“CONTROL SYSTEM DESIGN OF SMT PICK AND PLACE MACHINE “
Here we would like to discuss original design of control system of complete SMT Pick and Place machine.
Southern Machinery Provide different type of SMT Pick and Place Machines according to the requirements and Specification of Global Clients however one of our machine consists of four DC motors. Three of these motors are used to move machine head along X-axis, Y-axis and Z-axis. Fourth motor is for rotating SMT component clockwise and anticlockwise. Encoders are attached to shafts of all four motors. These motors are connected to motor drivers through electric connections. Encoder outputs routed to the EISA card mounted on EISA port. Data bus from EISA card is attached to external main board. Motor drive cards are mounted on main board. In addition to different signals for actuating different relays, data bus also carry control voltage signals. These analogue voltage signals vary in the range from +5V _-5V. Duty cycle of PWM signal vary with changing magnitude of this analogue signal.
This is the part of our machines control system which acts as a bridge between EISA card and machines motors and feeders. All data signals and control voltage signals from EISA control card terminate at the main board. Depending on purpose which it serves, main board has several main parts. These parts are discussed here one by one.
· This part of main board is associated with rectifying input AC voltage to DC voltage as shown in figure 5.1. Main functions of this part are following:
· Supply Power to motor drivers at 35v
· Supply 12V for powering operational amplifiers ICs. Supply 5V for powering TTL logic ICs.
· Supply 15V for actuating feeder plungers as shown in picture.
· This part contains relay switches to turn AC power on or off from software control as shown in picture.
Limit Switch Module
· This part deals with providing power source to proximity switches and receiving output of proximity or limit switches as shown in picture
Data Transmission Module
· This module receives data from some external data source through any programmable protocol (RS232 etc.) and routs that data to EISA card as shown in picture.
Feeder Relay Module
· This module consists of 15 relays. These relays actuate respective feeder plunger when decoded data is received. Each rely is connected with single plunger thus it controls one feeder at time as shown in picture.
· This module receives 4 bit data from EISA card and decodes this data to 16 bits. 15 bits of decoded data are used to actuate one feeder at time as show in picture.
PWM Generation Module
· This part consists of two PIC18F2431 microcontrollers. These microcontrollers receive analogue control voltages and generate PWM. Microcontrollers are programmed such a way that duty cycle of PWM is function of input control voltage.
· Motor driver used in our project are H Bridge Bipolar type drivers. Input signal to motor driver are either bipolar PWM or analogue control voltage as show in figure
· 5.8. Motor driver use two kinds of power sources. One source is for driving motor
· when bridge is in conducting state. Motor driver receive 35V from main board for this purpose. Motor driver receive isolation supply from external transformers rated for 10V at output as shown in figure 5.9. This isolation supply voltage is rectified to DC voltage.