NBSIR 75-773

Report on Characteristics of

Three Universal Force Testing

Machines

Ervin C. Palasky & J. Eryx Malcolm

Electrical and Mechanical Engineering Section

Product Engineering Division

Institute for Applied Technology

William H. Appleton

Engineering Mechanics Section

Mechanics Division

Institute for Basic Standards

September 1975

Final

Technical Report to Mechanics Division

Institute for Basic Standards

National Bureau of Standards

NBSIR 75-773

REPORT ON CHARACTERISTICS OF

THREE UNIVERSAL FORCE TESTING

MACHINES

Ervin C. Palasky & Eryx Malcolm

Electrical and Mechanical Engineering Section

Product Engineering Division

Institute for Applied Technology

William H. Appleton

Engineering Mechanics Section

Mechanics Division

Institute for Basic Standards

September 1975

Final

Technical Report to Mechanics Division

Institute for Basic Standards

National Bureau of Standards

U.S. DEPARTMENT OF COMMERCE, Rogers C. B. Morton, Secretary

James A. Baker, III, Under Secretary

Dr. Betsy Ancker-Johnson, Assistant Secretary for Science and Technology

NATIONAL BUREAU OF STANDARDS. Ernest Ambler. Acting Director

Table of Contents

Page

Section 1 - Introduction and general summary 1 1.0.0 Scope and purposes of manual 1

1.1.0 Basic machine operation logic 2

1.2.0 The Machine crosshead 2

1.3.0 The Crosshead drive controller 2

1.4.0 The measuring circuits 5

1.5.0 The sensors and indicators 5

1.6.0 The Automatic and external controllers . 5

Section 2 - Power 5

2.0.0 Machine Power 5

2.0.1 Control operations 5

2.0.2 Motive power 6

2.0.3 Power flow chart 6

2.1.0 Power control chassis 6

2.2.0 Master power control 6

2.3.0 Crosshead power 10

2.4.0 General power distribution 10

2.5.0 The 24 volt power supply PS301 12

2.6.0 Other functions on the power chassis 12

Section 3 - The machine crosshead 13

3.0.0 The machine crosshead 13

3.1.0 Crosshead power 13

3.2.0 The oil control valve (2) 16

3.3.0 The drive motor (5) 16

3.4.0 Signal summary in power source 16

3.5.0 Crosshead speed clutches (8), (9) and (10) 18

3.6.0 Synchronization summary 18

3.7.0 Clutch selection signals 18

3.8.0 Clutch operation 20

3.9.0 The fail safe brake (11) 20

3.10.0 Movement limiting switches 21

3.11.0 Isolated operation of the crosshead for test purposes ... 21

3.11.1 Synchronization circuit adjustment 21

3.11.2 Install Substitute crosshead control signal .... 23

3.11.3 Instrumentation of the test set up 23

3.11.4 Machine controls to be used 23

3.11.5 Test operation 23

3.11.6 Test results 23

Section 4 - Synchronization 25

4.0.0 Synchronization 25

4.1.0 Initialization of the synchronization 27
Page

4.2.0 uperation of sync or relay K^O^ 30

4.3.0 Importance of synchronization relay K404 3I

4.4.0 Details of failure detector 31

4.4.1 The control failure detector 31

4.4.2 Excessive speed signal 31

4.4.3 Out of control signal r• • 33

4.4.4 Detection of an error 33

4.4.5 Operation of the sensor detector electronics .... 33

4.4.6 The input rectifier 33

4.4.7 The amplitude comparator section 33

4.4.8 The threshold detector 36

' 4.4.9 The output drivers 36

4.4.10 The output signal characteristics 36

4.4.11 Reset of the system 38

Section 5 - Direction control ....... .... 38

5.0.0 Crosshead direction control relays 38

5.1.0 Motion relay turn-on 39

5.1.1 The system at rest 39

5.1.2 Relay turn on 39

5.2.0 Holding operation of motion direction relays 41

5.3.0 Turn-off of the direction control relays 41

5.4.0 Indicator lights 42

5.5.0 Associated safety functions 42

5.5.1 Range exceed problems 42

5.5.2 Limit exceed problems 42

Section 6 - Crosshead drive control ... 43

6.0.0 Crosshead drive servo control 43

6.1.0 Command servo motor 43

6.2.0 Command servo signal mixer 43

6.3-0 Input control signal 46

6.3.1 Control by relay K409 46

6.3.2 Control by jog relay K408 46

6.3.3 Operational control 47

6.4.0 The output signal 47

Section 7 - The measuring circuits 47

7.0.0 The measuring circuits 47

7.1.0 The load cells 49

7.2.0 The load cell amplifiers and mixer 49

7.3.0 Range selection 52

Section 8 - Maintain load 52

8.0.0 Introduction 52

8.1.0 Signal sources 52

8.2.0 The error signal 52
hage

8.3.0 Reaction rate control 54

8.^.0 Servo drive control 54

8.5.0 Cross reference 54

Section 9 - The indicating circuits 5^

Section 10 - Velocity node feedbacK ccntrcl syste'^. 5-j 10.0.0 Introduction 55

10. 1.0 Description and results of tests 55

10.2.0 Conclusions 65
Illustrations

1.1.0 General System Layout

1.1.1 General System Layout (Expanded)

2.0.3 Power Control Layout

2.1.0 115 VAC Power Control and Distribution

2.2.0 Main Power Control

2.3.0 Crosshead Power Control

3.0.0 Machine Crosshead System Layout

3.0.0a t-lachine Crosshead System Layout (Expanded)

