Application of SB70 Inverter in Position Control

In the speed regulation system of motor, there is a need to control the load position or angle. Simple position control is to align the target position at stop, while higher level position control requires high dynamic tracking function.

The built-in general function modules, rich programmable units and flexible interfaces of SB70 series inverters provide a basis for realizing position control. Point-to-point position control and position control with pulse frequency as given value have been developed. SB70 inverter has two counters, both of which can realize high-speed orthogonal counting function, and for input of increasement counting of the Counter #2, electronic gear is provided to facilitate use of zooming of given position.

A steel plant requires trolley to move forward and backward in the range of 0~8m and stop at 8m and then return in steel production. To facilitate use by users, inching function is added and the function that proximity switch at position 0 can remove accumulated error of Counter #2 is added, and multi-speed 1 as crawling speed can improve positioning accuracy. The run diagram of trolley is shown in Fig. 3:

Fig. 3 Trolley Run Diagram

This scheme uses the high-speed orthogonal counting function of the counter, that is, making increasement counting for Channels A and B of the orthogonal encoder with increasement counting for positive turning and decreasement counting for reverse turning. When the counting direction is not consistent with the positive and reverse turning, the wiring of Channels A and B can be changed, or change can be made through parameter Fd-03 “PG Direction Selection”.

The main concept is to make the travel distance of the trolley is fixed and reproducible.
The proximity switch at the starting position is used to make the counter preset or clear, to eliminate the accumulated error of the trolley in traveling.

The preset value of the counter is about the count value of the trolley from 0m to the preset proximity switch.

What needs to be pointed is that F9-14 "set count value" is about 5% greater that the count value at 8m, such as 36000. 

In positive turning, through the regulation of F9-15 "Designated Count Value", F4-18 "Multi-Band Frequency 1", FE-03 "Comparator #1 Number Setting", make the trolley stop at the required position, such as 8m; the setting that F9-15/F9-14 must be less than FE-03 must be met. For example, if FE-03 = 95%, then F9-15 = 90% × 36000 = 32400.

In reverse turning, contrary to the above, Fd-20 "Designation Count Value #2" should be less than the number set in Comparator #2. For example, if FE-08 "Comparator #2 Number Setting" = 10%, then Fd -20 = 5% × 36000 = 1800.

The multi-band frequency is set as 15Hz and can be changed in actual use.

The process of running is as follows:

When the trolley is at 0, the count value is small with counter percentage <95%. If the positive turning terminal FWD is valid, the output of Counter #1 is 1, and the starting motor turns positively and accelerates to the frequency set in F0-00 with count value increased; when the count value rises to "Designated Count Value", number output "Designated Count Value Reached" decelerates the motor by the Logic Unit #3 and Counter #4, and it crawls at the speed of "multi-band frequency #1"; when the count value continues to increase, and the percentage of the count value ≥ 95%, the output of Comparator #1 is 0, causing the output of Counter #1 is 0 and the internal virtual FWD terminal is invalid, the motor decelerates until stop. Adjustment of the comparison value of Comparator #1 can stop the motor at the required position. 

The condition of reverse turning is the reverse process of positive turning.

The commissioning on site and users' reflection shows that it meets the requirement of actual production and has high-level position accuracy and repeatability.