US20020014380A1 - Linear-acting controllable pneumatic motion control apparatus and control method therefor - Google Patents
Linear-acting controllable pneumatic motion control apparatus and control method therefor Download PDFInfo
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- US20020014380A1 US20020014380A1 US09/901,354 US90135401A US2002014380A1 US 20020014380 A1 US20020014380 A1 US 20020014380A1 US 90135401 A US90135401 A US 90135401A US 2002014380 A1 US2002014380 A1 US 2002014380A1
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- motion
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- output member
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- 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
- F16D—COUPLINGS FOR TRANSMITTING ROTATION; CLUTCHES; BRAKES
- F16D57/00—Liquid-resistance brakes; Brakes using the internal friction of fluids or fluid-like media, e.g. powders
- F16D57/002—Liquid-resistance brakes; Brakes using the internal friction of fluids or fluid-like media, e.g. powders comprising a medium with electrically or magnetically controlled internal friction, e.g. electrorheological fluid, magnetic powder
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- F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
- F15—FLUID-PRESSURE ACTUATORS; HYDRAULICS OR PNEUMATICS IN GENERAL
- F15B—SYSTEMS ACTING BY MEANS OF FLUIDS IN GENERAL; FLUID-PRESSURE ACTUATORS, e.g. SERVOMOTORS; DETAILS OF FLUID-PRESSURE SYSTEMS, NOT OTHERWISE PROVIDED FOR
- F15B11/00—Servomotor systems without provision for follow-up action; Circuits therefor
- F15B11/06—Servomotor systems without provision for follow-up action; Circuits therefor involving features specific to the use of a compressible medium, e.g. air, steam
- F15B11/072—Combined pneumatic-hydraulic systems
- F15B11/076—Combined pneumatic-hydraulic systems with pneumatic drive or displacement and speed control or stopping by hydraulic braking
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- F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
- F15—FLUID-PRESSURE ACTUATORS; HYDRAULICS OR PNEUMATICS IN GENERAL
- F15B—SYSTEMS ACTING BY MEANS OF FLUIDS IN GENERAL; FLUID-PRESSURE ACTUATORS, e.g. SERVOMOTORS; DETAILS OF FLUID-PRESSURE SYSTEMS, NOT OTHERWISE PROVIDED FOR
- F15B15/00—Fluid-actuated devices for displacing a member from one position to another; Gearing associated therewith
- F15B15/20—Other details, e.g. assembly with regulating devices
- F15B15/26—Locking mechanisms
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- F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
- F15—FLUID-PRESSURE ACTUATORS; HYDRAULICS OR PNEUMATICS IN GENERAL
- F15B—SYSTEMS ACTING BY MEANS OF FLUIDS IN GENERAL; FLUID-PRESSURE ACTUATORS, e.g. SERVOMOTORS; DETAILS OF FLUID-PRESSURE SYSTEMS, NOT OTHERWISE PROVIDED FOR
- F15B21/00—Common features of fluid actuator systems; Fluid-pressure actuator systems or details thereof, not covered by any other group of this subclass
- F15B21/06—Use of special fluids, e.g. liquid metal; Special adaptations of fluid-pressure systems, or control of elements therefor, to the use of such fluids
- F15B21/065—Use of electro- or magnetosensitive fluids, e.g. electrorheological fluid
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- F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
- F15—FLUID-PRESSURE ACTUATORS; HYDRAULICS OR PNEUMATICS IN GENERAL
- F15B—SYSTEMS ACTING BY MEANS OF FLUIDS IN GENERAL; FLUID-PRESSURE ACTUATORS, e.g. SERVOMOTORS; DETAILS OF FLUID-PRESSURE SYSTEMS, NOT OTHERWISE PROVIDED FOR
- F15B21/00—Common features of fluid actuator systems; Fluid-pressure actuator systems or details thereof, not covered by any other group of this subclass
- F15B21/08—Servomotor systems incorporating electrically operated control means
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- 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
- F16D—COUPLINGS FOR TRANSMITTING ROTATION; CLUTCHES; BRAKES
- F16D55/00—Brakes with substantially-radial braking surfaces pressed together in axial direction, e.g. disc brakes
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- 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
- F16D—COUPLINGS FOR TRANSMITTING ROTATION; CLUTCHES; BRAKES
- F16D63/00—Brakes not otherwise provided for; Brakes combining more than one of the types of groups F16D49/00 - F16D61/00
- F16D63/008—Brakes acting on a linearly moving member
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- F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
- F15—FLUID-PRESSURE ACTUATORS; HYDRAULICS OR PNEUMATICS IN GENERAL
- F15B—SYSTEMS ACTING BY MEANS OF FLUIDS IN GENERAL; FLUID-PRESSURE ACTUATORS, e.g. SERVOMOTORS; DETAILS OF FLUID-PRESSURE SYSTEMS, NOT OTHERWISE PROVIDED FOR
- F15B2211/00—Circuits for servomotor systems
- F15B2211/30—Directional control
- F15B2211/305—Directional control characterised by the type of valves
- F15B2211/30525—Directional control valves, e.g. 4/3-directional control valve
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- F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
- F15—FLUID-PRESSURE ACTUATORS; HYDRAULICS OR PNEUMATICS IN GENERAL
- F15B—SYSTEMS ACTING BY MEANS OF FLUIDS IN GENERAL; FLUID-PRESSURE ACTUATORS, e.g. SERVOMOTORS; DETAILS OF FLUID-PRESSURE SYSTEMS, NOT OTHERWISE PROVIDED FOR
- F15B2211/00—Circuits for servomotor systems
- F15B2211/30—Directional control
- F15B2211/32—Directional control characterised by the type of actuation
- F15B2211/327—Directional control characterised by the type of actuation electrically or electronically
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- F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
- F15—FLUID-PRESSURE ACTUATORS; HYDRAULICS OR PNEUMATICS IN GENERAL
- F15B—SYSTEMS ACTING BY MEANS OF FLUIDS IN GENERAL; FLUID-PRESSURE ACTUATORS, e.g. SERVOMOTORS; DETAILS OF FLUID-PRESSURE SYSTEMS, NOT OTHERWISE PROVIDED FOR
- F15B2211/00—Circuits for servomotor systems
- F15B2211/40—Flow control
- F15B2211/415—Flow control characterised by the connections of the flow control means in the circuit
- F15B2211/41527—Flow control characterised by the connections of the flow control means in the circuit being connected to an output member and a directional control valve
- F15B2211/41536—Flow control characterised by the connections of the flow control means in the circuit being connected to an output member and a directional control valve being connected to multiple ports of an output member
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- F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
- F15—FLUID-PRESSURE ACTUATORS; HYDRAULICS OR PNEUMATICS IN GENERAL
- F15B—SYSTEMS ACTING BY MEANS OF FLUIDS IN GENERAL; FLUID-PRESSURE ACTUATORS, e.g. SERVOMOTORS; DETAILS OF FLUID-PRESSURE SYSTEMS, NOT OTHERWISE PROVIDED FOR
- F15B2211/00—Circuits for servomotor systems
- F15B2211/60—Circuit components or control therefor
- F15B2211/63—Electronic controllers
- F15B2211/6303—Electronic controllers using input signals
- F15B2211/6336—Electronic controllers using input signals representing a state of the output member, e.g. position, speed or acceleration
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- F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
- F15—FLUID-PRESSURE ACTUATORS; HYDRAULICS OR PNEUMATICS IN GENERAL
- F15B—SYSTEMS ACTING BY MEANS OF FLUIDS IN GENERAL; FLUID-PRESSURE ACTUATORS, e.g. SERVOMOTORS; DETAILS OF FLUID-PRESSURE SYSTEMS, NOT OTHERWISE PROVIDED FOR
- F15B2211/00—Circuits for servomotor systems
- F15B2211/60—Circuit components or control therefor
- F15B2211/665—Methods of control using electronic components
- F15B2211/6654—Flow rate control
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- F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
- F15—FLUID-PRESSURE ACTUATORS; HYDRAULICS OR PNEUMATICS IN GENERAL
- F15B—SYSTEMS ACTING BY MEANS OF FLUIDS IN GENERAL; FLUID-PRESSURE ACTUATORS, e.g. SERVOMOTORS; DETAILS OF FLUID-PRESSURE SYSTEMS, NOT OTHERWISE PROVIDED FOR
- F15B2211/00—Circuits for servomotor systems
- F15B2211/60—Circuit components or control therefor
- F15B2211/665—Methods of control using electronic components
- F15B2211/6656—Closed loop control, i.e. control using feedback
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- F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
- F15—FLUID-PRESSURE ACTUATORS; HYDRAULICS OR PNEUMATICS IN GENERAL
- F15B—SYSTEMS ACTING BY MEANS OF FLUIDS IN GENERAL; FLUID-PRESSURE ACTUATORS, e.g. SERVOMOTORS; DETAILS OF FLUID-PRESSURE SYSTEMS, NOT OTHERWISE PROVIDED FOR
- F15B2211/00—Circuits for servomotor systems
- F15B2211/70—Output members, e.g. hydraulic motors or cylinders or control therefor
- F15B2211/705—Output members, e.g. hydraulic motors or cylinders or control therefor characterised by the type of output members or actuators
- F15B2211/7051—Linear output members
- F15B2211/7055—Linear output members having more than two chambers
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- F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
- F15—FLUID-PRESSURE ACTUATORS; HYDRAULICS OR PNEUMATICS IN GENERAL
- F15B—SYSTEMS ACTING BY MEANS OF FLUIDS IN GENERAL; FLUID-PRESSURE ACTUATORS, e.g. SERVOMOTORS; DETAILS OF FLUID-PRESSURE SYSTEMS, NOT OTHERWISE PROVIDED FOR
- F15B2211/00—Circuits for servomotor systems
- F15B2211/70—Output members, e.g. hydraulic motors or cylinders or control therefor
- F15B2211/75—Control of speed of the output member
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- F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
- F15—FLUID-PRESSURE ACTUATORS; HYDRAULICS OR PNEUMATICS IN GENERAL
- F15B—SYSTEMS ACTING BY MEANS OF FLUIDS IN GENERAL; FLUID-PRESSURE ACTUATORS, e.g. SERVOMOTORS; DETAILS OF FLUID-PRESSURE SYSTEMS, NOT OTHERWISE PROVIDED FOR
- F15B2211/00—Circuits for servomotor systems
- F15B2211/70—Output members, e.g. hydraulic motors or cylinders or control therefor
- F15B2211/765—Control of position or angle of the output member
- F15B2211/7656—Control of position or angle of the output member with continuous position control
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- F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
- F15—FLUID-PRESSURE ACTUATORS; HYDRAULICS OR PNEUMATICS IN GENERAL
- F15B—SYSTEMS ACTING BY MEANS OF FLUIDS IN GENERAL; FLUID-PRESSURE ACTUATORS, e.g. SERVOMOTORS; DETAILS OF FLUID-PRESSURE SYSTEMS, NOT OTHERWISE PROVIDED FOR
- F15B2211/00—Circuits for servomotor systems
- F15B2211/80—Other types of control related to particular problems or conditions
- F15B2211/885—Control specific to the type of fluid, e.g. specific to magnetorheological fluid
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- F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
- F15—FLUID-PRESSURE ACTUATORS; HYDRAULICS OR PNEUMATICS IN GENERAL
- F15B—SYSTEMS ACTING BY MEANS OF FLUIDS IN GENERAL; FLUID-PRESSURE ACTUATORS, e.g. SERVOMOTORS; DETAILS OF FLUID-PRESSURE SYSTEMS, NOT OTHERWISE PROVIDED FOR
- F15B2211/00—Circuits for servomotor systems
- F15B2211/80—Other types of control related to particular problems or conditions
- F15B2211/885—Control specific to the type of fluid, e.g. specific to magnetorheological fluid
- F15B2211/8855—Compressible fluids, e.g. specific to pneumatics
Definitions
- the invention relates to pneumatic apparatus. More particularly, the present invention is directed to a pneumatic apparatus, which is precisely controllable.
