Experiment #6c Final Project Option 3: RPM Motor Control ENPH 259

Transcription

1 Experiment #6c Final Project Option : RPM Motor ontrol ENPH 59 Prof. avid Jones November, 07 Objective Using the devices you have investigated previously in this lab (Opmps, counters, transistors) as well as some new ones (LEs, photo-transistor, buffers, resistor ladder newtork, etc.) you will build a circuit capable of setting and actively controlling the speed of an electric motor. Introduction/Overview servo control loop circuit (or servo) is a circuit that uses feedback for active control over some quantity (such a a length measurement, rotation speed, temperature, etc.). s you can image such a circuit is widely used in everyday devices. few examples include cruise control in your car, temperature in an oven, tracking systems in astronomical telescopes. In this experiment you will build a circuit that controls the revolutions per minute of an electric motor by electronically adjusting the current supplied to the motor (thereby changing the motor s speed. Figure shows the entire circuit. What follows is brief description of the operation. disc is attached to the motor with a single slit in it. When the motor is turned on the disc rotates and when the slit passes by the LE some light falls on a phototransistor, causing it to conduct thereby generating a clock(or LK) pulse (every time the slit passes over the LE/phototransistor). Next a counter counts the number of LK pulses between RESET pulses. Just before the RESET pulse, an 8 bit -latch stores the counter output (using the LT H output) which is then converted from a digital signal (in binary) to an analog signal (i.e., an digital-to-analog convertor or ) using an R R ladder network. The analog output of the is then compared (subtracted from) to an analog voltage (representing the set point for speed of the motor).

2 PIU?0 - PI0 PI0 PIU?0 PIU0 PIU606 PIU0 PIU0 PIU60 PIU0 PIU0 PIU0 PIU07 PIU0 PIU0 PIU05 PIR0 PIR0 PIU0 PIU00 PI0 PIU0 PIU05 PIU06 PIU0 PIU PI0 PIR0 PIU50 PIU605 PIU09 PIR00 PIR08 PIR07 PIR0 PIR0 PIR90 PIR60 PIR90 PIR60 PIU08 PIU05 PIU0 PIU0 PIU06 The output of this operation is then used to control the current through the motor via power transistor. "Measuring Period" Generator elay RESET Pulse Generator PIR0 OR PIR0 R PIU?0 Orange lack k OU? H PIR0 OR PIR0 PIU?0 hopping isc R OU OU OU OU OUE OUF OUG 5k PIU0 PIU0 White lack SN7HT PI0 PI0 OR R 00k PIR0 PIR0 O uf UF OR k PI0 O PI0 nf UE U O 7pF PIR50 PIU09 OR5 k PIR50 U PORESET OMotor Servo U PIU0 PIU0 POLTH PIMotor Servo0 + PIMotor Servo0 FYQM-6x00-5 O N8 ounts Number of Rotations between RESET pulses OU OU OU PIU0 Q0 PIU0 P Q PIU0 Q PIU05 MR Q PIU06 On LTH saves number of counted rotations PIU00 To 7-segment Indicators OP PIP0 PIP0 PIP0 PIP0 PIP05 PIP06 PIP07 PIP08 OU Vcc 7HT7 LR Q Q Q PIR09 8-bit igital-to-nalog onverter OR R R R R R R PORESET U Q0 PIU0 PIU0 P Q PIU00 Q PIU09 PIU0 MR Q PIU08 7HT9 PIU08 PIU0 PIU07 PIU LK Q 5Q 6Q 7Q 8Q PIU00 PIU09 PIU05 PIU06 PIU09 PIR06 PIR05 PIR0 PIR0 R R R R R R R R R R PIR0 R 60X-RR-0LF OU OU U7 PIU06 POLTH PIQ0 PIQ0 PIR0 OQ MJF PIQ0 OR PIR0 0 Ohm, W OR PIR0 PIR0.k Protecting uffer OU6 OU6 PIU60 U7 PI0OPI0 PI0 N8 PI0 O PI0 OR0 PIR00 k N8 PIR00 Error Signal mplifier OU5 OU5 PIU506 U7 OR7 PIR70 PIR70 k OR OR9 0k PIR90 k Setpoint k R9 PIU50 OR6 POSPEE0MESUREMNT SPEE_MESUREMNT I Power onnections PIU0 PIU07 UG SN7HT PIU0 PIU07 U 7HT9 U PIU07 U7 Offset- PIU0 Offset- PIU0 U5 PIU507 U7 Offset- PIU50 Offset- PIU50 PIU607 Offset- PIU60 Offset- PIU60 U6 U7-5V -5V E Figure : This is the entire setup of the servo control circuit.the lower panel shows the power connections for each I used. E F There are five components that you will construct and individually test that when properly connected will form your servo. For each component you need to build it, confirm its operation, describe how it works in your lab book (along with and then keep it assembled on its own your proto-board for eventual integration into the overall circuit. s such it will behove you to be areful, Neat, and Meticulous in your circuit construction. Moreover, you should plan where you are going to build each component on your proto-board. This will save your HOURS of troubleshooting. Listed below are the five components along with designation in the overall schematic. LT H and RESET generator ounter and -Latch F G G