3.2.0 Oil Gear Pump Illustration • 3.7.0 Manual Speed Selection System

3.11.0 Crosshead Test Layout

3.11.2 Crosshead Test Layout (Expanded)

3.11.6 Crosshead Speed Curve

4.0.0 Servo Motion Control Loops

4.1.0 Synchronization Circuits

4.4.0 Synchronization Null Detector

4.4.5 Synchronization Phase Sensor and Detector

4.4.6 Synchronization Input Signal

4.4.10 Synchronization Control Signal

5.0.0 Motion Direction Control Circuits

6.0.0 Servo Control Circuits - : 6.0.0a Servo Motion Control Loops

7.0.0 Measuring Circuits

7.1.0 Load Cell Equivalent Circuits

7.1.1 Load Cell Location

8.0.0 Maintain Load Circuits

9.0.0 Indicating Circuits

10.1. OA Bode Plots

10.1. OB Bode Plots

lO.l.OC Loop Diagram

lO.l.OD Bode Plots

lO.l.OE Bode Plots

10.1. OF Test Configuration
Section 1 - Introduction and general summary

1.0.0 Scope and purposes of manual

The manual is written to assist in the servicing of the universal

testing machines manufactured by Gilmore industries, Inc., and now

in use in the National Bureau of Standards. These machines are designated as models M421 and are further identified by the

numbers listed below.

The manual is intended to serve as a supplement to, and expansion

of, documentation supplied by the manufacturer, for the purpose of

study and repair of the machines. Operation and calibration

instructions are entirely left to the Gilmore industries manual.

The manufacturer's documentation consists of:

This manual supplements item 1 above and attempts to clarify item

2. Primary focus of the manual is on electrical or electronic

information or procedures. Circuit details found in the

schematics but not described in the literature are added.

Drawings are redrawn, assembling pertinent related material and

eliminating parts which are intercoupled to the functions but not

under examination in the explanation. This clarification

facilitates understanding and servicing the machines.

Mechanical and hydraulic details and maintenance are left to be

described in the manufacturer's catalog.

A procedure is developed and presented for isolating the crosshead

drive, for operation outside the control loop for testing

purposes.

The Gilmore manual, on pages 7, 8 and 9 lists the general

specifications and references further documentation which supports

understanding of the machines.

1. Model M421-200 S/N 4366

2. Model m21-50 S/N 4367

3. Model M421-10 S/N 4368

1.

2.

3.

An operation and maintenance manual.

A set of schematics.

A set of various manufacturing specifications

for components used as part of the machine.
1.1.0 Basic machine operation logic

Figure 1.1.0 outlines in very simplified form the operational

layout of the machines. The machines can be divided into three

basic systems. These systems are identified by number on the

diagram.

Figure 1,1.1 is a duplicate of Figure 1.1.0 with some details

added. The details are the major functions of the blocks. Minor

functions are omitted and will be added in later sections devoted

to detailed descriptions.

The blocks are generally described below in order to provide a summary overview to the reader. More detail is supplied in later

sections.

1.2.0 The machine crosshead .

The crosshead, mounted on the testing frame, applies force to the

specimen under test. It is a mechanical system, driven by a hydraulic force system which is electrically powered and

controlled.

The system is described in some detail on pages 11, 12, 12a and 13

in the Gilmore manual. It is a slave system, responding to

control and reporting its condition but with no ability to alter

its own operation. . i

1.3-0 The crosshead controller

The controller accepts external direction and monitors the

crosshead response to attain speed, direction and force as directed. The controller also monitors a series of safety sensors

and shuts down the crosshead motion in the event that a condition

is detected which might cause damage to the machine.

The function of operation of the crosshead controller is manually

selected prior to operation. Four methods of operation may be

used. The titles listed are generally descriptive of the function

itself.

1.

2.

3.

Control and movement.

Response and indication.

Feedback activated control due to response.

1. Manual operation.

2. Maintain load.

3. Cycle between fixed load points.

4. Remote control.

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l.il.O The measuring circuits

These circuits sense the force on the specimen through interpretation of the output signals of four load cells under the

crosshead bed plate. The load cells are described in the Gilmore

manual on pages 13, 3^ and 35. The load cells feed a signal mixer

which is followed by an amplifier.

The output of the amplifier is proportional to the total load on

the machine and is used to drive the dial indicator and the

retransmitting slidewires which in turn are used as references for

various balancing and indicating circuits.

1.5.0 The sensors and indicator

These are the dials and retransmitting slidewires which serve to

interface the measuring circuits to the operator or to oLher parts

of the machine. They serve as reference signals for the automatic

and remote control functions.

1.6.0 The automatic and external controllers

These systems provide a limited spectrum of operations which may

be called to replace the manual control. Functions which may be

accomplished are:

1. Unattended operation.

2. Cyclic operation.

3. Preset loading.

4. Cor.stant loading.

5. Remote control.

Section 2 - Power

2.0.0 Machine power is basically electrical. Specifications for

the power are found on page 10 section 3-2 of the Gilmore

manual. Two facets to the electrical power usage are apparent.

2.0.1 Control operations inside the machine are based on

a source power of 115 volt, single phase, 60 hertz.

In addition to a.c. use this is converted to numerous

and different direct voltages to specifically satisfy

requir^ents of various parts of the machine.

5
2.0.2 Motive power to drive the force parts of the machine

and load the samples is derived from a 4^10 volt, 3

phase, 60 hertz source. Use of this power is controlled

by the circuits driven by the power listed above under

section 2.0.1.