- More sophisticated pneumatic actuators such as the TOM THUMB® 3-position pneumatic actuator sold by PHD, Inc. of Fort Wayne, Ind., includes the ability to stop at an intermediate or middle position. Although more flexible than 2 -position actuators, these 3-position actuators are still very inflexible, in that, once designed, the intermediate position is largely unchangeable.
- actuators are available which can stop at any intermediate position.
- SMC Corporation of Tokyo, Japan manufactures a rodless pneumatic cylinder with an internal brake and positioning scale (e.g. model ML2B).
- This system includes a piston moveable within a housing and integral position sensor and a friction brake.
- the position sensor provides a position signal to the controller.
- the brake is actuated via air pressure to move a brake shoe into contact with a brake plate, thereby stopping the piston at the predetermined intermediate point.
- the system includes the ability to learn the distance from application of the brake to the actual stopping point, and makes adjustments to improve the accuracy for at the next commanded stop.
- the present invention provides a controllable pneumatic actuator and motion control apparatus including a field responsive medium and control method therefor whose motion may be accurately controlled at any point along its stroke.
- the controllable pneumatic apparatus comprises a pneumatic actuator coupled to a linear-acting brake such that a motion (e.g., a displacement, a velocity or an acceleration) of an output member of the actuator may be precisely controlled.
- the apparatus preferably includes a control system having a sensor for deriving a motion signal of a motion of a moving component of the apparatus, and a motion control for processing the motion signal and providing a control signal to the controllable brake.
- the actuator is included in a pneumatic system that further comprises a pressure supply providing a supply of pressurized gas and a pneumatic control controlling a pneumatic control valve for apportioning the pressurized gas from the source and providing differential pneumatic pressure to move the piston.
- the apparatus preferably includes a control system further comprising an input for inputting information to the pneumatic control and the motion control.
- the apparatus is preferably controlled according to a method in which the motion of the output member is controlled based upon a kinetic energy in the system. Most preferably, the control is also based upon an available braking force from the brake. More particularly, a shut down point for turning off the pneumatic actuator and activation of the controllable brake is determined based upon the kinetic energy and the available braking force.
- a controllable pneumatic apparatus comprising a pneumatic actuator having a housing with a gas cavity formed therein, a first piston slidably disposed in the gas cavity subdividing the gas cavity into first and second gas chambers, and an output member coupled to the first piston; and a controllable brake, including a medium containing cavity subdivided into a first and second chambers, a second piston rigidly interconnected with, and longitudinally aligned with, the first piston and moveable in the cavity along the axial axis, a passageway interconnecting the first and the second chambers, a field responsive medium (e.g., a magnetic fluid) contained in the passageway, a field generator for producing a field to change a rheology of the medium upon exposure to the field causing a braking force to be applied to the output member to control motion thereof.
- a controllable brake including a medium containing cavity subdivided into a first and second chambers, a second piston rigidly interconnected with, and longitudinally aligned with
- the field generator comprises a coil mounted stationary inside the housing.
- the first piston is formed of first and second faces which face away from each other and the second piston is formed of first and second surfaces which face towards each other.
- the passageway comprises an annulus formed between a pole piece and a shaft.
- the controllable pneumatic apparatus comprises a pneumatic system including a housing having a gas cavity formed therein, a first piston slidably disposed in the gas cavity subdividing the gas cavity into a first gas chamber and a second gas chambers, a pressure source providing a supply of pressurized gas, a pneumatic control which controls a pneumatic valve to apportion the supply of pressure to the first and second gas chambers thereby providing differential pneumatic pressure to move the first piston along an axial axis, and an output member coupled to the first piston; a controllable brake including a medium containing cavity, a second piston subdividing the medium containing cavity into a first medium chamber and a second medium chamber, the second piston being longitudinally aligned with the first piston and rigidly interconnected by an interconnecting shaft to the first piston, the second piston moveable in the cavity along the axial axis, a passageway interconnecting the first and the second medium chambers, a magnetically controllable fluid contained in the passage
- the controllable pneumatic apparatus also comprises a housing including first and second end caps, an intermediate member spaced between the end caps, a first sleeve intervening between the first end cap and the intermediate member, and a second sleeve intervening between the second end cap and the intermediate member, a pneumatic system, including a gas cavity formed by the second end cap, the intermediate member and the second sleeve, a first piston slidably disposed within the second sleeve and subdividing the gas cavity into a first and second gas chambers, a pressure source providing a supply of pressurized gas to the cavity, a pneumatic control which controls a pneumatic valve to apportion the supply of pressure to the first and second gas chambers thereby providing differential pneumatic pressure to move the first piston along an axial axis, and an output member coupled by an interconnecting shaft to the first piston; a controllable brake including a medium-containing cavity formed by the first end cap, the intermediate member and a first sle
- the controllable pneumatic apparatus comprises a housing including first and second end caps, and a sleeve spaced between the end caps; a pneumatic system, including a gas cavity formed by the end caps, the sleeve and outwardly disposed axial faces of a piston assembly, the piston assembly including a first member, a second member and an interconnecting shaft, the piston assembly slidably disposed in the sleeve subdividing the gas cavity into a first gas chamber and a second gas chambers, a pressure source providing a supply of pressurized gas to the cavity, a pneumatic control which controls a pneumatic valve to apportion the supply of pressure to the first and second gas chambers thereby providing differential pneumatic pressure to move the piston assembly along an axial axis, and an output member coupled to the piston assembly; a controllable brake including a medium containing cavity formed by the first sleeve and inwardly disposed axial surfaces of the piston assembly, and a partition sub
- a method of controlling a controllable pneumatic apparatus comprising the steps of: providing a pneumatic actuator which causes motion of an output member, providing a controllable brake coupled to the output member, providing a control system for controlling the pneumatic actuator and the controllable brake, inputting system performance information to the control system, measuring a motion of the output member and providing a motion signal, processing the motion signal and the desired motion information within the control system and providing control signals to control the pneumatic actuator and to activate the controllable brake, the processing being based upon a kinetic energy. More preferably, the processing is based upon available braking force, as well.
- the system performance information comprises desired motion information of the output member such as the desired stopping position, a desired accuracy, a desired velocity profile, an acceleration profile, a mass of any moving system elements, a braking force available from the controllable brake or combinations thereof.
- desired motion information of the output member such as the desired stopping position, a desired accuracy, a desired velocity profile, an acceleration profile, a mass of any moving system elements, a braking force available from the controllable brake or combinations thereof.
- ⁇ x is the distance from the shut down point to the desired stopping position
- m is the mass of any moving system components
- v is the velocity at the stopping point
- F mr is the available braking force
- control method allows optimization for accuracy or velocity based upon the kinetic energy of the system.
- FIG. 1 a is a schematic view of a first embodiment of controllable pneumatic actuator and motion control apparatus in accordance with the present invention
- FIG. 1 b is a cross-sectioned side view of the rotary-acting controllable brake of FIG. 1 a taken along line 1 b- 1 b;
- FIG. 2 is a schematic view of a second embodiment of apparatus in accordance with the present invention.
- FIG. 3 is a schematic view of a third embodiment of apparatus in accordance with the present invention.
- FIG. 4 is a schematic view of a fourth embodiment of apparatus in accordance with the present invention.
- FIG. 5 is a schematic view of a fifth embodiment of apparatus in accordance with the present invention.
- FIG. 6 is a schematic view of a sixth embodiment of apparatus in accordance with the present invention.
- FIG. 7 is a schematic view of a seventh embodiment of apparatus in accordance with the present invention.
- FIG. 8 is a plot of displacement versus velocity when one type of control method is implemented.
- FIG. 9 is a block diagram of one type of control method.
- FIG. 1 a A controllable pneumatic actuator and motion control apparatus 20 according to the invention is first illustrated in FIG. 1 a .
- the apparatus 20 comprises a pneumatic actuator 23 and an interconnected and coupled rotary-acting controllable brake 34 , such as a rotary-acting magnetorheological brake (e.g. MRB-2107-3 sold by Lord Corporation under the tradename RHEONETICTM rotary controllable brake).
- An output member 25 such as an axially-reciprocating or rotary-acting shaft, is coupled (interconnected such that force may be applied therebetween) to a moving piston 26 of an actuator 23 included within the pneumatic system 21 .
- the rotary-acting controllable brake 34 controls a motion parameter of the output member 25 , such as a stopping position (displacement), a velocity, an acceleration or a starting or stopping velocity or acceleration profile thereof.
- the pneumatic system 21 includes the pneumatic actuator 23 and a pneumatic control system 22 for supplying pressure to, and causing motion of the output member 25 of the actuator 23 .
- the pneumatic control system 22 includes a pneumatic pressure source or supply 27 , such as a reservoir (not shown) of pressurized gas (e.g., air) which may be replenished by and pump (not shown).
- the pressure supply 27 is regulated to a preset pressure, for example, to a presure in the range of between approximately 30 psi and 120 psi (207 kPa and 827 kPa), depending upon the application.
- the pneumatic control system 22 also includes controllable pneumatic valve 29 , such as a three-position solenoid valve (e.g. model SY5440 available from SMC Corporation of Tokyo, Japan), or any other type of suitable controllable valve.
- the valve 29 is operable in response to control signals 28 a generated by a pneumatic control 28 to appropriately apportion pressure to the pneumatic actuator 23 .
- the valve 29 may include a first position which causes a differential pressure where the pressure P 1 in a first gas chamber 31 a is higher than the pressure P 2 in a second gas chamber 31 b thereby causing the piston 26 to move in a first (e.g. rightward) direction.
- the valve 29 may also include a second position causing the pressure P 1 to be lower than the pressure P 2 thereby causing motion of the piston 26 in the opposite (e.g. leftward) direction.
- the valve 29 may include a neutral position which provides pressures P 1 , P 2 in the chambers 31 a , 31 b that are equal to atmospheric pressure thereby causing no differential pressure and allowing the piston 26 to come to rest.
- the pneumatic actuator 23 includes a piston 26 (including elements 26 a , 26 b and an intervening rack 26 c ) preferably disposed in sealed relation with the cylindrically-shaped cavity 54 formed in a housing 24 .
- the piston 26 which includes preferably cylindrically shaped elements 26 a , 26 b , is slidably received within, and subdivides, the cavity 54 and forms two opposed gas chambers 31 a , 31 b ; the piston 26 being reciprocatably moveable along a central axis A-A of the housing 24 .
