The servo in the industrial control industry is generally the abbreviation of AC servo system. At the project site, the servo we refer to is the servo driver. However, servo driver and servo motor are an inseparable system, and they are connected by encoder cable and power cable. Generally, the servo driver bears the control command of the controller, and then drives the servo motor through the power cable. The real-time orientation of the servo motor is reflected to the servo driver through the encoder cable, forming a closed-loop control. Obviously, in this form, the servo driver only acts as an amplifier, which is the operation form of most servo systems, such as Yaskawa, Fuji, Panasonic, Mitsubishi, Delta, etc.
Some servo drivers have built-in manipulator functions, which can be programmed inside the driver to complete motion control, electronic cam, phase synchronization and other high-end motion control functions. Mainly represented by Lenz servo, other Danfoss, CT and other converter devices can also complete this function.
Obviously, the servo motor upper control discussed in this paper is mainly the first form, that is, the servo driver works in the form of amplifier. At this moment, the PLC, motion controller and numerical control system act as the upper computer. If the servo driver is compared to an engine, then the upper computer is a high-grade driverless system. No matter which kind of upper computer is selected, the upper computer and servo driver generally use pulse and communication methods.
1. Pulse method
The upper computer completes the control by sending pulses to the servo driver. In this method, the speed is controlled by pulse frequency and the azimuth is controlled by pulse number. Similarly, the servo driver will also send the pulse number to inform the upper computer of the orientation and speed of the servo motor.
For example, let's say that the servo motor rotates for one circle with 10000 pulses. Then, when the upper computer sends 10000 pulses, the servo motor rotates for one circle to complete the azimuth control. If the upper computer sends the 10000 pulses in one minute, the speed of the servo motor is 1 r/min. If it does, the speed of the servo motor is 1 r/s, that is, 60 r/min.
Low-end PLC, numerical control system and various single-chip microcomputer systems are generally selected in this form, which is easy to operate and low cost. Obviously, when the number of servo axes is increased, the disadvantages of this control method will appear. The hardware cost of the upper computer will increase, the wiring will be very messy, and if the on-site EMC is not good, the pulse will be easily lost. Therefore, this form is generally under four axes. Therefore, most of the pulse control axes of PLC are in two or three axes, and few of PLC can complete four axes.
2. Communication method
The communication method is specially produced to deal with the lack of pulse method, and has become a development trend. He sends the pulse number and pulse frequency to the servo driver through the communication method. This method can not only transmit the orientation information of the servo motor, but also transmit various status information, such as the current and torque of the servo motor and the fault code of the servo driver. Obviously, when the number of shafts is large, The advantages of this method are obvious.
Source: Global Science and Technology Think Tank
