A stepper motor control system based on motion control card

1 Introduction
The upper control schemes of motion control systems generally include single-chip microcomputer systems, professional motion control PLCs, dedicated control systems, and "PC + motion control cards". The use of single-chip microcomputer systems to achieve motion control has low costs, but the development is difficult and the cycle is long. This solution is generally suitable for users with large product batches, simple control system functions, and experience in single-chip microcomputer system development. Many brands of PLCs can be equipped with positioning control modules, and some PLC CPU units have motion control functions themselves, such as Panasonic's FP0. This solution is generally suitable for equipment with relatively simple motion processes and fixed motion trajectories, such as feeders, automatic welding machines, etc. Dedicated control systems are generally aimed at special equipment or special industries, such as Siemens' lathe CNC systems and milling machine CNC systems. The "PC + motion control card" solution is increasingly used with the popularization of PCs, and will be the main development trend of motion control systems. This solution can make full use of computer resources and is used for machines and equipment with relatively complex motion processes and mechanical trajectories, and relatively strong flexibility. For example, most of the currently popular open CNC systems use this solution.
The control system introduced in this article adopts the "PC + motion control card" solution, which is the main content of this article.

2 System composition and hardware introduction
Figure 1 shows the hardware composition block diagram of this system. It uses the German Begel three-phase hybrid stepper motor (VRDM3910/LHA) and its matching driver (D921). The control card is the MPC02 motion control card produced by Chengdu Stepping Electromechanical Co., Ltd.

2.1 Driver panel and its function settings
Figure 2 shows the panel configuration and functions of the D921 driver.

Function selection: STEP1, STEP2 set the number of steps per motor revolution;

All input signals are optocoupler inputs.

2.2 Structure of motion control card
The structure of MPC02 motion control card is shown in Figure 3.

The card is inserted into the PCI expansion slot of the PC for use; the MPC02 card completes all the details of motion control, including the output of pulse and direction signals, the processing of automatic speed increase and decrease, the detection of origin and limit signals, etc. It uses advanced dedicated control integrated circuits and has trapezoidal and S-shaped speed increase and decrease curves. It uses a 68-core SISC interface, and shielded cables can be used for external wiring to improve the anti-interference ability of the control card. Its signal interface is defined as follows:
pulse quantity signal: pulse/direction (numbers 17 to 28); encoder feedback (35 to 52); optical isolation power supply (29, 30).
Switching signals: limit (55, 56, 60, 61, 65, 66); deceleration (53, 54, 58, 59, 63, 64); origin (57, 62, 67); servo enable (9, 11, 13); deviation clear (10, 12, 14); external alarm (68); general input (31~34); general output (1~8); optical isolation power supply (15, 16).

3 Software of motion control system
3.1 Software of control card
The units and function return values ​​used in the function library are usually agreed as follows.
3.1.1 Unit
1) The unit of displacement or distance is P (Pulse), that is, the number of pulses;
2) The unit of speed is P/S (Pulse/sec), that is, pulse/second;
3) The unit of acceleration and deceleration is P/s2 (Pulse/s2), that is, pulse/second2.

3.1.2 Function return value
Most functions in the motion library are integer functions, and their return meanings are as follows:
0 The function is executed correctly; -1 The function is executed incorrectly.
The functions used in the function library are as follows: control card and axis setting functions, independent motion and interpolation motion functions, braking functions, position and status setting and query functions, I/O port operation functions, error code functions and some other functions. There are six basic types of motion implemented by these functions, as shown in Figure 4.

The motion function with speed increase/deceleration control is called fast motion function, such as fast_pmove, fast_vmove and fast_hmove, and the constant speed motion function is called constant speed (con) motion function, such as con_pmove, con_vmove and con_hmove.
3.2 Software Program:

The motion parameter settings include axis number, initial speed, maximum speed, acceleration and moving distance, etc.; the motion control program includes emergency stop, slow stop, zero reset, normal speed and fast speed, etc.; the control effect display includes position and speed, etc. The program is as follows:

4 Conclusion
The motion control function of the motion control card with a dedicated motion control circuit as the main control is realized by hardware circuits, with high integration and good reliability. It only needs to receive control commands from the microcomputer, and then complete the motion-related control by itself, which hardly occupies the CPU time of the microcomputer. It is very convenient to use, which can not only greatly shorten the research and development cycle, but also realize a more complete motion control system, which can meet the control requirements of stepper motors.