Visio-TCS1 Control Block Diagram 12 12...

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TCS1 Control Block Diagram

University of HawaiiInstitute for Astronomy

TCS1-CBDTITLEDWG #

-REV

ENGINEEREric Warmbier

LAST EDIT12/12/2007 5:57:32 PM

SHEET

1 of 25SIZE B

REVISION BLOCKREV DESCRIPTION DATE INCORP. BY

OVERVIEW

The goal of this document is to present the TCS1 control system in a clear and understandable way and to derive the transfer functions to be used in SIMULINK.This document format combines notes, graphs, plots, graphics, etc. all on one page. It is not a traditional report style format.

The method used to present this material was to:1) Present a hybrid block diagram of the entire system on one page. The block is not 100% mathematically or functionally correct. It is meant to present the system in an understandable way.2) Explore each block or group of blocks, understand the function, and derive the transfer function for use in SIMULINK.

NOTE: Because of the way the blocks are implemented physically (e.g. inverting summer amplifier) the negative signs on some transfer functions may not show up in the SIMULINK model. For example, an inverting summing amplifier followed by an inverting amplifier with a gain of -1 can be simply shown as a simple summer. SO, keep in mind that if a negative sign is dropped, either the input has already been inverted into the block or its output will be inverted in the next block.

TABLE OF CONTENTS

PAGE BLOCK DESCRIPTION1 - TITLE PAGE (THIS PAGE)2 - OVERALL BLOCK DIAGRAM3 1 & 2 COMMAND RECTIFIERS, PRE-LOADS, HIGH FREQUENCY TACHOMETER COMPENSATION4 3 TACHOMETER & TACHOMETER INPUT BUFFERS5 4 TACHOMETER SUMMER CIRCUIT6 5 ACCELERATION LIMITER7 6 MOTORS & BULL GEARS8 6 MOTOR DATASHEET9 7 COMMAND MAGNITUDE LIMITER (SLEW or OFFSET)10 8 POWER AMPLIFIER MOTOR DRIVER11 9 MAIN SUMMING BLOCK (PROPORTIONAL GAIN, INTEGRATOR, SLEW FEED FORWARD)12 10 INCREMENTAL ENCODER & FRICTION GEAR13 11 PROPORTIONAL GAIN14 12 INTEGRATOR WITH SHORTING AND OFFSET FEED FWD PULSES15 12 OFFSET FEED FWD PULSE EXPLANATION16 13 DIGITAL TO ANALOG CONVERTER17 13 COMPUTER/DIGITALLY GENERATED CONTROL SIGNALS (SLEW, OFFSET, POSITION ERROR)18 - UNIT CONVERSIONS (SUMMER VOLTS to RAD/S & RAD/S to ARCSEC/S)19 - APPENDIX: ABSOLUTE POSITION ENCODERS20 - APPENDIX: TCS1 BLOCK DIAGRAM CIRCA 198021 - APPENDIX: IRTF 123 - TELESCOPE SERVO CONTROL HA COMPUTER CMD & MAGNITUDE DETECT22 - APPENDIX: IRTF 125 - TELESCOPE SERVO CONTROL HA SEQUENCE CONTROL BOARD23 - APPENDIX: IRTF 127 & 128 - TELESCOPE SERVO CONTROL D/A, JOYSTICK, & INTEGRATOR24 - APPENDIX: IRTF 130 - TELESCOPE SERVO CONTROL TACH SUMMER & TORQUE CMD25 - APPENDIX: IRTF 131 - TELESCOPE SERVO CONTROL DEC TACH SUMMER & TORQUE CMD

DAC-10

1014 bit

1.96(1.33)

Low Pass

1.59 kHz

Compensator.839(1.0)

Low Pass

338 Hz

Mag Limit

11

-11

+++++

+8V0V

FD FWD EAST

-8V0V

FD FWD WEST

+++++

.839(.513)

Low Pass

338 Hz

SWITCH

(active low)

SWITCH

(active low)

SLEW EAST/

SLEW WEST/0V

0V+8V

-8V

6.26(12.1)

6.26(12.1)

Low Pass

338 Hz

Low Pass

338 Hz

SWITCH

(active low)JoystickCircuit

0V

HA CLEAR INTEGRATOR

Integrator

Ki=

∫ dttvKi )(RESET

.002

Integrator

Ki=

∫ dttvKi )(RESET

0.02

Integrator

Ki=

∫ dttvKi )(RESET

0.02

4.7(4.7)

Low Pass

338 Hz

Mag Limit

ADJ

ADJ

POSITIVELIMIT

NEGATIVELIMIT

Low Pass

468 Hz

+-

Mag Limit

11

-111000 1000Mag Limit

4.5

-4.5Integrator

Ki=

∫ dttvKi )(RESET

330k680k

SWITCH

(active low)