3 8-bit Motor sensor and motor driver Error signal amplifier/buffer omponents. LT H and RESET generator The first step in building this component is to fully understand the M5/7H Inverters. They are a special type of inverter (known as a Schmitt-trigger Inverter) which incorporates hysteresis in the input triggering characteristic. In other words, the input voltage level required to cause the output to make a transition from one state to the other depends on which output state the inverter is currently in and is displayed in Fig.. Standard Hysteresis V out V out V in V in Figure : The input vs. output voltage of an inverter without and with hysteresis. Using the output of the power supply and the on-board potentiometer make an adjustable voltage source as the input to one of your inverters and measure the two threshold levels of the unit. That is, determine the amount of hysteresis characterizing the device. The presence of hysteresis of this kind increases the versatility of the unit. In particular, Schmitt-trigger circuits provide excellent noise immunity and the ability to square up signals with long rise and fall times. Explain how this is possible based on your measurements n application of interest to us is the ability to construct a simple square wave oscillator from such an inverter which will form the LT H signal enabling the -Latch to store counter output for every period of the square wave. For this and all other circuits that use inverters, you should ground the input(s) to any non-used inverters on the chips. Otherwise, the unused inverters will be an unstable state and through cross talk can influence other inverters. Next assemble the circuit shown in Fig. a and explain how it works. It will be helpful to measure the input voltage and output voltage simultaneously

4 on the oscilloscope when describing its operation. ompare the ideal period of the generator with your measured period. on t forget to include the second inverter (U) to create the proper polarity for the LT H signal. Now, construct the delay circuit and through your measurements of the input and output describe how a delay is introduced and compare the expected delay with what you measure. Finally build the RESET pulse generator which providing short pulses (i.e. a pulse train with a with a low duty cycle) that resets the counter after the -latch grabs the counter s output. s in the previous circuits, describe how the circuit works by measuring the input and output. s it will be likely difficult to trigger your oscilloscope RESET signal, I would suggest you can use the single-shot trigger capability of your oscilloscope (ask a T for help if necessary). When finished with all of these circuits, save them for integration below. a) "Measuring Period" Generator b) elay c) RESET Pulse Generator PI0 PI0 PIU0 OR 00k PIR0 PIR0 O uf UF PIU0 OR PIR0 k UE U O PIR0 PIU0 PIU00 PI0 PI0 PI0 PIR50 PIU09 O 7pF OR5 nf k PI0 PIR50 OU OU OU OUE OUF PIU0 PIU0 POLTH U PIU08 PIU06 PORESET PIU05 Figure : a) Pulse measuring period generator to create LT H signal. b) elay Generator. c) short pulse RESET generator.. ounter, -Latch, and s shown in Fig., connect the two 6counters to each other, so that a 56 (or 8-bit) counter is formed. First, connect the 8-bit counter connected to the 7 Segment ecimal isplay devices (not explicitly shown in Fig. ). Next verify the operation by disabling the RESET function (it can t be floating) and inputing a low frequency pulse train from the function generator. The frequency should be slow enough such that you should be able to see the 7 Segment display Title update (meaning you should see the numeric display increment in the usual base- 6 fashion (or Hex) from 0 to 5). Next, check the reset functionalitysizeas well Number with a push-button switch. What is the maximum that your counter can count to? heck what happens if you exceed this and discus? Now move the input of the 7 Segment display from the 8-bit counter to the 8-bit output of the -latch (or use the second 7 segment display on breakout board) and confirm you can grab a reading from the counter when the LT H is triggered. Finally, wire up the and at the output of the buffer/op amp confirm that the analog voltage scales properly with the output of the latch. In your lab notebook ate: Sheet of File: :\Users\..\lock_Generator.Schoc rawn y: Revision

