Electricity: electrical systems and devices – Control circuits for electromagnetic devices – Systems for magnetizing – demagnetizing – or controlling the...
Reexamination Certificate
2001-12-11
2003-12-02
Dinkins, Anthony (Department: 2832)
Electricity: electrical systems and devices
Control circuits for electromagnetic devices
Systems for magnetizing, demagnetizing, or controlling the...
C361S154000, C361S159000
Reexamination Certificate
active
06657844
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention relates to an electromagnetic drive control device for controlling electromagnetic driving devices which are employed in various instruments as a drive source.
An electromagnetic driving device typically drives an actuator making use of an electromagnetic force generated between a permanent magnet and a coil in which an electrical current flows. The driving force can be controlled by controlling the current flowing through the coil. Since the electromagnetic driving device can be made relatively compact in size, it is widely employed, as a driving source, for an objective lens driving device of a camera, a scanning position compensating device for a laser scanning device, a driving device for a linear motor car, and the like.
As an example, the scanning position compensating device will be described. In the scanning position compensating device for a laser scanning device, a driving coil is swingably (rotatably) supported in a magnetic field generated by a magnet which is secured to the electromagnetic driving device. As the electrical current is fed to the driving coil, it swings due to the electromagnetic force. The driving coil typically supports a prism, which swings with respect to the optical axis as the driving coil swings, thereby deflecting a passage of the laser beam. In this type of drive control device for controlling the electromagnetic drive that controls the direction of the electrical current flowing through the coil, a circuit as shown in
FIG. 9
is generally employed.
The circuit shown in
FIG. 9
includes a drive circuit
41
, which includes an operational amplifier OP, a resistor R, and a current buffer circuit
411
. The current buffer circuit
411
is configured such that an NPN transistor TR
1
and a PNP transistor TR
2
are connected in accordance with a complimentary emitter follower connection. The drive circuit
41
is a so-called voltage-current conversion circuit, which outputs an electrical current in accordance with a voltage of an input drive control signal CS to a drive circuit
30
.
In such a voltage-current conversion type drive control circuit, the output current I is grounded through a drive coil
24
and the resistor R. The drive circuit
41
operates such that the voltage R*I equals the drive control signal CS. When the drive control signal CS is positive, a positive voltage +Vcc is applied to an terminal A of the drive coil
24
, and thus, the current flows from the terminal A to a terminal B. When the drive control signal CS is negative, a negative voltage −Vcc is applied to the terminal A, thereby the electrical current flowing from the terminal B to the terminal A. As the direction of the electrical current flowing through the drive coil
24
switches as described above, the direction of the electromagnetic force caused between the drive coil
24
and the magnet
223
switches. Thus, the drive coil
24
can be driven to operate as desired. Further, depending on the voltage of the drive control signal CS, the voltage output by the drive circuit
41
varies. Then, the current flowing through the drive coil
24
varies, and the electromagnetic force between the drive coil
24
and the magnet
223
varies. Accordingly, by controlling the voltage of the drive control signal CS, the amount of the swing movement of the drive coil
24
can be controlled.
In the conventional drive control circuit as described above, when power sources (i.e., +Vcc and −Vcc) are turned from ON to OFF and the voltages change from 0V to designated values (+Vcc and −Vcc), one of the power sources may reach the designated voltage earlier than the other. In such a case, the performance of the circuit may become unstable. In a particular case, the output of the operational amplifier OP is fixed, for example, to +Vcc or −Vcc. In such a case, a maximum (or minimum) drive current is output from the drive circuit
41
to the drive coil
24
. Then, an electrical damage and/or a mechanical damage of the electromagnetic drive device will be caused.
Further to the above, when the power sources are in OFF condition, the following problem may occur. When the power sources are in OFF condition, no electrical current flows through the coil
24
. Since the drive coil
24
is in an electrically open status, no electromagnetic force is generated between the drive coil
24
and the magnet
223
when the power sources are in the OFF condition. If an oscillation or a shock is applied from outside to the drive coil
24
under such a condition, the drive coil
24
may be swung greatly exceeding a limited movable range. In such a case, thin feed lines connected to the drive coil
24
may be cut, or a supporting mechanism for the drive coil
24
may be mechanically damaged.
As described above, the conventional drive control device provided with two power sources has defects.
It should be noted that a drive control device employing a single power source also has a similar problem, if a relatively long time is required till the voltage of the power source reaches the designated value after turning ON the power source. In such a case, the maximum current may flow through the drive coil and the electromagnetic drive device may be electrically damaged when the power source is turned ON. Further, since the coil is in the unstable condition when the power source is in the OFF condition, the electromagnetic drive device may be mechanically damaged due to the external oscillation or shock.
As explained above, in the conventional electromagnetic drive control device, the operation of the electromagnetic driving device may be unstable, and the life thereof may be relatively short.
SUMMARY OF THE INVENTION
In view of the above problems, it is an object of the present invention to provide an improved electromagnetic drive control device for an electromagnetic driving device, in which the above-described problems when the power sources are turned ON and/or when the power sources are in the OFF condition are resolved.
For the above object, according to the invention there is provided a drive control circuit for an electromagnetic driving device including a magnet and a drive coil that moves due to an electromagnetic force, when an electrical current flows therethrough. The drive control circuit may include a drive circuit that feeds an electrical current to the drive coil, the drive circuit including at least one voltage source, a short-circuit system that short-circuits the drive coil, the short-circuit system releasing the short-circuited condition of the drive coil in accordance with an output voltage of the at least one voltage source.
With this configuration, when the voltage source is in the OFF condition, since the drive coil is short-circuited, a counter electromotive force is generated when the external shock or oscillation is applied, which prevents the excessive movement of the drive coil. Further, when the voltage source is turned ON, the output current of the drive control circuit will be or will not be fed to the drive coil depending on the output voltage of the voltage source. Thus, the above-described problem of the overcurrent across the drive coil can be prevented.
Optionally, the short-circuit system may include a voltage detection circuit that detects the output voltage of the at least one voltage source.
Still optionally, the short-circuit system may include an electromagnetic relay system, which is provided with a magnet coil actuated in accordance with an output of the voltage detection circuit, a contact switch provided between both end terminals of the drive coil, the contact switch neutrally connecting the both end terminals of the drive coil, the contact switch disconnecting the both end terminals of the drive coil when the magnet coil is actuated.
Further optionally, the voltage detection circuit may include a switching circuit connected between the at least one voltage source and the magnet coil, the switching circuit being turned ON to connect the at least one voltage source and t
Dinkins Anthony
Greenblum & Bernstein P.L.C.
Pentax Corporation
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