Design of Embedded Motion Controller Based on ARM and DSP

introduction

Motion control systems are widely used in the field of industrial control, but the application of embedded technology in the field of industrial control is not yet mature. In recent years, industrial control has placed higher and higher requirements on motion control systems. In order to meet the various performance requirements of the new generation of motion control systems, embedded motion controllers have emerged. The new generation of motion control systems based on the combination of ARM and DSP motion control chips give full play to the respective characteristics of ARM microcontrollers and professional motion control chips MCX314As, and can easily form a high-performance embedded motion control system.

Motion control chip MCX314As

MCX314As is a DSP motion control chip produced by NOVA Electronics Co., Ltd. of Japan. It is a motion control chip that controls 4-axis pulse sequence output to drive servo motors and stepper motors. It can be used in industrial automation equipment, industrial robots, measuring equipment, office equipment and household appliances. It can perform independent positioning control and speed control on each axis. On the other hand, it can also select 2 or 3 axes from the 4 axes to perform arc, straight line and bit pattern interpolation. The output pulse frequency is as high as 4MHZ, the error is less than ±0.5 minimum interpolation unit, and the magnification is 1 to 500. Each axis has a servo feedback input terminal, four input points and 8 output points. It can be independently set to constant speed, linear, asymmetric S curve addition/subtraction control, asymmetric trapezoidal addition/subtraction control, and has 2 32-bit logic, actual position counters and status comparison registers to achieve closed-loop position control [1].

The MCX314As motion control chip can interface with 8/16-bit data bus, and realizes 4-axis 3-link position, speed, acceleration and other motion control and real-time monitoring through registers such as command, data and status. In actual application, all extremely complex real-time motion control tasks can be handled by the MCX314As chip, and the host CPU only needs to send a series of control instructions to the MCX314As chip to realize various complex movements.

2 ARM microprocessor S3C2410

S3C2410 is a 32-bit RISC embedded processor from Samsung Electronics of South Korea. This processor provides a cost-effective, low-power, high-performance solution for handheld devices and general applications. The chip is based on the ARM920T core, adopts a five-stage pipeline and Harvard structure, and has a main frequency of up to 200MHz[3]. ARM920T has a full-performance memory management unit MMU, independent 16KB instruction and data caches, and a high-speed AMBA bus interface. In order to reduce the cost of application system design, S3C2410 integrates a large number of commonly used resources, such as LCD controller, NANDFlash controller, SDRAM controller, system chip select logic, and some commonly used communication interfaces, making it widely used in the field of industrial control.

The basic structure of motion controller

The motion controller is composed of S3C2410 and MCX314As. The development board S3C2410 is designed with a system bus reserved interface, which reserves the signal lines based on the general IO port on the S3C2410 chip, including 16-bit data lines, 12-bit address lines, chip select signals and some read-write control signal lines, so as to facilitate users to expand the application circuit. The connection between the motion control chip MCX314As and the S3C2410 processor is through this standard system bus interface circuit, connecting the data lines, address lines, read-write control lines, chip select signals and interrupts of the two. The SN74ALVC164245 chip is added between the signal connections to realize level conversion and drive the signal at the same time. It should also be noted that we use the transmission of 16-bit data lines, so the H16L8 pin of the MCX314As chip must be connected to a high level.

Figure 1 Interface circuit diagram of S3C2410 and MCX314As [page]

The processing process of the embedded motion control system is actually the process of transmitting data from the ARM host computer to the MCX314As slave computer. The control process is as follows:

(1) When the machining program starts running, the MCX314As chip is initialized first. The initial speed, acceleration, deceleration, acceleration change rate, forward and reverse rotation mode, logical position counter clearing, actual position counter clearing, etc. are set for the MCX314As chip.

(2) Select the axis to be processed. The MCX314As chip has four axes: X, Y, Z, and U. They all have the same functional capabilities and can achieve four-axis three-linkage.

(3) Set the selected axis mode and operating parameters, including linear constant speed mode, single-step interpolation output mode, and interrupt request.

(4) Initialize the position counter, that is, write the row number in the database into this counter for subtraction calculation, and reduce it by one after each row of data is processed.

(5) Carry out command and data transmission, check the status register after sending data, send a signal after processing a section and then send the next set of data, until the processing is completed. Once an interruption occurs during the processing, first read the data in each register and save it, wait for the processing to resume, and then read and write it out. After the entire database file is output, save the data information after the running system is completed and the status information of the system in preparation for the next part processing, and the processing is completed.

Application of motion controller in XY two-axis CNC servo worktable

The XY two-axis worktable is a cross worktable (X and Y axes are perpendicular) driven by ball screws and rolling guides. There is a limit switch at each end of the X and Y axes. A Panasonic AC servo motor (model MSMA022A1C, power 200W, rated speed 3000r/min, rated torque 0.64Nm) is used to drive the worktable. The motor driver uses Panasonic servo driver MSDA023A1A. A photoelectric encoder is used as a position feedback device (an 11-line 2500P/r incremental encoder is coaxially installed on the servo motor)[3]

Figure 2 is the X-axis drive schematic diagram of the platform [1]. The Y-axis drive circuit is the same as the X-axis drive circuit. In the figure, M is the servo motor and EC is the encoder. Set the "control mode" of the servo drive to "position control" and set the command pulse to CW/CCW mode. S3C2410 operates MCX314As according to the flowchart, sets the corresponding motion parameters, and writes the function command to complete the motion trajectory control of the platform.

Figure 2 Interface block diagram of a single-axis signal drive system

Conclusion

Motion control systems are widely used in industrial control. MCX314As is a highly integrated motion control chip that can realize position, speed, acceleration control of four-axis three-linkage and continuous interpolation and position closed-loop control of three modes: linear, circular, and bit. The ARM processor has powerful 32-bit RISC performance, small size, and low power consumption. Using ARM and professional motion control chips to design motion controllers can greatly reduce R&D tasks, speed up R&D, and obtain an embedded motion control system with excellent control performance in a relatively short time.