Device for controlling an electric motor

A device for controlling an electric motor adapted for rotating a drive shaft of a movable member, the device comprising:

• a hybrid encoder, including means for generating a pulse output signal in response to the rotation of the drive shaft, and a shaft position encoder;
• the pulse signal generating means including a rotatable apertured disc operatively linked to the drive shaft to rotate therewith, the apertured disc including a plurality of apertures arranged circumferentially thereabout, the apertures being formed through the thickness of the disc, the apertured disc having opposite flat sides;
• and an optoelectronic emitter and receiver arranged on opposite flat sides of the apertured disc and in alignment with the apertures, the emitter being adapted to emit a light beam through the apertures and the receiver being adapted to receive the light beam, the apertured disc being interposed between the emitter and the receiver to periodically interrupt the light beam upon rotation of the apertured disc,
• the shaft position encoder including at least two rotatable encoder discs arranged coaxially with the apertured disc, the apertured disc and each of the at least two encoder discs being mechanically linked to proportionally rotate at different speeds so that a complete revolution of the apertured disc will result in a partial revolution of one of the at least two encoder discs, and a complete revolution of said one of the at least two encoder discs will result in a partial revolution of the other of the at least two encoder discs;
• each of the at least two encoder discs including at least one electrically conductive continuous emitting track mounted thereon and at least one electrically conductive discontinuous receiving track mounted thereon;
• and electrically conductive contacts positioned adjacent to and in contact with each of the emitting and receiving tracks of each encoder disc, the shaft encoder providing an output signal representative of the angular position of the drive shaft;
• means for regulating a desired angular stopping position, the stopping position regulating means including switching means, the switching means providing an output signal;
• means for controlling the rotation of the motor, the motor controlling means including switching means, the switching means of the motor controlling means providing an output signal;
• a logic processing unit responsive to the output signals of the pulse signal generating means and the shaft encoder of the hybrid encoder and to the output signals of the switching means of the regulating means and the motor controlling means, the logic processing unit providing a control signal to the electric motor, the logic processing unit including a working memory for storing a desired angular stopping position, the logic processing unit being provided for analyzing the output signal of the pulse signal generating means, for calculating the angular position of the drive shaft, for comparing the angular position of the drive shaft with the desired stopping position, and for interrupting the rotation of the motor when the angular position of the drive shaft is equal to the desired stopping position;
• and
• an erasable and non-volatile memory for protectively storing the desired angular stopping position in the event of a power failure, the non-volatile memory being connected to the logic processing unit.