Lab Sistem Kontrol Servo Ind

TELECOMMUNICATIONS LABORATORY

DE LORENZO s.r.l. Viale Romagna, 20 - 20089 Rozzano (Milano) Italy - Tel. ++39 2 8254551 - Fax ++39 2 8255181 • Telex 321122 DELOR I

BUKU PENTUNJUK

PELATIHAN

DC SERVO

TABEL [MUATAN/INDEKS]

1. Pengenalan

2. Percobaan menggunakan ' DL 2305 Servo Sistem

Percobaan 1 Kecepatan Motor dan watak masukan

Percobaan 2 Kecepatan Motor dan karakteristik pembebanan

percobaan 3 Reaksi transien suatu motor

percobaan 4 Penguat operasional

percobaan 5 Teknik pengendalian Kecepatan Motor Loop tertutup

percobaan 6 Sistem Gain Dan Kendali kecepatan Motor

percobaan 7 Bi-Directional Kendali Kecepatan Motor

percobaan 8 Efisiensi Kendali Kecepatan Motor

percobaan 9 Isyarat Kesalahan Kontrol posisi

percobaan 10 Pengontrol Posisi Loop tertutup

percobaan 11 Reaksi transien suatu pengontrol posisi

percobaan 12 Pengontrol Posisi dengan umpan balik kecepatan

percobaan 13 Stabilisasi pengontrol posisi tidak stabil

DC Servo Triner Delorenzo Lab Sistem Control1

percobaan 14 Konstruksi suatu pengontrol posisi


Alat bantu Peralatan

Untuk memaksimalkan efisiensi pembelajar, dengan daftar di atas instrumen yang

berikut adalah penting melakukan untuk eksperimen. Para pemakai harus

menyediakan peralatan. Instrumen ini siap tersedia pada paket DE LORENZO

Osiloskop : osiloskop dengan kemampuan jejak rangkap. Jejak yang rangkap harus

bisa mulai menghasilkan X dan Y keluaran pada layar. Pada osciloskop

lebih baik mempunyai suatu penyesuaian variabel untuk mempelihatkan

gambar yang muncul pada layar dengan periode waktu yang lebih

panjang.

Voltmeter : Voltmeter harus mempunyai impedans masukan tinggi. Tegangan DC

diperlukan minimum 15V.


1. Pendahuluan

Pelatih DC servo DL 2305 dari DE LORENZO adalah Kontruksi dengan kontruksi

modul DC servo sistem loop tertutup. Konsep utama DL 2305 sistem adalah untuk

memepelajari DC Servo Loop tertutup dengan modul yang praktis dari para pemakai

dengan mengintegrasikan teori dasar dan tahap demi tahap percobaan dengan

permasalahannya. Untuk memaksimalkan pengajaran, masing-masing bagian

diakhiri dengan suatu ringkasan untuk menyimpulkan apa yang telah dipraktekan.

Konstruksi yang modular pada DL 2305 sangat sederhana dan mudah untuk

melakukan percobaan. Semua percobaan hanya melakukan penyambungan sistem

dengan kabel sesuai dengan petunjuknya. Total 14 percobaan di lakukan dalam

modul ini. Pada akhir manual ini, terdapat karakteristik motor menggunakan DL 2305

dan informasi ini bersifat tambahan

.


2. GENERAL GUIDELINES IN USING ED-4400 SERVO SYSTEM

The following guidelines are common to all experiments in this manual. The

user should be well aware of these guidelines before setting up DL 2305

for actual experiments.

· When modules are placed on a panel for an experiment, there is no

specific location for each module. Modules are placed as the

user prefers. Whenever the servo motor and potentiometer (U-

158) are required to be linked together, make sure it is done

correctly. Otherwise, the motor will experience unnecessary loads.

Make the connection to the low speed shaft (1/60 of the motor speed) by

hand.

· The high speed shaft of the servo motor can adapt the electronic brake

set (U-63). The "0" indication on the brake means the load from the

brake is zero.

· The tacho generator is mechanical ly coupled to the servo

motor. I t generates AC voltage and frequency outputs proportional to

motor's RPM. The Tacho Amp Unit (U-155) converts the

frequency to an equivalent voltage through a WV(frequency-to-

voltage) converter. The converted voltage is used as a feedback

signal.

· When the "OVERLOAD" indicator of the Power Supply Unit (U-156) is on, it

means that there is an excessive current flowing in the circuit. Turn the

power off immediately, and check for the cause of the overload. Throughout

the experiments in this manual, rotating speed is expressed in volts, which is

proportional to the speed.

· In order to display the system response in an easy way, the U-

162 Function Generator generates a ramp signal which is in phase

with the output. Therefore, the internal time reference of an

oscilloscope is not necessary.

· The ± 15V power supply is omitted from wiring diagrams.


· The ± 15V power supply is omitted from wiring diagrams.

· Functional descriptions of each module:

U-151 Dual attenuator (0, 9/10 • •• 1/10 attenuation)

U-152 Summing amplifier (gain : 0 dB, EXT, NET)

U-153 Pre-amplifier (gain : 20 dB)

U-154 Motor driver amplifier (10 watts)

U-155 Tacho Amp unit

U-156 DC power supply ( -±15V 0.2A and Motor Power)

U-157 Potentiometer (Reference) ( 11(S2 or 10 kš2 5W)

U-158 Potentiometer (Motor Coupling) (1k..Q or 10 kS2 5W)

U-159 Tachometer (FS 4000 RPM)

U-161 Servo motor

Motor : 12V, 4.5W

Tacho Generator : Approx. 3Vp-p/4000RPMU-162 Function Generator ( 0.1"1 Hz, 1Hz"10Hz and Ramp output)U-163 Magnet Brake

air gap : 4mm, 10 step variable

input power : AC 220V, 50 60Hz


Module Identifications


Experiment 1MOTOR SPEED AND INPUT CHARACTERISTICS

1. Basic theory

In general, a motor is a machine that converts electrical energy into

mechanical rotation. The key elements of a DC motor are a field winding and

an armature winding. As electric currents flow through the windings, torque

is developed between these two windings. In DL 2305 trainer system, the

field winding is replaced by permanent magnets. The permanent magnets

provide . constant lines of magnetic flux and therefore, the motor speed

becomes only a function of the voltage applied to the armature winding. This

relationship is shown in Figure 1-1.