2.0.3 Figure 2.0.3 is a flow chart depiction of pov/er

control chassis 300 which is described in sections"

immediately below.

2.1.0 Power control chassis

Power control is located on chassis 300. This is the central

control point and source of power for the machine. However,

auxiliary power supplies will often be found on local chassis

when they are dedicated to use on that chassis. Input power

to these supplies is controlled on chassis 300.

There are several distinct parts to chassis 300 and they are

described in the following sections. Figure 2.1.0 is a schematic diagram of chassis 300.

2.2.0 Master power control - chassis 300

Figure 2.2.0, an extraction of part of Figure 2.1.0, is a schematic of the master power control.

Fuse F301 with a rating of 10 amperes is the basic protection

in this circuit. A burnout of this fuse will turn off the

entire machine, including the crosshead power.

This subsystem is based on locking relay K301 which is

activated by depressing normally open switch S301. This

switch is labelled power on. As soon as relay K301 picks

up, a set of contacts on the relay maintains the hold condition

through the normally closed switch S302. This switch is

labelled power off.

Power is turned off by depressing switch S302 which breaks

the holding current through relay K301.

An indicator lamp 1301 senses the operation of relay K301

and gives a visual indication that power is present at this

point

The power applied to the machine is routed through two contact

sets of relay K301 to the distribution point on the chassis.

The contacts of this relay all carry the entire control current

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used in the machine. Failure of a set of these contacts could

result in an operated relay and the absence of power in the

machine, even though the indicator light is on.

2.3-0 Crosshead Power

The 440 volt power breaker is on the loading frame. This

must be on to operate the crosshead. It does not actually

apply power to the system but rather makes the power available

on call of the circuits on chassis 300. The 440 volt power

drives an oil pump on the loading frame. This is the source of the hydraulic energy used in the system.

Figure 2.3-0 is an extraction of part of the schematic figure

2.1.0 and details the parts of chassis 300 which directly

command the crosshead driving power.

The input power to this ptart of the circuit is from the

distribution point on chassis 300. Section 2.2.0 details the

method in which power reaches this point. The crosshead

power control is hung on this point along with a number of

other connections to other parts of the machine.

This subsystem is based on locking relay K302 which is

activated by depressing normally open switch 3303- This

switch is labelled crosshead power on. As soon as relay

K302 picks up, a set of contacts on the relay maintains

the hold condition through the normally closed switch S304.

This switch is labelled crosshead power off.

Power is turned off by depressing switch S304 which breaks

the holding current through relay K302.

An indicator lamp 1303 senses the operation of relay K302

and gives visual indication that power is present at this

point.

The power applied to the crosshead is routed through

two contact sets of relay K302. Failure of either of these

sets of contacts would result in the absence of power to

the crosshead even though the indicator lamp shows power

to be on.

2.4.0 General power distribution

The power distribution point on chassis 300 services some system parts without interposing any protective devices.

These parts thereby relate back to the basic 10 ampere fuse

F301 for protection. Fuses may exist for later local uses

10

and the above comment is related only to protection on chassis 300.

Direct 120 volt service is provided to:

1. Chassis 200.

2. Chassis 400.

3. The Oil-Gear Co. amplifiers which regulate the

hydraulic valve speed control.

4. Positive 24 volt power supply PS301. This supply

is on chassis 300 and is used as operating power

for relays.

Figure 2.1.0 shows the abo^e listed connections.

2.5.0 The 24 volt power supply PS301

This supply is located on chassis 300 and is used for

operating relays.

Indicator light 1302 is energized by the output of this

supply and indicates that voltage is present at the output.

Fuse F302, with a rating of 3 amperes, protects this supply

from excessive current demand in all uses. Failure of this

fuse will be evidenced by the failure of indicator 1302 to

light.

All 24 volt current is either used on or traverses chassis 400.

2.6.0 Other functions on the power chassis.

Four machine control switches not associated with power

supply are mounted on this chassis. These will be listed

here and discussed in sections where they relate to some specific operation.

The operation technique of all four of these switches is to

provide a ground return for relays on other chassis. This

is a return to the 24 volt supply. This means that they

function by operating a relay which in turn performs the

control listed on the switch label.

1.

2.

3.

4.

Crosshead manual up.

Crosshead manual down.

Crosshead jog up.

Crosshead jog down.

12
Section 3 - The machine crosshead

3.0.0 The machine crosshead

The crosshead is the mechanism by which the system converts

all instruction and control to useful output. This section

of the manual outlines its relationship to other parts of

the system and details a m,ethod in which it may be essentially

isolated Troa other systems for either study or adjustmicnt.

Gilmore manual pages 11, 12, 12a and 13 should be referred

to for many details not listed here.

Communication between the crosshead and other systems is in an electrical form.

Input signals to the crosshead are:

1. Power.

2. Movement control.

3. Power control.

Output signals from the crosshead are:

4. Movement response.

5. Force signals.

6. Safety condition signals.

Figure 3.0-0 is a basic layout of the relationship of the crosshead to the overall system. Legend and numbers on this layout

show the signal distribution as outlined above.

Figure 3-C.O is too simplified to permit effective description of

necessary details. Figure 3. 0.0. a is an expansion of Figure 3.0.0

to serve as a reference for discussions immediately following.

3.1.0 Crosshead power

Power to the crosshead starts with a 440 volt electrical system

which drives an electrically powered hydraulic pump. Application

of this power is by procedures outlined in sections 2.2.0 and

2.3.0 of this report. In summary here we list following

requirements

1. Console power must be on.

2. Crosshead power must be on.

Under these conditions, the pump will be running and oil pressure

will be present. No movement will occur until further control

requirements are satisfied. The representation of this part of

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the system is indicated by block (1) of Figure 3- 0.0a. It will be seen that the pump is isolated from the drive motor by the oil

control valve (2).

