Brakes – Internal-resistance motion retarder – Using diverse fluids
Reexamination Certificate
1999-03-08
2001-10-16
Schwartz, Christopher P. (Department: 3613)
Brakes
Internal-resistance motion retarder
Using diverse fluids
Reexamination Certificate
active
06302249
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 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.
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 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, a
Jolly Mark R.
Wilder Richard
Bartz Clifford
Gnibus Michael M.
Lord Corporation
Schwartz Christopher P.
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