In Figure 1- 1, the point

"a" occurs because a motor requires a certain minimum voltage to overcome the

mechanical friction from brushes, bearings and other moving parts before it starts to

move. Once the input voltage exceeds the minimum voltage, the speed of the motor

begins to increase in linear fashion as the input voltage is increased. However, this

linear characteristics is not maintained beyond the saturation point. It is because the

counter electromotive force in the armature coil is also increased as the input voltage

is increased, and at some point, any further increase in input voltage does not

produce increased electric currents in the coil.

The motor in DL 2305 system is driven by U-154 Motor Driver Amplifier with U-151


Attenuator as a voltage control. The detection of the motor speed is accomplished by

converting the Tacho output of the motor (U-161) through the F/V Converter (U-155).

The converted output is indicated on the Tacho meter, U-159. The AC output from

the Tacho motor is converted into DC which is proportional to the motor speed

through U-155


2. Experiment. procedure.

1. Referring to Figure 1-2 and 1-3, place the modules needed in the

experiment on flat surface or on top of the DL 2305 cover, and

connect modules as indicated in the figure.

2. Connect the Tacho-meter U-159 across U-155 meter

and GND.

3. Set the angle on U'-157 to 180 degrees.

4. Verify that the line voltage is correct (100V or 220V). Plug U-156

line cord to the power outlet, and turn the power switch ON.

5. Turn U-157 slowly counterclockwise until the motor begins to move.

Record the U-157 position and the input voltage.

6. Increase the input voltage by slowly turning the U-157 clockwise.

For every one volt increment of the input voltage (1V, 2V, 3V .... ),

record the U-159 indication.

7. Make a g raph on i npu t vo l t age vs . mo to r speed us i ng t he

above measurement data.

[Caution] When the motor is saturated, increasing the input voltage will

not increase motor speed. Avoid saturation in this experiment.

8. Make a graph on motor speed vs, motor current using the data

obtained in step 5 and 6. Review the relationships between these two

parameters.

9. Repeat the steps 5 -7 several times to reduce the measurement error.

2. Summary

· The motor speed in a servo system is proportional to the input

voltage.

· The motor current is not l inearly proportional to the input

voltage. At saturation, the motor input current no longer increases

even if the input vol tage is increased. The saturat ion ef fect is


caused by the counter electromotive force in the armature coil.

· There exists a "deadband input voltage; range in a motor,

below which a motor can't start. Motor input voltage is required to

be greater than the largest value of the deadband to initiate motion.

The; deadband is caused by various mechanical frictions in the system.


Experiment 2MOTOR SPEED AND THE LOAD CHARACTERISTICS

1. Basic theory

Typical output ratings of permanent magnet based DC motors range from

a few watts to several hundred watts, and this type of motors exhibit an

excellent power efficiency.

As was mentioned earlier, permanent magnets in the motor provide

constant magnetic flux (KΦ). Therefore, the torque (T) generated in the

motor becomes a function of only the input current (Ia). Also, the counter

emf (electromotive force) of a motor (E a) is generated by the action of

the armature conductors cutting lines of force, and is proportional to the

speed of the motor (Wm). These relationships are nexpressed in the following

formulas.

KΦ=constant .................................. (2-1)

Ea = KΦWm....................................... (2-2)

T = KΦIa .......................................... (2-3)

where KΦ = magnetic flux (line of force) of the permanent magnet

Ea = counter emf in volts

Wm = speed of the motor in rad/sec

T = torque in N.m

Ia = input current in amps

The input voltage and speed of the motor are related to other

parameters according to the following equations:

Vt = Ea+ Ra Ia............................................. (2-4)

………………... (2-5)

where Vt = input voltage in Volt

Ra = Resistance of armature coil in Ohms


It should be noted that the input current increases as the mechanical load of

the motor is increased, resulting in increased input power. Also, the

counter emf keeps the motor speed constant when a motor is not loaded.

The relationship between motor speed and load is illustrated in Figure 2-2.


2. Experiment procedure

1. Referring to Figure 2-1 and 2-3, arrange the modules and connect

them together.

2. Set U-151 attenuator to "8" , and turn the power switch of U-156

on. Adjust U-157 to obtain maximum speed on U-159 without saturation.

1. Attach the aluminum disk to the high speed shaft of U-161 as

shown in Figure 2-4. Raise the electric brake setting on U-163 from

0 to 10 by one step each time, and push the button and measure the

RPM on U-159. See also Step 5.

4. Repeat the measurements in Step 3 by starting from 10, and moving

toward O. See also Step 5.

5. In Step 3 and 4, record the corresponding motor current readings


as indicated on U-156 Power Supply module. This is the current

f lowing between U-154 (Motor Driver Amp) and U-161 (Motor).

6. Plot the data points obtained in Steps 3 and 4, showing the

relationships between brake setting and motor speed and motor currents.

3. Summary

· When a motor is loaded, the speed of the motor decreases, and the input

current increases.

· Overloading a motor causes excessive currents in the motor winding, and

could result in damage to the motor due to the heat generated by the product

of the motor voltage and motor current.


