Compared with roller feeder and air feeder, NC feeder has higher feeding precision, more stable feeding performance and more convenient operation, and these advantages are fundamentally derived from its advanced control system.The control system of NC feeder is composed of (Mitsubishi) PLC, (Yaskawa) servo system and (Weilun) touch screen. PLC can improve the stability of the control system and enhance the anti-interference ability of the system.The servo system can accurately locate the position of mechanical motion and improve the accuracy of mechanical transmission.The touch screen can directly display and modify the NC feeder parameters, which simplifies the field operation.
PLC is the core component of NC feeder. The NC feeder is standard with Mitsubishi PLC. With built-in high-speed pulse output function, it can directly send out quantitative pulse number to control servo driver operation.The servo driver controls the rotation position and speed of the servo motor according to the number and channel of the pulse output from PLC, so as to give the feeding length accurately.The touch screen can display all kinds of parameters directly and personalize the system, which provides a good man-machine interface for users and simplifies the field operation.
NC feeder has two working modes: manual and automatic. The servomotor can turn forward or by turning in manual mode, while the servomotor can only turn forward in automatic mode.
In manual operation mode, ACC (frequency acceleration and deceleration control) instruction is executed along the rising edge of the servo forward signal, and mode control data is set to realize CW (clockwise) rotation and make the servo motor turn forward.At the falling edge of the servo forward signal, execute the INI command to stop the pulse output.The servomotor reversal situation can be similarly.
When in the automatic working mode, the PLC sends the preset pulse to the servo drive device, and then executes THE PLS2 (positioning) instruction.
Description of several key parts in PLC program of NC feeder:
1. PLC program will set the length of the conversion pulse number on the touch screen
PLC calculates the number of pulses sent to the servo driver according to the set length. The set length rotation pulse number can be expressed by the following formula:
Pulse number = (set length × standard pulse number)/(electronic gear number × standard length)
Note: the standard length is set at 1m. The standard pulse number refers to the number of pulses needed to deliver 1m material.
PLC output USES floating-point arithmetic, and input parameters must be in floating-point format.The pulse setting quantity in the high-speed pulse output instruction must be BIN number, so after FIXL, the instruction converts the calculated pulse number into B1N number format.The number of servo drive electronic gears is set to 5.
2. Actual length of pulse number revolution
In order to make the operator better grasp the work of the feeder, it is very necessary to display the feed length in real time.The method is to read the actual pulse number of PLC, convert it to the actual length value of generalists, and display it on the touch screen.The actual length of pulse number revolution can be expressed by the following formula:
Actual length = actual pulse number × number of electronic gears and teeth × (standard length/standard pulse number)
3, feeding speed turn pulse frequency
For different length of workpiece, feeding speed requirements are different;Longer workpiece needs higher feeding speed, otherwise it will conflict with other equipment.For shorter workpiece, lower feeding speed can be selected to protect the motor.Therefore, the high speed times the set percentage is read from the touch screen to give the feeder speed, which is then converted to pulse frequency.
4, pulse frequency transfer speed
While displaying the feeding length in real time on the touch screen, it is also very necessary to display the feeding speed. The method is to read out the pulse frequency issued by PLC and then divide it by the high speed to show the percentage.