5 PORESET ounts Number of Rotations between RESET pulses OU OU Q0 PIU0 PIU0 P Q PIU0 Q PIU05 PIU0 MR Q PIU06 U Q0 PIU0 PIU0 P Q PIU00 Q PIU09 PIU0 MR Q PIU08 7HT9 On LTH saves number of counted rotations PIU0 PIU0 PIU0 PIU07 PIU08 PIU0 PIU0 PIU07 PIU08 PIU0 PIU00 To 7-segment Indicators OP PIP0 PIP0 PIP0 PIP0 PIP05 PIP06 PIP07 PIP08 OU Vcc 7HT7 LR Q PIU0 Q PIU05 Q PIU06 Q PIU09 5 5Q PIU0 6 6Q PIU05 7 7Q PIU06 8 8Q PIU09 LK PIU00 8-bit igital-to-nalog onverter OR PIR00 R PIR09 R R PIR08 R R PIR07 R R OU PIR06 PIU0 R R PIU06 PIR05 PIU0 R R PIR0 U7 R R PIR0 R R PIR0 PIR0 R 60X-RR-0LF POSPEE0MESUREMENT SPEE_MESUREMENT POLTH Figure : This portion of your circuit counts the number of LK pulses between RESET pulses and stores the result before converting the binary (or digital) measurement to analog value. When setting up the circuit Title it can be helpful to display the 8-bit value between the counter and latch. Size Number ate: Sheet of File: :\Users\..\Speed_apture.Schoc rawn y: you should document and explain on each component works using data taken by your circuit...and discuss your troubleshooting procedures. You should also describe how the R-R resistor ladder network performs its duties and the function of the op-amp in the circuit. Remove the function generator input to the counter to prepare for integration below. Revision. Motor sensor and motor driver First make proper connect connections to the LE and phototransistor as shown in the upper left corner of Fig. 5 and manual rotate the disc to confirm a LK pulse is generated when the hole in the disc passes over the LE/phototransistor (You will likely need to use the single shot trigger capability of your scope for this task). Next, wire the LK to the input of the counter and connect the motor driver input to 5V to ground via the 0Ω resistor...make sure this resistor is the W version!...thereby bypassing the transistor and verify that 7-segment display updates the rotation speed. Then enable RESET to counter to allow the counter to be cleared periodically (and confirm this operation).. Error signal amplifier/buffer s shown in Fig. 5 complete the feedback circuit by wiring together the error signal amplifier, buffer and controlling power transistor to complete the feedback circuit. t this point the adjustment of the potentiometer should successfully adjust the speed. If the speed does not track the voltage set point, then you need to troubleshoot this part of the circuit. isconnect the SP EE MESUREMENT from the output of the and use an adjustable input voltage or a slow speed square wave from your function 5

6 - PIR0 OR PIR0 R kou? PIU?0 Orange lack PIU?0 H OMotor Servo PIR0 OR PIR0 R 5k OU PIU?0 PIU0 PIU0 White PIU?0 lack SN7HT hopping isc PIMotor Servo0 + PIMotor Servo0 FYQM-6x00-5 O PI0 PI0 N8 PIQ0 PIQ0 PIR0 OQ MJF PIQ0 OR PIR0 0 Ohm, W OR PIR0 PIR0.k Protecting uffer OU6 PIU60 PIU606 PIU60 U7 PI0 O PI0 PI0 PI0 N8 OR0 PIR00 PIR00 k O N8 Error Signal mplifier Setpoint OR OR9 0k PIR0 PIR0 PIR90 PIR90 OU5 k R9 PIR90 PIU50 PIU506 OR6 PIU50 PIR60 PIR60 k U7 OR7 PIR70 PIR70 k POSPEE0MESUREMNT SPEE_MESUREMNT Figure 5: This schematic shows both the motor sensor and driver (upper left and left) and the error signal amplifier/buffer for feeding back to the motor. Title op-amps to figure out the error. Size Number generator for the SP EE MESUREMENT to trace through the various ate: Sheet of File: :\Users\..\Motor_river.Schoc rawn y: Revision onclusions ll explanations and observations should be written by you alone even though you are working with a partner sharing the same data. ny duplication between lab notebook (including that of your partner s book) will be considered a violation under U s cademic misconduct. In addition, although not an exhaustive list your lab notebook you should contain at a minimum: observations as you work through the lab; what problems you experienced and how you troubleshoot them to ultimately produce a working circuit; explanations of how each component works with measurements/data taken by you on your circuits; the reason for each diode and buffer; answers to any questions asked in the lab instructions; 6

7 a conversion table showing the relationship between the voltage you set, what RPM that voltage produces and what value is displayed on the 7 segment display. How could you modify the circuit so that the display shows the RPM (keep in mind there are 0 holes in the disc and you need to know the latch frequency) What is the maximum speed of the motor? 7