Experiment 3TRANSIENT RESPONSE OF A MOTOR

1. Basic theory

Previous experiments defined steady state motor characteristics. Due

to the existence of non-ideal parameters in the real motors, a motor

can't respond instantaneously to a step input. Instead, a motor responds in

an exponential rise in speed. When the input is removed, the motor speed

decreases linearly to zero. This relationship is il lustrated in Figure 3-1

and 3-2. It 's obvious that the inertia in a motor affects the rate of delay

in response. When an inertia load, such as a flywheel, is added to the rotating

shaft, the response of a motor is significantly slow as shown in Figure 3-2.

These f igures are obtained from an osci l loscope with the motor

input and horizontal time signals as shown in Figure 3-4 are applied to

the oscilloscope. The point "a" in Figures 3-1 and 3-2 indicates where the

motor begins to move. The point "b" is where the motor input is

removed, and the speed of the motor begins to fall.




1. Referring to Figure 3-3 and 3-5, arrange modules and an oscilloscope and

connect them together.

2. Set the oscilloscope for X-Y mode. Apply the Ramp output from U-162 to the

X-input of the oscilloscope.

3. Set the frequency of the Function Generator (U-162) to 0.1Hz.

4. Turn the power of U-156 on.

5. Adjust the gain of X-input (CH2) of the oscilloscope for proper display on the

screen.

6. Adjust U-151 to set the motor speed which is indicated on U-159 below

saturation. If necessary, use U-157 instead of U-151.


7. Adjust the gain of Y-input (CH1) of the oscilloscope for proper display on the

screen.

8. Observe the trace on the oscilloscope.

9. Turn the power off (U-156). Attach a flywheel to the high speed shaft of U-

161. Turn the power on, and observe the trace on the oscilloscope.

10.Move the flywheel to the low speed shaft of U-161, and repeat the above

experiments.

11.Plot the obtained data.

3. Summary

· Unlike an ideal motor, real motors respond to a step input with an exponential

rise in speed.

· The rotational inertia in the motor affects the transient response of a motor.

The larger the inertia, the worse the response.


Experiment 4OPERATIONAL AMPLIFIERS

1. Basic theory

A closed loop servo system needs information as to how much the output

speed of the motor is different from the preset input. The detected

difference is returned to the system controller as an error signal. Once the

amount of error is defined, the closed loop reacts in a way to reduce

the error , and the loop repeats the process until the error detected

becomes zero. The error detection is done by comparing the input and

sampled output voltage using an operational amplifier.

The key elements of an operational(OP) amplifier circuit are the resistors

and the gain of the amplifier itself which is typically in the range of 1000

to 100,000. Several OP amp circuits using U-152 Summing Amplifier

Unit are shown in Figure 4-1. Because the gain of the amplifier "A" is

very large, the output of the amplifier is given by the following equation.



In equation (4-1), it can be seen that when R 1 = R2, the output Vo

becomes the sum of the inputs. Also when a voltage divider network is used

as in Figure 4-1 (b), the Vo can be scaled down by a factor of with the

a representing the ratio between the divided resistance to the

entire resistance of the divider network. When a capacitor is

placed in the feedback path in parallel with a resistor, as in Figure

4-1 (c), the response of the output to a step input is affected by the

time constant of the RC network. In this case, the output Vo is

obtained from;

where …………………. (4-2)

The above expression of Vo assumes that the Vo does not exceed

12V supply voltage. In U-152, setting the selector switch to "a" will

configure the amplifier to Figure 4-1 (a) with R 1 = R2. When the

selector is set to "b" , the amplifier will be configured to Figure 4-1 (c)

-with R1 = R2, and CR2 = 0.1 second. In this experiment, only Figure 4-1

(b) circuit is utilized.



1. Referr ing to Figure 4-2 and 4-3, arrange the necessary modules

and connect them together.

2.Set the selector switch of Summing Amp U-152 to "EXT" .


3. Using a high input impedance (1 Mohm or larger) vol tmeter or

an oscilloscope, measure the voltage at U-157 and U-158 terminals

(slide side). Adjust the voltage to O.

4. Set U-151 to O.

5. Measure the output of the U-152 using a high input impedance

voltmeter. Make sure the output is at near 0 (around O.01V).

2. Adjust such that the outputs of U-157 and U-158 are +1V respectively.

3. Measure the output voltage of U-152, and observe the relationships to

the input.

4. Set U-151 to "5" , and measure the output of U-152.

10. Set U-151 to "0" . Vary the output of U-157 and U-158. Check

the summed output appearing at U-152.

11.Observe how the U-151 position affects the input and output

relationships. When the polarity of the output changes to "-" ?

Examine the summed output value.

12.Notice that when U-151 is set to "0" , Rl a = R2 and the gain

becomes unity (one). When U-151 is set to "10" , the gain is at

maximum because R2 is maximized.

3. Summary

· An operational amplifier is a linear Amplifier. 'rile output is proportional to

thc input, and inversely proportional to the negative feedback.

· Operational amplifiers are used in error detection circuits where more

than two signals are compared and added together. The high input

impedance of an operational amplifier results in negligible signal loss.

The summing output includes the polarity of the input signals.


Experiment 5CLOSED LOOP MOTOR SPEED CONTROL TECIINIQUES

1. Basic theory

Quite often, when a motor is used as a source of mechanical force, the motor

is required to provide constant speed regardless of the change in loads. A

closed loop speed control system is a self-regulating system in which the

measured speed of the motor is compared to the preset value to produce an

error output. The detected error voltage is, then, amplified and fed back to

the control circuit to compensate the di f ference between the actual and

preset speed. This self-correcting process continues until the detected

error' voltage becomes zero. At this point, the actual speed of the motor is

equal to the preset speed, and the motor maintains a constant speed.