SWITCH

(active low)

0VBUF EAST SLEW DISABLEBUF EAST MOTION DISABLE

Adj 0 to 0.5VAdj 0 to 8V

G=5

SWITCH

(active low)

SWITCH

(active low)

0VBUF WEST SLEW DISABLEBUF WEST MOTION DISABLE

Adj 0 to -0.5VAdj 0 to -8V

G=5

HA CLEAR INTEGRATOR

0.35 V (on output)

Adj. pre-load

AMPLow Pass

240 Hz

Mag Limit

10

0

AMPLow Pass

240 Hz

Mag Limit

10

0

Low Pass

723 Hz

Low Pass

723 Hz

++

Low Pass

3.77 Hz

Bandpass

8.6Hz 240Hz

Bandpass

8.6Hz 240Hz

++

++

MOTOR

MOTOR

Tele-scope

Mount

.2105.2105

5.36 5.36

Tach

Tach

MECHANICAL

OPPOSING MOTORS -APPLY TORQUE IN

ONE DIRECTION ONLY

CompensatorCompensator

2

1

2

1

2 12 1

2 1

2

1

WEST

EAST

2

1

3

3

33

4

4

3

3

6

6

144:1 ratio(motor to bull gear)

Bull gear10Incremental

Encoder

~180:1 friction gear ratio(encoder to bull gear)

8

8+

-

2

1

-0.35 V (on output)

Adj. pre-load

EAST

WEST

G=-2

G=-2 + +

++

4-1.2

0.488

SWITCH

(active low)01

SWITCH

0

1

5 5 55

5

5

577

777

77

7

9999

9

9 9

9

9

9

9

9

9

9

1111

12 12

12

12 1212

12

1212 12

12SWITCH

0

1

SWITCH

0

1

SWITCH

0

1

SWITCH

0

1

13

PEC B0:B12,B25

Digital position error CMD.

Counter

3 8 9 12

5

4

4

Desired Position

+-

PEC B0:B12,B25

14

A

B

C

D

E

F

A

B

C

D

E

F

2 3 4 5 6 7 81

2 3 4 5 6 7 81

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D

SLEW

SLEW WEST/

SLEW WEST/

Active low SLEW signals present when SLEW commanded in a direction. When SLEW is nearly complete and deceleration is required, the SLEW signals are removed (high) and the control goes back to standard control. This is based on DIP switch settings representing when to begin deceleration in number of counts from the end of the SLEW. Integrator is also shorted during this event.

HA CLEAR INTEGRATOR

BUF EAST SLEW DISABLE

BUF WEST SLEW DISABLE

FD FWD EASTIf an offset is commanded, variable amounts of pulses are added to the integrator of opposite polarity to remove charge from the integrator and reduce overshoot.

FD FWD WEST

Half Wave Rectifier+

Half Wave Rectifier-

TRANSFER FUNCTION(S) FOR SIMULINK

A

B

C

D

A

B

C

D

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BLOCK GROUP #1 & #2

Inverting Amp (Gain = -2)

Half Wave Rectifier Output EAST=negative output (positive for WEST)Inverting Amp with low pass.Gain =-300k/100k

=-3f(-3dB) =1/(2πRC)

=1/(2π*300k*2200pF)=240 Hz

Inverting Amp with band pass.Gain =-300k/56k

=-5.357 in pass bandf(low) =1/(2πRC)

=1/(2π*300k*2200pF)=240 Hz

~f(high) =1/(2πRC)=1/(2π*56k*0.33uF)=~8.58 Hz

HOWEVER, the compensation up front will cause lower gain overall and will cause additional lower gain at lower frequencies. Also, filter is not a “brick wall” filter. Pass band will have lower gain than calculated as the simulation illustrates..

INVERTING SUMMING

Positive Values Only (EAST)Negative Values Only (WEST)

Sets maximum output clamp, which must be less than the series Zeners, or ~10.7V.

Low pass filterf(-3dB) =1/(2πRC)

=1/(2π*100*0.1uF)=16 kHz

This is really high compared to 240 Hz upstream filter. This is for high frequency electronic noise induced or picked up.

ACTUAL GAIN(input signal is 1V)

Pass band, shorted C8,R33

Actual circuit

Adds a preload to the output and will be adjusted to add to the DAC output about: +0.35V

(East) or -0.35 (West).

Gain adjust

--

++

0.35

Mag Limit

10

0G=-2Mag Limit

12

0

--

++

-0.35

Mag Limit

0

-10G=-2Mag Limit

0

-12

Compensated Input Plot from Mathcad

EAST

WEST

A

B

C

D

A

B

C

D

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BLOCK GROUP #3

Clamp

Gain= Rf/Rs10k/47k0.213

f(-3dB) =1/(2πRC)=1/(2π*10k*0.022uF)=723 Hz

DIFFERENTIAL AMPw/ filtering

Very high frequency passive filteringf(-3dB) =1/(2πRC)Where R is the line + source impedance which is low.