- the piston 26 is coupled to, and movement of it produces movement of, at least one output shaft 25 .
- the actuator 23 includes first 25 and a second 25 ′ output members.
- the actuator's output member 25 , 25 ′ may be a rotatable output shaft 25 or a axially moveable piston rod shaft 25 ′.
- the actuator 23 may also include a transmission 30 , which, for example, converts linear motion of the piston 26 to rotary motion of the shaft 25 .
- the transmission 30 may include a rack 25 c and pinion 25 d or other gearing system for converting linear to rotary motion, as is well understood by those of ordinary skill in the art.
- the transfer shaft 25 ′′ extending from the other side of transmission 30 is coupled to the transmission 30 and is, therefore, interconnected and coupled to, and moves in unison with, the piston 26 and output members 25 , 25 ′.
- the output member 25 is coupled to the piston 26 via the pinion 26 d and the output member 25 ′ is coupled to the piston 26 by a rigid interconnection to the cylindrical element 26 b .
- the rotary-acting controllable brake 34 includes a field responsive medium 44 contained therein and is coupled to the piston 26 , preferably through the transmission 30 or other suitable means.
- the rotary brake 34 as best shown in FIG. 1 b , includes a brake shaft 32 coupled (e.g. by pin) for rotation with a disc-shaped rotor 38 manufactured from a soft-magnetic material, such as low carbon steel.
- a magnetic field generator 39 such as a magnet wire coil circumferentially wound (100-300 winds of wire) about a plastic bobbin, produces a magnetic field 43 upon being activated with suitable electrical current (e.g. 1-3 amps).
- Pole pieces 40 manufactured of a soft-magnetic material direct the flux across the preferably radially directed gaps 42 formed between the poles 40 and the rotor 38 .
- the gaps 42 may be disposed axially or in other suitable orientations, as is known to those of ordinary skill in the art.
- the gaps 42 contain a field responsive medium 44 , such as a magnetorheological fluid or dry magnetic particles.
- a suitable magnetorheological fluid is described in commonly assigned U.S. Pat. Nos. 5,599,474, 5,683,615 or 5,705,085.
- a suitable dry magnetic particle is manufactured from 410 series stainless steel power and sifted through a minus 325 mesh and is available from Hoeganaes Corpration of Riverton, N.J.
- Rotary brakes such as described herein are described in detail in U.S. Pat. No. 5,842,547 to Carlson et al. entitled “Controllable Brake,” U.S. Pat. No. 5,816,372 to Carlson et al. “Magnetorheological Fluid Devices And Process Of Controlling Force In Exercise Equipment Utilizing Same,” and U.S. Pat. No. 5,711,746 to Carlson entitled “Portable Controllable Fluid Rehabilitation Devices.”
- the apparatus 20 further includes a sensor 35 , such as a rotary potentiometer (POT), for providing a motion signal 33 representative of a motion (e.g., a position, velocity or acceleration) of a moving component of the apparatus 20 .
- a sensor 35 may measure the motion (e.g., displacement) of the piston 26 .
- a sensor 35 may sense motion between the output member shaft 25 or 25 ′ and the housing 24 or of the interconnected component 41 or 41 ′ relative to the housing or some other stationary point.
- the interconnected component 41 or 41 ′ may be, for example, a caliper, manipulator, a pusher block, a tool plate, a carriage, a platform or other item useful for grasping, contacting or positioning an article such as a device, product, computer chip, or subassembly component to be assembled in a larger assembly.
- a motion control system 36 processes the motion signal 33 and provides an electrical control signal 37 to the controllable brake 34 .
- the control signal 37 energizes the field generator 39 in the brake 34 causing a resistance force to be applied to the output shaft 32 , and to interconnected shaft 25 , 25 ′, piston 26 , and to any interconnected component 41 , 41 ′ thereby controlling at least one selected from a group consisting of a position, velocity and acceleration of the output member 25 , 25 ′ and, thus, of the interconnected component 41 or 41 ′.
- FIG. 2 illustrates another embodiment of the apparatus 20 .
- the pneumatic actuator 23 comprises a rotary-acting pneumatic motor including a piston (rotor) 26 rotatably mounted for rotation in the housing 24 .
- Application of a differential pressure to the piston 26 by the pneumatic control system 22 causes the rotation of the piston 26 .
- a rotary-acting controllable brake 34 identical to that described in FIG. 1 b is coupled to the piston 26 by transfer shaft 25 ′′.
- a flexible coupling may be included if desired.
- the housing of the brake 34 may be mounted directly to the housing 24 of the actuator 23 .
- the control system 66 includes a motion control 36 , a pneumatic control system 22 and an input 58 and collectively controls the motion of the actuator 23 and brake 34 and, thus, the motion of the output member 25 and interconnected component 41 .
- the sensor 35 provides a motion signal 33 to the motion control 36 and to the pneumatic control 28 via the data interconnection 51 .
- the controls 36 , 28 process the input data regarding desired motion 58 a , 58 b and the instantaneous motion signal 33 from sensor 35 to derive: 1) a control signal 28 a to be provided to the pneumatic valve 29 , and 2) a control signal 37 to the controllable brake 34 .
- FIG. 3 illustrates another embodiment of the apparatus 20 .
- the pneumatic system 21 includes an actuator 23 , such as rotary pneumatic motor, for example, the one HP model 2AM-NRV-589 manufactured by Gast Manufacturing Corporation of Benton Harbor, Mich.
- the actuator 23 includes a housing 24 and a rotor-like piston 26 supported for rotary motion therein.
- An output member shaft 25 is coupled to the piston 26 and rotates in unison therewith.
- the actuator 23 is securely mounted on a frame 47 (a portion of which is shown in cross section).
- An interconnected component 41 (a carriage) is threaded onto, and mounted on, the threaded power screw member 48 .
- Downward extensions 50 ride on either side of the frame 47 and prevent rotation of the component 41 relative to the frame 47 .
- the rotary-acting controllable brake 34 Secured to the frame 47 at the other end of the apparatus 20 is the rotary-acting controllable brake 34 .
- the brake shaft 32 of brake 34 is interconnected, and coupled, to the power screw member 48 thereby coupling it to the output shaft 25 of the actuator 23 .
- a flat (not shown) or other suitable means formed on the shaft 32 prevents rotation between the shaft 32 and the power screw member 48 .
- the brake 34 herein is the same in construction as the brake previously illustrated in FIG. 1 b and its energization by the motion control system 36 causes a breaking torque to be exerted between the frame 47 and the power screw member 48 thereby controlling its stopping position, its velocity or acceleration characteristics.
- the control method stops the interconnected component 41 at a desired position x des (axial or rotary) with the end result of positioning the article 19 at the appropriate position.
- the inertia of the system components e.g., the component 41 , article 19 , member 48 , coupling 49 and internal components of actuator 23
- the component 41 may be stopped precisely and quickly at any desired position x des .
- the motion control 36 may receive appropriate information from the pneumatic control 28 through data interconnection 51 , or visa versa, such that the action of the actuator 23 and the brake 34 are appropriately coordinated.
- the desired stopping position x des , desired velocity or acceleration profile is input via the input 58 for controlling the motion of the output member 25 .
- the controls 28 , 36 may be programmed to precisely stop the component 41 at any axial position along the axial axis A-A. Desirable control methods are described with reference to FIGS. 8 - 9 later herein.
- FIGS. 4 - 7 illustrate four alternate embodiments of the controllable pneumatic actuator and motion control apparatus 20 .
- the pneumatic actuator 23 is positioned longitudinally in line with a linear-acting brake 34 .
- an apparatus 20 is provided comprising a pneumatic actuator 23 coupled with a linear-acting controllable brake 34 which together cooperate to precisely control the motion of an output member 25 and, thus, the motion of an interconnected component 41 relative to a mounting member 18 .
- the output member 25 is preferably a piston rod shaft and is coupled to the piston 26 .
- the pneumatic system 21 includes a pneumatic actuator 23 and a pneumatic control system 22 .
- the actuator 23 includes a housing 24 with a generally cylindrically-shaped gas cavity 54 formed therein.
- a first puck-shaped piston 26 is slidably disposed in the gas cavity 24 and subdivides it into first 31 a and second 31 b gas chambers.
- a pressure source 27 e.g. a reservoir and pump, etc.
- the pneumatic control 28 controls the operation of a pneumatic valve 29 to properly apportion the supply of pressure to the gas chambers 31 a , 31 b in accordance with predetermined input 58 b from the input 58 .
- This provides differential pneumatic pressure (P 1 >P 2 or P 2 >P 1 ) to move the first piston 26 rightwardly or leftwardly along the axial axis A-A.
- An output member 25 such as a piston rod shaft, is coupled to the first piston 26 .
- the interconnected component (IC) 41 which may be, for example, a caliper, manipulator, a pusher block, a platform or other item.
- the controllable linear-acting brake 34 includes a cylindrical medium containing cavity 53 which is subdivided into first 52 a and second 52 b medium containing chambers.
- the subdivision is by way of the second piston 45
- the subdivision is via a piston assembly 65 including cylindrical members 67 a , 67 b interconnected by an interconnecting shaft 64 .
- the first piston 26 is formed of first and second faces 62 a , 62 b which face outwardly away from each other.
- the second piston 45 is formed of first and second surfaces 63 a , 63 b which face towards each other.
- the term “piston” as used herein, means an element which broadly functions to displace fluid upon movement thereof or which is moveable in response to pressure applied thereto.
- the second piston 45 is rigidly interconnected with, and longitudinally aligned with, the first piston 26 and moveable within the cavity 53 along the axial axis A-A.
- the rigid interconnection is by way of the interconnecting shaft 32 .
- the rigid interconnection comprises the cylindrical elements 67 a , 67 b .
- a passageway 46 interconnects the first and the second medium containing chambers 52 a , 52 b .
- a field responsive medium 44 e.g. a magnetically controllable fluid such as a magnetorheological fluid as is described in U.S. Pat. No.
- a field generator 39 such as a wound magnet wire coil, when energized, produces a magnetic field 43 which is directed by pole pieces 40 to change the rheology of the medium 44 exposed thereto.
- the coil 39 is mounted to the piston 45
- the coil 39 is immovably mounted to the inside surface of the cylindrical sleeve 57 of the housing 24 .
- Energizing coil causes a braking force to be applied to both the first 26 and interconnected second 45 piston thereby allowing the motion (position, velocity or acceleration) of the output member 25 to be precisely controlled.
- a stopping position of the output member 25 may be precisely controlled.
- the field may be an electrical field produced by supplying a sufficient voltage to spaced electrode plates spaced across the passageway. The voltage applied then would change the rheology of an electrorheological fluid, thus applying a resistance force to brake the output member.
- the control system 66 also includes a sensor 35 , such as a linear position sensor, which supplies a motion signal 33 representative of an axial position, velocity or acceleration of a moving component of the apparatus 20 as described above (e.g. an axial position of the output member 25 ).
- a sensor 35 such as a linear position sensor, which supplies a motion signal 33 representative of an axial position, velocity or acceleration of a moving component of the apparatus 20 as described above (e.g. an axial position of the output member 25 ).