Compared to the closed loop system, the systems built in the previous

experiments are identified as an open loop system.

The conceptual difference between an open laop and closed loop

systems is graphically illustrated in Figure 5-1.


In Figure 5-1, it 's clear that a system with feedback is far superior than


an open loop system in maintaining a constant speed against load variations.

In a closed loop system, it's important that the error signal is amplified to

a proper level to eliminate "deadband" effect. For this reason, the error

signal is amplified before it arrives to the input of the Servo Driver (U-

154). Also it is critical that the feedback signal is 180 degrees out of

phase to the reference signal to maintain proper control.


1. Referring to Figure 5-2 and 5-3, arrange the required modules and


2. Set the selector switch of Summing Amp U-152 to "a" .

3. Set ATT-2 of the U-151 to "10" to prevent Tacho output from entering

the system. Set ATT-1 to "5" .


2. Adjust U-157 to obtain about one half of the maximum speed. This is

same as setting for 2500 RPM on U-159 meter.

3. Attach an electronic brake U-163 as was done in Figure 2-4. With

the brake's setting increased by one notch at a time, record the RPM

reading at each setting.

4. Measure the error voltage at each brake setting.


[Note] There is no feedback signal at this point. Therefore, the error

Voltage will vary only when the preset speed is changed to a different

value.

8. Set ATT-2 of U-151 to "5" . Adjust U-157 to obtain the same speed

as in Step 5 (around 2500 RPM) .

8. Measure the Tacho output and error voltage at different brake points.

Plot the data points on the chart provided in Figure 5-4.

9. Change ATT-2 setting to "0" . Adjust U-157 to obtain 2500 RPM.

10.Measure the speed and error voltage at each brake setting, and plot

the data on the chart.

11.Compare the results between Steps 3-7 and Steps 8-11. Notice that the

loop was closed for Steps 8 through 11.

3. Summary

· In a c losed loop system, reduct ion in motor speed due to a load

is compensated, within the limit, by an error signal which is proportional

to the drift of speed and is 180 degrees out of phase to the reference setting.

· Excessive feedback signals will reduce the reference setting.

Therefore, the feedback signals at the input of the summing amp can't

be larger than the reference signal. The feedback signal should be

adjusted to the right level for given load and amplifier gain.


Experiment 6SYSTEM GAIN AND MOTOR SPEED CONTROL

1. Basic theory

A simplified diagram of a closed loop constant motor speed control

system is shown in Figure 6-1. As the reference or control voltage is

applied to the input of the comparator, and the Tacho generator produces a

signal which is equivalent to the speed of the motor, the two signals are

compared at the input of the summing amplifier through addition of two

signals with opposite polarity. The output of the comparator is, then, an

error signal which represents the difference between the preset and

actual speed. Because the error signal is out of phase to the reference

signal, this signal compensates the motor speed in the direction to achieve

a constant speed.

In general, the speed of a motor and the error signal have the following relationship.

θo = KE ……………………………………..(6-1)

Where θo = the motor speed

E = error signal K = system gain

K = system gain


The error signal is defined as:

E= V ref - Kgθ0 …………………………. (6-2)

where Vref = reference voltage

Kg θ0 = output of the Tacho generator

Replacing E in (6-1) with (6-2) yields;

θ0 = K(V ref - Kgθ0) ………… (6-3)

θo = K • Vref - K • Kg θ0

……………… (6-4)

In case the K is very large in forward direction, Equation (6-4) is reduced to;

…………………. (6-5)

From equation (6-5), it's clear that for a given Tacho generator constant Kg,

the motor speed is linearly proportional to Vref only, and is not dependent

on the deviation of the system gain. This is the most beneficial advantage

of a closed loop motor speed control system.

Similar relationships can be developed for the error signal in a closed


loop system. Replacing 60 in (6-2) with (6-1),

E = Vref - Kg K • E ………………….. (6-6)

… … … … … … … . ( 6 - 7 )

Equation (6-7) indicates that the error voltage E can be reduced when the

gain K is increased.

In a practical system, maintaining a high system gain means reduction of

the deadband, as well as desensitizing motor speed to the load changes.

Although large system gain is desired in general, the gain should be

l imited to an acceptable level. when the gain is beyond the acceptable

level, the transient characteristics of the system wil l suffer, and it wil l

cause irregular motor rotation.

The relationships between load, error and motor speed are shown in Figure

6-2 at two different system gain levels.


F o r a n e q u i v a l e n t s y s t e m d i a g r a m o f F i g u r e 6 - 3 , t h e o u t p u t o f

t h e Frequency-to-Voltage converter U-155 should be large enough to

provide sufficient feedback signal. Otherwise, the motor will not run at

constant speed. Also, when the gain of the amplifier U-153 is low, the

system response will be slow and the "deadband" effect wil l get worse.

However, in case the gain is too high, the system will become unstable.



2.Experiment procedure

1. Referring to Figure 6-4, arrange all the modules and an oscilloscope

and connect them together.

2. Set the selector switch of U-152 to "a" .

3. Set ATT-1 of U-151 to "9" and ATT-2 to "10" . This wi l l minimize

the reference setting, and the feedback will be almost zero.

1. Turn the power of U-156 on. Adjust U-157 to approximately one half

of the maximum motor speed (2500 RPM).

2. Referring to Figure 2-4, attach the disk brake to the high speed shaft

of the servo motor, and set the brake to "0" . Raise the . , brake

setting by one increment, and each time, press the brake button

and measure the motor speed and the associated error signal.

6. Set the U-151 A T T - 2 to "5" . Adjust the motor speed to 2500 RPM, and

repeat Step 5. Plot the data obtained in Figure 6-5 (a).

