Motor Control Device

1. Field of the Invention

This invention relates to a motor control device, and more particularly to a motor control device suitable for driving the picture-taking lens moving motor of the automatic focusing apparatus of a camera.

2. Description of the Prior Art

As a focus detecting device for detecting the condition of focusing of the picture-taking lens of a camera with respect to an object to be photographed, a device which produces three different signals to control the driving device of a motor for driving the focusing optical system of the picture-taking lens, namely, a front focus signal for moving the optical system in one direction during the front focus condition in which the picture-taking lens is focused to the front side of a major object to be photographed, a rear focus signal for moving the optical system in the other direction during the rear focus condition in which the picture-taking lens is focused to the rear side of the major object, and an in-focus signal for stopping the movement of the optical system when the picture-taking lens has become in-focus to the major object has already been proposed in U.S. application Ser. No. 167,912 filed on July 11, 1980 by the applicant and corresponding German Laid-open Patent (DOS) No. 30 27 729. The above-described driving device for causing the rotation of the motor to respond to such three different signals is usually provided with three input terminals to operate switching elements for forming the forward rotation circuit, the reverse rotation circuit and the circuit for suddenly stopping the motor, respectively. Particularly, in a camera wherein the camera body and the picture-taking lens sturcture are separable from each other, when it is taken into account that a signal is transmitted from the focus detecting device provided in the camera body to the driving device provided in the lens structure, at least three electrical contacts are required between the camera body and the lens structure to transmit respective signals to three input terminals. An increase in the number of such electrical contacts is inconvenient for the designing of modern cameras in which transmission of numerous types of information must be made possible between the camera body and the lens.

It is an object of the present invention to provide an improved motor control device which is capable of controlling forward rotation, reverse rotation and sudden stopping of a motor.

The motor control device according to the present invention is provided with two input terminals for said control. The device of the present invention is further provided with a transistor bridge circuit comprising first and second transistors connected in series with each other and third and fourth transistors also connected in series with each other, a motor connected between the junction between the first transistor and the second transistor and the junction between the third transistor and the fourth transistor, a fifth transistor which, when conductive, turns on both the first transistor and the fourth transistor opposed to each other diagonally of the bridge circuit, a sixth transistor which, when conductive, turns on both the second transistor and the third transistor opposed to each other diagonally of the bridge circuit, a seventh transistor which, when conductive, forcibly turns off the third transistor in spite of the turn-on of the sixth transistor, and an eighth transistor which, when conductive, forcibly turns off the first transistor in spite of the turn-on of the fifth transistor, and one of the two input terminals is connected to the fifth transistor and the seventh transistor while the other input terminal is connected to the sixth transistor and the eighth transistor. The motor control device of the present invention is best suited for a device for driving the picture-taking lens of the automatic focusing apparatus of a camera.

The invention will become more fully apparent from the following detailed description thereof taken in conjunction with the accompanying drawing.

The FIGURE of the drawing is a circuit diagram of the motor control device according to an embodiment of the present invention.

Referring to the drawing, four transistors Q.sub.1, Q.sub.2, Q.sub.3 and Q.sub.4 together constitute a transistor bridge circuit connected in the form of a bridge, and a motor M is connected between the junction between the transistors Q.sub.1 and Q.sub.2 connected in series with each other and the junction between the transistors Q.sub.3 and Q.sub.4 also connected in series with each other. A transistor Q.sub.5, when turned on, turns on both of the transistors Q.sub.1 and Q.sub.4 opposed to each other diagonally of the above-described transistor bridge circuit. A transistor Q.sub.6, when turned on, turns on both of the remaining transistors Q.sub.2 and Q.sub.3 opposed to each other diagonally of the above-described transistor bridge circuit. The collector of a transistor Q.sub.7 is connected to the junction between the base of the transistor Q.sub.3 and the emitter of the transistor Q.sub.6, and the transistor Q.sub.7, when turned on, forcibly turns off the transistor Q.sub.3 and supplies an emitter current to the transistor Q.sub.6. The collector of a transistor Q.sub.8 is connected to the junction between the base of the transistor Q.sub.1 and the emitter of the transistor Q.sub.5, and the transistor Q.sub.8, when turned on, forcibly turns off the transistor Q.sub.1 and supplies an emitter current to the transistor Q.sub.5. A terminal T.sub.1 is connected to the bases of the transistors Q.sub.5 and Q.sub.7, and a terminal T.sub.2 is connected to the bases of the transistors Q.sub.6 and Q.sub.8. A manually operated switch S.sub.1 is normally open, and one end thereof is connected to the negative pole of a power source E.sub.1 and the other end thereof is connected to the terminal T.sub.1 through a diode D.sub.1 and to the terminal T.sub.2 through a diode D.sub.2.

