Method and device for controlling an electric motor driven roller

Abstract: In a motor driven roller rotated by a brushless motor (2) and stopped by an electric brake and an electromagnetic brake (7), in order to reduce abrasion of the brake parts of the electromagnetic brake, a motor driver (13) for drive-controlling a brushless motor (2) is provided with a delay circuit (15) that detects the motor pulse. When a stop signal is input, a transistor is activated, which in turn activates an electric brake to brake the brushless motor, while at the same time, the motor pulse detected by the motor driver (13) is input to the delay circuit (15). After the stop signal is input, the motor pulse declines, which is detected by the delay circuit to activate the electromagnetic brake (7). The delay circuit is provided on the driver substrate (14) for the motor driver.

Description: The present invention relates to a method and a device for controlling a motor driven roller, which is powered by a brushless motor equipped with a brake mechanism. Such a motor driven roller can be used, for example, in a conveyor, in particular a conveyor that is repeatedly switched on and off. A motor driven roller for a conveyor is usually stopped by an electric brake. What is stopped, however, is only the rotation of the roller itself. The conveyor itself can be moved easily by an external force, etc. On the other hand, in a mechanism in which the conveyor is stopped mechanically using an electromagnetic brake only, the brake pad is subjected to friction, which causes abrasion and shortens the life of the brake pad. In order to solve these problems, a number of methods have been devised to increase the electric brake power. Another method that has been devised for ensuring the stopping position uses both an electric inverter brake and a physical electromagnetic brake. In such a conventional method for controlling a motor driven roller for a conveyor using both an electric brake and an electromagnetic brake, the electric brake and the electromagnetic brake are activated at the same time. In the conventional method in which an electric brake and an electromagnetic brake are activated at the same time, the electromagnetic brake is activated at high speed. This causes the brake parts to wear out quickly, shortening the life of the motor roller. On the other hand, adding an independent delay circuit in order to delay the activation timing of the electromagnetic brake with respect to the activation of the electric brake increases the cost. The present invention aims at solving these problems associated with the conventional methods by using a simple method to delay the activation timing of the electromagnetic brake until after the revolution of the brushless motor is reduced, thereby providing an economical motor driven roller that can be used over an extended period of time because the brake parts wear less. To achieve the above objective, a motor driven roller powered by a brushless motor is provided with a built-in electromagnetic brake, and a delay circuit is provided in a drive-controlling device for the motor. The delay circuit uses the motor pulse detected by a motor driver. When a stop signal is input, the motor pulse rate declines. This decline of the motor pulse rate is detected to activate an electromagnetic brake. Because the motor pulse can be detected by the motor driver, it is sufficient to mount the delay circuit for activating the electromagnetic brake on the driver substrate of the motor driver; there is no need to provide a special delay circuit device. According to the method for controlling a motor driven roller of the present invention, the electromagnetic brake can be activated only after the electric brake has been activated and the revolution of the brushless motor has been sufficiently reduced. This minimizes the abrasion of the brake parts. Accordingly, the present invention is quite effective for use with a belt conveyor that needs to be switched on and off frequently. Because the delay circuit employed in the present invention uses the motor pulse that is detected by the motor driver, the present invention can be embodied by simply adding the delay circuit to the motor substrate. Therefore, there is no need to install a special delay circuit device. This makes it possible to embody the present invention simply and inexpensively. An embodiment of the motor roller of the present invention will now be described with reference to the accompanying drawings. FIG. 1 is a block diagram showing the control method of the delay circuit. FIG. 2 is a longitudinal section view of the motor driven roller. FIG. 2 is a longitudinal section of a motor driven roller. This roller includes a brushless motor 2 inside the outer casing 1. The rotation of the brushless motor 2 is transmitted to the outer casing from the output part 2b by first reducing the rotation of the rotor shaft 2a via the reduction gear 3. In other words, the outer casing 1, which is linked to the rotor shaft, rotates with respect to the fixed shaft 4, which is attached to one part of the conveyor. Between the outer casing 1 and the fixed shaft 4, a bearing 5 is mounted to smooth the rotation. Inside the outer casing 1, there is a fixed case 6, which is provided with an electromagnetic brake 7 so that the rotation of the rotor shaft 2a can be physically stopped. FIG. 2 also shows an enlarged view of a section of the electromagnetic brake. This electromagnetic brake has an inner disk 8 at the tip of the rotor 2a. The inner disk 8 is sandwiched by an outer disk 9, which is a fixed part, and an electromagnetic plate 10, which is movable in the axial direction. The electromagnetic plate 10 is constantly pressed against the inner disk 8, which functions as a brake pad, by a spring 11. When the inner disk 8 is gripped by the outer disk 9 and the electromagnetic plate 10, a braking condition takes effect. The electromagnetic plate 10, which is movable in the axial direction, is designed to be attracted by the electromagnetic coil 12 of the electromagnetic brake 7. When the electromagnetic coil 12 is not turned on, the electromagnetic brake works by the resilience of the spring 11. When the electromagnetic coil 12 is turned on and magnetic attraction is generated, the electromagnetic plate 10 is attracted to the electromagnetic coil 12, resisting the resilience of the spring 11, thereby releasing the brake. FIG. 1 shows a schematic drawing of the motor-roller-controlling device with the brushless motor 2 built in. When the start switch of the conveyor is turned on, a start signal is sent to a motor driver 13. Then an electric current runs to the electromagnetic coil of the electromagnetic brake. This releases the electromagnetic brake while at the same time powering the brushless motor 2. The brushless motor 2 is rotated, and the rotation is transmitted to the outer casing of the roller. When a stop signal is transmitted, a transistor is activated, which in turn activates an electric brake to slow down the brushless motor 2. Activation of an electric brake using a transistor is a widely used technique in a brushless motor. The motor pulse rate, which inevitably reflects the revolution of the brushless motor 2, is fed back to the motor driver 13. In this invention, the driver substrate 14, on which the motor driver is mounted, is also provided with a delay circuit 15 . The delay circuit 15 uses the motor pulse rate fed back to the motor driver to detect the decline of the motor pulse rate. In other words, after detecting that the motor pulse rate has sufficiently declined after the stop signal has been given, the electric current to the electromagnetic coil 12 of the electromagnetic brake 7 is cut off. When the electric current to the electric magnetic coil 12 is cut off, the attraction of the electromagnetic plate 10 by the electromagnetic coil is released, and the electromagnetic plate 10 is pressed against the inner disk 8 by the resilience of the spring 11. In other words, the electromagnetic brake 7 is activated, and the rotation of the brushless motor 2 is completely stopped. The delay circuit 15 may activate the electromagnetic brake by either detecting the declining trend of the motor pulse or by confirming the cessation of the motor pulse. In the method in which the electromagnetic brake is activated when the declining trend of the motor pulse is detected, the roller can be stopped in a short period of time. According to this method, because the electromagnetic brake is activated after the electric brake is activated, the motor roller can be stopped with little shock, making it possible to avoid sudden friction with the inner disk 8, which is a friction part. In the method in which the electromagnetic brake 7 is activated when the motor pulse rate of the electromagnetic brake becomes zero or very small, the time to a complete halt is determined by the characteristic of the electric brake. In this case, the time to a complete halt is longer than in the above case. After the electromagnetic brake is activated and the brushless motor is stopped, it is possible to prevent the motor driven roller or the conveyor from moving unnecessarily. The abrasion of the inner disk can also be reduced significantly. The delay circuit 15 of the present invention need only consist of a circuit that detects changes in the motor pulse rate on the driver substrate 14 on which the motor driver is mounted, and there is no need to install a timer, an electromagnetic valve or other special delay circuits on the control board. This makes it possible to embody the present invention simply and inexpensively.