Identical amplifier input stage for EAST & WEST.


Velocity(rad)

Tachometer

TCS Tachometer Voltage vs. Speed

y = 0.008654x - 0.001271R2 = 0.999997

y = 0.008845x + 0.005803R2 = 0.999922

y = 0.008764xR2 = 0.999979

-0.200

0.000

0.200

0.400

0.600

0.800

1.000

1.200

1.400

1.600

1.800

2.000

0 50 100 150 200 250

Speed (as/s)

Volta

ge (V

)

East

West

Average

Linear (West)

Linear (East)

Linear (Average)

(Intercept set to Zero)

sradVTach

sradsarc

sarcVTach

sradsarc

sarcVTach

/704.1807

/sec/206264.81

sec/008764.0

/sec/

sec/

=

⋅=

⋅=

For the tachometer rad/s to volt conversion: NOTE:This conversion is from TELESCOPE axis rotational velocity to volts. The mechanical model in SIMULINK provides axis velocity in rad/s at each motor geared output (after the 1:144 ratio).

A

B

C

D

A

B

C

D

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BLOCK GROUP #4

INVERTING SUMMINGw/ filtering

Gain= -Rf/Rs33.2k/68.1k-0.4875

f(-3dB) =1/(2πRC)=1/(2π*33.2k*(1uF+0.27uF)=3.77 Hz

By adding together ~½ of two individual signals, the output is approximately the average.

INVERTING SUMMINGGain = -120/100Gain = -1.2

East Tach IN

West Tach IN

Velocity CMD

++

Low Pass

3.77 Hz4

+-

4-1.2

0.488

4

4

4

West Tach IN

East Tach IN


++

+-

-1.2

West Tach IN

East Tach IN

VEL CMD

VEL CMD

NOTE: Be careful with the polarity signs here. The equation will be worked through to demonstrate the polarities.

))(4875.0(2.1))(4875.0(2.1

)))(4875.0((2.1)_(2.1

WtachEtachVCMDVoutWtachEtachVCMDVout

WtachEtachVCMDVoutampVsumVCMDVout

+−−=++−⋅=

+⋅−−−⋅=−−⋅=

A

B

C

D

A

B

C

D

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BLOCK GROUP #5

+-

Mag Limit

11

-111000 1000Mag Limit

4.5

-4.5Integrator

Ki=

∫ dttvKi )(RESET

330k680k

SWITCH

0

1

5 5 55

5

5

5

HA CLEAR INTEGRATOR

INVERTING AMPGain = -1000

1n5240 are 10V Zener Diodes, so output is limited to about:10+0.7=10.7V.Roundoff to ~11V

INVERTING AMPGain = -1000

Output is clamped to about: 3.1+0.7+0.7 = ~4.5V

INTEGRATORSince the input to the integrator will always be either +/-4.5V due to the total gain of 1 million and the clamping diodes, the current going into the integrator will always be +/- a constant value (4.5V/resistor) and the result is a signal with a +/- constant slope. This slope is change in velocity, which is acceleration. The integrator uses a capacitor.Where the capacitor voltage change over time:i=Cdv/dti/C=dv/dt

Therefore:

1010kΩ case:i=4.5V/1010kΩi=4.46μAdv/dt=4.46μA/1μFdv/dt=4.46V/s

330kΩ case:i=4.5V/330kΩi=13.64μAdv/dt=13.64μA/1μFdv/dt=13.64V/s


Results,

330kΩ simulation:dv/dt=-1V/83.5msdv/dt=~12V/s

Notice the feedback and high gain of a million. This can be represented as a slew limited amplifier with a gain of +1.

This circuit functions as an acceleration limiter.

Rate Limit

+/- 13.64V/s

Rate Limit

+/- 4.46V/sSWITCH

0

1

HA CLEAR INTEGRATOR

NOTE: In this simulation the first stage was unclamped (it just saturated) and a 3.3V (1n746A) Zener was used. The result will be nearly identical with the exception that the slope will be a slightly larger value. 330kΩ used for integrator in simulation.

Mag Limit

12

-12

Op-amp supplies limit output to about +/- 12V.

A

B

C

D

A

B

C

D

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MOTOR

MOTOR

Tele-scope

Mount

6

6


Bull gear

BLOCK GROUP #6

The motors are driven by a current amplifier. The output of the motor has a 144:1 gear ratio to the HA Axis. Since the motor is driven by a current drive amplifier, the equations for the torque involve the torque constant of the motor, current, and gear ratio. The back EMF produced by the motor is used as feedback for the amplifier in the amplifier model. The back EMF reduces the maximum current output of the amplifier. See the amplifier section for more details. See next page for motor datasheet and parameter values.