When an L-level potential and an H-level potential are applied to the terminals T.sub.1 and T.sub.2, respectively, the L-level potential turns on the transistors Q.sub.5 and Q.sub.7 and both of the opposed transistors Q.sub.1 and Q.sub.4 of the bridge circuit are turned on. On the other hand, the H-level potential of the terminal T.sub.2 turns off the transistors Q.sub.6 and Q.sub.8 and the turn-off of this transistor Q.sub.6 turns off both of the other opposed transistors Q.sub.2 and Q.sub.3. Accordingly, a current flows from the power source E.sub.1 through the transistor Q.sub.1, the motor M and the transistor Q.sub.4, so that the motor M rotates in a forward direction. When an H-level potential and an L-level potential are applied to the terminals T.sub.1 and T.sub.2, respectively, the L-level potential turns on both of the transistors Q.sub.6 and Q.sub.8 and both of the opposed transistors Q.sub.2 and Q.sub.3 of the bridge circuit are turned on. On the other hand, the H-level potential of the terminal T.sub.1 turns off the transistors Q.sub.5 and Q.sub.7 and the turn-off of this transistor Q.sub.5 turns off both of the other opposed transistors Q.sub.1 and Q.sub.4. Accordingly, a current flows from the power source E.sub.1 through the transistor Q.sub.3, the motor M and the transistor Q.sub.2, so that the motor M rotates in a reverse direction.

When an L-level potential is applied to both of the terminals T.sub.1 and T.sub.2, as previously described, the L-level potential of the terminal T.sub.1 turns on the transistors Q.sub.5 and Q.sub.7 and the L-level potential of the terminal T.sub.2 turns on the transistors Q.sub.6 and Q.sub.8. The turn-on of this transistor Q.sub.7 forcibly turns off the transistor Q.sub.3 and supplies the emitter current thereof to the transistor Q.sub.6. By the turn-on of this transistor Q.sub.6, the transistor Q.sub.2 is turned on. On the other hand, the turn-on of the transistor Q.sub.8 forcibly turns off the transistor Q.sub.1 and supplies the emitter current thereof to the transistor Q.sub.5. The turn-on of this transistor Q.sub.5 turns on the transistor Q.sub.4. In this manner, the transistors Q.sub.2 and Q.sub.4 of the transistor bridge circuit are turned on to constitute a short-circuiting circuit for the motor M. Therefore, the motor M in rotation suddenly stops rotating. When the driving of the motor is not required, an H-level potential is applied to both of the input terminals T.sub.1 and T.sub.2. By this, all of the transistors Q.sub.1 -Q.sub.8 are turned off and power is not supplied to the motor M, which thus remains stopped. When the manually operated switch S.sub.1 is closed, the terminals T.sub.1 and T.sub.2 are forcibly rendered into an L-level potential through the diodes D.sub.1 and D.sub.2, respectively. Therefore, the motor M suddenly stops rotating just in the same way as previously described.

Such a motor control device is best suited for the picture-taking lens driving device of the automatic focusing apparatus of a camera. That is, the output terminal of a focus detecting device 10 is connected to the input terminals T.sub.1 and T.sub.2 of the motor control device. This focus detecting device 10 applies an L-level signal and an H-level signal to the terminals T.sub.1 and T.sub.2, respectively, during detection of front focus, applies an H-level signal and an L-level signal to the terminals T.sub.1 and T.sub.2, respectively, during detection of rear focus, and applies an L-level signal to both of the terminals T.sub.1 and T.sub.2 during detection of in-focus. Thus, during front focus and during rear focus, the motor M rotates in a forward direction and in a reverse direction, respectively, thereby moving the picture-taking lens in one direction or in a reverse direction and during in-focus, the motor is suddenly stopped to stop the picture-taking lens at the in-focus position. In order that the picture-taking lens may be stopped independently of the focus detecting device 10, the manually operated switch S.sub.1 may be closed.

The relation between the input signal level and the motor drive can be determined conversely. That is, an H-level signal and an L-level signal may be applied to the terminals T.sub.1 and T.sub.2, respectively, to thereby rotate the motor in a forward direction. Also, the polarities of the transistors may be arbitrarily determined.