- the motion control 36 processes the signal 33 and the input motion information 58 a from input 58 and provides a control signal 37 to the controllable brake 34 . This controls at least one motion selected from a group consisting of a position, velocity and acceleration of the output member 25 .
- the input 58 a , 58 b may be input from a key pad, from a PC, from a Programmable Logic Controller (PLC), hard coded data into a micro-controller or electronic component or other suitable input means.
- the input data 58 a , 58 b from input 58 may comprise: 1) the desired stopping position (x des ), 2) an error (Ax) about that stopping position, 3) a velocity profile for startup (from point a to point b), 4) a stopping velocity profile (from point c to point d), or 5) both, as well as 6) during the stroke (from point b to point c), or 7) an acceleration profile at any point along the stroke.
- the terms x, x des and ⁇ x are used to denote linear translational motions or rotational motions, depending upon the type of apparatus 20 .
- control logic in the pneumatic control 28 turns off the pneumatic actuator 23 upon sensing a rotation or displacement signal 33 (x) from sensor 35 which is approximately equal to the desired position (e.g., x des ) by sending an appropriate signal 28 a to the pneumatic valve 29 .
- the motion control 36 then activates the brake 34 to generate a braking force or torque and decelerate the output member 25 and stop its motion (axial or rotary).
- the turning off of the pneumatic actuator 23 and activation of the brake 34 both occur preferably simultaneously upon entering a predetermined tolerance band ⁇ x surrounding the desired stopping position x des .
- This braking force controls the motion (rotational or translational displacement, velocity or acceleration), as desired, of the output member 25 at any desired point along its stroke.
- FIGS. 8 - 9 To illustrate the control aspects, reference is again directed to FIGS. 8 - 9 wherein the output member 25 is initially positioned at some point, for example, at point a.
- the pneumatic control 28 based on an input signal 33 from the sensor 35 transmitted via data interconnection 51 and signals 58 b of the target position x des . input from the input 58 , via control logic commands the valve 29 to move the member 25 in a first direction.
- System dynamics and flow capacity/characteristics determine the slope and rate of acceleration to a maximum velocity between points a and b in FIG. 8. Notably, this profile may also be precisely controlled, as desired, by application of low level braking forces.
- a low level control signal 37 by the motion control 36 will set the actual velocity v from points b to c to a value v des commanded by the input 58 a .
- the control logic of motion control 36 Upon entering the tolerance band Ax at point c, the control logic of motion control 36 generates a higher level control signal 37 to further energize the field generator 39 . This creates a strong magnetic field which acts upon and changes the rheology (apparent viscosity) of the medium 44 and produces a braking force which controls the motion of the output member 25 almost instantaneously.
- the output device 25 comes to a stop within the band ⁇ x at point d following a direct path 74 .
- the apparatus 20 may hunt, i.e., exceed the tolerance band ⁇ x on the right side and cause the pneumatic control 28 to be momentarily actuated to drive the output member 25 back in the opposite direction along indirect path 75 and back into the tolerance band ⁇ x, thus again bringing the member 25 to rest within the tolerance band at point d.
- the desired velocity profile is input via the input 58 and to a velocity control 77 of the motion control 36 . It should be recognized that a similar control may be utilized for control of the FIGS. 1 a , 2 and 3 embodiments where the signal 33 comprises a rotational position, the velocity is a rotational velocity.
- the various controls 28 , 36 of the control system 66 may be implemented in separate logic or electronic modules, in a single logic or electronic unit or by any other suitable means.
- the position information x des is subtracted from the measured displacement signal 33 (representative of the position x) derived from sensor 35 to produce an error signal e.
- the error and the ⁇ x information are compared in logic. If the error e is above positive and greater than the Ax value then the logic dictates a 0,1 output control signal 28 a to valve 29 causing the piston 26 to move towards the desired position x des .
- the logic dictates a 1,0 output control signal 28 a to valve 29 causing the piston to move towards (in the opposite direction) the desired position x des .
- the control signal provided via the position control 76 would preferably be zero.
- the velocity control 77 may provide a low level velocity control signal 80 to achieve the desired velocity v des 58 a input from the input 58 for any point along the stroke.
- the velocity control 77 may perform any desired velocity profile, which may be a function of position information x. If the error e is less than the ⁇ x value, then the pneumatic control 28 send out a 0,0 control signal 28 a to the valve 29 which is the neutral position of the valve 29 .
- the logic causes the brake 34 to be activated to add a position control signal 79 at junction 78 b which sums with any velocity control signal 80 present and thereby produces a substantial braking force to stop the motion of the output member 25 within the tolerance band.
- the brake 34 is activated to a high level at a calculated shut down point x 0 before the desired stopping point x des based upon the kinetic energy in the system and upon the braking force available from the brake 34 .
- the exact time to shut down the pneumatic actuator 23 and apply the brake 34 is easily and readily determined for any desired position x des . This hereinafter will be referred to as “kinetic energy control.”
- Kinetic energy control virtually eliminates overshoot and hunting associated with prior art methods, especially on systems where the system inertia is large.
- the kinetic energy of the system is equated with the braking energy in the system (see eqn. 4-6 below) to provide an intelligent tradeoff between accuracy and speed.
- E mr is the braking energy available
- F mr is the braking force available
- x des is the desired stopping position (rotary or linear)
- x 0 is a shut down position (rotary or linear) away from the desired position where if the force available were applied, it would bring the output member 25 to a stop at the position x des .
- E k is the kinetic energy at x 0 .
- m is the mass (or rotational inertia) of the moving components in the system including the payload article 19 .
- v is the velocity (rotary or linear) of the output member 25 at x 0 .
- Equation 7 becomes the basis for the kinetic energy control method, where the inputs provided via the input 58 are the desired rotational or translational accuracy Ax, the braking force available F mr and the mass or rotational inertia m.
- the point-to-point e.g., point b to c of FIG. 8
- velocity v can be controlled such that the resultant actual stopping position is substantially at x des . without any substantial overshoot.
- the force F mr is a factory set value which may be updated via on-line learning.
- the input may include the mass m and the braking force available F mr (e.g. hard coded) and the velocity v (derived from the motion signal 33 ) to calculate the value ⁇ x according to equation 6 ; the value ⁇ x corresponding to where the pneumatic actuator 23 is shut down and the brake 34 is applied.
- the velocity v may be derived via differentiating the position signal in differentiator 81 (FIG. 9).
- the accuracy desired ⁇ x, the mass m and the desired velocity v des can be inputted via input 58 and an applied braking force F calculated and then applied to stop the output member 25 at the desired position.
- Known pairs of velocity v des and accuracy ⁇ x would be input to ensure no overshoot.
- the passageway 46 passes through the piston 45 .
- the construction of the piston 45 of FIG. 4 is identical to that taught in U.S. Pat. No. 5,878,851 to Carlson et al. entitled “Controllable Vibration Apparatus.” Contrarily, in the FIGS. 5 - 6 embodiments, the passageway 46 comprises an annulus formed between the piston 45 and the housing 24 and the medium 44 passes about the piston 45 . Piston constructions whereby the medium passes about the piston are taught in U.S. Pat. No. 5,277,281 to Carlson et al entitled “Magnetorheological Fluid Dampers.” In the FIG. 7.
- the passageway 46 comprises an annulus formed between the pole pieces 40 of a partition 71 and an interconnecting shaft 64 of magnetically-soft material.
- the coil 39 is mounted to the inside of the housing 24 , thus, the wires 70 are desirably not subject to movement.
- the magnetic field 43 is carried by the sleeve 57 , pole pieces 40 and the interconnecting shaft 64 .
- the housing 24 comprises first and second rigid end caps 55 a , 55 b positioned at respective ends of the housing 24 and an intermediate member 56 spaced therebetween.
- a first sleeve 57 a is disposed between the first end cap 55 a and the intermediate member 56
- a second sleeve 57 b is disposed between the second end cap 55 b and the intermediate member 56 .
- the sleeves 57 a , 57 b may be made of any rigid material, except that in the case of the FIGS.
- the sleeve 57 a must be manufactured from a magnetically-soft material; the reason being that a portion of the field 43 generated by the generator 39 is carried in the sleeve 57 a .
- the intermediate member 56 includes an elastomer seal 60 which seals about the shaft 32 to prevent flow of the field responsive medium 44 into the first and second gas chambers 31 a , 31 b .
- the wires 70 are received through a bore (not shown) in the respective shafts.
- the controllable brake 34 further comprises a volume compensator 59 .
- the compensator 59 includes a gas charged chamber 72 and a flexible elastomeric partition 73 .
- the compensator 59 functions to take up the volume of rod 32 as it reciprocates into the cavity 53 as well as any expansion of the medium 44 due to temperature variations.
- the rod volume compensation issue is addressed by the addition of a second shaft 25 exiting from the cavity 53 , such that the rod volume is always constant.
- the rod volume in the cavity 53 is constant, as well. Temperature compensation in the FIGS.
- 5 - 7 embodiments if needed, may be provided by gas containing capsules or an external accumulator (not shown) attached to the housing 24 and interconnecting to the cavity 53 .
- the medium containing cavity 53 is formed within the housing 24 .
- the apparatus 20 includes a first shaft 25 secured to the second piston 45 and received in sealed relationship through a first end cap 55 a of the housing 24 , and a second shaft 32 received in sealed relationship (via seal 60 ) through an intermediate member 56 of the housing 24 .
- the gas cavity 54 is formed by an end cap 55 b , an intermediate member 56 and a sleeve 57 b similarly to the formation of the medium containing cavity 53 .
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Abstract
A controllable pneumatic apparatus including a pneumatic actuator coupled with a linear-acting brake including a field responsive medium. The pneumatic actuator has a housing with a gas cavity, a first piston slidably disposed in the gas cavity subdividing the gas cavity into first and second gas chambers, and an output member coupled to the first piston. The linear-acting controllable brake includes a medium containing cavity subdivided into a first and second chambers, and a second piston rigidly interconnected with, and longitudinally aligned with, the first piston. A passageway interconnects the first and the second chambers and a field responsive medium (e.g., a magnetic fluid) is contained in the passageway. A field generator produces a field to change a rheology of the medium and cause a braking force to be applied to the output member to control motion thereof. A preferable control method implements motion control based upon the kinetic energy and the braking force in the system.
Description
- This application is a divisional of pending U.S. patent application Ser. No. 09/264,273, filed Mar. 8, 1999.
- The invention relates to pneumatic apparatus. More particularly, the present invention is directed to a pneumatic apparatus, which is precisely controllable.
- For industrial applications, it is sometimes desired to accurately position items in assembly or manufacturing processes, such as in a packaging, tensioning, positioning, stacking, guiding, pick-and-place or other industrial automation applications. Many times, pneumatic actuators are used to provide the motive force for such applications. In simple operations, certain simple pneumatic actuators are utilized. The simplest types are 2-position pneumatic actuators only capable of stopping at the end positions, i.e., all the way to one end or all the way to the other end of the stroke. Although cost effective, they are only useful in a very limited set of automation applications.
