Firstly, it analyzes how to realize pulse control in actual combat and its advantages and disadvantages.
Generally, we control the positive and negative rotation of the servo motor, position control, or position+speed control, all of which are controlled by the controller sending pulses, such as FX2N of Mitsubishi PLC and Mitsubishi servo driver. We can use the PLC editing program to calculate the number of pulses to be sent, the sending speed and other parameters according to the equivalent conversion you want, and then drive the equipment to run the corresponding distance. Of course, controllers such as Siemens and Omron are inseparable from servo machines of different brands, and their principles are similar.
Then the problem is coming. What is bus control? Next, let me introduce you:
Second, the application of fieldbus control and its advantages and disadvantages analysis
With the vigorous development of IT industry, the automation of factory equipment has entered the era of online connection, which also makes the use of "PC-based" controllers in factory equipment more and more high. Figure 1 shows the open architecture network structure of factory automation, including hardware and various communication protocols.
1. multi-axis motion control
Due to the improvement of automation, the number of shafts required on a single machine increases, and it is very common for a machine to have more than ten shafts. After the number of axes increases, how to coordinate the movement of each axis is an important topic.
2. Small size
Due to the limitation of workshop space, the smaller the size of the machine, the smaller the size of the controller in the machine and the smaller the wiring space.
More accurate
With the accuracy of semiconductor manufacturing process below 100nm, the motion accuracy required by manufacturing process and testing related equipment is also more accurate.
More stable
Thirdly, the traditional AC servo positioning system
Fig. 2 shows a block diagram of a traditional "analog AC servo positioning system". The inner loop of the driver is a phasor-controlled current infinite loop system to control the torque of the motor, and the outer loop is a speed infinite loop control. The motion control card reads back the encoder position and is used for positioning infinite loop control. Usually, the control card will use the DA output voltage as the speed command of the driver.
It is shown as an improved "pulse AC servo positioning system". Because of the progress of servo driver, the infinite loop control of positioning has been moved to the driver for execution. (that is, the speed loop is moved inside the drive). The motion control card outputs pulse instructions to control the position and speed of the motor at the same time, and reads back the encoder position for positioning correction.
Both traditional and improved control architectures are bound to encounter the following bottlenecks:
3. Offset and noise. As long as there is an analog signal, there must be a so-called offset error, which will cause the level error of the transmission command. This problem will be particularly obvious near zero speed and must be compensated by correction. In addition, in the AC servo system with high voltage and high current, special attention must be paid to the interference caused by noise, otherwise it is easy to cause pulse command errors.
4. Lack of self-checking function. For external controllers, these two types of driver architectures are difficult to read or adjust servo parameters in real time. There are hundreds of parameters in the servo driver, which cannot be read by traditional wiring, so there is no way to fully grasp these parameters on the controller, and there is no way to self-check and debug.
Fourth, various serial motion control communication protocols
With the rapid development of serial communication technologies such as Ethernet, great progress has been made in using serial communication to solve the problem of traditional server driver. As mentioned in the first section, the inconvenience of serial system is that there is no communication standard that everyone abides by, and even a single motion control system has no standard that everyone abides by at present, whether it is hardware or communication protocol.
Although there is no standard, the requirements for technical connotation are the same:
1. In order to transmit control instructions in real time in a fixed period,
2. This period is as fast as about 0. 1 ms ~ 5 ms,
3. Collect all peripheral I/O data irregularly,
4. Selectively and aperiodically send and receive servo parameter data,
5. The data structure should include data correctness coding to prevent data correction in the case of noise interference.