3.2.0 The oil control valve (2)

The oil control valve controls both machine speed and direction.

: This unit and its associated amplifiers (3) and (^) are supplied

by the Oilgear Company. Figure 3-2.0 is an illustrative diagram

of how this unit works.

An electrical signal drives the torque motor powered swing valve.

The differential pressure resulting from the swing plate movement

then moves the slide block to an off center position. This

results in an oil pressure proportional to the slide block

displacement.

An LVDT reports the position of the slide block. This signal is

sensed by the same amplifier system which drives the swing plate

torque motor. The LVDT signal is compared with the original drive

signal to reach a balance on the slide block position needed to

properly drive the system at the requested speed.

The original signal is a 60 hertz sinusoidal signal, applied to

the preamplifier, whose amplitude is proportional to the speed

requested. The phase of the signal determines the direction of

the crosshead movement. Gains are set so that a 1 volt r.m.s. signal drives the machine at maximum rated speed.

3.3.0 The drive motor (5)

The speed of the drive motor is proportional to the oil pressure

output of the oil control valve. It should be noted here that the

drive motor output is extended over the three speed ranges by

clutching using clutches (8), (9) and (10).

The drive motor is an important part of the speed control loop.

Attached to its output shaft are a d.c. tachometer (6) and a position synchro (7). The outputs of these units are constantly

monitored by the speed control circuits in the electronics

cabinet. The units report the speed of the motor and the shaft

position.

. This hydraulic drive motor is the means of actually moving the

crosshead by way of the clutching system.

3.4.0 Signal summary in power source

1. A.c. power to turn on drive power (115V a.c).

16
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. 2. A.c. input drive power to drive oil pump 3 0 a.c).

3. Swing valve drive input, 1 volt r.m.s. = full speed.

4. LVDT feedback output from slide block.

5. D.C. tachometer output, voltage proportional to speed.

6. Synchro motor shaft position signal.

3.5.0 Crosshead speed clutches (8), (9) and (10)

Operation of the machine to this point is simple and free of

interfaces which could cause machine damage. Activation of the

clutches changes this picture since the machine can now move.

The first safety feature enters at the clutch circuit level. This

is the synchronization circuit. Details of this circuit are given

elsewhere but it is necessary to summarize its method of operation

here for clarification.

3.6.0 Synchronization summary

The position synchronizer located on the drive motor shaft is

monitored and as this shaft departs in position from a reference

shaft inside the electronic console a voltage proportional to the

departure is generated.

If the displacement voltage is greater than a preset limit, power

to operate the clutches is removed or prevented from appearing.

Relay K404 is the synchronizing relay and must be operated before

the clutches are engaged. Gilmore manual pages 39 and 40 deal

with this circuit.

3.7.0 Clutch selection signals

The upper part of Figure 3.7.0 shows the schematic of the clutch

speed selection circuits. Clutch operation is by means of locking

relays K401, K402 and K403. These relays are mutually

interconnected in addition to being self locking. Only one can be on at a time. Page 17 of the Gilmore manual details operator use of the speed range clutch selection.

These relays are operated by push buttons on the front face of

chassis 400. The push buttons are numbered as follows:

Operation of any of these buttons will cause contacts on that

button to open the holding circuit of the other two relays. No

1.

2.

3.

Low speed push button is S404.

Medium speed push button is S405.

High speed push button is S406.

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power may be applied to any of the speed select relays unless the

.. sync, relay is activated. contacts supply current to

the entire circuit.

Another relay can enter the picture. Jog relay K408 if operated

will open the holding circuits normally used by all relays. A

special path is then available to turn on the low speed clutch

only. Circuit details of this function are unclear and will have

to be traced out. The Gilmore drawing D27142 sheet ^ of 6 shows an earlier circuit which is redlined out. The low speed selection

parts of this circuit may still be in. The Jog function is

operational

Indicator lights on chassis 400 show v^ich, if any, clutch relays

are operated.

3.8.0 Clutch operation •

The lower half of Figure 3.7.0 shows the operating path of the

clutches.

The power source to operate the clutches is a 100 volt d.c.

supply located on chassis 700. This supply receives an a.c. 120

volt input fron the power distribution set up.

Sync relay K404 is in series with all uses of this power. The use of K404 at this point and in the clutch selection circuit

described above (section 3.7.0) is a double safety measure.

Since only one relay of the group K401, K402 and K403 may be on at

any time, only one of the clutches shown in this diagram may be on at a time.

3.9.0 The fail safe brake (11)

Whenever none of the clutches is energized, a brake is applied to

- the crosshead drive. This brake is of a type that does not

require power when it is in the braking mode. It is therefore

i

. necessary to supply an active signal to release it.

Figure 3.7.0 shows the brake connections. Contacts on relays

K401, K402 and K403 are connected to form an "OR" circuit so that

.when any one of then is activated, the fail safe brake will be

released. Gilmore manual pages 12a and 57 refer to the fail safe

brake

20
3.10.0 Movement limiting switches

There are switches mounted on the loading frame which sense the

crosshead travel if it is either higher than or lower than

presetable points. These switches are shown on Figure 5.0.0 and

illustrated on Figure 3.0.0a parts (12) and (13-)

These switches act as a safety device and also may be used at the

operator's discretion to stop the machine at a fixed point.

