Electrical generator or motor structure – Non-dynamoelectric – Piezoelectric elements and devices
Reexamination Certificate
1998-12-22
2001-04-10
Dougherty, Thomas M. (Department: 2834)
Electrical generator or motor structure
Non-dynamoelectric
Piezoelectric elements and devices
C310S316020, C310S317000
Reexamination Certificate
active
06215223
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a driving circuit of a motor, which is used to drive a motor, particularly, an ultrasonic motor.
2. Description of the Related Art
There has conventionally been known an ultrasonic motor which employs ultrasonic vibration as driving force. In a traveling-wave ultrasonic motor which is a kind of ultrasonic motor, a stator is formed with a piezoelectric body attached to a ring-shaped elastic body and a rotor mounted on a driving shaft press-contacts the stator. The driving circuit of the ultrasonic motor supplies, to the piezoelectric body, driving signals of two phases (sine wave and cosine wave) which differ from each other by 90 degrees at a predetermined frequency. Due to mechanical vibration of the piezoelectric body caused by the driving signals of the two phases, the elastic body is excited by ultrasonic vibration (traveling wave) in which the antinode and node of the vibration move annularly along the elastic body. The traveling wave causes the rotor, which press-contacts the elastic body, and the driving shaft to rotate.
As described above, the ultrasonic motor produces driving force by frictional force generated by the piezoelectric body and the elastic body, and therefore, when the ultrasonic motor is driven continuously for a long time, there have existed problems in that the piezoelectric body may crack, degradation of performance caused by heat may occur, and elements which form the driving circuit (for example, MOS-FET and the like) may be broken.
In order to solve the above-described problems, generally, there is applied a method in which, with a temperature detecting element such as a thermistor used, when the temperature rises, the driving of an ultrasonic motor is stopped.
However, in the above-described method, there is a possibility that, even if a switch is turned on by an operator, the ultrasonic motor suddenly stops irrespective of whether the ultrasonic motor is broken or not, which makes the operator believe that something is wrong.
SUMMARY OF THE INVENTION
In view of the above-described circumstances, it is an object of the present invention to provide a driving circuit of a motor, which can prevent failure of parts, which is caused by driving of the motor for a long time, or degradation of performance of the motor caused by heat without making the operator believe that something is wrong.
A circuit for driving a predetermined device by a motor in a first aspect of the present invention comprises: switching means for switching the motor on and off; counting means which adds a count value with the motor being driven due to being switched on by said switching means and which subtracts the count value with the motor being stopped due to being switched off by said switching means; determination means which determines whether the count value counted by said counting means becomes an upper limit value or greater; stopping means which stops driving of the motor when the count value becomes the upper limit value or greater; and delaying means which, when the count value is the upper limit value or greater and said switching means is in an on state, delays execution of said stopping means until said switching means is changed from on to off.
According to the first aspect of the present invention, when the motor is driven, a count value counted by the counting means is added. When the motor is stopped, the count value is subtracted. When the count value has reached the upper limit value, the driving of the motor must be inevitably stopped. However, until the switch is changed from an on state to an off state, the predetermined device is moved to a predetermined position without stopping the motor by the delaying means. For this reason, there is no possibility of the motor being suddenly stopped, and thereby making the operator feel that something is wrong.
A circuit for driving a predetermined device by a motor in a second aspect of the present invention comprises: switching means for switching the motor on and off; counting means which adds a count value with the motor being driven due to being switched on by said switching means and which subtracts the count value with the motor being stopped due to being switched off by said switching means; determination means which determines whether the count value counted by said counting means becomes an upper limit value or greater or becomes a lower limit value or less; and stopping means which stops driving of the motor until the count value comes to the lower limit value, when the count value is the upper limit value or greater and when said switching means is changed from on to off.
According to the second aspect of the present invention, after the predetermined device has been moved to a predetermined position and the switching means has been changed from an on state to an off state, until the count value comes to the lower limit value or less, driving of the motor is stopped by the stopping means even when the switching means is turned on again. As a result, driving of the motor for a long time is prevented.
A circuit for driving a predetermined device by a motor in a third aspect of the present invention comprises: switching means for switching the motor on and off; counting means which adds a count value with the motor being driven due to being switched on by said switching means and which subtracts the count value with the motor being stopped due to being switched off by said switching means; determination means which determines whether the count value counted by said counting means becomes a first upper limit value or greater, or becomes a second upper limit value, which is greater than the first upper limit value, or greater, or becomes a lower limit value or less; and stopping means which stops the driving of the motor until the count value comes to the lower limit value, when the count value is the first upper limit value or greater and said switching means is changed from on to off and when the count value is the second upper limit.
According to the third aspect of the present invention, even if the switching means remains on without being changed to an off state, when the count value comes to the second upper limit value, driving of the motor is stopped. For this reason, there is no possibility of the motor being continuously driven with the switching means on.
A circuit for driving a predetermined device by a motor in a fourth aspect of the present invention is characterized by further comprising stop maintaining means which, when the driving of the motor is stopped by said stopping means, maintains a stopped state of the motor, even if said switching means is turned on, until the count value becomes a lower limit value after the stopping of the motor.
According to the fourth aspect of the present invention, after the count value has reached the upper limit value and the switching means has changed from an on state to an off state to stop the motor, until the count value comes to the lower limit value, the motor is maintained in a stopped state with the switching means on. For this reason, when the motor is driven for a long time, a stopping time is compulsorily set, thereby preventing a failure of the motor caused by heat, degradation of performance of the motor, and the like.
REFERENCES:
patent: 4630245 (1986-12-01), Dam
patent: 4713571 (1987-12-01), Suzuki et al.
patent: 4926084 (1990-05-01), Furutsu et al.
patent: 5616979 (1997-04-01), Nishikawa
patent: 9-98583 (1997-04-01), None
Adachi Yoshihiro
Furukoshi Hiroyuki
Morizaki Satoshi
Naito Shinichi
Asmo Co. Ltd.
Dougherty Thomas M.
Parkhurst & Wendel L.L.P.
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