In the motor speed control system, it is necessary to control the position or angle of the load. Simple position control only aligns position targets when stopped, and advanced position control requires higher dynamic tracking performance.
The SB70 inverter has a built-in universal function module, a rich programmable unit and various flexible interfaces to provide a basis for position control, and has developed point-to-point position control and pulse frequency for given position control.
The SB70 has two counters, both of which can realize high-speed quadrature counting function, and the up-counting input of counter 2 has electronic gears, which is convenient for zooming in and out of the position in use. The following is a case study of a steel mill in Shenyang to introduce the application of the SB70 in position control.
First, a steel mill trolley round-trip positioning control
In the production of a steel mill in Shenyang, the trolley is required to walk back and forth between 0 and 8 m, and it is required to stay at 8 m and then return; and for the convenience of users, the jog function is added; the proximity switch near the 0 position can be added to eliminate the counter. The cumulative error of 1; multi-speed 1 as the crawling speed can improve the positioning accuracy. The running diagram of the car is shown in Figure 3:
Car running diagram
This scheme uses the high-speed quadrature counting function of the counter, that is, it increases the counting of the A and B channels of the quadrature encoder, increases the counting when forward rotation, and counts down when it reverses. When the counting direction is inconsistent with the positive and negative rotations, the wiring of the A and B channels can be exchanged, or can be exchanged by the parameter Fd-03 "PG direction selection".
The main control idea is to make the trolley travel a fixed distance and repeatable.
The preset error at the starting position is used to preset or clear the counter to eliminate the cumulative error of carriage travel.
The preset value of the counter is approximately equal to the count value of the trolley from 0m to the preset proximity switch.
It should be pointed out that the F9-14 "set count value" is slightly larger than the count value of 8m, such as 36000.
In the forward rotation, the car is stopped at the required position by adjusting F9-15 "specified count value", F4-18 "multi-segment frequency 1", FE-03 "comparator 1 digital setting", such as 8m; F9 must be satisfied -15/F9-14 should be smaller than the setting of FE-03, such as FE-03=95%, then F9-15 takes 90% & TImes; 36000=32400.
When inverting, contrary to the above, Fd-20 "specified count value 2" is smaller than the digital setting of comparator 2, such as: FE-08 "comparator 2 digital setting" = 10%, then Fd-20 = 5% & TImes; 36000=1800.
Set the multi-segment frequency 1 to 15 Hz, which can be modified in practice.
The operation process is as follows:
When the trolley is in the 0 position, the count value is very small, the counter percentage is <95%. If the forward rotation terminal FWD is valid, the output of the timer 1 is 1, the starting motor rotates forward, and accelerates to the frequency set by F0-00. The count value increases; when the count value increases to the "specified count value", the digital output "specified count value arrives", the motor is decelerated by the logic unit 3 and the timer 4, and crawls at the speed of "multi-segment frequency 1"; the count value Continue to increase, when the count value percentage is ≥95%, the output of comparator 1 is 0, the output of timer 1 is 0, the internal virtual FWD terminal is invalid, the motor decelerates to stop, and the comparison value of comparator 1 is adjusted to make the motor stop at the request. s position.
In the opposite direction, it is the opposite of the forward rotation.
After on-site debugging and user feedback, it meets actual production needs and has high positional accuracy and repeatability.
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