The switches operate by disengaging the direction control relays,

K405 and K406, which select the direction of crosshead travel.

The limit switch will disengage only the relay causing the

movement which made the crosshead approach it. The machine is

halted by an insistence under these conditions of a zero velocity

in the direction of travel toward the switch.

The reason for this type disengagement is to allow the machine to

be reversed from the switch. Other circuits must be kept alive.

The movement control relays are discussed in detail in section 5.

3.11.0 Isolated operation of the crosshead for test purposes.

A method is presented for operating the crosshead without using

the crosshead control circuitry. This procedure is useful in

testing and calibrating the machine. Caution is advised since some of the safety devices are defeated in order to make this

method convenient and simple. Most danger is eliminated by

starting this procedure with the crosshead position a safe

distance away from the limits of travel. Figure 3.11-0 shows the

test configuration.

3.11.1 Synchronization circuit adjustments

The synchronization circuit through relay K404 will

defeat any attempt to move the crosshead. This

circuit must be circumvented.

1. Remove card X402 from its connector in

chassis 400.

2. Short-circuit connector pin 23 to pin 21 on X402's connector.

Relay K404 will now stay operated and permit powering

the clutch circuits. K404 will no longer provide any

safety protection.

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3.11.2 Install substitute crosshead control signal

A calibratible and measurable signal whose character

is not subject to feedback variation is needed to

establish a constant input to the system. A small

test box has been built for this purpose. Figure

3.11.2 shows the circuit of this box and the interconnection of the box with the crosshead assembly

and the current source.

1. Disconnect the leads on the oil gear preamplifier pin no. 1.

2. Install the test box as shown in Figure 3-11.2.

Start with the Variac set at zero.

3.11.3 Instrumentation of the test set up

1. Connect a d.c. voltmeter to the drive

motor tachometer. Use a ten volt scale.

2. Connect an a.c. voltmeter to the test box

output terminals. Signal here should not

exceed 2 volts. Positions of these meters

are shown on Figure 3-11.2.

3.II.M Machine controls to be used

1. Main power on.

2. Crosshead power on.

3. Speed range select (Any one of the three is

usable). Selection depends on the speed

the tester wishes to use.

3.11.5 Test operation

1. Direction of crosshead movement is now under

control of the reversing switch on the test box.

2. Speed of movement of the crosshead is now under

control of the Variac.

3.11.5 Test results

Nominal maximum speed is attained in any range with the

input signal equal to 1 volt. This may be ascertained in

either of two ways:

1. When a reading of 6.48 volts appears on the

tachometer voltmeter.

2. By measuring the distance the crosshead moves

in one minute.

23

The gain controls on the oil gear preamplifier and/or

amplifier are varied to attain this condition. Since

both input and feedback gains are involved, this

adjustment may not be attained immediately. When

satisfactory points of operation are reached, it is

suggested that the gain settings be recorded for future

reference

.

A further note of caution is in order. The tester may

obtain an apparently good set of values for these gains

and find that there is some tendency toward oscillation

under operational or loaded conditions. Under these

circumstances it is necessary to find a new set of gain

settings which will characteristically be lower in value

than the previous ones.

More precisely settable procedures will require

significantly more study of the resonance

characteristics of the crosshead assembly and probably a more sophisticated test procedure.

Figure 3. 11 -6 is a graph showing crosshead speed plotted

against tachometer voltage.

Section 4 - Synchronization

M.0.0 Synchronization is a title, covering the machine alignment

function, which is used as an indicator of control performance.

Gilmore manual page 40 is suggested as additional reading to

understand this function.

The crosshead drive motor is controlled by circuits on chassis

400. The crosshead drive motor has a slave to master relationship

with a small servo-control motor in this chassis. The

synchronization circuit measures the relationship between these

two motors and disconnects the drive train if evidence appears

that the drive motor is not fully responsive to the position of

the servo control motor.

The servo control motor is driven by electrical signals called

into play by the operator of the machine. These are direction and

speed signals. An error signal develops proportional to the

difference in shaft positions of the two motors. This signal is

applied to the crosshead control amplifier and the crosshead drive

motor moves in a direction and at a rate that tends to cancel the

error signal.

25
»<i^»»l WOTOH %HAFT- T^eWftMSieR OOTPuT +0.0. v/oltS
Figure 4.0.0 shows the motion control loops. Further reference is

made to this diagram later. The section of interest in this

discussion is the dotted block labeled Control Failure Detector,

which is attached to the crosshead control amplifier input.

Two things are immediately evident:

1. The synchronization circuit monitors the crosshead control signal itself.

2. The crosshead control signal itself monitors the

relationship of the servo to drive motors, through

the synchros. Any instability in the system will

be seen at this point.

4.1.0 Initialization of the synchronization

A method exists to start the system with the motors synchronized.

This is acconplished by preventing movement of the crosshead drive

motor and turning the servo motor until the attached synchros

yield the information that the two shafts are aligned.

A relay K409 is assigned to the direction of this process. Figure

4.1.0 shows the relationship of this relay to the rest of the

synchronization circuit. The actual movement of the servo motor

is also a function of K409 and is discussed under a later section.

For this section we need only know that movement occurs.

The movement of the servo motor occurs whenever K409 is operated.

There are six paths by v^ich K409 is initiated:

1. By sync on switch.

2. By the remote console lead.

3- % manual down switch.

4. By jog down switch.

5. By manual up switch.

6. By jog up switch.

Relay K409 can be prevented from operating by:

1. Operation of synchronizing relay K404. This

means that since K404 is operated, the machine

is already aligned and K409 cannot be useful.