Notes : The same motor speed can be obtained by increasing the reference

signal level and decreasing the amplifier gain. However, this method

will reduce the amount of feedback control signal and thus decrease

the over-all ability to control the system.

7. Using U-157, set the motor speed to 2500 RPM. Set U-151 ATT-2

to "5". Adjust ATT-1 from 0 to 9, and measure the error voltage at each

point.

8. For each point of ATT-1 setting, hold the high speed motor shaft by

hand and repeat the experiments in Step 7. Compute the error

deviation ratio as defined by the following equation, and plot the results in

Figure 6-5 (b).

Note


3. Summary

· In a closed loop servo system, lower system gain produces larger

error voltage, reducing controllability a constant motor speed.

· Constant motor speed is obtained when the detected motor speed

signal is equal to the preset reference signal. As a motor approaches to

constant speed operation, the magnitude of the error signal becomes

very small. Therefore, the gain of the error amplifier requires to be large.


Experiment 7BI-DIRECTIONAL MOTOR SPEED CONTROL

1. Basic theory

The closed loop speed control system that has been investigated so far

has negative feedback based speed control ability only in one direction.

However, in real applications, motor speed control requires to be available in

both directions: forward and reverse. The motor used in DL 2305 changes

its direction as the input polarity changes. The error signal polarity follows the

input polarity change at the same time.

The direction of the rotation is determined by the position of the

potentiometer setting referenced to O. The speed of the motor which should

be constant after proper regulation is linearly variable as a function of the

potentiometer setting.

Figure 7-1 shows the bi-directional response of a motor at two different

loads when a squarewave input signal is applied to the system. The curves

labeled as "1" represent the response in forward direction, and the curves

labeled as "2" represent the response in reverse direction.

The Tacho output in DL 2305 is an AC signal which does not discriminate


the direction of the motor. However, when the AC Tacho output is

converted into DC in U-155, the input polarity is monitored and correct

polarity is assigned to the converted DC signal.



1. Referring to Figure 7-2, arrange necessary modules and connect

them together. Set U-152 switch to "a" .

2. Set ATT-1 of U-151 to "10" , and ATT-2 to "6" or "7" . Adjust U-

157 dial to the mid point (180 degrees). Turn the power of U-156 on.

1. Turn the dial on U-157 to left or right from its 180 degree position

and observe the motor direction. Bring back the dial setting to 180

degrees. Stop the motor by adjusting the Zero Count of U-153. When

the motor stops, fix the Zero Count setting.

2. Turn the dial on U-157 clockwise until the motor speed reaches one

half of the maximum speed. Increase brake setting from 0 , and

record the motor speed at each brake setting. Insert an ammeter

between U-154 output and U-161 and record the current reading at each

brake setting.

1. Turn the dial on U-157 counterclockwise until the motor speed reaches

one half of the maximum speed. Repeat experiments as described in Step 4.

2. Plot the data obtained in Steps 4 and 5.

3. Set the U-157 dial to 180 degree position. Set U-162 frequency to

0.2Hz. Reduce ATT-1 of U-151 from 10 to 5. Observe the motor

changing i ts direction for every 2.5 seconds.

4. Apply U-155 output to Y- input of an oscilloscope, and U-162 Ramp

output to X-input of the osci l loscope. Adjust X and Y input gains

for proper display.

1. Increase the load (brake) and observe the trace on the

oscilloscope. Turn U-157 slightly to left as well as right from 180

degree position, and observe the trace on the oscilloscope. Set U-157

back to 180 degrees.

10. Set U-152 switch to "b" and repeat Steps 7 through 9. Compare the

difference in waveforms on the oscilloscope between setting "a"

and setting "b" . Sketch the difference.

Note : when U-152 switch is in posit ion "b", the system

response is delayed and may cause oscillation in servo motion.


11.Set ATT-1 of U-151 to "7" or "8", and change ATT-2 from "5" to "9". Observe

and sketch oscillation pattern in servo motion.

Note : It should be observed that as delays are introduced into the system,

oscillation lasts longer as feedback is increased.

3. Summary

· The rotational direction of a DC servo motor can be changed depending upon

the polarity of the control input signals.

· For a bi-directional motor, the motor speed is not the same between identical

forward and reverse direction settings of U-157 (same magnitude of input

signals).

· Any delays in a servo system will slow down the system response and will

cause oscillation. The duration of oscillation depends on the magnitude of the

feedback.


Experiment 8MOTOR SPEED CONTROL EFFICIENCY

1. Basic theory

The key elements affecting motor speed control have to do with deadband and

system response time. So far, previous experiments demonstrated that a higher gain

has minimized the deadband effect, and improved over-all system response time. In

a practical system, the existence of time constants in the system can add to the

delay. Time delays in the error channel means the error signal can't change fast

enough to catch the change in speed. Such a characteristic has been experimented

with U-152 selector switch set at "b" .

Closed loop motor speed characteristics can be made visual on an oscilloscope.

Some of the characteristic curves are shown in Figure 8-1. when the system gain is

large, the system response is very good as shown in Figure 8-1 (a). The error

voltage in this case is significant only when the motor changes its direction, as

shown in Figure 8-1 (b). However, when the gain is not sufficient, the response of the

motor slows down with the final speed reduced than before as in Figure 8-1 (c). Also

the error is significantly increased throughout the operation period as shown in

Figure 8-1 (d).


The effect of time delay in the error channel is displayed in Figure 8-2 (a) and (b). It's

clearly demonstrated that the time delay in the error channel causes oscillation in the

system. Oscillation also occurs in the error signal.

