Design of VCM low-frequency active vibration isolation control system based on DSP

Publisher:cangartLatest update time:2011-06-26 Reading articles on mobile phones Scan QR code
Read articles on your mobile phone anytime, anywhere

Abstract: Voice coil motor (VCM) is increasingly favored as a driver of active vibration absorber in active vibration isolation system due to its good linear driving performance. This paper designs a DSP-based VCM control system for low-frequency active vibration isolation system, gives the software and hardware design methods, and introduces the working principle of a software system based on clock beat and message mechanism.
Keywords: Voice coil motor; DSP; Clock beat; Message mechanism

Introduction
In recent years, with the vigorous development of micro/nano technology, processing and measurement require a stable environment to improve the accuracy of processing and measurement. However, vibration interference is everywhere, and outdoor traffic, indoor personnel walking, mechanical equipment operation, etc. may cause vibration interference. The vibration frequency generated by the ground is about 0.1~10 Hz, the vibration frequency generated by laboratory personnel walking is about 1~3Hz, and the vibration frequency of general buildings is about 10~100 Hz. Moreover, these vibrations are difficult to completely eliminate, so vibration suppression and isolation are particularly important.
There are many methods for vibration suppression and isolation. Vibration isolation technology is usually divided into passive vibration isolation technology and active vibration isolation technology. Voice coil motor (VCM) is a type of electromagnetic linear motor, and was first used in loudspeakers. Because of its simple structure, direct drive, easy maintenance, and good acceleration and deceleration performance, VCM actuators are often used in occasions where fast and motion-controlled equipment is required, such as servo control in DVDs, hard disks, and camera lenses. This paper selects VCM as the driver of the active vibration absorber in the low-frequency active vibration isolation system, and gives software and hardware design methods.

1 System hardware design
The hardware circuit of the VCM control system uses TI's TMS320F2812 (hereinafter referred to as F2812) as the core of the control system. This chip is a very powerful 32-bit fixed-point DSP chip that has both digital signal processing capabilities and powerful event management capabilities and embedded control functions. The clock frequency is 150 MHz, which can meet the real-time requirements of the system. In addition, the chip also supports 96 external interrupts, rich external memory interfaces, etc. The block diagram of the VCM control system is shown in Figure 1.

a.JPG


In Figure 1, the power module provides the system with various power requirements; the DSP minimum system module is the computing and processing core of the control system; the data storage module uses IS61LV25616AL and SST39VF800Q to expand 8 MbFlash and 4 Mb RLM respectively; the CPLD expansion module uses the EPM3256A series CPLD to expand the human-computer interaction module and the RS232 and USB2.0 communication modules; the acceleration sensor signal acquisition circuit is the vibration interference detection module of the active vibration isolation system, that is, the forward channel of the control system; the VCM drive circuit module is the backward channel of the control system.
In the active vibration isolation system, an ICP type acceleration sensor is used to detect the vibration of the vibration isolation platform. The output of the sensor is a ±5 V voltage signal. In order to obtain sufficient resolution and linearity, the 24-bit ∑-△ ADC conversion chip AD7734 of ADI Company is selected. Its nonlinearity does not exceed ±0.0025%, and it has an SPI communication interface. By configuring the internal registers of AD7734, the ±5 V signal output by the acceleration sensor can be directly sampled. The circuit schematic of the forward channel is shown in Figure 2. Among them, AD780 is an ultra-high precision bandgap reference voltage source that can provide 2.5 V output.

b.JPG


The principle of the VCM drive circuit is shown in Figure 3. VCM is a permanent magnet linear motor. By changing the direction and size of the coil control voltage, the movement direction and positioning position of the VCM can be changed, and its positioning accuracy is closely related to the resolution accuracy of the control signal. In order to obtain a larger driving capability, TI's dual full-bridge PWM motor driver chip DRV8402 was selected. The driver chip can operate at a switching frequency of 500 kHz, with an operating voltage of 12 to 50 V, a continuous output current of 10 A, and a peak current of up to 24 A; it can 100% linearly restore the input PWM without loss of control accuracy. Using the F2812 PWM output module in conjunction with the DRV8402, the control accuracy of the VCM can reach 16 bits.

c.JPG


2 System software design
In order to meet the real-time requirements of the control system, a software system based on clock beats and message mechanisms was written based on μC/OS-I and the 32-bit hardware timer Timer 2 of F2812. The software system is completely written in C language, has low dependence on hardware, and can be easily ported to other hardware platforms. The description of the core files of the software system is listed in Table 1. Among them, the hardware dependence is divided into 3 levels (1 to 3), and the larger the number, the greater the dependence.

d.JPG


The include calling relationship between the core files is shown in Figure 4. Among them, math.h is the header file that comes with the compiler.

e.jpg


The architecture of the software system can be represented by the three processes shown in Figure 5. Figure 5(a) is the main program flow, that is, the foreground operation flow of the software system. In the main program's large loop (while(1){;}), the system will continuously take messages from the message queue, determine the message type, and then perform corresponding operations based on the message type and message value. Figure 5(b) is the interrupt service function flow of the system clock beat. The clock beat is generated by the hardware timer Timer 2 (T2), and the beat period is adjustable, usually 20ms. After each clock beat period, the system interrupts and enters the interrupt service function to execute the T2 routine, which is the background operation of the system. Figure 5(c) is the flow of the T2 routine. When entering the routine, first check whether there is a software clock. If there is, call the software clock service function, and then execute the system routine. If not, call the system routine directly.
The software clock is a timing operation based on the system clock beat. It can be understood as an alarm clock, that is, a certain operation is performed every certain time, or it is only a single operation. The operations corresponding to the software clock can be sent to the message queue and executed in the foreground or in the interrupt. However, it is not advisable to set too many software alarms to be executed in the message queue.
The message passing mechanism is the link between the front and back ends of the software system. All background operations or external requests can be sent to the message queue in the form of message packets, and then the information to be processed can be obtained in the foreground by taking and decrypting messages, and then the corresponding operations are performed. At present, the message queue is FIFO mode and does not support priority. In actual application, the capacity of the message queue must be large enough.

Conclusion
After experimental debugging, the low-frequency vibration isolation platform based on the VCM control system can effectively and dynamically suppress external vibration interference. In addition, the software system based on clock beats and message mechanisms has been transplanted to other project applications many times, and good results have been achieved.

Reference address:Design of VCM low-frequency active vibration isolation control system based on DSP

Previous article:Design of digital thermometer based on AT89C51&DS18820
Next article:Research and design of dual-screen LCD controller based on CPLD

Latest Industrial Control Articles
Change More Related Popular Components

EEWorld
subscription
account

EEWorld
service
account

Automotive
development
circle

About Us Customer Service Contact Information Datasheet Sitemap LatestNews


Room 1530, 15th Floor, Building B, No.18 Zhongguancun Street, Haidian District, Beijing, Postal Code: 100190 China Telephone: 008610 8235 0740

Copyright © 2005-2024 EEWORLD.com.cn, Inc. All rights reserved 京ICP证060456号 京ICP备10001474号-1 电信业务审批[2006]字第258号函 京公网安备 11010802033920号