Claims: A method for controlling a motor driven roller powered by a brushless motor (2), in which the motor driven roller has a built-in electromagnetic brake (7), and the motor has a drive-controlling device provided with a delay circuit (15), characterized in that the motor pulse rate detected by a motor driver (13) is input to the delay circuit (15), and the decline of the motor pulse rate after a stop signal has been input is detected at the delay circuit (15) to activate the electromagnetic brake (7). A device for controlling a motor driven roller powered by a brushless motor (2) and having a built-in electromagnetic brake (7), characterized by comprising: a motor driver (13) capable of detecting the pulse rate of the motor (2); a delay circuit (15) to which said motor pulse rate is inputted; said delay circuit (15) being capable of detecting a decline of the motor pulse rate; and means to activate the electromagnetic brake (7) responsive to a decline or cessation of the motor pulse rate as detected by said delay circuit (15). A device as claimed in claim 2, wherein said motor driver (13) and said delay circuit (15) are formed on the same substrate (14).

Inventors: FUKATA SHIGEKI, ITOH KAZUO, TACHIBANA TOSHIYUKI, FUKATA, SHIGEKI, ITOH, KAZUO, TACHIBANA, TOSHIYUKI
Applicants: ITOH ELECTRIC CO LTD, ITOH ELECTRIC CO., LTD.
Application year: 2000
Main classification: H02P3
IPC codes: H02P6, B65G39, H02P3, B65G13, H02K7, B65G23