Electromagnetic holding brakes serve to hold the shaft of a motor as long as the motor is out of operation and must not move, even when an external torque is applied thereto. The safe condition of such a holding brake is when the holding brake is engaged and the shaft is held fast. Therefore, electromagnetic holding brakes are designed such that they are released by an electromagnet to which an operating voltage is applied to lift the brake shoes. When this operating voltage is turned off, or when the operating voltage fails for other reasons, the braking shoes are pressed against the shaft again by means of mechanical springs.
Electromagnetic holding brakes are also used in connection with linear motors, where they lock the armature in position on the stator when in the de-energized state.
U.S. Pat. No. 3,614,565 proposes to use a higher operating voltage for releasing a holding brake than for holding the brake in the released position. In this way, on the one hand, the brake can be released more quickly and, on the other hand, the heat produced in the electromagnet during operation of the motor is significantly reduced.
EP 2503682 B1 describes a circuit arrangement in which the different voltages used for releasing the brake and holding the brake in the released position are set by pulse-width modulation. Here, the voltage at the electromagnet of the holding brake is equal to the time average of the applied voltage pulses. This publication discloses that in decentralized drive technology, it is advantageous if the drive controller and the circuit arrangement for controlling the holding brake are disposed directly in or on the motor. In this configuration, the signals for pulse-width modulated power supply to the holding brake can be generated locally by the drive controller. However, in some areas of technology, the requirement is rather for central drive control, for example, by means of a numerical control system on a multi-axis machine tool. According to EP 2503682 B1, then, in addition to the supply line for transmitting the brake voltage, a sensor line is needed to measure the voltage or current directly at the holding brake and transmit it to the central drive controller. This makes it possible, for example, to detect a voltage drop on the supply line and compensate for it by adjusting the duty factor of the pulse-width modulation. However, an additional sensor line means increased wiring complexity in a drive system and also represents an additional source of error.