When a motor is mechanically loaded, by a brake in this experiments, the motor

reaches the same final speed as it would without a load, ..but at a slower pace as

shown in Figure 8-3 (a). The corresponding error signal is displayed in Figure 8-3

(b). When the load exceeds the rated value, it will overload the system power supply.

Finally, some of the oscilloscope output due to an injection of electrical delay, by

selecting U-152 switch to "b" , is shown in Figure 8-4 (a) and (b).




1. Referring to Figure 8-5, arrange necessary modules and connect them together.

Set U - 152 switch to "a" and do not connect the squarewave output ( )

of U-162 at this time.

2. Set ATT - 1 and ATT - 2 of U - 151 to "0" . Set U - 157 to exactly 180 degrees to

make the output ±OV.

3. Turn the power of U - 156 on. In case the motor turns, stop the motor by

adjusting U - 153 Zero Adjust.

4. To measure the deadband, turn the control on U - 157 from its 180 degree

position to first clockwise until the motor begins to move. Record the position,

and return back to 180 degree position. Turn U - 157 control to

counterclockwise this time, and find the angle where the motor begins to move.

Add two angles together.

Set ATT - 1 of U - 151 to "9" and repeat the above procedure. Compare the

difference in deadband between two ATT - 1 settings.

5. Set ATT - 1 and ATT - 2 to 5 respectively. Set U - 157 to stop position (180

degrees). Apply the squarewave output ( ) of U - 162 to the input of U -

152, and set the frequency to 0.1Hz. Connect the Ramp output to X-input of an

oscilloscope. Adjust the gains of X - and Y - inputs to see the Tacho output and

the error signal on the oscilloscope. Repeat this experiment with ATT - 1 set to

"0" first, then to "9" . Sketch the outputs obtained on the oscilloscope.

6. Set U-152 switch to "b" . Measure the Tacho output and error signal at "0" as

well as "9" position of ATT - 1. Sketch the output, and compare the results

between the switch setting of "a" and "b" .

7. Reset U-152 switch to "a" . Set ATT - 1 to "3" . With ATT - 2 set to "0" first, then

to "9" respectively, and U - 162 output connected as in Step 5, observe the

results on the oscilloscope.

8. Set U-152 to "b" . Repeat the experiments in Step 7. Compare with the results of

Step 7.

9. Set U - 152 switch to "a" . Attach a flywheel to the high speed shaft of U - 161.

Set ATT - 1 and ATT - 2 to "5" respectively. Observe the Tacho and error

signal on the oscilloscope .

10. Repeat Step 9 with ATT - 2 set to "9" .


11. Set U - 152 switch to "b" , and repeat Steps 9 and 10.

3. Summary

· The impact on the system performance, due to the time delay in the amplifier

and the load change, has been experimented in this section. An oscilloscope

with an X - Y display is used to display the relationships between two

variables more effectively. Optimum settings of the system parameters to

maintain stable and constant speed have been experimented also.


Experiment 9ERROR SIGNALS IN A POSITION CONTROLLER

1. Basic theory

The basic function of an angular position controller is to provide an output angular

position signal which precisely follows the input angular position signal. The input or

output position information is expressed in terms of the selected angle around a

circle.

To achieve the control function, its necessary to rotate a motor until the signal

detected for the motor position is equal to the signal representing the reference or

the input position. A potentiometer is used to convert the angular position to an

equivalent electrical signal. Figure 9-1 shows a circuit diagram which utilizes

potentiometers as an angle-to-voltage converter.

The Pi in the figure is the input potentiometer, and Po the output potentiometer. The

amplifier (-A) is configured as an inverting amplifier. Due to the polarity applied to P i


and Po, when the input and output positions are identical, the output of the amplifier

becomes zero.

In general, when the angular position of P i is 8 i, and θi. is the angular position of Po.

Also the relative angular position error between P i and Po is defined as (θi – θo). The

converted and amplified output of the error from the amplifier can be set to Ke (θi –

θo), where Ke represents a conversion factor. Ke can be determined for a given

system when the actual output voltage of the amplifier is measured.

A closed loop control system can be formed when the error signal is further amplified

and applied to a motor. As the motor reacts to the incoming error signal, and also the

motor is coupled to the output potentiometer Po, the loop is closed. As the loop is

closed, error detection and associated motor reaction processes continue until the

error signal is reduced to zero.



1. Referring to Figure 9 - 2, arrange modules and a voltmeter and connect them

together.

2. Set U - 157 and U - 158 dials to 180 degrees.

3. Turn the power of U - 156 on. Set U - 152 switch to "a" .

4. Measure the voltage at the rotating contacts of U - 157 and U - 158. In case

the voltage is not zero, adjust each dial for zero reading.

5. Measure the output of U - 152. It should be zero.

6. Turn U - 157 clockwise 15 degrees (same as 195 degrees), and measure the

U - 152 output voltage. Repeat the process at 5 degree increment for up to 30

degree (120 degree) position.

7. Keep U - 157 as in Step 6. Turn U - 158 clockwise 5 degrees each time and

measure U - 152 output voltage. Make sure the U - 152 output is zero when

the relative position of U - 157 and U - 158 is identical. Measure the contact

voltage of U - 157 and U - 158 (P1 and P2).

Note : The voltage polarity of U - 157 and U - 158 is opposite each other for

the same direction of rotation.

8. Repeat Steps 6 and 7 for counterclockwise rotation.

9. Plot the relationships between the positional difference and corresponding

error voltage.

3. Summary

• The output of the summing amplifier produces zero output when the two inputs

are same in magnitude but opposite in polarity (Vo = V1 + (-V2)).


Experiment 10CLOSED LOOP POSITION CONTROLLER

1. Basic theory

In a closed loop position controller system, the positional information from an output

potentiometer (Po) which is mechanically coupled to a motor is fed back to a control

amplifier. Then, the reference position input from the input potentiometer (P i) is

combined with the feedback signal at the input of the amplifier which drives the

motor in proportion to the difference between two signals. When the two positions

are identical, the output of the amplifier becomes zero.

