Electrical generator or motor structure – Non-dynamoelectric – Piezoelectric elements and devices
Patent
1991-07-15
1993-03-30
Budd, Mark O.
Electrical generator or motor structure
Non-dynamoelectric
Piezoelectric elements and devices
H01L 4108
Patent
active
051987147
DESCRIPTION:
BRIEF SUMMARY
BACKGROUND OF THE INVENTION
The present invention relates to a method and an apparatus for controlling a traveling wave motor as disclosed in DE 3,306,755.A1. The vibrating stator of such a motor includes ultrasound excitation systems which are equipped with electrodes and are connected in a friction lock with the actual vibrating body. At a surface region of the vibrating body, the vibrating stator is axially pressed into contact with a rotor. Rotational rotor movements are generated by mechanical waves that are excited in the excitation system, with the individual vibrating surface elements of the vibrating body moving on an approximately elliptical path so that, due to the friction lock between the stator and the rotor surface, tangential forces are generated in the contact zone between the two surfaces and lead to the formation of a rotary movement and a torque on the rotor.
The operating state of such a traveling wave motor is dependent on a plurality of parameters, particularly the temperature, the axial pressure between stator and rotor and the frequency, amplitude and shape of the excited traveling waves. The setting of the desired operating parameters, adaptation of the motor feeding frequency if there is a change in the natural mechanical frequency due to temperature and long-term influences, and the required limitation of the amplitude of the traveling waves in order to protect the excitation system and the contact zone between the rotor and the vibrating stator, require such motors to be guided by one or several control circuits. For this purpose, information about the actual state of the stator-rotor system, particularly the frequency, amplitude and shape of the traveling wave, must be supplied to the control system.
DE 3,634,329 already discloses an actuating circuit for an ultrasonic wave motor in which it is ensured that the motor is always actuated at its resonant frequency. For this purpose, a monitoring electrode is provided to detect the phase difference between the signal of the monitoring electrode and a periodic actuation voltage applied to drive the motor.
A drawback of this and is that only indirect information about the presence and characteristics of the traveling waves is evaluated since only one sensor surface is available and therefore only the amplitude of one surface region can be sensed. Amplitude values and phase relationships of the deflections of different surface regions of the vibrating body are not detected by the prior art actuation circuit. In particular, a standing wave, which does not directly produce any effects on the motor, cannot be distinguished from a traveling wave since both create the same signal image on a single-surface sensor.
SUMMARY OF THE INVENTION
It is an object of the present invention to avoid the listed drawbacks of the prior art system for evaluating and controlling the driving state of a traveling wave motor and to provide an apparatus in which the actual value signals from a sensor device unequivocally characterize the vibration state of the vibrator.
This is accomplished according to the invention by providing an apparatus for evaluating and controlling the driving state of a traveling wave motor composed of a stator, having an elastic vibrating body and an excitation system including a plurality of segments and generating ultrasound vibrations, as well as a rotor which in a surface region is pressed into contact with the stator and is provided with a sensor device disposed at the vibrating body or at the excitation system, with the signals of the sensor device being fed to the regulating circuit of an evaluation and control unit for controlling the excitation system, the excitation system being composed of two circular ring shaped partial systems which are shifted in space relative to one another by an amount of (n+1/4).multidot..lambda., where n indicates a positive integer and .lambda. the wavelength of a traveling wave to be excited, the apparatus being characterized in that: first to third sensor surfaces are provided which are arr
REFERENCES:
patent: 4692649 (1987-09-01), Izukawa et al.
patent: 4794294 (1988-12-01), Shimuzu et al.
patent: 4833358 (1989-05-01), Suzuki et al.
patent: 5001404 (1991-03-01), Kataoka
Technische Rundschau, vol. 81, No. 46, Nov. 17, 1989, Beru, CH Seiten 102-105; G. Schadebiodt et al: "Der Piezo--. . . " Seike 104.
Patent Abstracts of Japan, vol. 13, No. 192 (E-753) (3540) May 9, 1989; JP-A-1 12881 (Canon Inc.) Jan. 17, 1989.
Orthmann Reinhard
Salomon Bernd
Budd Mark O.
Licentia Patent-Verwaltungs-GmbH
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