Imai measured 1Ω and 1.3Ω across the motors at the junction box with the amplifiers off but still connected on 11/2/07. This suggests “A” version of motor.


761.427Current (A) Torque (N•m/A)

AmNITorque

ftlbAftlbITorque

AftlbITorque

AftlbITorque

RatioGearIKTorque T

⋅⋅=

⎥⎦

⎤⎢⎣

⎡⋅

⋅⋅⎥⎦⎤

⎢⎣⎡ ⋅

=

⎥⎦⎤

⎢⎣⎡ ⋅

=

⋅⎥⎦⎤

⎢⎣⎡ ⋅

=

⋅=

427.761

mN 952 817 1.3556.561

6.561

)144(90.3

_

MOTOR TORQUE

sradVEMFBack

KEMFBack

M

bM

/30.5_

_

⋅=

⋅=

θ

θ

BACK EMF (used in amplifier section)

MOTOR IMPEDANCE (@25C)

Ω+Ω=

+=

97.0)008.0(_

sZ

RZZ

motor

windingwindingLmotor

ORIGINAL, Model 12016A SPARE, Model 12016A

AmNITorque

ftlbAftlbITorque

AftlbITorque

AftlbITorque

RatioGearIKTorque T

⋅⋅=

⎥⎦

⎤⎢⎣

⎡⋅

⋅⋅⎥⎦⎤

⎢⎣⎡ ⋅

=

⎥⎦⎤

⎢⎣⎡ ⋅

=

⋅⎥⎦⎤

⎢⎣⎡ ⋅

=

⋅=

04.2499

mN 952 817 1.3552.1843

2.1843

)144(8.12

_

MOTOR IMPEDANCE (@25C)

Ω+Ω=

+=

50.4.0)017.0(_

sZ

RZZ

motor

windingwindingLmotor

sradVEMFBack

KEMFBack

M

bM

/4.17_

_

⋅=

⋅=

θ

θ

BACK EMF (used in amplifier section)

A

B

C

D

A

B

C

D

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BLOCK GROUP #6 CONTINUED

SPARE MOTOR

MOTOR

MOTOR

Tele-scope

Mount

6

6


Bull gear

CURRENT MOTOR IN USE

Imai measured 1Ω and 1.3Ω across the motors at the junction box with the amplifiers off but still connected on 11/2/07. This implies model “A”.

A

B

C

D

A

B

C

D

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BLOCK GROUP #7

Mag Limit

ADJ

ADJ

POSITIVELIMIT

NEGATIVELIMIT

Low Pass

468 Hz

SWITCH

(active low)

SWITCH

(active low)

0VBUF EAST SLEW DISABLEBUF EAST MOTION DISABLE

Adj 0 to 0.5VAdj 0 to 8V

G=5

SWITCH

(active low)

SWITCH

(active low)

0VBUF WEST SLEW DISABLEBUF WEST MOTION DISABLE

Adj 0 to -0.5VAdj 0 to -8V

G=5

77

777

77

7

INVERTING Summing AMP with half wave rectifier.Only positive outputs allowed.

Op-amp equation when Vcmd is ≤ -5*Vrefp:Vout=-Vrefp-0.2*Vcmd

Else, Vout=0.

INVERTING Summing AMP with half wave rectifier.Only negative outputs allowed.

Op-amp equation when Vcmd is ≥ -5Vrefn:Vout=-Vrefn-0.2*Vcmd

Else Vout=0.

INVERTING summing amp.This stage subtracts the exact amount from the command that is required to clip it and keep it within 5*ref voltage . The final result is the inverted value.

It also provides a filter.

This is just a selectable magnitude limiter with a filter.The “BUF MOTION DISABLE” can be ignored since it is a personnel safety feature, which isn’t part of the servo analysis.Also, it can be assumed that EAST and WEST slewing will have equal magnitude limiting.

(-5*VREFP is the actual negative output voltage limit of Z9)

(-5*VREFN is the actual positive output voltage limit of Z9)


(Velocity CMD input only, excludes limit refs)

Testing 11/7/07

Z8A-9= 160 mV (EAST track)Z8A-5= 717 mV (EAST slew)Z7A-5= -720 mV (WEST track)Z7A-9= -150 mV (WEST slew)

For model, use+/- 160 mV for tracking/offset+/- 720 mV for SLEW

BUF EAST SLEW DISABLE0.1600.720

BUF WEST SLEW DISABLE-0.160-0.720

G=5

G=5

Mag Limit

ADJ

ADJ

POSITIVELIMIT

NEGATIVELIMIT

SWITCH

0

1

SWITCH

0

1

A

B

C

D

A

B

C

D

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BLOCK GROUP #8

Each of the two motors is operated by a dedicated power amplifier (CSR Contraves, NC307). These amplifiers are classic switching amplifiers, in that they utilize an alternating polarity square wave with an adjustable duty cycle, to control the equivalent DC current. Their switching frequency is 20 kHz.