2. Operation of the sync off switch. This is a logical error. There is no point in calling

for sync on at the same time that a call is

issued for sync off. This condition will occur only v^en someone is pushing buttons in a random

or illogical manner.

Both relays K409 and K404 are operated by grounding, one

27
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29

FiG-. W.l.o
terminal. Except in error detected or manual sync off modes,

the terminals of the relays sensing the 24 volt drive

source are awaiting operation, with the voltage present.

All six methods of turning K409 on are by grounding the low

terminal

.0 Operation of sync on relay K404

When K409 has been turned on by any of the six means, it

locks itself on and the servo motor searches for the

synchronized position.

At this time the error signal of the synchros is sensed by

detector X402 which is also shown on Figure 4.1.0.

The fact that K404 is not operated causes the following

actions:

1. The crosshead clutches cannot operate.

, - 2. The fail safe brake is on.

3- The crosshead control signal is removed from

the crosshead drive amplifiers.

4. The null detector X402 is forced into a sensitive

mode so that it will not report the null until

the alignment of the shafts is very close. In a practical operational state, the shafts are never exactly lined up. The starting alignment forced

by this system is closer than the shafts will

travel in relation to each other except when halted.

Relay K409 also sensitizes relay K404 by closing the path to the

null detector along which the relay K404 will ultimately be turned on by grounding through the null detector.

When the null detector senses a very close alignment, it grounds

the return lead of K404, and the relay and the sync on light are both operated. The sync on light is a variable intensity light

and glows with a brillance related to the closeness of the shaft

positions. In operation, dimming of this light gives warning

prior to an out of sync shutdown.

Operation of K404 disconnects K409 and sensitizes machine circuits

such as clutch control and the control amplifier.

The locking circuit for relay K404 is now held through a series of

a set of contacts of K404, a set of contacts of a non-operated

K408 (the jog relay) and the null detector circuit. The action of

the null detector is now broadened to a point where it will hold

the relay K404 operated even with a one volt error signal.

30
Relay can be turned off, thereby stopping the machine, by

three methods. These three methods are representative of abnormal

or forced stops. Just stopping the motion of the crosshead does

not call for a disconnect of relay K404. However, disconnect of • relay K404 will force a stop of the crosshead. Aborted stops occur as a result of three conditions:

1. Manual operation of the sync off button.

2. The detection, by the null detector, of a crosshead

drive signal in excess of 1.1 volts.

3- Operation of the jog relay K408.

4.3.0 Importance of synchronization relay K404

This relay serves as a safety valve in the machine. Its contacts

open or close paths which have the potential to damage the machine

if not used properly. The sensor which controls KhOH is in a position to sense the feedback control loop where out of control

signals appear as excessive attempts to compensate for

fluctuations.

4,4.0 Details of the failure detector

A plug-in failure detector is included in the machine on chassis

400. Gilmore industries entitles this as null detector no. X402.

Figure 4.4.0 is the Gilmore schematic.

Operation of the circuit might be better explained by describing

it as a synchro phase detector and trigger. It monitors the phase

relationship between the main drive synchro and the servo control

synchro.

4.4.1 The control failure detector

The control failure detector monitors the output of the

servo control synchro. This signal is the drive signal

fed into the Oil Gear Ccmpany preamplifier as the

crosshead drive signal. Figure 3.11-0 shov/s the

position of the circuit.

This signal is a 60 hertz sine wave varying from zero volts to nominal 1 volt for full crosshead speed.

Maximum voltage is over 2 volts r.m.s. but this will be

attained only during an out of control situation.

4.4.2 Excessive speed signal

This is defined as a controlled crosshead movement at

greater than nominal rated speed. Such conditions could

be due to poor adjustment of system variables, to

31
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32
certain ccmponent failures, or to failure of the

crosshead to move as directed. *

Signal characteristics just prior to detecting this

condition will show a steady 60 hertz signal of nearly

1.1 volts r.m.s.

This fault is characterized by the failure of the two

system synchros to track with each other.

The signal is a rapidly fluctuating 60 hertz signal from

0 to over 2 volts r.m.s. and alternating in and out of

phase with the 60 hertz system supply power.

Either type of error is detected by an amplitude

detection based on a 1.1 volt threshold accepted at the

output of the servo control synchro.

If this voltage exceeds 1.1 volts the system is shut

down by opening relay K404.

4.4.5 Operation of the sensor detector electronics

Figure 4.4.5 shows the working parts of this system.

This schematic has been stripped of parts vrtiich are superfluous to this explanation.

The unit can be divided into four sectors as outlined

below:

1. Input amplifier and rectifier.

2. Amplitude comparator.

3. Threshold detector.

4. Output drivers.

4.4.6 The input rectifier is a unity gain operational amplifier

which offers a choice of a negative or positive one half

wave sample of the crosshead drive signal. The negative

signal was chosen for use in this system. Figure 4.4.6

illustrates this signal.

The amplitude comparator sector compares the output of

the input rect^-fier with a d.c. bias signal and

4.4.3 Out of control signal

4.4.4 Detection of an error

4.4.7 The amplitude comparator sector

33


amplifies the difference. The lower section of Figure

;

' 4.4.6 illustrates this signal.

The d.c. bias used in this sector has two levels of

operation. The selection of level of operation is based on relay K404.

The operational level is used whenever the machine is in

normal operation and is the mode described heretofore in

this manual.

An alignment mode also exists. This mode is automatically called for when relay K404 is in the non- operate condition.

The purpose of this mode is to require that the starting

alignment be very close to in-phase before the machine

is initially turned on. This avoids a surge when the

clutches are powered up.

