Electrical generator or motor structure – Dynamoelectric – Rotary
Reexamination Certificate
2003-06-18
2004-09-14
Le, Dang (Department: 2834)
Electrical generator or motor structure
Dynamoelectric
Rotary
C310S083000
Reexamination Certificate
active
06791219
ABSTRACT:
CROSS-REFERENCE TO RELATED APPLICATIONS
None
REFERENCE TO SEQUENCE LISTING, TABLE, OR COMPUTER PROGRAM LISTING APPENDIX SUBMITTED ON A COMPACT DISC
N/A.
STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH OR DEVELOPMENT
N/A.
BACKGROUND OF THE INVENTION
1. Field of Invention
This invention relates generally to electromechanical actuators of the type having an electric motor driving a rotary output shaft through a torque amplifying gear train.
More specifically, the invention relates to an electromechanical actuator with a brushless motor and contactless angular position sensors that provide both motor commutation signals and output shaft angular position signals to achieve a high-reliability, precision actuator.
2. Background Art
Electromechanical actuators have historically utilized AC or brush DC motors with potentiometers for feedback. Brushes in the motors and wipers in the potentiometers have led to limited life and low reliability for these types of actuators. More recently, the trend in precision electromechanical actuators is to utilize a brushless DC motor with a resolver, optical encoder, or switching Hall-effect device for motor commutation, a gear reducer for torque amplification, and a resolver, optical encoder, or rotary-variable-differential-transformer (RVDT) for sensing the angular position of the output shaft. These output shaft position feedback sensors are typically self-contained units driven by gears off the actuator output shaft. They are also substantially more expensive than conventional potentiometers, often requiring AC excitation and demodulation electronics to obtain useable output signals, and/or are unreliable in low temperature, moist environments. Consequently, precision actuators utilizing these types of sensors are generally more complicated and more expensive than actuators with more conventional potentiometer feedback.
Recent efforts to achieve lower-cost, yet reliable and accurate electromechanical actuators have included use of integrated contactless magnetic field sensor elements such as Hall-effect devices or magnetoresistive (MR) sensors. These sensor elements are relatively low cost, and are capable of generating electrical output signals when exposed to a rotating magnetic field. Hall-effect sensors utilize a current-carrying semi-conductor membrane to generate a low voltage perpendicular to the direction of current flow when subjected to a magnetic field normal to the surface of the membrane. Magnetoresistive sensors utilize an element whose resistance changes in the presence of a changing external magnetic field.
One group of prior electromechanical actuators utilize integrated Hall-effect sensors to provide signals that are digital in nature, generating pulses as a function of shaft rotation, or discrete signals for incremental shaft angles. These digital signals are generally developed by sensing the passage of notches, magnets, saturating magnet poles, or other discrete signal generating arrangements on a rotating shaft, and are used for motor commutation and/or actuator output shaft position sensing in the actuator. For example, Takeda et al., U.S. Pat. No. 5,422,551 uses Hall-effect sensors to generate pulse signals for motor control in a power window drive mechanism. Collier-Hallman et al., U.S. Pat. No. 6,002,226 uses Hall-effect sensors to generate pulse signals for motor control in an electric power steering system. Integrated Hall-effect sensors generating digital control signals are also shown in the motor controls of Coles et al., U.S. Pat. Nos. 6,104,152 and 6,124,688; Redelberger, U.S. Pat. No. 6,091,220; and Hans et al., U.S. Pat. No. 5,598,073. In Ritmanich et al., U.S. Pat. No. 6,198,243, integrated Hall-effect devices generate a pulsed output from rotation of an actuator output shaft for stepper motor control. As noted above, actuator and motor controls utilizing integrated magnetic field sensors as digital signal generators often require pulse-width modulation, or are otherwise relatively complicated to obtain, process and utilize the digital output signals from the sensors. And the accuracy of such devices is limited by the number of pulses per revolution developed from the sensed rotating element.
Another group of prior electromechanical actuators utilize integrated Hall-effect devices to produce analog signals indicative of the angular position of the output shaft for closed-loop control of the actuator. Electromechanical actuators of this type are shown in Peter et al., U.S. Pat. No. 5,545,961, Weiss et al., U.S. Pat. No. 6,097,123, and Fukumoto et al., U.S. Pat. No. 6,408,573. In general, these include annular magnets provided with sets of alternating N-pole/S-pole combinations coupled to the rotary output elements of the actuator, and Hall-effect sensors arranged around the magnet to produce analog output signals that are processed to obtain the angular position of the output element. Although capable of sensing angular position through 360 degrees of rotation, the accuracy of these types of actuators is limited to the accuracy of the Hall-effect sensing elements, which is currently, typically in the neighborhood of ±2 degrees, without provisions for special magnet magnetization processes, special sensor configurations, temperature compensation or reference calibration.
To advance the electromechanical arts, and to address the above-identified drawbacks of prior actuators of the same general type, there is a need for an improved electromechanical actuator that is capable of accurately controlling the angular position of a rotary output shaft, with the high reliability and long life available with the use of a brushless motor and contactless sensors, but without the high cost and complexity associated with use of resolver, encoders, or RVDTs. There is also a need for an improved accurate, high-reliability actuator that can be economically manufactured and compactly packaged.
For detailed discussion of position sensor configurations utilizing such magnetic field sensor elements, reference is made to Frederick et al, U.S. patent application Ser. No. 10/087,322, filed Feb. 28, 2002, and Seger et al, U.S. patent application Ser. No. 10/367,459, filed Feb. 14, 2003, both of which are assigned to the assignee of the present invention, and the discussions of which are incorporated herein by reference.
SUMMARY OF THE INVENTION
An important objective of the present invention is to provide an improved electromechanical actuator which can precisely control the angular position of an output shaft, but which is economical to manufacture.
Another important objective of the invention is to provide an actuator without motor and sensor contacts, brushes and wipers to improve actuator life and reliability as compared with many prior economical actuators of the same general type.
Another important objective of the invention is to provide an actuator that accurately computes and controls the position of the output shaft with enhanced accuracy without the high cost and complexity associated with use of resolver, encoders, RVDTs and like sensor components of many prior precision actuators.
Another important objective of the invention is to provide the foregoing high-reliability, accurate actuator in a compact package utilizing economical, standard components.
A detailed objective is to achieve the foregoing by providing an electromechanical actuator with high-reliability contactless brushless motor and contactless angular position sensing elements comprising simple magnets and magnetic field sensing elements to produce both motor commutation signals and shaft position signals.
Another detailed object is to achieve a compact actuator design by integrating the functional motor and sensor components around a common axis of rotation.
Another detailed objective is to use both the motor commutation signals and output shaft position signals in a unique algorithm to achieve enhanced precision control of the angular position of the output shaft.
These and other objectives and advantages of the invention will become apparent from the f
Eric Seger
Gary Frederick L.
BVR Technologies Company
Frantz Keith
Le Dang
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