Functionally, the amplifier becomes a transconductance amplifier - with a transfer function of 10.5 amps of equivalent output current per volt of input command voltage. This is the nominal specified value. See test results below. However, the amplifier output current is limited by the impedance it is driving and its +90V supply used in the TCS. The motor impedance will change with frequency due to the inductance and the motor will also create a back EMF, which further reduces the available voltage to drive the motor. The CSR amp uses an H-Bridge driver. This means that it only uses a +90V supply but it can reverse the polarity on the motor, resulting in current flowing the opposite direction. In regards to modeling, it would appear as if the amplifier could supply +/- 90V to the motor.

AMP

8

Ideal amplifier model:This model is a very simplified model of a transconductance amplifier. It does not take into account any frequency response of any kind. However, for the purposes of the TCS model, it should be sufficient. The switching frequency of the amplifier is 20 kHz. The response of the amplifier is DC to 1000 Hz at rated current. The TCS control system is limited to the hundreds of hertz.

10.5 A/V

+

-

+90V(supply voltage)

BACK EMF(see motor modeling)

Current CMD

(in volts)

1/(Motor Inductance)(see motor)

-

+

Motor Drive Current (A)

|Maximum current| that the amplifier can provide to the motor due to the back EMF and motor impedance.

Desired command current

Select the lower value between desired and available:IF desired < available, control value is positive “1”, use desired valueIF desired > available, control value is negative “0”, use max value

SWITCH

1

0


-6.2

+

-

+90V

Current CMD

(in volts)

-

+

Motor Drive Current (A)

SWITCH

1

0

5.30 Rotational Speed (rad/s)|ABS|

|ABS|

The voltage could be positive or negative for the back EMF. These blocks are used as a comparison to see if the current magnitude requested can be supplied.

Absolute value of power supply.

|ABS|

|ABS|

970.0008.01+s

MOTOR & FLUKE Term 6 Term 8 Axis Tracking CMD MonitorAXIS Current (A) CMD (V) Monitor (V) Speed (as/s) (A/V) (A/V)WEST 4.9 -0.79 0.42 10 -6.202532 11.66667WEST 5.3 -0.86 0.45 6 -6.162791 11.77778WEST 5 -0.82 0.42 30 -6.097561 11.90476NORTH 2.74 -0.448 0.16 15 -6.116071 17.125NORTH 2.7 -0.45 0.162 30 -6 16.66667NORTH 3.14 -0.48 0.17 50 -6.541667 18.47059

average -6.18677 14.60191 WESTaverage 17.42075 NORTH

Date Created: 11/28/07Author: E. Warmbier

DESCRIPTIONMeasurments taken at NC307 amplifiers to compare the volts to amps command conversion and the amps to volts current monitor. FLUKE DVM put in series with actual armature wire originating at the NC307. "+" of multimeter was hooke up to "+" armature, so current flow is measured coming out of the amplifier.

A

B

C

D

A

B

C

D

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BLOCK GROUP #9

JOYSTICK(ignore)

SLEW WEST/

SLEW EAST/

(integrator output ->)

(proportional output ->)


Not using during servo modeling – ignore.

INVERTING Summing Amp with filtering and output magnitude limiting to about +/- 10.7V or ~11V.

w/ amp above

w/ amp above

INVERTING Summing Amp with filtering and output magnitude limiting to about +/-10.7V or roundoff to ~+/-11V. However, the +/- 11V clamp may be ignored for the purposes of this model. There is another limiter of lower magnitude that follows this stage. See block #7.

SWITCH

(active low)

SWITCH

(active low)

SLEW EAST/

SLEW WEST/0V

0V+8V

-8V

+++++

(integrator output ->)

(proportional output ->)

A

B

C

D

A

B

C

D

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BLOCK GROUP #10

Teledyne Gurley Incrementel encoders, model 8626.

Both of the current incremental encoders have a 3600 line count and associated electronicscapable of 40x interpolation for a total of 144 000 pulses/ revolution.

