valve 16 is configured as a known constantly closed-type three-port solenoid valve, i.e., a valve comprising a supply port P, an output port A and a exhaust port R, all being adapted to deal with compressed air, with the output port A communicating with either the supply port P or the exhaust port R, which is changed over depending on whether the solenoid 16a is energized or de-energized. In this solenoid valve 16, the supply port is connected to a source of compressed air 18 via an air tank 17.

The air-cylinder mechanism 4 is intended to accelerate the activation motion of the operating rod 7 under pressure from the auxiliary rod 6 when the voice coil-type actuator 5 activated, and hence it is smaller than the voice coil-type G I actuator 5, with the stroke of the auxiliary rod 6 being shorter than that of the operating rod 7.

The voice coil-type actuator 5 includes an electromagnetic servo drive 20 which comprises a magnetic frame 24 made up of a center yoke 21, bottom yokes 22, 22 located at the front and rear sides thereof, and side yokes 23, 23 connecting the top and bottom ends of these yokes, magnets 25, 25 on the surface of the bottom yoke 22 on the side surface of the center yoke, and a movable coil 26, which is wound around the center yoke 21 and can move along it. The magnetic frame 24 is mounted in the case assembly 2 with a retaining bolt (not shown) which passes through the side yokes 23, 23. The servo drive 20 is intended to vary the direct current inputs to the magnetic coil 26 in a magnetic field produced by the magnets 25, 25 to create an upward or a downward thrust in the coil according to Fleming's left-hand rule, said thrust causing the movable coil 26 to move in a vertical direction along the center yoke 21.

The movable coil 26 has a coil press 28 and a coil holder 29, both made of synthetic fiber or some other non-magnetic material and mounted by means of retaining screws 30, 30, with the coil holder being provided with a metallic moving element 31 by use of suitable means not shown. At the bottom of the case assembly 2 there is mounted a linear guide rail 32. A linear guide 33 is 7 adapted to move along the linear guide rail 32, and is mounted to the moving element 31 by means of retaining screws 34.

In the case assembly 2, a lin;ar scale 36 is placed on the wall opposite to the side where the servo drive 20 is installed, and at the top of the moving element 31, there is mounted an encoder electric substrate 37, which is designed to read an indication on the linear scale 36 and which generates a signal in response thereto.

The operating rod includes a large-diameter portion and a small-diameter portion, and is mounted on the moving element 31 so that a male thread formed at the bottom end of the smaller portion is threaded into an internally threaded through bore in the moving element 31, bringing the stepped portion between these parts into contact with the upper surface of the moving element 31. Supported by a bearing 38 and extending outside the case assembly 2, the top end of the small-diameter portion is provided with an air chuck, an adsorption pad or some other suitable tools (not shown).

A multipolar connector 40 intended to deliver electricity and signals is mounted on the side wall of the case assembly 2, an intermediate connector 41 on a mounting boss 2a of the case assembly 2, and the connector 42 on the coil holder 29, all retained by means of retaining screws. An receiving connector 43 electrically connected to the 8 multipolar connector 40 and the intermediate connector 41, and the intermediate connector 41 and a connector 42 as well, are electrically connected to each other via a flat ribbon cable 44. The multipolar 6onnector 40 is also coupled with a DC power supply 46 via a servo controller 45.

The servo controller 45 is designed to control the magnitude and direction of the direct current input into the movable coil 26 to make the coil move vertically. The encoder electric substrate 37 moving in combination with the movable coil 26 reads an indication on the linear scale 36 and, based on this, generates a position signal for the operating rod 7, and feeds it back to the servo controller 45.

The servo controller 45 is connected with a controller 47 which constitutes a compressed-air supply means. This controller 47 is devised to activate and energize the solenoid 16a of the solenoid valve 16 so that compressed air enters a cylinder chamber 12 during the initial stage of the process in which a current is supplied by the ser'vo controller 45 into the movable coil 26, and to de-magnetize the solenoid 16a, allowing the air to be vented out of the cylinder chamber 12 when the resultant downward movement of the auxiliary rod 6 pushes down the operating rod 7.

Number 48 in FIG.1 denotes a sliding seal consisting of an 0 ring which is fitted around the outer peripheries of 9 the auxiliary rod 6 and the piston 11.