- More sophisticated pneumatic actuators, such as the TOM THUMB® 3-position pneumatic actuator sold by PHD, Inc. of Fort Wayne, Ind., includes the ability to stop at an intermediate or middle position. Although more flexible than2-position actuators, these 3-position actuators are still very inflexible, in that, once designed, the intermediate position is largely unchangeable.
- In the next level of sophistication, actuators are available which can stop at any intermediate position. For example, SMC Corporation of Tokyo, Japan manufactures a rodless pneumatic cylinder with an internal brake and positioning scale (e.g. model ML2B). This system includes a piston moveable within a housing and integral position sensor and a friction brake. The position sensor provides a position signal to the controller. By comparing the instantaneous position with inputted desired position data, the brake is actuated via air pressure to move a brake shoe into contact with a brake plate, thereby stopping the piston at the predetermined intermediate point. The system includes the ability to learn the distance from application of the brake to the actual stopping point, and makes adjustments to improve the accuracy for at the next commanded stop.
- Adding the ability to stop at an intermediate position in such pneumatic systems is very desirable, however, such friction braking tends to add significant mechanical and pneumatic complexity and additional expense to the system. Moreover, such systems can only be full on or full off at any position along the actuator stroke, thus, by their very nature they are inflexible. Moreover, such systems tend have good accuracy only at low speeds.
- Robohand, Inc. of Monroe, Conn., manufactures pneumatic position control systems under the tradename POSITIONEX™. These systems include a pneumatic servo-actuator having a piston moveable in, and subdividing, a cylinder into a first and second chamber. They also include an output shaft interconnected to the piston, a position transducer providing a signal of a position of the output shaft and a servo-valve controlled by a control system to apply the appropriate pressure to position the output shaft at the appropriate predetermined position. Problematically, such systems tend to overshoot and hunt (oscillate about) the desired stopping position. Moreover, the servo-valves tend to be very complex and expensive.
- Accordingly there has been a long felt, and unmet need for a cost effective pneumatic actuator and positioning system which is capable of accurately stopping at any point along its stroke.
- The present invention provides a controllable pneumatic actuator and motion control apparatus including a field responsive medium and control method therefor whose motion may be accurately controlled at any point along its stroke. According to the invention, the controllable pneumatic apparatus comprises a pneumatic actuator coupled to a linear-acting brake such that a motion (e.g., a displacement, a velocity or an acceleration) of an output member of the actuator may be precisely controlled.
- The apparatus preferably includes a control system having a sensor for deriving a motion signal of a motion of a moving component of the apparatus, and a motion control for processing the motion signal and providing a control signal to the controllable brake. The actuator is included in a pneumatic system that further comprises a pressure supply providing a supply of pressurized gas and a pneumatic control controlling a pneumatic control valve for apportioning the pressurized gas from the source and providing differential pneumatic pressure to move the piston. The apparatus preferably includes a control system further comprising an input for inputting information to the pneumatic control and the motion control.
- The apparatus is preferably controlled according to a method in which the motion of the output member is controlled based upon a kinetic energy in the system. Most preferably, the control is also based upon an available braking force from the brake. More particularly, a shut down point for turning off the pneumatic actuator and activation of the controllable brake is determined based upon the kinetic energy and the available braking force.
- According to the invention, a controllable pneumatic apparatus is provided comprising a pneumatic actuator having a housing with a gas cavity formed therein, a first piston slidably disposed in the gas cavity subdividing the gas cavity into first and second gas chambers, and an output member coupled to the first piston; and a controllable brake, including a medium containing cavity subdivided into a first and second chambers, a second piston rigidly interconnected with, and longitudinally aligned with, the first piston and moveable in the cavity along the axial axis, a passageway interconnecting the first and the second chambers, a field responsive medium (e.g., a magnetic fluid) contained in the passageway, a field generator for producing a field to change a rheology of the medium upon exposure to the field causing a braking force to be applied to the output member to control motion thereof.
- In one embodiment, the field generator comprises a coil mounted stationary inside the housing. In this embodiment, the first piston is formed of first and second faces which face away from each other and the second piston is formed of first and second surfaces which face towards each other. Preferably, the passageway comprises an annulus formed between a pole piece and a shaft.
- According to another aspect of the invention, the controllable pneumatic apparatus comprises a pneumatic system including a housing having a gas cavity formed therein, a first piston slidably disposed in the gas cavity subdividing the gas cavity into a first gas chamber and a second gas chambers, a pressure source providing a supply of pressurized gas, a pneumatic control which controls a pneumatic valve to apportion the supply of pressure to the first and second gas chambers thereby providing differential pneumatic pressure to move the first piston along an axial axis, and an output member coupled to the first piston; a controllable brake including a medium containing cavity, a second piston subdividing the medium containing cavity into a first medium chamber and a second medium chamber, the second piston being longitudinally aligned with the first piston and rigidly interconnected by an interconnecting shaft to the first piston, the second piston moveable in the cavity along the axial axis, a passageway interconnecting the first and the second medium chambers, a magnetically controllable fluid contained in the passageway, a field generator further including a coil for producing a magnetic field to change a rheology of the fluid upon exposure to the magnetic field; a motion sensor for providing a motion signal representative of a motion of the output member; and a control system for processing the motion signal and providing a control signal to the controllable brake thereby controlling motion of the output member.
- According to the invention, the controllable pneumatic apparatus also comprises a housing including first and second end caps, an intermediate member spaced between the end caps, a first sleeve intervening between the first end cap and the intermediate member, and a second sleeve intervening between the second end cap and the intermediate member, a pneumatic system, including a gas cavity formed by the second end cap, the intermediate member and the second sleeve, a first piston slidably disposed within the second sleeve and subdividing the gas cavity into a first and second gas chambers, a pressure source providing a supply of pressurized gas to the cavity, a pneumatic control which controls a pneumatic valve to apportion the supply of pressure to the first and second gas chambers thereby providing differential pneumatic pressure to move the first piston along an axial axis, and an output member coupled by an interconnecting shaft to the first piston; a controllable brake including a medium-containing cavity formed by the first end cap, the intermediate member and a first sleeve, a second piston positioned relative to the first sleeve and subdividing the medium-containing cavity into a first and second medium chambers, the second piston being longitudinally aligned with the first piston and rigidly interconnected by the interconnecting shaft to the first piston, the second piston moveable in the cavity along the axial axis, a passageway interconnecting the first and second medium chambers, a magnetically controllable fluid contained in the passageway, a field generator for producing a magnetic field to change a rheology of the fluid upon exposure to the magnetic field; a sensor for providing a motion signal representative of motion of the output member; and a control system for processing the motion signal and providing a control signal to the controllable brake thereby controlling the motion of the output member.
- According to another aspect of the invention, the controllable pneumatic apparatus comprises a housing including first and second end caps, and a sleeve spaced between the end caps; a pneumatic system, including a gas cavity formed by the end caps, the sleeve and outwardly disposed axial faces of a piston assembly, the piston assembly including a first member, a second member and an interconnecting shaft, the piston assembly slidably disposed in the sleeve subdividing the gas cavity into a first gas chamber and a second gas chambers, a pressure source providing a supply of pressurized gas to the cavity, a pneumatic control which controls a pneumatic valve to apportion the supply of pressure to the first and second gas chambers thereby providing differential pneumatic pressure to move the piston assembly along an axial axis, and an output member coupled to the piston assembly; a controllable brake including a medium containing cavity formed by the first sleeve and inwardly disposed axial surfaces of the piston assembly, and a partition subdividing the medium containing cavity into a first medium chamber and a second medium chamber, a passageway formed between the interconnecting shaft and the partition, the passageway interconnecting the first and the second medium chambers, a field responsive medium contained in the passageway, a field generator for producing a field to change a rheology of the medium upon exposure to the field; a sensor for providing a motion signal representative of a motion of the output member; and a motion control for processing the motion signal and providing a control signal to the controllable brake thereby energizing the field generator and controlling motion of the output member.
- According to another aspect of the invention, a method of controlling a controllable pneumatic apparatus is provided comprising the steps of: providing a pneumatic actuator which causes motion of an output member, providing a controllable brake coupled to the output member, providing a control system for controlling the pneumatic actuator and the controllable brake, inputting system performance information to the control system, measuring a motion of the output member and providing a motion signal, processing the motion signal and the desired motion information within the control system and providing control signals to control the pneumatic actuator and to activate the controllable brake, the processing being based upon a kinetic energy. More preferably, the processing is based upon available braking force, as well. According to a preferred aspect, the system performance information comprises desired motion information of the output member such as the desired stopping position, a desired accuracy, a desired velocity profile, an acceleration profile, a mass of any moving system elements, a braking force available from the controllable brake or combinations thereof. Preferably, the shut down point is determined based upon the kinetic energy and the available braking force. Most preferably, the shut down point is determined based upon the equation:
- where Δx is the distance from the shut down point to the desired stopping position, m is the mass of any moving system components, v is the velocity at the stopping point and Fmr is the available braking force.
- It is an advantage of the present invention that precise positioning of pneumatic actuators may be accomplished for assembly, packaging and other industrial automation applications.
- It is an advantage of the present invention that it provides a stiff actuator when stationary as compared to servo-pneumatic positioning apparatuses of the prior art.
- It is an advantage of the present invention that various velocity or acceleration profiles may be implemented during stopping, starting and during travel.
- It is an advantage of the present invention that progressive braking/acceleration is allowed as compared to pneumatic systems including friction brakes.
- It is an advantage of the present invention that precise positioning is accomplished within a very compact and cost effective package.
- It is an advantage of the present invention that it is insensitive to environmental contaminants.
- It is an advantage of the present invention that the control method allows optimization for accuracy or velocity based upon the kinetic energy of the system.
- The above-mentioned and further features, advantages and characteristics of the present invention will become apparent from the accompanying descriptions of the preferred embodiments and the attached drawings.
- The invention will become better understood by reference to the description that follows, in conjunction with the appended drawings, in which:
- FIG. 1a is a schematic view of a first embodiment of controllable pneumatic actuator and motion control apparatus in accordance with the present invention;
- FIG. 1b is a cross-sectioned side view of the rotary-acting controllable brake of FIG. 1a taken along
line 1b-1b; - FIG. 2 is a schematic view of a second embodiment of apparatus in accordance with the present invention;
- FIG. 3 is a schematic view of a third embodiment of apparatus in accordance with the present invention;
- FIG. 4 is a schematic view of a fourth embodiment of apparatus in accordance with the present invention;
- FIG. 5 is a schematic view of a fifth embodiment of apparatus in accordance with the present invention;
- FIG. 6 is a schematic view of a sixth embodiment of apparatus in accordance with the present invention;
- FIG. 7 is a schematic view of a seventh embodiment of apparatus in accordance with the present invention;
- FIG. 8 is a plot of displacement versus velocity when one type of control method is implemented; and
- FIG. 9 is a block diagram of one type of control method.