Tele-scope

Mount

Bull gear10Incremental

Encoder

~180:1 friction gear ratio(encoder to bull gear)

5035.762Encoder

The encoder input is in terms of rotation position (radians) and output is in volts ultimately at the digital to analog converter.

radiansV

RadiansVoltageOutput

pulsebit

bitsV

turnsturns

radiansrevolution

revolutionpulses

RadiansVoltageOutput

Radianspulsebit

bitsV

turnsturns

radiansrevolution

revolutionpulsesVoltageOutput

762.5035_220

1180

)2(403600_

220

1180

)2(403600_

14

14

=

⎟⎟⎠

⎞⎜⎜⎝

⎛⋅⋅⋅⋅

⋅=

⋅⎟⎟⎠

⎞⎜⎜⎝

⎛⋅⋅⋅⋅

⋅=

π

π From BEI’s website gloassary: http://www.motion-control-info.com/encoder_glossary.html

radianspulsepulse

radianspulse

radiansrevolution

radianspulses

revolution

99

9

1041.24211041.242

1041.242180

1)2(403600

−−

−

⋅=⋅⋅

⋅=⋅⋅⋅

π

Friction Gear Ratio

A/DScaling

(see block #12)Encoder

1 encoder pulse

increments position

counter by 1

There is quantization of position due to the encoder. The encoder provides pulses, not a continuous output. The quantization is the number of radians that must be traveled before the next pulse. This is calculated as follows:


242.41E-9 quantization interval

A

B

C

D

A

B

C

D

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BLOCK GROUP #11

1.96(1.33)

Low Pass

1.59 kHz11

11

HA TRANSFER FUNCTION(S) FOR SIMULINK

Inverting amplifier with filtering:Gain= Rf/Rs

10k/5.11k1.96

f(-3dB) =1/(2πRC)=1/(2π*10k*0.01uF)=1.59 kHz

DEC TRANSFER FUNCTION(S) FOR SIMULINK

DEC AXIS:HA AXIS

This is proportional gain of the PID with a low pass filter.

A

B

C

D

A

B

C

D

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BLOCK GROUP #12

INVERTING Summing Integrator under normal operation.

Very low gain inverting summer with filter when R17 via switch is active (SLEW mode).Essentially the integrator is shorted out since 300Ω is a low value and therefore the gains become very small.

Bottom line: “I” term for the PID controller is either active or it is shorted.

+8V0V

FD FWD EAST

-8V0V

FD FWD WEST

HA CLEAR INTEGRATOR

SWITCH

(active low)01


300Ω “Short”

Normal

300Ω “Short” Normal

+++++

Position Error Signal(from DAC)

SWITCH

0

1

SWITCH

0

1

SWITCH

0

1

SWITCH

0

1

A

B

C

D

A

B

C

D

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CH1: “VOUT” TP

CH2: Integrator Output TP2

CH3: FD FWD East

MANUAL (finger pushing button), REPETITIVE +/- 60 ARCSEC OFFSETS, 11/7/07BLOCK GROUP #12 Continued

From Ev Irwin Memo:

“In addition to using the PEC D/A signal as an input, during offset or beam switching operations, the Integrator receives pulses of fixed amplitude but varying numbers. These pulses inject charge into the integrator of opposite polarity as is the direction of desired position change. The purpose of these pulses is to reduce overshoot and improve settling time. The number of pulses –and therefore total injected charge is one-for-one equal to the commanded number of steps required for relative position change. In other words, when the telescope is commanded to step 400 steps to the east, there is a delay while the telescope moves to the east. During that time, the integrator integrates the error so that when the telescope finally reaches the desired new position, there is excess charge in the integrator. To remove this charge, there would have to be an overshoot with a negative error. The feed-forwarding pulses inject negative charge into the integrator thereby shortening or eliminating the need for overshoot. NOTE – At first, one might wonder why not simply short out the integrator, as is done during slew operations? Unfortunately, during tracking, the integrator contains the amount of charge necessary to produce an output voltage equal to the value required to track the telescope. To short the integrator, would remove that charge, forcing the telescope to briefly stop and thereby worsening the settling time – not improving it.”

Below is a portion of the Ev Irwin memo about the offset operation and how the FD FWD is used.

FD FWD pulse initially causes large jump in opposite polarity of error signal.

Error signal is then integrated which brings output back close to initial value.

Remember: inverting amplifier configuration.

The scope plot seems to confirm the above statement. When the error reaches zero (CH1) the integrator output (CH2) is approximately the same as the value when the offset started. This is due to the charge injected by the FD FWD pulse (CH3). If this pulse did not exist, the integrator would have a positive value on its output due to integrating the error signal when the error reaches zero.

(Keep in mind that the op-amp is inverting.)

A

B

C

D

A

B

C

D

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BLOCK GROUP #13

DAC-10

1014 bit13

PEC B0:B12,B25


Digital to analog converter.Voltage output.

Note: no datasheet was located on the internet. (It’s an older obsolete DAC.)

It is known from operation and the above schematic that the DAC uses +/- 15V supplies, outputs +/-10V, and is 14 bits.

Given this information, the resolution can be calculated as:

This value is used as the quantization interval for the quantization block in Simulink.