In the first embodiment as previously described, when a current with the direction and magnitude to make the movable coil 26 move downward is 'supplied by the servo controller 45 to the coil 26, the movable coil 26 and the operating rod 7 start moving downward from the positions indicated in FIG. 1. Concurrently-with energization, the controller 47 is activated to magnetize the solenoid 16a of the solenoid valve 16, allowing the compressed air in the air tank 17 to be fed rapidly by the solenoid valve 16 to the cylinder chamber 12. The resulting rapid downward action of the piston 11 and the auxiliary rod 6 pushes the operating rod 7 down, permitting the rod 7 to be activated quickly and to travel to a predetermined target position, with little influence from counter-electromotive force.

When the operating rod 7 has moved to its target position, the solenoid 16a is de-energized by the controller 47, thus establishing a communication between the-cylinder chamber 12 and the outside.

Guided by the linear guide rail 32 and the linear guide 33, the movable coil 26 and the operating rod 7 move up and down smoothly. The encoder electrical substrate 37 on the moving part 31 reads the value then indicated on the linear scale 36 and feeds back a generated position signal to the servo controller 45, which, in turn, employs this I () information to control the magnitude and direction of current inputs to the movable coil 26 so that the operating rod 7 can be accurately positioned at a predetermined stop position. In this case, a current supplied into the movable coil 26 has sufficient magnitude to generate a force which balances the load applied to the whole system, including the movable coil 26 and the operating rod 7.

When a current with the magnitude and direction to make the movable coil 26 move upward is delivered by the servo controller 45 to the coil 26, the movable coil 26 and the operating rod 7 shift upward, accompanied by a simultaneous upward action of the auxiliary rod 6 in the air-cylinder mechanism 4, thereby causing them to return to the positions indicated in FIG. 1.

FIG. 3(A) indicates the relationship between the displacement and time of an operating rod of a known voice coil-type actuator, FIG. 3 (B) the relationship between the displacement and time of the auxiliary rod 6 of the aircylinder mechanism 4, and FIG. 3 (C) the relationship between the displacement and time of the operating rod 7 under pressure from the auxiliary rod 6. The symbol "a" in the figure denotes the time when the movable coil 26 becomes electrically charged.

As is evident from a comparison between FIGS. 3 (A) and (C), application of pressure from the auxiliary rod 6 1 1 to the operating rod 7 enables the operating rod 7 to be activated quickly.

The linear actuator may sometimes be employed as a transfer device designed to hold 6 workpiece (not shown) by means of an air chuck 49 (see FIG.4) mounted on the top of an operating rod 7, and to lift and carry it to a different place.

Since the weight of the workpiece held by the air chuck 49 is added, this application requires the supply of a correspondingly greater current to the movable coil 26 than that supplied during the upward movement of the operating to the operating rod 7 enables the operating rod 7 to be activated quickly.

The linear actuator may sometimes be employed as a transfer device designed to hold a workpiece (not shown) by means of an air chuck 49 (see FIG.4) mounted on the top of an operating rod 7, and to lift and carry it to a different place.

Since the weight of the workpiece held by the air chuck 49 is added, this application requires the supply of a correspondingly greater current to the movable coil 26 than that supplied during the upward movement of the operating rod 7 under no load. This means that the heavier a workpiece is, the greater the current input that must be supplied to the movable coil 26 will be, increasing not only 1 2 power dissipation, but coil heating as well.

FIG. 4 illustrates a second embodiment which overcomes the problems just described, in addition to the foregoing problems solved by the first embodiment. A linear actuator 51 in the second embodiment includes a double-acting air-cylinder mechanism 52, wherein the auxiliary rod 6 of the air-cylinder mechanism 52 and the operating rod 7 of the voice coiltype actuator 5 are coupled by means of a connecting pin 53, so that there is no axial loose. At the top of the operating rod 7 extending out of the case assembly 2, there is mounted an air chuck 49. In this embodiment, the strokes of the auxiliary rod 6 and the operating rod 7 are of substantially the same length.

Supply and exhaust ports 55a, 55b communicating with a pair of cylinder chambers 54a, 54b divided with a piston 11 are connected with proportional electromagentic pressureregulating valves 56a, 56b, which are capable of controlling output pneumatic pressure based on the magnitude of current inputs to proportional solenoids 57a, 57b. The magnitude of currents supplied to the proportional solenoids 57a, 57b is controlled by a controller 58, constituting a compressed-air supply means- The other configurations of the second embodiment are the same as those of the first embodiment, and accordingly, 1.' the reference numbers used in the first embodiment are used to identify similar major components of the second embodiment, and no further description is provided.