- A controllable pneumatic actuator and
motion control apparatus 20 according to the invention is first illustrated in FIG. 1a. Theapparatus 20 comprises apneumatic actuator 23 and an interconnected and coupled rotary-actingcontrollable brake 34, such as a rotary-acting magnetorheological brake (e.g. MRB-2107-3 sold by Lord Corporation under the tradename RHEONETIC™ rotary controllable brake). Anoutput member 25, such as an axially-reciprocating or rotary-acting shaft, is coupled (interconnected such that force may be applied therebetween) to a movingpiston 26 of anactuator 23 included within thepneumatic system 21. The rotary-actingcontrollable brake 34 controls a motion parameter of theoutput member 25, such as a stopping position (displacement), a velocity, an acceleration or a starting or stopping velocity or acceleration profile thereof. - In more detail, the
pneumatic system 21 includes thepneumatic actuator 23 and apneumatic control system 22 for supplying pressure to, and causing motion of theoutput member 25 of theactuator 23. Thepneumatic control system 22 includes a pneumatic pressure source orsupply 27, such as a reservoir (not shown) of pressurized gas (e.g., air) which may be replenished by and pump (not shown). Preferably, thepressure supply 27 is regulated to a preset pressure, for example, to a presure in the range of between approximately 30 psi and 120 psi (207 kPa and 827 kPa), depending upon the application. - The
pneumatic control system 22 also includes controllablepneumatic valve 29, such as a three-position solenoid valve (e.g. model SY5440 available from SMC Corporation of Tokyo, Japan), or any other type of suitable controllable valve. Thevalve 29 is operable in response to controlsignals 28 a generated by apneumatic control 28 to appropriately apportion pressure to thepneumatic actuator 23. For example, thevalve 29 may include a first position which causes a differential pressure where the pressure P1 in afirst gas chamber 31 a is higher than the pressure P2 in asecond gas chamber 31 b thereby causing thepiston 26 to move in a first (e.g. rightward) direction. Thevalve 29 may also include a second position causing the pressure P1 to be lower than the pressure P2 thereby causing motion of thepiston 26 in the opposite (e.g. leftward) direction. Finally, thevalve 29 may include a neutral position which provides pressures P1, P2 in thechambers piston 26 to come to rest. - The
pneumatic actuator 23 includes a piston 26 (includingelements rack 26 c) preferably disposed in sealed relation with the cylindrically-shapedcavity 54 formed in ahousing 24. Thepiston 26, which includes preferably cylindrically shapedelements cavity 54 and forms twoopposed gas chambers piston 26 being reciprocatably moveable along a central axis A-A of thehousing 24. Thepiston 26 is coupled to, and movement of it produces movement of, at least oneoutput shaft 25. In the FIG. 1a embodiment, theactuator 23 includes first 25 and a second 25′ output members. The actuator'soutput member rotatable output shaft 25 or a axially moveablepiston rod shaft 25′. - The
actuator 23 may also include atransmission 30, which, for example, converts linear motion of thepiston 26 to rotary motion of theshaft 25. Thetransmission 30 may include a rack 25 c and pinion 25 d or other gearing system for converting linear to rotary motion, as is well understood by those of ordinary skill in the art. Thetransfer shaft 25″ extending from the other side oftransmission 30 is coupled to thetransmission 30 and is, therefore, interconnected and coupled to, and moves in unison with, thepiston 26 andoutput members output member 25 is coupled to thepiston 26 via thepinion 26 d and theoutput member 25′ is coupled to thepiston 26 by a rigid interconnection to thecylindrical element 26 b. Moreover, it should be recognized that applying appropriate pressures to thechambers cylindrical elements rack 26 c andpinion 26 d and coupledoutput members - The rotary-acting
controllable brake 34 includes a field responsive medium 44 contained therein and is coupled to thepiston 26, preferably through thetransmission 30 or other suitable means. Therotary brake 34, as best shown in FIG. 1b, includes abrake shaft 32 coupled (e.g. by pin) for rotation with a disc-shapedrotor 38 manufactured from a soft-magnetic material, such as low carbon steel. Amagnetic field generator 39, such as a magnet wire coil circumferentially wound (100-300 winds of wire) about a plastic bobbin, produces amagnetic field 43 upon being activated with suitable electrical current (e.g. 1-3 amps).Pole pieces 40 manufactured of a soft-magnetic material direct the flux across the preferably radially directedgaps 42 formed between thepoles 40 and therotor 38. Alternatively, thegaps 42 may be disposed axially or in other suitable orientations, as is known to those of ordinary skill in the art. Thegaps 42 contain a fieldresponsive medium 44, such as a magnetorheological fluid or dry magnetic particles. A suitable magnetorheological fluid is described in commonly assigned U.S. Pat. Nos. 5,599,474, 5,683,615 or 5,705,085. A suitable dry magnetic particle is manufactured from 410 series stainless steel power and sifted through a minus 325 mesh and is available from Hoeganaes Corpration of Riverton, N.J. under the tradename ANCOR® 410L. Application of the magnetic field 43 (shown dotted) formed by energizing thefield generator 39 with suitable electrical current causes a change in the rheology, i.e., the apparent viscosity, of the medium 44 contained in thegaps 42. This rheology change creates a resistance torque between therotor 38 andpoles 40, thus making it hard to turn theshaft 32. The relative resistance to rotation of therotor 38 may be smoothly variable based upon the applied electrical current. When theoutput shaft 32 of thecontrollable brake 34 is coupled to thepiston 26, application of such current to thebrake 34 may be controlled to stop the actuator'spiston 26 at any intermediate point along its stroke. Alternatively, the brake may be activated to control the velocity or acceleration profile during startup, stopping, or at any point along its travel. - Rotary brakes such as described herein are described in detail in U.S. Pat. No. 5,842,547 to Carlson et al. entitled “Controllable Brake,” U.S. Pat. No. 5,816,372 to Carlson et al. “Magnetorheological Fluid Devices And Process Of Controlling Force In Exercise Equipment Utilizing Same,” and U.S. Pat. No. 5,711,746 to Carlson entitled “Portable Controllable Fluid Rehabilitation Devices.”
- Again referring to FIG. 1a, the
apparatus 20 further includes asensor 35, such as a rotary potentiometer (POT), for providing amotion signal 33 representative of a motion (e.g., a position, velocity or acceleration) of a moving component of theapparatus 20. For example, thesensor 35 may measure the motion (e.g., displacement) of thepiston 26. Alternatively, asensor 35 may sense motion between theoutput member shaft housing 24 or of theinterconnected component interconnected component - A
motion control system 36, such as a position control, processes themotion signal 33 and provides anelectrical control signal 37 to thecontrollable brake 34. Thecontrol signal 37 energizes thefield generator 39 in thebrake 34 causing a resistance force to be applied to theoutput shaft 32, and tointerconnected shaft piston 26, and to anyinterconnected component output member interconnected component - FIG. 2 illustrates another embodiment of the
apparatus 20. In this embodiment, thepneumatic actuator 23 comprises a rotary-acting pneumatic motor including a piston (rotor) 26 rotatably mounted for rotation in thehousing 24. Application of a differential pressure to thepiston 26 by thepneumatic control system 22 causes the rotation of thepiston 26. Preferably, a rotary-actingcontrollable brake 34 identical to that described in FIG. 1b is coupled to thepiston 26 bytransfer shaft 25″. A flexible coupling may be included if desired. Optionally, the housing of thebrake 34 may be mounted directly to thehousing 24 of theactuator 23. - The
control system 66 includes amotion control 36, apneumatic control system 22 and aninput 58 and collectively controls the motion of theactuator 23 andbrake 34 and, thus, the motion of theoutput member 25 andinterconnected component 41. As will be described in more detail later, thesensor 35 provides amotion signal 33 to themotion control 36 and to thepneumatic control 28 via thedata interconnection 51. Thecontrols motion instantaneous motion signal 33 fromsensor 35 to derive: 1) acontrol signal 28 a to be provided to thepneumatic valve 29, and 2) acontrol signal 37 to thecontrollable brake 34. - FIG. 3 illustrates another embodiment of the
apparatus 20. In this embodiment, thepneumatic system 21 includes anactuator 23, such as rotary pneumatic motor, for example, the one HP model 2AM-NRV-589 manufactured by Gast Manufacturing Corporation of Benton Harbor, Mich. Theactuator 23 includes ahousing 24 and a rotor-like piston 26 supported for rotary motion therein. Anoutput member shaft 25 is coupled to thepiston 26 and rotates in unison therewith. Theactuator 23 is securely mounted on a frame 47 (a portion of which is shown in cross section). Interconnected to theoutput shaft 25 by amisalignment coupling 49, and supported in bushings at the ends offrame 47, is a threadedpower screw member 48. An interconnected component 41 (a carriage) is threaded onto, and mounted on, the threadedpower screw member 48.Downward extensions 50 ride on either side of theframe 47 and prevent rotation of thecomponent 41 relative to theframe 47. - Secured to the
frame 47 at the other end of theapparatus 20 is the rotary-actingcontrollable brake 34. Thebrake shaft 32 ofbrake 34 is interconnected, and coupled, to thepower screw member 48 thereby coupling it to theoutput shaft 25 of theactuator 23. A flat (not shown) or other suitable means formed on theshaft 32 prevents rotation between theshaft 32 and thepower screw member 48. Thebrake 34 herein is the same in construction as the brake previously illustrated in FIG. 1b and its energization by themotion control system 36 causes a breaking torque to be exerted between theframe 47 and thepower screw member 48 thereby controlling its stopping position, its velocity or acceleration characteristics. Preferably, the control method stops theinterconnected component 41 at a desired position xdes (axial or rotary) with the end result of positioning thearticle 19 at the appropriate position. - For example, as the
actuator 23 is shut off by thepneumatic control 28, the inertia of the system components (e.g., thecomponent 41,article 19,member 48,coupling 49 and internal components of actuator 23) will cause thecomponent 41 to continue to move along for some finite distance. By engaging thebrake 34 at the appropriate time, thecomponent 41 may be stopped precisely and quickly at any desired position xdes. Accordingly, themotion control 36 may receive appropriate information from thepneumatic control 28 throughdata interconnection 51, or visa versa, such that the action of theactuator 23 and thebrake 34 are appropriately coordinated. The desired stopping position xdes, desired velocity or acceleration profile is input via theinput 58 for controlling the motion of theoutput member 25. Notably, in some cases, it may be desirable to fully engage thebrake 34 slightly before shutdown of theactuator motor 23. Moreover, sensor information, such as position, velocity or acceleration from thesensor 35 may be provided to thepneumatic control 28 viadata interconnection 51. Thus, thecontrols component 41 at any axial position along the axial axis A-A. Desirable control methods are described with reference to FIGS. 8-9 later herein. - FIGS.4-7 illustrate four alternate embodiments of the controllable pneumatic actuator and