In addition, the DAC can only output +/- 10V. A limiter can be placed on the output.

bitmVbits

V /22.12

)10(1014 =−−

DEC TRANSFER FUNCTION(S) FOR SIMULINK

PEC B0:B12,B25


Mag Limit

10

-10DAC

1.22E-3 quantization interval

The digital to analog converter gain was lumped into the encoder block. See block #10.

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B

C

D

A

B

C

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BLOCK GROUP #13 CONTINUED

The SIMULINK modeling of this will be much simpler than the large amounts of digital circuitry that were required to create these signals.

SEE BLOCK #12 for more information on the offset pulses.(“FD FWD EAST” and “FD FWD WEST”)

More work needs to done here. As of 11/27/07 two things are unknown:1) Position error magnitude at which a slew ends2) Offset pulse characteristics

The model currently uses values that work well in the simulation.

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B

C

D

A

B

C

D

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CONVERSIONS

CONVERSION FOR SIMULINK

206264.81

secsec81.206264

sec

minsec60

degmin60deg180

secsecarcradians

arcarcarc

radianradianradians

=

⋅⋅⋅

⋅=π

In Simulink, some of the outputs will be displayed on a scope. Radians/second are used in the model for radial velocity, but arcsec/sec is what the telescope control displays and uses. Converting it makes it easier to understand and compare to actual telescope data.

radians/sec arcsec/sec

CONVERSION FOR SIMULINK

548.78

VsarcVOutputradians

sradsrad

VVOutputradianssrad

conversionsarcinputtachNumgainsummerAmpDiffconvTach

VOutputarc

sec/78.548)(sec

/rcsec/s206264.81a

21

488.01

213.01

/1808

1)(sec

/_sec/

__1

_1

_1

_1)(

secsec

⋅=

⋅⋅⋅⋅⋅=

⋅⋅⋅⋅⋅=

The tachometer summer circuit has a scaled, averaged, tachometer output in volts. In the SIMULINK simulation, it is convenient to display this in arcsec/sec. See conversion derivation for rad/s to arcsec/s used below. This is the feedback that the control system uses.

tach summer out (volts) radian/sec

A

B

C

D

A

B

C

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The current RA absolute position encoder (APE) is located in the North Pier. It is an inductosynencoder with one half mounted on the yoke, and the other half mounted to the pier.

The DEC APE is located in the west arm of the yoke. It is also an induction type encoder(identical to the RA encoder) with one half mounted to the telescope central section, and theother half mounted on the yoke.

Both of the current APEs have a resolution of 0.1 arcsec.

APPENDIX: ABSOLUTE POSITION ENCODERS

PRECISIONAMPLITUDE

LIMITER

PRECISIONRAMP

AMPLIFIER

3HZHIGHFREQ

FILTER

COMPENSATIONNETWORK

LOWFREQ

FILTER

LOWFREQ

FILTER

SUMMINGAMP

+--

SUMMINGAMP

+++++

BUFFERAMP

INTEGRATOR

MANUALSLEW

JOYSTICKBUFFER,

DUAL SLOPGENERATOR

MCC2 JOYSTICK SIGNAL

-8V+8V

COMPUTER SLEWEAST (SOUTH) COMMAND

COMPUTER SLEWWEST (NORTH) COMMAND

SUMMINGAMP

+

+

SUMMINGAMP & PRECRECTIFIER

+

-

SUMMINGAMP & PRECRECTIFIER

+

-

SUM

MIN

GA

MP

& P

REC

REC

TIFI

ER

+ +

SUM

MIN

GA

MP

& P

REC

REC

TIFI

ER

+ +

CSRPOWER

AMP

CSRPOWER

AMP

DCTACH

DCTACH

WEST(NORTH)

DRIVEMOTOR

EAST(SOUTH)

DRIVEMOTOR

BULLGEAR

SWITCH

SHORTEDDURINGSLEWS

WEST(NORTH)DRIVETACHSIGNAl

ACCELERATION LIMITED

VELOCITY LIMITED

EAST(SOUTH)DRIVETACHSIGNAl

EAST DRIVETACH SIGNAL

WEST DRIVETACH SIGNAL

HIGH FREQ EAST DRIVE MOTORTACH SIGNAL

HIGH FREQ WEST DRIVE MOTORTACH SIGNAL

TORQUE SPLITTER

PRODUCES WEST (NORTH)TORQUE COMMAND ONLY

EAST (SOUTH) DRIVE MOTOR TORQUE COMMAND

WES

T (N

OR

TH) D

RIV

E TO

RQ

UE

CM

D

PRODUCES EAST (SOUTH)TORQUE COMMAND ONLY

WEST(NORTH)PRE-LOAD

EAST(SOUTH)PRE-LOAD

EASTDRIVETACHSIGNAL(SOUTH)

WESTDRIVETACHSIGNAL(NORTH)

INLAND

DIGITALTO

ANALOGCONV.