In accordance with the foregoing second embodiment, when a current with the direction and magnitude to make the movable coil 26 move downward is supplied by the servo controller 45 to the coil 26, with the simultaneous excitation of the proportional solenoid 57a of the proportional electromagnetic pressure-regulating valve 56a by a controller 58, compressed air is supplied to a cylinder chamber 54a, bringing the auxiliary rod 6 downward, and also moving the operating rod 7 connected to the rod 6 in the same direction. In this way, the auxiliary rod 6 accelerates the activation of the operating rod 7, enabling it to move downward more quickly to a predetermined target position.

When the operating rod 7 moves down and approaches the predetermined stop position, the proportional solenoid 57a becomes de-magnetized, and the proportional solenoid 57b becomes activated, causing a consequent inflow of compressed air into the cylinder chamber 54b. At the same time, the pneumatic pressure inside the cylinder chamber 54b is adjusted by the controller 58 so that it can generate a force substantially in equilibrium with the loads created when various components, such as the air chuck 49, act on 1 /1 the operating rod 7. Thereafter, the servo controller 45 controls the magnitude and direction of the current flowing into the movable coil 26 to bring the operating rod 7 to a stop exactly at the stop positi'on predetermined for chucking a workpiece.

Once the air chuck 49 grips the workpiece, the movable coil 26 is deenergized by the servo controller 45, at which time the air pressure in the cylinder chamber 54b forces the auxiliary rod 6 to move upward, thereby lifting the operating rod 7.

The above-mentioned second embodiment functions to substantially balance the forces exerted by the air pressure in the cylinder chamber 54b below the air-cylinder mechanism 52 with a load acting on the operating rod 7. This feature results in a decrease in the demand for current inputs to the movable coil 26 to hold the operating rod 7 in its stop position.

Additionally, since the force of the air pressure supplied to the cylinder chamber 54b is employed to lift the operating rod 7, even when the air chuck 49 is holding a heavy workpiece, no current input to the movable coil 26 is required to return them. This results in a decrease in power dissipation, as well as in heat buildup in the coil.

In the second embodiment described above, there is fitted a sliding seal 48 around the piston 11 and the 1 5 auxiliary rod 6 of the air-cylinder mechanism 52, so that if the sliding resistance of the sliding seal is large, there may be a delay in the downward movement of the auxiliary rod 6.

FIG. 5 indicates another modification of the second embodiment which provides solutions to the foregoing problems. In the air-cylinder mechanism 62 of this linear actuator apparatus 61, circumferential grooves constituting an air bearing 63 are formed, each between the outer periphery of the piston 11 and the case assembly 2 and between the end plate 10 and the auxiliary rod 6. These circumferential grooves communicate with a compressed-air source through channels 64, 65 having numerous openings at equal intervals in the circumferential direction of the circumferential groove.

Since the other configurations of this modification of the second embodiment are identical to those of the-second embodiment, further description is omitted.

As distinguished from a design which has a sliding seal 48, the modified design of the second embodiment can eliminate essentially all sliding resistance and hence enable quicker action of the auxiliary rod 6, since the piston 11 and the auxiliary rod 6 of the air-cylinder mechanism 62 are supported floatingly by the air bearing 63.

The air-cylinder mechanism 52 creates virtually no 1 (; sliding resistance, making it Possible to accurately control the operating rod 7 so that it stops at the target Position, even when it is coupled with the auxiliary rod 6 by means of a connecting pin 53.

FIG. 6 illustrates a third embodiment.

As shown, this linear actuator apparatus 71 comprises arms 72, each located at the top of the auxiliary rod 6 of the air-cylinder mechanism 52, and at the top of the operating rod 7 of a voice coil-type actuator 5, and extending parallel to each other. At the top of each arm 72 there is mounted an engaging portion 74 that can be engaged with the other arm, and at the bottom end, there is a contact portion 73 with which the engaging portion 74 comes into contact.

The contact portions 73 and the engaging portions 74 on these arms 72, 72 are related to each other as follows: when the auxiliary rod 6 and the operating rod 7 are at their respective replaced positions as indicated in the figure, the attaching portion 73 of each arm is brought into contact with the engaging portion 74 of the other; and when these rods are extended for operation, the engaging portions 74, 74 of both arms are spaced slightly apart, and when they are retracted to their initial positions, they are engaged.

