Electricity: motive power systems – Positional servo systems
Utility Patent
1999-08-16
2001-01-02
Ip, Paul (Department: 2837)
Electricity: motive power systems
Positional servo systems
C318S561000, C318S472000, C360S073030
Utility Patent
active
06169381
ABSTRACT:
TECHNICAL FIELD
The present invention relates to a drive apparatus and a driving method with a motor for controlling the number of revolutions of the motor at a constant rate and particularly, to an apparatus for recording and/or playing back on a recording medium where the running speed of the recording medium can be made constant.
BACKGROUND ART
A conventional portable record and/or playback apparatus employing a tape cassette as the recording medium is known using a set of dry cells or a rechargeable battery as the power source. In such record and/or playback apparatus, as the voltage in the power source is decreased, the revolution of the motor becomes slow and will retard the running speed of a magnetic tape. For maintaining the running speed of the magnetic tape at a constant rate, various techniques are provided. One of them involves varying the number of windings used in the motor corresponding to the source voltage.
More particularly, the conventional record and/or playback apparatus has a motor, e.g., of three-phase direct-current type, in which an intermediate tap is provided in the winding coil of each phase, and a driving unit for driving the motor by changing the path of drive current through the coil of each phase in response to a source voltage. It is now defined that a mode where the entire coil is filled with the drive current or the number of windings in the coil is large is termed the first mode and another mode where the drive current is passed between the intermediate tap and one end of the coil or the number of winding in the coil is small is termed the second mode.
The driving unit comprises a motor driver composed of transistors for switching the flow of the drive current in the coil. a voltage detector for detecting the source voltage, and a motor controller for controlling the motor driver in response to the source voltage detected by the voltage detector. When the source voltage supplied from the voltage detector exceeds a threshold level, the motor controller selects the first mode. It selects the second mode when the source voltage is smaller than the threshold level.
In response to pressing of the playback button, the motor in the conventional record and/or playback apparatus is driven in the first mode. When the source voltage detected by the voltage detector exceeds the threshold level, the motor controller directs the motor driver to maintain the first mode. When the source voltage detected by the voltage detector drops to below the threshold level, the motor in the conventional record and/or playback apparatus directs the motor driver to switch the motion of the motor to the second mode.
More particularly, the motor controller selects the first mode when the source voltage exceeds the threshold level to reduce the flow of the drive current passed through the coils and thus provide a degree of energy saving. When the source voltage drops down to smaller than the threshold level and the revolution of the motor is slowed down, the motor controller selects the second mode to increase the flow of the drive current passed through the coils and thus the number of revolutions of the motor so that the revolution of the motor remains constant. In this manner, the motor driver is successfully controlled to drive the motor at a constant number of revolutions and run the magnetic tape at substantially a constant speed.
The threshold voltage is set to a lower limit of the number of revolutions where the servo control for maintaining the constant revolution of the motor is hardly conducted with the source voltage. More specifically, the threshold level is determined by considering the fact that when the ambient temperature about the motor in the conventional record and/or playback apparatus which is placed under a low temperature condition drops down significantly, it may increase the load to the motor.
As shown in
FIG. 1
, the torque-revolution characteristic of the motor is set such that the motor can normally run at a predetermined number of revolutions under a lower temperature condition, regarding the load P
1
on the motor exerted when the conventional record and/or playback is placed at a lower ambient temperature. In other words, the point
101
on the revolution-torque characteristic line has to be located above the load P
1
exerted onto the motor under a low temperature condition.
It is however unusual that the conventional record and/or playback apparatus is placed under as a low temperature condition as 5° C. Generally, the conventional record and/or playback apparatus is used at a room temperature, e.g., 20° C. At the room temperature, the average of load to the motor is moderate as denoted by P
2
in FIG.
1
. For use at the room temperature, the revolution-torque characteristic line is preferably set just above the load P
2
as denoted by
102
. When it is desired to run the motor at a constant number N of revolutions, there is produced a difference C between the two revolution-torque lines
102
and
101
, at a room temperature and a lower temperature. For compensation of the difference C, the motor has to be driven at a higher torque by an increased rate of the drive current applied to the coils.
Also, the setting of the threshold voltage depends considerably on variations of the torque constant, the coil resistance, and the turn-on resistance of transistors used for supplying the coils with the drive current as well as common thermal change and aging of the conventional record and/or playback apparatus which is fabricated in mass production. The threshold voltage has to be determined through translating the above factors to parameters of the load and calculating the largest P
1
of the load. In every conventional record and/or playback apparatus, the revolution-torque characteristic of the motor is set to such a grade that the revolution of the motor is maintained at a constant speed. In practice,. the revolution-torque characteristic is held just above the largest load P
1
as denoted by the dotted line
101
in FIG.
1
.
However, the largest load P
1
resulting from a combination of the above factors appears very rarely. It is accepted in general use for holding the revolution-torque characteristic of the motor just above the average load P
2
like the real line
102
. This creates the difference C between the two revolution-characteristic lines
102
and
101
for the average load P
1
and the largest load P
2
respectively. For eliminating the difference C, the motor has to be driven at a higher torque with an increased flow of the drive current applied through its coils.
DISCLOSURE OF THE INVENTION
It is an object of the present invention to provide a drive apparatus and a drive method with a motor capable of maintaining the revolution of the motor at a constant number of revolutions and having a higher degree of energy saving.
It is another object of the present invention to provide an apparatus and a method for recording and/or playing back on a recording medium capable of maintaining the running of the recording medium at a constant speed and having a higher degree of energy saving.
For achievement of the foregoing object of the present invention, a drive apparatus with a motor is provided comprising: a driving means for driving the motor of multiple phase, of which the number of windings in the coil of each phase can be changed, either in a first mode where all the windings in the coil of each phase are used or a second mode where the number of windings used is smaller than that of the first mode; a source voltage detecting means for supplying the driving means with a source voltage; a temperature detecting means for detecting an ambient temperature about the motor; and a controlling means for switching the action of the driving means to run the motor in either the first mode or the second mode in response to a result of the detection released from the source voltage detecting means or the temperature detecting means. Accordingly, the revolution of the motor can be maintained a at contant speed regardless of a change in the loa
Arai Toshiyuki
Kato Tomonori
Kushima Tatsuya
Nakajima Ichiro
Ip Paul
Maioli Jay H.
Sony Corporation
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