Chapter 21 Gear Motor Speed Control - PID

Ch 21 Gear Motor Speed Control - PID 1

Chapter 21 Gear Motor Speed Control - PID DC Motor Position Control Lab

This lab has a history from a number of previous developers. One was the original lab for the

Auto Controls course manufactured by a former instructor in EET, John Rich. Another was a

paper “A Low-Cost Control System Experiment for Engineering Technology Students” by Dr.

Curtis Cohenour Ph.D., P.E. P.E., Ohio University. Dr. Cohenour’s implementation is shown

here:

Ch 21 Gear Motor Speed Control - PID 2

Prof. Rich’s design is shown next:

and here.

Speed and Position

Control of DC

Motor

Ch 21 Gear Motor Speed Control - PID 3

At present, the PID block controlling a dc gear motor seems to be the best approach. The

controller is a Siemens S7-1200 with encoder inputs and PWM output.

Several different dc gear motors are shown here. We are presently using the first of these

although, the other lower-cost ones will also work.

Ch 21 Gear Motor Speed Control - PID 4

The description of the gear motor is as follows:

Description

DC 12V 7RPM 50Kg. cm Self-Locking Worm Gear Motor With Encoder And Cable, High Torque Speed Reduction

Motor

Specification:

Voltage: DC12V

No-Load Speed: 7rpm

Reduction Ratio: 1:522

Torque: 50Kg. cm

Error: ±10%

Wire Length: 20cm / 7.87 inch

Output Shaft Diameter: 8mm / 0.31 inch D-type

Output Shaft Length: 15mm / 0.59 inch

Total Size (not include shaft): 40*36*125mm / 1.57 * 1.41 * 4.92 inch

Wirings:

1. The yellow and green wires are the speed signal output line, and they can't be connected any power supply, or it

will be burnt.

2. Positive and negative power supply of encoder do not allow connect wrong; voltage is 3.3 -5V.

3. Control CW or CCW of motor by changing the positive and negative power supply of encoder (change Red Wire

and White Wire connect)

Red Wire - positive power supply of motor(+)

White Wire - negative power supply of motor(-)

Black Wire - negative power supply of encoder(-) (positive and negative power supply of encoder do not allow connect wrong; voltage is 3.3 -5V)

Blue Wire - positive power supply of encoder(+) (positive and negative power supply of encoder do not allow connect wrong; voltage is 3.3 -5V)

Yellow Wire - signal feedback (11 signals per motor turns a circle)

Green Wire - signal feedback (11 signals per motor turns a circle)

The interface between the PLC and the motor and the motor controller is shown in the next

diagram.

Ch 21 Gear Motor Speed Control - PID 5

2.2 k

+24 V

Signal from

Encoder0-5 VDC

Signal to PLC Input0-24 V DC

4.7 k

PWM Output Signal

PWM Signal to MD20AMotor

Controller1.0 k

A note from Siemens:

Ted, We discussed the use of the S7 1200 v2.2 CPU in relation to the Quadrature encoder. The 1200 with 24V DC inputs support up to six High Speed Counters. a. Up to 3 of the addresses Ia.0 to Ia.5 can be used for Quadrature Mode at 80Khz. b. Up to 3 of the addresses Ia.6 to Ib.5 can be used for Quadrature Mode at 20Khz. The DI4 5 VDC signal board with part number 6ES7 221-3AD30-0XB0 must be used since the encoder is 5V. It supports 160 KHz for Quadrature Mode. The input is "source" type. So, the encoder must support this which means that it is NPN or Open Collector type. If not, the 1200 cannot be used with this encoder. An ET 200SP with the Position Input module would be a viable option. I can help further with the ET 200SP if needed. Does the encoder, have A and A not, B and B not, Z and Z not signals? If so, please wire these as well because this readings will be more accurate. For the S7 1200 v2.2 when configuring the HSC, please select the Input Source as "signal board input". Please note that the option is only available if the signal board has been added in the hardware configuration. Please note that the addresses of the HSC will be the address of signal board (default 4.x). In v4.x S7 1200's, the user selects the address rather than the Input Source. Let me know if I can help further. Best Regards, C. Wayne Scott Siemens Industry, Inc. Customer Services Technical Support Customer Care Center: 800 333 7421 Outside USA +1 423 262 5710

Ch 21 Gear Motor Speed Control - PID 6

We used the 24 V input/output model since that is what was available. The set-up of the inputs

for pulse and outputs for PWM are included in the program shared later. The dc motor controller

is shown below. We used 12 V for power since the motor was rated at 12 V DC. This controller

is very inexpensive and can accommodate any of the motors shown above. It is also used in the

tank-over-tank lab in Hybrid Text Ch. 25. It works well with cheap power supplies for most

applications.

Ch 21 Gear Motor Speed Control - PID 7

The wiring for the motor from the PLC and motor drive board is shown below:

2.2 k

L (+24 VDC)

Signal from

Encoder0-5 VDC(either

yellow or green wire)

Signal to PLC Input0-24 V DC

(I0.0)

4.7 k

PWM Output Signal(Q0.0)

Signal to MD20AMotor

Controller

1.0 k

M (0 VDC)

Dir does not need

to be connected

12 V +

0V (M)

0V (M)

Ch 21 Gear Motor Speed Control - PID 8

The program for the single dc motor follows. First the Project Tree:

Next is the set-up for the high speed inputs for the pulses in and the PWM for the output.

Ch 21 Gear Motor Speed Control - PID 9

The program is in a cyclic interrupt program that is executed each 100 ms. It consists of a rung

to get the input count for the last 100 msec followed by the PID block and finally the output to

the PWM block.

Ch 21 Gear Motor Speed Control - PID 10

The following is a watch table built to display the variables for the PID block. The video gives

additional detail of the PID block and uses this watch table to vary the speed.