POSITIONERROR

UP/DOWNCOUNTER

(PEC)(24 BITS)

IRTF 125 HAIRTF 126 DEC

POSITIONERROR

WINDOWLOGIC


INCREMENTALENCODER

PECLOADERIRTF 122

ANTICOINCIDENCESCANNER


DIVIDE BY 2LOGIC

(BINARY SHIFT)IRTF 123 HA

IRTF 124 DEC

ARITHMETICSUBTRACTION

LOGICIRTF 123 HA

IRTF 124 DEC

DIGITALSWITCH


RAMPDOWNDISTANCE

SWITCHMEMORY


COMPUTERCOMMAND

MAGNITUDEANALYSIS

LOGICIRTF 123 HA

IRTF 124 DES

SLEWMODE

MINIMUMCOMMAND

SWITCHMEMORY


COMPUTERCOMMAND

TIMINGAND

MODESEQUENCECONTROL


DISTANCEBEFORE

RAMPDOWNCOUNTER


COMPUTERINTERFACE

IRTF 122

Y

X

X - Y

BEGIN DECEL.

LOAD AND COUNT

COMMAND > MINIMUM COMMAND SETTING FOR SLEW

COMMAND ≥ 2 TIMES DECELERATING DISTANCE

COMPUTER SLEW WEST (NORTH) COMMAND

COMPUTER SLEW EAST (SOUTH) COMMAND

EXCESS POSITION ERROR

SELE

CT

CO

MM

AN

D M

INU

S D

ECEL

. DIS

TAN

CE

*OR

* CO

MM

AN

D /

2

24 BIT PARALLEL COMMANDMASTER CONTROL BUS(MCB)

HARDWARECONTROLLEDSLEW LOGIC

0 TO ±10 VOLT ANALOG POSITION ERROR SIGNAL

CO

UN

TDO

WN

OPE

RA

TIO

N C

OM

PLET

E

COUNT UP/DN CONTROL

BITS 0 - 23

BIT 23 (MSB)

BITS 0 - 12

ERROR NULL=10000000000000

0V = NULL

EXCESSPOSITIONERROR

MANUALSLEWCLEAR

OPPOSING DRIVES

LOW FREQUENCY TACH SUM

EAST (SOUTH) TELESCOPE MOTION PULSES

WEST (NORTH) TELESCOPE MOTION PULSES 19.9028 PULSES/ARC-SEC ≈ 0.05 ARC-SEC/PULSE

19.9472 PULSES/ARC-SEC ≈ 0.05 ARC-SEC/PULSE

MC

C T

RA

CK

WES

T PU

LSES

MC

C T

RA

CK

EA

ST P

ULS

ES(M

AN

UA

L M

OD

E A

ND

C

OM

PUTE

R S

LEW

S O

NLY

)

(MA

NU

AL

MO

DE

AN

D

CO

MPU

TER

SLE

WS

ON

LY)

TELEDYNEGURLEYMODEL 8626144,000 PULSESPER ENCODERREVOLUTION

(TELESCOPE LIMIT SWITCH INITIATED)

HARDWARE CONTROLLED SLEW LOGIC CONTROLS TELESCOPE DURING COMPUTER INITIATED SLEW OPERATIONS. IT INITIATES ACCELERATION, CALCULATES THE DECELERATION POINT, AND RETURNS THE SERVO TO LINEAR MODE.

TELE

SCO

PE W

EST

(NO

RTH

) STO

P LI

MIT

SW

ITC

H

TELE

SCO

PE E

AST

(SO

UTH

) SLE

W L

IMIT

SW

ITC

H

A

B

C

D

E

F

A

B

C

D

E

F

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D

APPENDIX: TCS1 BLOCK DIAGRAM CIRCA 1980

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B

C

D

E

F

A

B

C

D

E

F

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APPENDIX: IRTF 123 - TELESCOPE SERVO CONTROL HA COMPUTER CMD & MAGNITUDE DETECT

A

B

C

D

E

F

A

B

C

D

E

F

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APPENDIX: IRTF 125 - TELESCOPE SERVO CONTROL HA SEQUENCE CONTROL BOARD

A

B

C

D

E

F

A

B

C

D

E

F

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APPENDIX: IRTF 127 & 128 -TELESCOPE SERVO CONTROL D/A, JOYSTICK, & INTEGRATOR

A

B

C

D

E

F

A

B

C

D

E

F

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APPENDIX: IRTF 130 - TELESCOPE SERVO CONTROL TACH SUMMER & TORQUE CMD

A

B

C

D

E

F

A

B

C

D

E

F

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APPENDIX: IRTF 131 - TELESCOPE SERVO CONTROL DEC TACH SUMMER & TORQUE CMD

Visio-TCS1 Control Block Diagram 12 12...

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