motion control apparatus 20. In each of these embodiments, thepneumatic actuator 23 is positioned longitudinally in line with a linear-actingbrake 34. According to the invention, anapparatus 20 is provided comprising apneumatic actuator 23 coupled with a linear-actingcontrollable brake 34 which together cooperate to precisely control the motion of anoutput member 25 and, thus, the motion of aninterconnected component 41 relative to a mountingmember 18. In all embodiments of FIGS. 4-7, theoutput member 25 is preferably a piston rod shaft and is coupled to thepiston 26. - The
pneumatic system 21 includes apneumatic actuator 23 and apneumatic control system 22. Theactuator 23 includes ahousing 24 with a generally cylindrically-shapedgas cavity 54 formed therein. A first puck-shapedpiston 26 is slidably disposed in thegas cavity 24 and subdivides it into first 31 a and second 31 b gas chambers. A pressure source 27 (e.g. a reservoir and pump, etc.) provides a supply of pressurized gas at a regulated pressure (30-120 psi) as described above. As part of thecontrol system 66, thepneumatic control 28 controls the operation of apneumatic valve 29 to properly apportion the supply of pressure to thegas chambers predetermined input 58 b from theinput 58. This provides differential pneumatic pressure (P1>P2 or P2>P1) to move thefirst piston 26 rightwardly or leftwardly along the axial axis A-A. Anoutput member 25, such as a piston rod shaft, is coupled to thefirst piston 26. Interconnected to theoutput member 25 is the interconnected component (IC) 41 which may be, for example, a caliper, manipulator, a pusher block, a platform or other item. - The controllable linear-acting
brake 34 includes a cylindricalmedium containing cavity 53 which is subdivided into first 52 a and second 52 b medium containing chambers. In the FIGS. 4-6 embodiments, the subdivision is by way of thesecond piston 45, whereas, in the FIG. 7 embodiment, the subdivision is via a piston assembly 65 includingcylindrical members shaft 64. In the FIG. 7 embodiment, thefirst piston 26 is formed of first and second faces 62 a, 62 b which face outwardly away from each other. Contrarily, thesecond piston 45 is formed of first andsecond surfaces - In the embodiments of FIGS.4-7, the
second piston 45 is rigidly interconnected with, and longitudinally aligned with, thefirst piston 26 and moveable within thecavity 53 along the axial axis A-A. In the FIG. 4-6 embodiments, the rigid interconnection is by way of the interconnectingshaft 32. In FIG. 7, the rigid interconnection comprises thecylindrical elements brake 34, apassageway 46 interconnects the first and the secondmedium containing chambers chambers passageway 46. - A
field generator 39, such as a wound magnet wire coil, when energized, produces amagnetic field 43 which is directed bypole pieces 40 to change the rheology of the medium 44 exposed thereto. In the FIGS. 4-6 embodiments, thecoil 39 is mounted to thepiston 45, whereas in the FIG. 7 embodiment, thecoil 39 is immovably mounted to the inside surface of thecylindrical sleeve 57 of thehousing 24. Energizing coil causes a braking force to be applied to both the first 26 and interconnected second 45 piston thereby allowing the motion (position, velocity or acceleration) of theoutput member 25 to be precisely controlled. For example, a stopping position of theoutput member 25 may be precisely controlled. Alternatively, the field may be an electrical field produced by supplying a sufficient voltage to spaced electrode plates spaced across the passageway. The voltage applied then would change the rheology of an electrorheological fluid, thus applying a resistance force to brake the output member. - The
control system 66 also includes asensor 35, such as a linear position sensor, which supplies amotion signal 33 representative of an axial position, velocity or acceleration of a moving component of theapparatus 20 as described above (e.g. an axial position of the output member 25). Within thecontrol system 66, themotion control 36 processes thesignal 33 and theinput motion information 58 a frominput 58 and provides acontrol signal 37 to thecontrollable brake 34. This controls at least one motion selected from a group consisting of a position, velocity and acceleration of theoutput member 25. For example, theinput input data input 58 may comprise: 1) the desired stopping position (xdes), 2) an error (Ax) about that stopping position, 3) a velocity profile for startup (from point a to point b), 4) a stopping velocity profile (from point c to point d), or 5) both, as well as 6) during the stroke (from point b to point c), or 7) an acceleration profile at any point along the stroke. Herein, the terms x, xdes and Δx are used to denote linear translational motions or rotational motions, depending upon the type ofapparatus 20. - For example, in a simple control method for controlling the
apparatus 20 illustrated in FIGS. 8 and 9, control logic in thepneumatic control 28 turns off thepneumatic actuator 23 upon sensing a rotation or displacement signal 33 (x) fromsensor 35 which is approximately equal to the desired position (e.g., xdes) by sending anappropriate signal 28 a to thepneumatic valve 29. Themotion control 36 then activates thebrake 34 to generate a braking force or torque and decelerate theoutput member 25 and stop its motion (axial or rotary). In actuality, the turning off of thepneumatic actuator 23 and activation of thebrake 34 both occur preferably simultaneously upon entering a predetermined tolerance band Δx surrounding the desired stopping position xdes. This braking force controls the motion (rotational or translational displacement, velocity or acceleration), as desired, of theoutput member 25 at any desired point along its stroke. - To illustrate the control aspects, reference is again directed to FIGS.8-9 wherein the
output member 25 is initially positioned at some point, for example, at point a. Thepneumatic control 28, based on aninput signal 33 from thesensor 35 transmitted viadata interconnection 51 and signals 58 b of the target position xdes. input from theinput 58, via control logic commands thevalve 29 to move themember 25 in a first direction. System dynamics and flow capacity/characteristics determine the slope and rate of acceleration to a maximum velocity between points a and b in FIG. 8. Notably, this profile may also be precisely controlled, as desired, by application of low level braking forces. Upon reaching the desired speed, application of a lowlevel control signal 37 by themotion control 36 will set the actual velocity v from points b to c to a value vdes commanded by theinput 58 a. Upon entering the tolerance band Ax at point c, the control logic ofmotion control 36 generates a higherlevel control signal 37 to further energize thefield generator 39. This creates a strong magnetic field which acts upon and changes the rheology (apparent viscosity) of the medium 44 and produces a braking force which controls the motion of theoutput member 25 almost instantaneously. - In the case where the kinetic energy of the system is low and the braking force is adequate, the
output device 25 comes to a stop within the band Δx at point d following adirect path 74. However, if the system kinetic energy is high or the braking force available is inadequate, then theapparatus 20 may hunt, i.e., exceed the tolerance band Δx on the right side and cause thepneumatic control 28 to be momentarily actuated to drive theoutput member 25 back in the opposite direction alongindirect path 75 and back into the tolerance band Δx, thus again bringing themember 25 to rest within the tolerance band at point d. Moreover, as suggested above, it may be desirable under some circumstances to control the acceleration/deceleration or the velocity profiles between points a-b and c-d. In this case, the desired velocity profile is input via theinput 58 and to avelocity control 77 of themotion control 36. It should be recognized that a similar control may be utilized for control of the FIGS. 1a, 2 and 3 embodiments where thesignal 33 comprises a rotational position, the velocity is a rotational velocity. - As should be recognized also, the
various controls control system 66 may be implemented in separate logic or electronic modules, in a single logic or electronic unit or by any other suitable means. As shown in FIG. 9, atjunction 78 a the position information xdes is subtracted from the measured displacement signal 33 (representative of the position x) derived fromsensor 35 to produce an error signal e. Within thepneumatic control 28, the error and the Δx information are compared in logic. If the error e is above positive and greater than the Ax value then the logic dictates a 0,1output control signal 28 a tovalve 29 causing thepiston 26 to move towards the desired position xdes. Contrarily, if the error e is negative and greater than the Δx value then the logic dictates a 1,0output control signal 28 a tovalve 29 causing the piston to move towards (in the opposite direction) the desired position xdes. In each of these cases, the control signal provided via theposition control 76 would preferably be zero. Thevelocity control 77 may provide a low levelvelocity control signal 80 to achieve the desiredvelocity v des 58 a input from theinput 58 for any point along the stroke. Thevelocity control 77 may perform any desired velocity profile, which may be a function of position information x. If the error e is less than the Δx value, then thepneumatic control 28 send out a 0,0control signal 28 a to thevalve 29 which is the neutral position of thevalve 29. Simultaneously upon sensing entry into the tolerance band by theposition control 76, i.e., where e=Δx, the logic causes thebrake 34 to be activated to add aposition control signal 79 atjunction 78 b which sums with anyvelocity control signal 80 present and thereby produces a substantial braking force to stop the motion of theoutput member 25 within the tolerance band. - According to a more sophisticated control method of the invention, the
brake 34 is activated to a high level at a calculated shut down point x0 before the desired stopping point xdes based upon the kinetic energy in the system and upon the braking force available from thebrake 34. In essence, if the kinetic energy and the braking force available are known quantities, then the exact time to shut down thepneumatic actuator 23 and apply thebrake 34 is easily and readily determined for any desired position xdes. This hereinafter will be referred to as “kinetic energy control.” - Kinetic energy control virtually eliminates overshoot and hunting associated with prior art methods, especially on systems where the system inertia is large. In particular, according to the kinetic energy control method, the kinetic energy of the system is equated with the braking energy in the system (see eqn. 4-6 below) to provide an intelligent tradeoff between accuracy and speed.