A simplified system diagram of a closed loop position controller which will be used in

this experiment is shown in Figure 10-1.

There are three amplifiers in Figure 10-1. The Al is an error signal generator, A2 is

an error signal amplifier and A3 is the driver for the motor M. As P i is turned away

from Po, the difference between two potentiometer voltages become an error signal

which appears at the input of Al. The error signal is further amplified through A2 and

A3, and drives the motor in the direction to reduce the error voltage between P i and

Po. Therefore, as Pi is turned clockwise, Po follows the same direction. This feedback

action continues until the output of Al is reduced to zero. At this point, the voltage

measured at Pi and Po are same but in opposite polarity. For example, if P i is at +3V,

then Po is at -3V, making the sum of two zero.

The final relative position between Pi and Po depends upon the gain of the amplifiers.


For a large gain, the position of Po can be almost equal to the position of Pi. But

when the gain is not sufficient, there can be an offset in the relative position. This

offset is the "deadband" for a position controller.



1. Referring to Figure 10-2, arrange the modules, including coupling of U-158 to U-

161, and connect them together.

2. Set U-152 switch to "a" and U-151 to "10" . Turn the power of U-156 on. Set U-

157 dial to 180 degrees.

3. Adjust U-153 to make the output of U-154 zero. Once the adjustment is done, do

not alter U-153 setting.

4. Set U-151 to "9" . Within -±20 degrees from the original 180 degree setting, turn

U-157 either clockwise or counterclockwise, and see if U-158 follows the

movement. U-158 motion should lag U-157. In case U-158 leads U-157, switch

the wires of U-161 motor.

5. Turn U-157 clockwise from 0 degree position by 10 degree increment up to 150

degrees. Measure the angle of U-158 at each position of U-157. Repeat the

measurements with U-157 turned counterclockwise. Calculate the offset error

angle between U-157 and U-158 at each position.

6. Increase the system gain by setting U-151 to 7, 5, 3 and 1. At each U-151

setting, repeat Step 5 experiment. Observe the change in offset error angle as a

function of the system gain.

7. Plot the results of Steps 5 and 6. Plot the relationships between system gain and

deadband.

3. Summary

· Reducing the system gain worsens the deadband as well as the offset error.

· Increasing the system gain improves the system response and reduces the

offset error.

· Angular resolution of P; and Po affects the position control accuracy. To

improve the resolution, a potentiometer is required to have larger

circumference and the winding is prefered to have large number of turns.


Experiment 11TRANSIENT RESPONSE OF A POSITION CONTROLLER

1. Basic theory

When a step input is given to a position controller, the loop takes time to react to the

applied input. Also, depending upon the given system parameters, oscillation can

occur at the output during the transient time period. The major cause of the time

delay comes from the added inertia of the moving parts. Therefore, the higher the

inertia, there will be more delay.

Usually, the system gain is preferred to be high to improve system response time.

However, when the gain becomes excessive, it will cause undesired overshoot at the

output.

Transient response of a system can be easily observed on an oscilloscope when the

system is stimulated with a squarewave input. Such an arrangement is shown in

Figure 11-1.


The function generator in Figure 11-1 provides synchronized squarewave and ramp

signals. As it is shown in the figure, the ramp signal is used to drive the X - input of

an oscilloscope. When the output voltage from Po is fed into the Y - input of the

oscilloscope, transient response curves as shown in Figure 11-2 can be obtained. To

get the best results, it is recommended that the frequency of the squarewave be kept

below 1 Hz.




1. Referring to Figure 11-3, arrange the modules and an oscilloscope, and


2. Set U - 151 to "10" . Set U-152 to "a" . Turn the power of U - 156 on.

3. While monitoring the output of U - 153 with a voltmeter, adjust U - 153 for

zero output.

4. Set U - 162 frequency to 0.2Hz. With an oscilloscope in X - Y mode, adjust

the horizontal range for best display on the screen.

5. Set U - 151 to "8" and observe U - 158 turning to left and right. Adjust the

Y-input of the oscilloscope for best display. Sketch the trace on the

oscilloscope on a piece of paper.

6. Set U-151 to 6, 4, 2, 0 in sequence and observe impact on the trace at

each time. Sketch each trace on a piece of paper. At what gain setting

oscillation appears in the trace ?

7. Set U - 152 switch to "b" , and repeat Step 6. Sketch the resultant

response.

8. Attach the flywheel to the high speed shaft of the servo motor. Set U - 152

switch to "a" , and repeat Step 6. Sketch the resultant response.

3. Summary

· When the system gain is low, the rise time (tr) in Figure 11-2 is long. This

means that the response of the system is slow.

· As the system gain is increased, the response of the system improves.

However, if the gain is too high, it will cause overshoot in the response.

· When the load to a motor is an inertia type, it will slow the transient response.

Even if there is a delay in the transmission characteristics, oscillation can still

take place in the system response.


Experiment 12POSITION CONTROL WITH SPEED FEEDBACK

1. Basic theory

When the gain is raised in a position control system to minimize the deadband effect,

the closed loop system responded with an overshoot which resulted in undesired

system oscillation. One way to mitigate oscillation is to add a brake which is

proportional to the speed to the output shaft. The brake method may produce a

satisfactory result. However, it consumes a significant power and makes acceleration

of the load difficult.

Better way of preventing oscillation is to add a speed control loop to the position

control loop. The speed control loop provides a negative feedback signal from the

output of the Tacho generator which is proportional to the speed of the motor.