During alignment, the positive d.c. bias is reduced and

the detector becomes responsive to very small signals.

The synchros will align themselves in a position to

satisfy this small signal sensitivity.

4.4.8 The threshold detector

This amplifier reports the output of the amplitude

conparator as either a go or no go signal addressing the

output drivers. The crossover input is at ground level.

The output of this detector is able to drive the inputs

of the output drivers.

4.4.9 The output drivers

The output drivers are transistors in series with the

driven units.

1. Relay K404 cannot operate without the output

driver because its coil current is returned

to ground through the driver.

2. The front panel indicator light is driven in

the same manner by another transistor.

4.4.10 The output signal characteristics in the relay driver

setups are illustrated in Figure 4.4.10 and are explained below:

1. Steady state +25 volts when totally inoperative.

2. Steady state ground level when fully operative.

36
8

i

1

1 4-

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^ROR 6^ TWt 4ot.lt> tl^/l^^ UOWeR Pit] " USCOHH-NBS-DC
3. A pulsed +25 volt signal when operative but

approaching cut off. When the variable pulse

duty cycle (time variable) reaches approximately

^5% of full time, relay K40U will open up and the

system will be shut down.

4. Approaching cut off will be audibly indicated by

increasing buzzing from relay K404. The

inductance of relay coil K404 is the source of

this behavior. It integrates the pulse duration

and when the duty cycle reaches the value

defined above, the relay opens.

Except for the positive voltage attained, the signal

driving the indicator lamp is the same. The lamp drive

transistor is in parallel with the relay drive

transistor. Dimming of the lamp signals approaching cut

off.

4.4.11 Reset of the system

The null detector system is self resetting. Removing

the conditions which caused shut down allov^s the unit to

resume its normal settings.

The operation of K404 is self locking if triggered,

however. Manual operator intervention is needed to

restore the entire system to an operable condition.

Service is restored by realigning the synchros and

reactivating other desired conditions and controls.

Section 5 - Direction Control

5.0.0 Crosshead direction control relays control the direction of the

crosshead in most but not all test conditions in which the machine

is used. The exception is in Maintain Load Function where a different control system is employed.

Direction is selected by the polarity of input to the crosshead

servo control motor. Two relays, mutually exclusive, are used to

achieve this polarity control.

1. Relay K405 will direct downward movement.

2. Relay K406 will direct upward movement.

The shifting of direction is shown by labelled relay contacts on the

servo motor control diagram Fig. 6.0.0. This section deals with the

operation of the relays themselves.

38
In addition to direction control functions, there are certain

safety measures which enter the system at the direction control

points. These are discussed below.

Figure 5.0.0 is a schematic of the circuits treated in this

section.

.1.0 Motion relay turn-on

Motion relay turn-on is by grounding the return terminal of relay.

5.1.1 The system at rest can have both motion relays in the

off position. Certain safety responses will in fact

return both relays to off at the same time.

5.1.2 The relays can be turned on by four different paths:

1. By a signal from the remote console through

position 1 of the function switch. An example

is switch section S401G on this diagram.

2. By a jog switch through a diode by using position

2 (Manual) of the function switch. An example

on switch S401G is by the jog down switch, via

diode CR409 and position 2 of switch S401G.

3. By closing the contacts of a pickup relay

dedicated to this purpose and driven by the

manual control select switches.

An example of this operation starts with the

depressing of the manual down switch. This

picks up relay K410 as we are not in a jog

phase. Relay K410 holds on through the following

series of contacts.

1. Jog relay K408 not operated.

2. Relay K410 operated.

3. Sync relay K404 is operated.

4. Up drive relay K411 is not operated under

these conditions.

4. By a null detector which senses the attainment of

a preset limit in the cycle mode. This system

is outlined immediately below:

1. Null detector X401B compares the retransmitting slidewire R102 with the preset

upper limit and will, when a match is made,

turn on, through ccrapression-tension selector

switches S205K and S205L, the proper up or

down control relay to start the crosshead

39

moving in the direction opposite to that

which brought it to this balance point. This

selection of relay is accomplished through

position 4 of the function switches SMOIG and

S401H.

2. The reversing action at the other limit is

a function of null detector X401A.

5.2.0 Holding operation of motion direction relays

Each of the four means of turning on the direction control

relays has associated with it a variation of a relay hold

scheme

1. The remote connection is a direct line, and the

holding pattern is a function of the remote console.

2. The jog operation will hold the direction relay on

only as long as the jog button is held depressed.

3. In manual operation, the drive relay (K410 or K411) serves as a holding relay.

H. In cycle the null detectors serve as hold down

drivers also.

5.3.0 Turn-off of the direction control relays

These relays do not guarantee motion since other machine

factors must be satisfied or called upon to actually achieve

motion. The four paths of operation are again the basis for

the list below of how the direction control relays are cancelled.

I. Remote turnoff is a function of unspecified (as

far as this discussion is concerned) procedures.

2. Turn-off in jog is automatic as soon as the button

is released.

3. Turn-off in manual has two forms. This discussion

excludes those safety features which are part of

this schematic. Since the relays lock on in manual

mode, turn-off must be a deliberate process. It

is accomplished as follows:

1. Whenever the alternate direction control

is activated, it cancels the one in

existence.

2. Activation of the sync off procedure will

cancel both direction control relays by

cancelling the driver-hold relays K410

and K411.

4. There is no provision for turning off both relays

41
in the cycle mode since that action is logically

incompatible with the cycle mode. Turning off a particular direction control is accomplished by

turning on the opposite direction control.