- The energy associated with the controllable
magnetorheological brake 34 is given by: - E mr =∫ x F mr dx=F mr(x des −x 0) (1)
- where
- Emr is the braking energy available,
- Fmr is the braking force available,
- xdes is the desired stopping position (rotary or linear), and
- x0 is a shut down position (rotary or linear) away from the desired position where if the force available were applied, it would bring the
output member 25 to a stop at the position xdes. -
- where
- Ek is the kinetic energy at x0,
- m is the mass (or rotational inertia) of the moving components in the system including the
payload article 19, and - v is the velocity (rotary or linear) of the
output member 25 at x0. - In order to bring the mass m to a stop at the target position xdes, the kinetic energy Ek must be equal to the braking energy Emr. Setting the values equal to each other provides:
- Ek=Emr (3)
-
-
-
- Thus, it can be readily seen that Δx can be regarded as a position tolerance, and it is easily recognized that there is a tradeoff between positioning accuracy and positioning speed. Equation 7 becomes the basis for the kinetic energy control method, where the inputs provided via the
input 58 are the desired rotational or translational accuracy Ax, the braking force available Fmr and the mass or rotational inertia m. Thus, using these inputs, the point-to-point (e.g., point b to c of FIG. 8) velocity v can be controlled such that the resultant actual stopping position is substantially at xdes. without any substantial overshoot. As should be understood, the force Fmr is a factory set value which may be updated via on-line learning. - Optionally, the input may include the mass m and the braking force available Fmr (e.g. hard coded) and the velocity v (derived from the motion signal 33) to calculate the value Δx according to equation 6; the value Δx corresponding to where the
pneumatic actuator 23 is shut down and thebrake 34 is applied. In this case, the velocity v may be derived via differentiating the position signal in differentiator 81 (FIG. 9). Further, according to an alternate method, the accuracy desired Δx, the mass m and the desired velocity vdes can be inputted viainput 58 and an applied braking force F calculated and then applied to stop theoutput member 25 at the desired position. Known pairs of velocity vdes and accuracy Δx would be input to ensure no overshoot. - In the FIG. 4 embodiment, the
passageway 46 passes through thepiston 45. The construction of thepiston 45 of FIG. 4 is identical to that taught in U.S. Pat. No. 5,878,851 to Carlson et al. entitled “Controllable Vibration Apparatus.” Contrarily, in the FIGS. 5-6 embodiments, thepassageway 46 comprises an annulus formed between thepiston 45 and thehousing 24 and the medium 44 passes about thepiston 45. Piston constructions whereby the medium passes about the piston are taught in U.S. Pat. No. 5,277,281 to Carlson et al entitled “Magnetorheological Fluid Dampers.” In the FIG. 7. embodiment, thepassageway 46 comprises an annulus formed between thepole pieces 40 of apartition 71 and an interconnectingshaft 64 of magnetically-soft material. Thecoil 39 is mounted to the inside of thehousing 24, thus, thewires 70 are desirably not subject to movement. Themagnetic field 43 is carried by thesleeve 57,pole pieces 40 and the interconnectingshaft 64. - In each of the embodiments of FIGS.4-6, the
housing 24 comprises first and secondrigid end caps housing 24 and anintermediate member 56 spaced therebetween. Afirst sleeve 57 a is disposed between thefirst end cap 55 a and theintermediate member 56, and asecond sleeve 57 b is disposed between thesecond end cap 55 b and theintermediate member 56. Thesleeves sleeve 57 a must be manufactured from a magnetically-soft material; the reason being that a portion of thefield 43 generated by thegenerator 39 is carried in thesleeve 57 a. Theintermediate member 56 includes anelastomer seal 60 which seals about theshaft 32 to prevent flow of the field responsive medium 44 into the first andsecond gas chambers wires 70 are received through a bore (not shown) in the respective shafts. - In the FIG. 4 embodiment, the
controllable brake 34 further comprises avolume compensator 59. Thecompensator 59 includes a gas chargedchamber 72 and a flexibleelastomeric partition 73. The compensator 59 functions to take up the volume ofrod 32 as it reciprocates into thecavity 53 as well as any expansion of the medium 44 due to temperature variations. In the FIGS. 5-6 embodiment, the rod volume compensation issue is addressed by the addition of asecond shaft 25 exiting from thecavity 53, such that the rod volume is always constant. In the FIG. 7 embodiment, the rod volume in thecavity 53 is constant, as well. Temperature compensation in the FIGS. 5-7 embodiments, if needed, may be provided by gas containing capsules or an external accumulator (not shown) attached to thehousing 24 and interconnecting to thecavity 53. In each of the FIGS. 4-7 embodiments, the medium containingcavity 53 is formed within thehousing 24. - In the FIGS. 5 and 6 embodiments, the
apparatus 20 includes afirst shaft 25 secured to thesecond piston 45 and received in sealed relationship through afirst end cap 55 a of thehousing 24, and asecond shaft 32 received in sealed relationship (via seal 60) through anintermediate member 56 of thehousing 24. This results in an efficient construction with a minimum amount of seals and minimal size. In the FIGS. 4-6 embodiments, thegas cavity 54 is formed by anend cap 55 b, anintermediate member 56 and asleeve 57 b similarly to the formation of the medium containingcavity 53. - The invention has been described in terms of preferred principles, method steps, and structure, however, the particular examples given are meant to be illustrative and not limiting. Substitutions and equivalents as will occur to those skilled in the art are included within the scope of the invention as defined by the following claims.
Claims (27)
1. A controllable pneumatic apparatus, comprising:
(a) a pneumatic actuator including a housing with a gas cavity formed therein, a first piston slidably disposed in the gas cavity subdividing the gas cavity into first and a second gas chambers, and an output member coupled to the first piston;
(b) a controllable brake coupled to the actuator, the brake comprising a medium containing cavity subdivided into a first and second chambers, a second piston rigidly interconnected with, and longitudinally aligned with, the first piston and moveable in the cavity along an axial axis, a passageway interconnecting the first and the second chambers, a field responsive medium contained in the passageway, a field generator for producing a field to change a rheology of the medium upon exposure to the field causing a braking force to be applied to the output member to control motion thereof; and
(c) A control system, comprising a sensor for providing a signal representative of a motion of a moving component of the apparatus, and a motion control for processing the signal and providing a control signal to the brake thereby controlling at least one motion selected from a group consisting of a position, velocity and acceleration of the output member.
2. The apparatus of claim 1 wherein the motion comprises a position, velocity or acceleration.
3. The apparatus of claim 1 wherein the sensor comprises a position sensor.
4. The apparatus of claim 1 wherein said apparatus is controlled according to a method, comprising the steps of:
(a) inputting desired motion information for the output member to said pneumatic and motion controls from an input,
(b) measuring with a sensor an instantaneous motion of the output member and providing a measured motion signal, and
(c) processing the measured motion signal and the desired motion information within the pneumatic and motion controls and providing control signals to the pneumatic actuator to control the supply of differential pressure and to activate the controllable brake.
5. The apparatus of claim 4 wherein the pneumatic actuator is turned off and the controllable brake is activated within a tolerance band about a desired axial position.
6. A controllable pneumatic apparatus, comprising:
(a) a pneumatic system, including a housing having a gas cavity formed therein, a first piston slidably disposed in the gas cavity subdividing the gas cavity into a first gas chamber and a second gas chambers, a pressure source providing a supply of pressurized gas, a pneumatic control which controls a pneumatic valve to apportion the supply of pressure to the first and second gas chambers thereby providing differential pneumatic pressure to move the first piston along an axial axis, and an output member coupled to the first piston,
(b) a controllable brake, including a medium containing cavity, a second piston subdividing the medium containing cavity into a first medium chamber and a second medium chamber, the second piston being longitudinally aligned with the first piston and rigidly interconnected by an interconnecting shaft to the first piston, the second piston moveable in the cavity along the axial axis, a passageway interconnecting the first and the second medium chambers, a magnetically controllable fluid contained in the passageway, a field generator further including a coil for producing a magnetic field to change a rheology of the fluid upon exposure to the magnetic field,
(c) a motion sensor for providing a motion signal representative of a motion of the output member, and
(d) a control system for processing the motion signal and providing a control signal to the controllable brake thereby controlling motion of the output member.
7. A method of controlling a controllable pneumatic apparatus, comprising the steps of:
(a) providing a pneumatic actuator which causes motion of an output member,
(b) providing a controllable brake coupled to the output member,
(c) providing a control system for controlling the pneumatic actuator and the controllable brake,
(d) inputting system performance information to the control system,
(e) measuring a motion of the output member and providing a motion signal, and
(f) processing the motion signal and the desired motion information within the control system and providing control signals to control the pneumatic actuator and to activate the controllable brake, said processing being based upon a kinetic energy.
8. A method of claim 7 wherein said measuring step further comprises measuring an axial position of said output member.
9. A method of claim 7 further comprising an additional step of obtaining a velocity.
10. A method of claim 9 wherein the velocity is obtained based upon the axial position.
11. A method of claim 7 wherein the system performance information comprises desired motion information of the output member.
12. A method of claim 11 wherein the desired motion information further comprises a desired stopping position.
13. A method of claim 11 wherein the desired motion information further comprises a desired accuracy.
14. A method of claim 11 wherein the desired motion information further comprises a desired velocity.
15. A method of claim 11 wherein the desired motion information further comprises a desired velocity profile.
16. A method of claim 11 wherein the desired motion information further comprises a desired acceleration profile.
17. A method of claim 7 wherein the system performance information comprises a mass of moving system elements.
18. A method of claim 7 wherein the system performance information comprises a braking force available from the controllable brake.
19. A method of claim 7 wherein the system performance information comprises a braking force available from the controllable brake, a mass of any moving system components and desired motion information of the output member.
20. A method of claim 7 wherein the system performance information comprises a braking force available from the controllable brake, a mass of all moving system components, a desired stopping position of the output member and a desired accuracy.
21. A method of claim 7 wherein the system performance information comprises a braking force available from the controllable brake, a mass of all moving system components, a desired stopping position of the output member and a desired accuracy.
22. A method of claim 7 wherein the processing is further based upon an available braking force.
23. A method of claim 7 wherein a shut down point is determined based upon the kinetic energy and the available braking force.
24. A method of claim 7 wherein a shut down point for activation of the brake and shut down of the pneumatic actuator to stop the output member at the desired stopping position is determined based upon the equation:
where Δx is the distance from the shut down point to the desired stopping position, m is the mass of any moving system components, v is the velocity at the stopping point and Fmr is the available braking force.
25. A method of claim 7 wherein the controllable brake contains a field responsive fluid.
26. A method of controlling a controllable pneumatic system, comprising the steps of:
(a) providing a pneumatic actuator which, when provided with a supply of differential pressure, moves a position of an output member,
(b) providing a controllable brake coupled to the output member,
(c) providing a control system to control the pneumatic actuator and the controllable brake,
(d) inputting desired motion information for the output member to the control system from a input,
(e) measuring with a sensor a motion of the output member and providing a measured motion signal, and
(f) processing the measured motion signal and the desired motion information within the control system and providing control signals to control the pneumatic actuator and to activate the controllable brake, the processing being based upon a kinetic energy.
27. A motion control apparatus, comprising:
(a) a pneumatically controlled actuator including a housing with a gas cavity formed therein, a first piston slidably disposed in the gas cavity, the first piston subdividing the gas cavity into first and a second gas chambers, and an output member coupled to the first piston, the output member being movable in response to movement of the first piston, the first piston being movable along an axial axis of the housing as a result of a differential pressure between the first and second chambers; and
(b) a controllable brake for controlling the motion of the output member, the brake being coupled to the pneumatically controlled actuator, the brake including a medium containing cavity subdivided into a first and second chambers, a second piston rigidly interconnected with the first piston and moveable in the medium containing cavity along said axial axis, a passageway interconnecting the first and the second chambers, a field responsive medium contained in the chambers and passageway, a field generator for producing a field to change the rheology of the field responsive medium in the passageway upon exposure to the field causing a braking force to be applied to the output member to control motion thereof.
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US09/901,354 US20020014380A1 (en) | 1999-03-08 | 2001-07-09 | Linear-acting controllable pneumatic motion control apparatus and control method therefor |
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US09/264,273 US6302249B1 (en) | 1999-03-08 | 1999-03-08 | Linear-acting controllable pneumatic actuator and motion control apparatus including a field responsive medium and control method therefor |
US09/901,354 US20020014380A1 (en) | 1999-03-08 | 2001-07-09 | Linear-acting controllable pneumatic motion control apparatus and control method therefor |
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US09/264,273 Expired - Fee Related US6302249B1 (en) | 1999-03-08 | 1999-03-08 | Linear-acting controllable pneumatic actuator and motion control apparatus including a field responsive medium and control method therefor |
US09/901,354 Abandoned US20020014380A1 (en) | 1999-03-08 | 2001-07-09 | Linear-acting controllable pneumatic motion control apparatus and control method therefor |
Family Applications Before (1)
Application Number | Title | Priority Date | Filing Date |
---|---|---|---|
US09/264,273 Expired - Fee Related US6302249B1 (en) | 1999-03-08 | 1999-03-08 | Linear-acting controllable pneumatic actuator and motion control apparatus including a field responsive medium and control method therefor |
Country Status (3)
Country | Link |
---|---|
US (2) | US6302249B1 (en) |
EP (1) | EP1159532A1 (en) |
WO (1) | WO2000053937A1 (en) |
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-
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- 2000-03-02 EP EP00916012A patent/EP1159532A1/en not_active Withdrawn
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Also Published As
Publication number | Publication date |
---|---|
WO2000053937A1 (en) | 2000-09-14 |
EP1159532A1 (en) | 2001-12-05 |
US6302249B1 (en) | 2001-10-16 |
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