Interrelated power delivery controls – including engine control – Electric engine
Reexamination Certificate
1999-05-27
2001-07-10
Estremsky, Sherry (Department: 3681)
Interrelated power delivery controls, including engine control
Electric engine
C477S020000, C074S640000
Reexamination Certificate
active
06258007
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
This invention relates to harmonic drive transmissions, and more particularly to sensor driven actuator arrangements to improve the positional accuracy of harmonic drive systems.
2. Prior Art
Harmonic drive transmissions, sometimes known as controlled-ratio deflection type transmissions, are used where rotary to rotary transmission is needed. In such a transmission, the gear tooth engagement is induced at a plurality of points by the deflection of a thin ring gear or the like. The tooth engagement at a plurality of points around the circumference is propagated along the periphery of a thin ring gear as the crest of the induced deflection ring is made to move around this periphery. As the deflection moves around the gear, each tooth moves radially in and out of engagement as it progresses from one tooth to the next, tracing during this motion, a curve which is generally of the character of a sinusoidal wave, giving rise to the term “strain-wave gearing”.
Examples of such early transmissions of this type are shown in U.S. Pat. No. 2,906,143, issued in 1959 to Musser, U.S. Pat. No. 2,931,249 issued to Musser, and U.S. Pat. No. 3,196,713 issued to Robinson, all of which are incorporated herein by reference.
Those transmission have found use in certain industries where rotary power is needed and increasingly so in the robotics industry. Such use, particularly in the robotics industry requires extreme accuracy. Heretofore, robotic transmissions and drive units have been empowered by direct drive motors which are able to repearably position the rotation of a shaft, within plus or minus 3 arc seconds. These motors typically are brushless and have a high output torque at a low velocity. Direct drive motors unfortunately are also very expensive.
It is an object of the present invention to provide a harmonic drive assembly, which may function as a direct drive motor replacement in the robotic industry.
It is yet a further object of the present invention, to provide a harmonic drive actuator arrangement, which permits highly accurate corrective positioning of the output shaft.
It is yet still a further object of the present invention to provide a harmonic drive apparatus with a sensor/encoder arrangement for speed and/or torque, position, vibration, temperature, performance degradation and/or tooth wear sensing utilizing self-diagnostic control of the apparatus.
BRIEF SUMMARY OF THE INVENTION
The present invention comprises a harmonic drive transmission coupled together with and being driven by an electric motor. This electric input motor is in a driving relationship with the input motor shaft connected to the input wave generator of the harmonic drive transmission. The electric input motor has a stator and a rotating rotor arranged within its housing. A sensor, here, an input shaft encoder, is disposed on the input end of the rotor of the electric motor. The input encoder, preferably of the optical type, or possibly the magnetic type, is arranged on the rotor of the electric motor, and is in electrical communication, via a proper circuit, with a control logic unit.
The flexspline in the harmonic drive transmission, is connected to an output shaft of the electric motor, the flexspline/harmonic drive transmission all driven by the electric motor. A sensor here, such as an output encoder, such as a magnetic or optical output encoder, may be arranged on the output shaft of the harmonic drive transmission. The output encoder is in electrical communication with the control logic unit, as is the input encoder. The control logic unit controls a power drive converter, which is in electrical communication with the electric motor.
A control signal from a proper operator control unit is inputted to the control logic unit. The control logic unit received signals from both the input encoder and the output encoder, making an analysis and comparison therebetween. The control logic unit governs the converter, to regulate the electric input motor. Alignment and matching of the signals between the output encoder on the output shaft of the harmonic drive transmission and the input encoder on the rotor of the electric motor permits the apparatus to have a power output from the harmonic drive transmission which is speed controllable and positionally governable with a repeatability to about 3 arc seconds of accuracy. The output encoder, which may be the magnetic or optical type, is preferably arranged as close to the output bearing on the harmonic drive transmission as possible, to minimize any possible error from axial loading upon the output shaft of the harmonic drive transmission. Thus, high precision rotational output control is achieved within the multisensor/encoder harmonic drive actuator assembly of the present invention.
A further embodiment of the present harmonic drive actuator assembly consists of a harmonic drive transmission similar to that of the aforementioned embodiment, having an input wave generator arranged within the housing and in wave generating communication with a flexspline attached to an output shaft of the harmonic drive transmission. An electric input motor has a shaft connected to the input shaft on the input wave generator. The electric motor has a stator and a rotor shaft at a first end thereof. A control logic and power drive unit is arranged about the rotor shaft on the electric input motor. An input encoder of the magnetic or optical type is attached about the rotor shaft adjacent the control logic and power unit on the electrical motor.
An output encoder, either the magnetic or optical type, is arranged about the output shaft of the harmonic drive transmission, extending from the flexspline. The output encoder is in electrical communication with the control logic and power drive unit on the electrical input motor. The input encoder arranged on the rotor shaft is in electrical communication with the control logic and power drive unit mounted adjacent the rotor shaft. An AC/DC converter is in communication with the control logic and power drive unit. An operator control signal is in electrical communication with the control logic and power drive unit on the electric motor rotor shaft, and operates the harmonic drive actuator assembly. Rotational input from the input motor drives the input wave generator to provide proportionate corresponding motion of the flexspline and the output shaft. Position and speed performance of the output shaft is monitored by the output encoder, which sends an output performance signal to the control logic and power drive unit. A corresponding speed and rotational position sensor on the rotor shaft of the electric motor sends a performance signal of the motor shaft of the electric motor, to the control logic and power drive unit. Correspondence between the input performance from the electric motor, and output performance from the harmonic drive transmission is maintained by the comparison between the sensor signals of the input encoder and the output encoder, to provide high precision position correction between the two assembly components. Torque control may be achieved with additional sensors such as torque (current) sensors in place at or in addition to the position sensors already identified hereinabove.
Thus, by having the appropriate sensors preferably arranged at one or opposite ends of a motor/harmonic drive transmission assembly, to optically, electrically, eletromechanically and/or magnetically determine speed, torque, and position performance between the input and the output of such assembly, permitting position control and accuracy of that assembly.
The invention thus includes an actuator controlled harmonic drive transmission for the speed and positioned control of an output shaft of the harmonic drive transmission, comprising: a motor having a rotor shaft for providing rotational power to harmonic drive transmission; and a control arrangement for permitting rotational positional and speed control between the rotor shaft and the output shaft of the harmonic drive transmission. The
Estremsky Sherry
Halgren Dan
Teijin Seiki Boston, Inc
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