The effect of adding a speed loop is illustrated in Figure 12-1 (a), (b), and (c). - An

optimum control of the speed feedback loop produces a system response as shown

in (b).


An actual system with both the speed and position control loops is shown in Figure

12-2. As it can be seen in the figure, this system is essentially the same system as

experimented in the previous two sections, except that one more loop which is

consisted of the Tacho circuit and VR2 is added. To obtain the waveforms in Figure

12-1, it is needed to replace the input potentiometer with a squarewave input and

connect Po signal to an oscilloscope,




1. Referring to Figure 12-3, arrange the modules and an oscilloscope, and connect

them together.

2. Set ATT-1 and ATT-2 of U-151 to "10" respectively, and set U-152 switch to "b" .

3. Turn the power of U-156 on. Using U-153 Zero Adjust, set the output of U-153 to

"0" . Set an oscilloscope to X-Y mode. Also set a Function Generator to 0.2Hz.

Adjust the oscilloscope X and Y inputs for best display.

4. Increase the system gain by changing ATT-1 from "10" toward "0" until

oscillation is observed. Place ATT-1 right before where oscillation takes place.

5. Change ATT-2 from "10" to "0" . Observe the pattern on the oscilloscope and

sketch the pattern on a piece of paper.

6. Set ATT-1 to half of the gain setting in Step 4, and repeat Step 5.

7. Set U-153 output switch to "a" , and repeat Steps 4 and 5. Compare the

difference in servo time delay.

3. Summary

· A position control system without a speed control loop can generate

oscillation when the system gain is too high. Adding a speed control negative

feedback loop can stabilize the system.


Experiment 13STABILIZING AN UNSTABLE POSITION CONTROLLER

1. Basic theory

For a properly designed system, the transient response effect should gradually

decay within a few seconds, and the system should reach a steady state operation.

However, for an improperly. designed system, the transient response can lead into

an oscillation which can be sustained over a long period of time. Such a system is

unstable and should be corrected for a stable operation.

The instability of a system is mainly caused by either A long time constant in the

system, or an excessive gain in the system. A closed loop speed controller can

mitigate oscillation up to certain extent. However, in case a highly stable system is

desired with a maximum gain, the system needs more advanced technique than a

simple speed control loop. The experiment in this section is limited to a speed

controlled stabilization method. The same experiment system as in the previous

section is used for this experiment.




1. Referring Figure 13-1, arrange all modules and connect between them. Make

sure the coupling of U-161 and U-158 shaft is straight.

2. Set ATT-1 and ATT-2 (U-151) to "10" respectively. Set U-152 switch to "b" and

turn the power of U-156 on. Also set the Function Generator frequency to O.1Hz.

3. Set the Zero Adjust of U-153 so that the output of U-153 is zero. Set an

oscilloscope for X-Y mode operation.

4. Scan ATT-1 from "10" to "0" , and find a place where oscillation begins to take

place in the system. Leave ATT-1 where oscillation occurs.

5. Adjust ATT-2 to stop oscillation. Explain why oscillation has stopped.

6. Turn U-156 off. Keep U-152 switch at "b" .

7. Set both ATT-1 and ATT-2 to "10" . Remove the squarewave output of U-162

from U-152 input. Connect U-157 output to U-152 input as indicated by the

broken line in the figure. Set U-157 to 180 degree position. Turn the power of U-

156 on.

8. Turn ATT-1 of U-151 from "10" to "0" . Find a place where system begins to

oscillate. Leave ATT-1 slightly before where oscillation starts.

9. Quickly turn U-157 clockwise about 30 degrees, and observe U-158. In case U-

158 oscillates, adjust U-158 to eliminate oscillation.

10.Set U-152 switch to "a" and repeat Steps 8 and 9. Compare the results.

11.Maximize the speed feedback by setting ATT-2 to "0" . Set U-152 switch to EXT.

Oscillation may occur due to excessive gain.

12.With U-152 switch left at EXT, connect a 1 MD variable resistor to NET

terminals. Vary R and observe the results.


3. Summary

A. Typical problems associated with a position control servo system:

· Increased position error and slow response when the gain of the error

amplifier is not sufficient

· Increased position error, slow response and unstable oscillation due to

excessive delays in the system

· Oscillation or vibration due to an overshoot during transient time period

· When a servo motor is loaded with an inertia type . load, the system response

is slow. Also, instability occurs in the system due to the phase shift of the

feedback signal.

B. Requirements for a stable position control operation:

· Optimum system gain

· Optimum speed feedback

· Avoid inertia type load

· Reduce delay parameters in the system


Experiment 14CONSTRUCTION OF A PRACTICAL POSITION CONTROLLER

1. Basic theory

This section is the conclusion of all the preceding experiments. A practical and

working position controller will be built in this section. The key considerations for a

stable position controller are reviewed below:

Avoid excessive system gain.

1. Optimum system settings between a moderate transient response and the

response time.

2. Increased error due to insufficient system gain

3. Response time vs. delay parameters of the system

4. The impact to a servo motor due to inertia and torque

5. Phase relationship between feedback signal and control input signal. When

these two signals are in phase, then oscillation would occur in the system.


1. Referring to Figure 14-1, arrange modules and connect them together.

2. Observe the relationship between the speed feedback (ATT-2 adjust) and the

response time.

3. Observe the relationship between the speed feedback and transient

suppression.

4. Observe the relationship between the system gain ( ATT-1 adjust) and response

time.

5. Observe the relationship between the system gain and the position control error

signal.

6. Turn slightly the position control input potentiometer from "0" position to either

left or right. Also try the following either increase the amplifier gain significantly,

or reduce the speed feedback to improve the response time. Explain why

oscillation tends to occur at "0" position.










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Lab Sistem Kontrol Servo Ind