Motors: expansible chamber type – Working member position feedback to motive fluid control – Electrical input and feedback signal means
Reexamination Certificate
1999-03-08
2001-05-22
Ryznic, John E. (Department: 3745)
Motors: expansible chamber type
Working member position feedback to motive fluid control
Electrical input and feedback signal means
Reexamination Certificate
active
06234060
ABSTRACT:
FIELD OF THE INVENTION
The invention relates to pneumatic apparatus. More particularly, the present invention is directed to a pneumatic apparatus which is precisely controllable.
BACKGROUND OF THE INVENTION
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 than 2-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 chamber and a 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 servovalve 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 foregoing illustrates limitations known to exist in present devices and methods. Thus, it is apparent that it would be advantageous to provide an alternative directed to overcoming one or more of the limitations set forth above. Accordingly, a suitable alternative is provided including features more fully disclosed hereinafter.
SUMMARY OF THE INVENTION
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 rotary-acting brake such that a motion (e.g., a displacement, velocity or acceleration) of an output member of the actuator may be precisely controlled. The pneumatic actuator includes a housing, a piston disposed in the housing and moveable responsive to a pressure differential acting thereupon and at least one output member coupled to the piston. The rotary-acting controllable brake includes a field responsive medium contained therein, and a brake shaft coupled to the output member. The apparatus preferably includes a control system having a sensor (such as a rotational potentiometer) 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 rotary-acting 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 desired information to the pneumatic control and the motion control.
The rotary-acting controllable brake preferably comprises a rotor rotationally coupled to the brake shaft, a pole piece adjacent to, and spaced from, the rotor forming a gap therebetween, the field responsive medium (e.g. a powdered metal, a magnetically controllable fluid or a magnetorheological fluid) being contained in the gap, and a field generator (such as a wound coil) which when energized produces a field which acts if across the gap changing a rheology of the medium and producing a resistance to relative rotation between the rotor and the pole piece.
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 rotary-acting controllable brake is determined based upon the kinetic energy and the available braking force.
Preferably, the apparatus also comprises a pneumatic system including 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 gas chambers thereby providing differential pneumatic pressure to move the piston. The control system preferably also includes a sensor (e.g., a rotational position 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 position, velocity and/or acceleration of the output member.
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:
Δ
x
=
m
v
2
2
F
mr
,
where &Dgr;x is the distance from the shut down point to the desired stopping position, m is the mass (or inertia) of any moving system components, v is the velocity at the stopping point and F
mr
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 ind
Gnibus Michael M.
Lord Corporation
Ryznic John E.
Wayland Randall S.
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