The solenoid valve 76 is a spring-centered 3-position 1 7 5-port valve designed to supply and exhaust compressed air into and out of the cylinder chambers 54a,54b of the air cylinder mechanism 52; said valve comprising a supply port P, output ports A, B, and exhaust ports EA, EB, all of which are adapted for pressurized fluid. (In operation,) upon energization of the solenoid 76a, the supply port P and the output port A, and the output port B and the exhaust port EB are made to communicate with each other. When the solenoid 76b is energized, communication is established between the supply port P and the output port B, and between the output port A and the exhaust port EA- While at the intermediate stop position, neither of them is energized, and the output ports A and B communicate with the exhaust ports FA and EB. The output ports A, B communicate with the supply and exhaust ports 55a. and 55b, respectively. Energization and de-energization of the solenoids 76a, 76b are controlled by a controller 77.

The other configurations of the third embodiment are the same as those of the first embodiment- Therefore the same numbers are used to identify the same major components in the figure, and detailed descriptions are omitted.

In accordance with the foregoing third embodiment, with the solenoid valve 76 at the intermediate stop position, an electrical current with the direction and magnitude to make the coil move upward is supplied to the movable coil 26 by 1 2 the servo controller 45, and the movable coil 26 and the operating rod 7 travel upward and cause the engaging portion 74 to contact the attaching portion 73, thereby shifting the auxiliary rod 6 upward.

When a current that causes the downward motion of the movable coil 26 is supplied by the servo controller 45 to the coil 26, during the initial stage of the process, the solenoid 76a is energized by the controller 77. Then, compressed air is fed to the cylinder chamber 54a to cause the auxiliary rod to move down and bring the attaching portion 73 into contact with the engaging portion 74, pushing the operating rod 7 down, and accelerating the downward action thereof. When the operating rod 7 is subject to pressure, the solenoid 76a is de-energized by the controller 77, causing the solenoid valve 76 to return to its intermediate stop position.

The stop position of the extended operating rod- 7 is controlled by the servo controller 45 in the same manner as in the first embodiment of this invention. Even when the auxiliary rod 6 and the operating rod 7 are fully extended, there is a small clearance between their respective engaging portions 74, 74.

When the solenoid 76b is energized by the controller 77, compressed air is supplied to the lower cylinder chamber 54b to bring the auxiliary rod 6 upward.When the auxiliary rod 1 9 6 moves upward slightly, the engaging portion 74 thereof is engaged with the engaging portion 74 of the operating rod 7, causing the operating rod 7 to be pulled up by the auxiliary rod 6. The engaging portions 74, 74 of both rods 6, 7 become engaged only during the activating phase of the upward movement process where a particularly large force is required, and after the auxiliary rod 6 with a shorter stroke completely returns to the upper limit of its stroke, the operating rod 7 rises under the thrust of the servo drive portion 20.

This means that less current input is required to the movable coil 26 to produce the upward motion of the operating rod 7 than in the case where there is no aircylinder mechanism 4.

The other operations of the third embodiment are identical to those of the first embodiment, and thus their descriptions are omitted.

Although it is not shown, the auxiliary rod 6 and the piston 11 may also be supported in a floating state with the air bearing 6, without the use of the sliding seal 48.

In the foregoing embodiments, descriptions have focused on longitudinal linear actuators designed to cause the operating rod 7 to move up and down; however, it must be noted that the present invention may be applied to a horizontal linear actuator that can move an operating

2 0 1 rod 7 in a transverse direction.

2 1

Claims

22 CLAIMS

1. A linear actuator apparatus comprising an operating rod disposed so that it can move axially, an electromagnetic servo drive designed for moving said operating rod by thrust generated by directing electrical current into a coil in a magnetic field, and an air cylinder mechanism having a compressed air operated piston and an auxiliary rod which moves with the piston between a retracted position and an extended position, and is arranged to apply pressure to the operating rod such as to increase the activation speed of the operating rod.

2. A linear actuator as claimed in Claim 1, wherein the stroke of said auxiliary rod is shorter than that of the operating rod, and wherein said auxiliary rod and operating rod are not coupled to each other.

3. A linear actuator as claimed in Claim 1, wherein said operating rod and auxiliary rod have portions engaged with the other when both rods are at their respective retracted positions, so that the return operation of the operating rod may be assisted by said air cylinder mechanism via the auxiliary rod.

4. A linear actuator as claimed in Claim 1, wherein the strokes of said auxiliary rod and operating rod are 23 substantially the same and the rods are connected with each other, so that support of a load on the operating rod and the return operation of said operating rod may be assisted by said air-cylinder mechanism via said auxiliary rod.

5. A linear actuator as claimed in any preceding Claim, wherein the piston and rod of said air cylinder mechanism are supported by means of an air bearing in a way that permits sliding.

6. A linear actuator - omnibus.