Electricity: motive power systems – Torquing motors
Reexamination Certificate
1999-12-06
2001-10-09
Ro, Bentsu (Department: 2837)
Electricity: motive power systems
Torquing motors
C318S538000, C318S437000
Reexamination Certificate
active
06300739
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates generally to brushless direct current (DC) motors and more particularly to a limited angle torque DC brushless motor for use in pneumatic servovalves and a variety of other applications.
2. Prior Art
Pneumatic servovalves are employed wherever there is a need for high-precision, closed loop motion control systems such as in automotive vehicle component testing and manufacturing, semiconductor manufacturing, packaging, equipment assembly, industrial automation and robotics, lumber processing and the like. Limited angle torque motors for use in pneumatic spool and sleeve servovalves usually comprise a DC brushless motor, a Hall sensor and an integrated controller. The limited angle torque motor drives the valve spool through an eccentric which is built into the motor shaft. Rotary operation of the motor shaft is translated into linear motion of the spool which modulates the gas flow through the control ports of the servovalve. The spool position is monitored by the Hall sensor with the controller comparing spool position with the valve input command. The resulting difference generates a current signal from the controller which drives the valve spool to the desired position.
Conventional DC brushless motors are widely used in limited angle torque applications and have satisfactory and reliable performance but are relatively expensive components for the servovalve manufacturer which is a major disadvantage as a significant portion of the retail cost of a pneumatic servovalve is directly related to the cost of the integrated DC brushless motor. DC brush motors, on the other hand, are relatively inexpensive but are never used in such applications as DC brush motors do not possess the high cycling and high frequency capability demanded by servomotors of this type. The problem lies in the commutator/brush interface with the brush/commutator connection becoming unreliable and impractical to use with high cycle and high frequency use. Carbon brushes typically tend to wear out quickly in high cycling and/or high frequency applications due to friction between the brushes and the commutator segments. Furthermore, brush control in high cycle limited angle torque applications is a major problem whereby complex and expensive controller circuitry may be needed to overcome the problem which, however, would further raise the cost of the servomotor and is undesirable. Therefore, the need arises for a low cost limited angle torque DC brushless servomotor which can provide reliable performance thereby presenting a viable alternative cost efficient solution for servovalve customers. Such a motor should preferably be easy to assemble in very short time and should be constructed from relatively inexpensive yet reliable components.
SUMMARY OF THE INVENTION
The present invention is directed to an improved limited angle torque DC brushless servomotor including a hollow cylindrical stator having embedded permanent magnets and a rotor having winding coils and commutator with a plurality of commutator segments mounted concentrically on a rotor shaft along the longitudinal rotor axis, the improvement comprising a bearing assembly mounted on the rotor shaft proximate to the commutator, a controller operatively associated with the rotor for rotating the rotor in a controlled limited angular fashion about the longitudinal rotor axis in response to an external rotor shaft angular displacement command signal, a sensor coupled to the bearing assembly for sensing the limited angular rotation of the rotor about the longitudinal rotor axis, the sensor producing a feedback signal representative of the rotor shaft angular displacement from a pre-determined rotor shaft angular displacement null position, and a circuit for electrically coupling the controller to the commutator and the sensor to the controller, the controller receiving and comparing the feedback signal with the external rotor shaft angular displacement command signal and generating a corresponding rotor motion control error signal, the controller communicating the rotor motion control error signal to the commutator to control the limited angular rotation of the rotor about the longitudinal rotor axis, the circuit having at least one portion flexing in consonance with the controlled limited angular rotation of the rotor about the longitudinal rotor axis during motor operation.
In accordance with one aspect of the present invention, the circuit is a flexible circuit having a plurality of flexible electrical conductors embedded between sheets of flexible insulating material. The flexible circuit comprises a generally L-shaped multiconductor body having a first multiconductor arm extending from one end of the body for removably coupling to the commutator and for flexing in consonance with the controlled limited angular rotation of the rotor about the longitudinal rotor axis and a second multiconductor arm extending upstream from the first multiconductor arm away from the L-shaped multiconductor body for coupling to the sensor, the L-shaped multiconductor body having its other end adapted for removably coupling to the controller. The controller is an electronic circuit board comprising at least a pulse width modulator integrated circuit (IC) chip. The circuit board further comprises a surface mounted flexible circuit connector for connecting to the other end of the L-shaped multiconductor body of the flexible circuit.
In accordance with another aspect of the present invention, the sensor comprises a surface mount Hall effect device for coupling to the mounted bearing assembly and a ring shaped permanent Hall magnet for coupling to the rotor shaft proximate to the Hall effect device. The ring-shaped permanent Hall magnet is fixed on the rotor shaft proximate to the surface mount Hall effect device. The surface mount Hall effect device measures variations in magnetic flux generated by the fixed Hall magnet as a result of angular displacement of the rotor shaft, the Hall effect device producing a corresponding feedback signal representative of the rotor shaft angular displacement from the pre-determined rotor shaft angular displacement null position.
In accordance with yet another aspect of the present invention, a method for improving the limited angle torque performance of a DC brush motor having a stator, brush assembly and a rotor, the rotor having winding coils and a commutator with commutator segments mounted concentrically on a rotor shaft along the longitudinal rotor axis is disclosed. The method comprises the steps of:
(a) providing a DC brush motor;
(b) removing the brush assembly from the DC brush motor;
(c) providing a bearing assembly having a bottom portion and a top portion;
(d) mounting the bearing assembly on the motor shaft proximate to the commutator, the bottom portion of the bearing assembly facing the commutator, the bearing assembly being stationary during motor operation;
(e) providing a surface mount Hall effect device;
(f) providing a permanent ring-shaped Hall magnet;
(g) mounting the permanent ring-shaped Hall magnet on the motor shaft proximate to the top portion of the bearing assembly;
(h) fixing the mounted Hall magnet to the rotor shaft;
(i) providing a controller for rotating the rotor in a controlled limited angular fashion about the longitudinal rotor axis;
(j) providing a flexible circuit including a substantially L-shaped multiconductor body having a first multiconductor arm extending from one end of the body for electrically coupling to the commutator and for flexing in consonance with the controlled limited angular rotation of the rotor about the longitudinal rotor axis, a second multiconductor arm extending upstream from the first multiconductor arm away from the L-shaped multiconductor body for electrically coupling to the Hall effect device, the other end of the L-shaped multiconductor body adapted for electrically coupling to the controller circuit board;
(k) removably coupling the other end of the L-shaped multiconductor body to the co
Coakley Kim Lige
Ratliff William Edward
Starbird John Jay
Fulbright & Jaworski L.L.P.
HR Textron Inc.
Ro Bentsu
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