1. Field of the Invention
This invention relates to a motor drive system used with industrial robots, processing machines, and the like.
2. Description of the Prior Art
Conventional motor drive systems use sensors to detect the rotation of a motor, and with the detection signals from the sensors as feedback signals a host controller generates a command signal to control the rotational position and speed of the motor based on the feedback signals. A drive object, such as a robot arm or the like, is shifted to a target position, at a desired speed, by the motor being subjected to the above feedback control.
In such a system, it is desirable that the characteristics of the motor driving circuit, power source, etc, be modifiable to cope with the user's various requirements.
The host controller, which provides commands to the system, includes various types of controllers or controller functions, such as providing command values in the form of digital signals, providing command values in the form of analog signals, etc. It is, therefore, desirable that the motor drive system be connectable to these various host controllers.
The sensor for detecting motor revolutions may be an optical resolver or a magnetic resolver. Generally, the optical resolver is of high precision and high resolution, but, is expensive. On the other hand, the magnetic resolver is relatively inexpensive, but is inferior in precision and resolution as compared to the optical resolver. Because of the differences in characteristics, the optical resolver and the magnetic resolver are usually used selectively according to whether precision or cost is most desired.
Also, a different motor drive system is used for the optical resolver and the magnetic resolver.
According to the embodiment, the motor drive system to be used with the sensor must be selected properly each time so as to cope with the particular sensor to be used therewith. The motor drive system is originally expensive. Thus, if the entire motor drive system has to be replaced to handle different applications, the costs will be disadvantageously expensive.
For driving a robot arm on the motor drive system, there may occur a case where the absolute rotational position of the motor must be identified so as to ensure the position of the arm, etc. However, an absolute type sensor is expensive to install originally. Accordingly it is desired to have a system which is inexpensive and readily usable for detecting the absolute rotational position.
On the other hand, in case an incremental type sensor is used, the origin of the rotational position will be required. An origin detection means which is moderate in cost and high in precision is preferable.
As mentioned, the motor drive system has many desired requirements However, no motor drive system satisfying all of the desired requirements concurrently has yet been realized.