5.'4.0 Indicator lights on the face of chassis 300 show which, if

any, of the direction control relays is on. The control

circuits for turning on these lights are shown in Figure 5.0.0

5.5.0 Safety functions associated with the direction control system

All normal turning on of the direction control relays is

accomplished by grounding the return terminal of the relays.

All safety turnoffs are accomplished by removing the current

supply to the relays.

Response to a safety violation is to prevent further movement in

the direction that has led to the problem but to leave open

optional travel in the opposite direction to relieve the condition

which led to the problem.

5.5.1 Range exceed problems

Two forms of range exceed are recognized:

' 1. Load range.

2. Strain range.

Both conditions are detected at appropriate points and

reported by opening a normally closed relay K407. This

circuit is shown on schematic Figure 5.0.0.

Opening K407 would cut off current to both directional

relays except for the presence of tension-compression

switch S205F, which holds current on whichever of the

two will carry the crosshead in the direction needed to

relieve the strain or load.

5.5.2 Limit exceeded problems

These problems are caused by the crosshead reaching the

microswitches that detect a motion so extreme that no further motion in that direction is to be permitted.

A switch is positioned at each limit of travel to

prohibit travel in that direction. No bypass is

possible of these switches.

42
Section 6 - Crosshead Drive Control

6.0.0 Crosshead drive servo control

This controller acts through the Oil Gear amplifiers to actually

control the rate of movement as well as the direction of movement

of the crosshead.

Figure 6.0.0 shows the elements involved in this control.

The principle of operation is to drive the servo control motor in

the desired manner and then to entice (via the Oil Gear

amplifiers) the crosshead drive system to follow this movement.

Figure 6.0.0a is a block diagram showing the control loops

involved

6.1.0 The command servo motor

iMotor X403 is the servo control motor. (See Figure 6.0.0) This

m.otor has a d.c. tachometer on its shaft and is directly coupled

to a synchro labelled the synchro receiver.

A meter is connected to the driving signal to show the rate of

loading of the motor.

The motor is driven by amplifier X404 whose purpose is to provide

the power gain needed to convert the drive signal to a level

capable of driving the motor. A special power supply X403

supplies the current for this amplifier to use in driving the

command servo motor. This supply is not well regulated and does

not have to be. Ripple on its output will not introduce problems.

6.2.0 Command servo signal mixer

Operational amplifier P65AU is the source of the signal which was

the subject of section 6.1.0 above. This is a feedback amplifier

mixer which combines the motion command with the motion response

of both the command servo and the crosshead drive motor. Its

output is the one amplified to drive the command servo.

Three signals are fed into a current summing input of this

amplifier:

1. The motion control signal. This signal has a number of sources, the sum of which appears on

the input of R21 as the effective drive signal.

2. A negative feedback signal derived from the

command servo tachometer. This is on the shaft

43
1|14
45
of the command servo motor and acts to stabilize

^ or counteract the motion control signal. The

magnitude of this feedback is determined by

resistor R2 which is its input resistor.

3. A negative feedback signal derived from the cross- head motor tachometer. A significantly larger

negative feedback signal, similar to 2. above,

, originates in a tachcmeter attached to the drive

motor shaft. This signal enters the amplifier

; through resistor fi3. Frcm the resistance of R3,

the contribution of this path is 7-1/2 times

larger than that from the servo motor tachometer.

Recapitulating the above, we see an input signal which is

stabilized by two feedback responses. Fortunately for the

simplicity of operation, these loops do not require adjustment in

normal operation. It is possible that further study of this

system will dictate more desirable relationships between the

feedback ratios. Such adjustments are not operationally necessary

but will be preset to a single optimum set of values.

6.3.0 Input control signal ^

This section will deal with the sources and adjustment of the

input signal to the command servo signal mixer. This signal

enters, as outlined above, through resistor R21.

6.3.1 Control by relay K409

The first control path encountered when tracing

backwards from R21 is that dictated by relay K409. This

is the special path for synchronizing the machine by

alignment of the Synchro receiver with the synchro

transmitter. This input enters through resistor Rl.

These signals are isolated by relay contacts and no interference between them exists.

6.3.2 Control by jog relay K408

The next choice presented to the servo control is that

dictated by relay K408. A special short movement is

called for by jog and this is a direction sensitive

command. Relay K408 selects a special signal via

resistor divider R402 and R401 whose polarity is

determined by up-down selection relays K405 and K406,

via terminal board 406 pins 13 and 14. Operation of jog as outlined in another section forces the operation of

one or the other of relays K405 or K406 thus assuring

/ that a current source will exist for this operation.

46
6.3.3 Operational Control

Absence of K409 and K408, as outlined immediately above,

will result in the input signal coming through selector

switches S401-D and S401-E. These are arms of the

machine function selector switch.

1. Remote function places control in the remote

console entirely.

2. Manual function and cycle function obtain

current through the speed control potentiometer, through resistor R408 and ultimately

through the direction control relays K407

and K405 at the same point as the jog operation

in section 6.3.2.

3. I'feintain load uses the same speed control

potentiometer as in 2 above. Its signal source is the maintain load amplifier MI8OA

via switch S401-I.

6.4.0 The output signal

Discussion in this section has been related to driving the command

servo motor. The output or crosshead drive signal is derived from

the positional relationship of the synchro transmitter on the

crosshead drive motor and the synchro receiver on the command

servo motor. The command synchro is shown on Figure (6.0.0). The

drive signal appears on TB405 pins 4 and 5. The signal is fed

directly to the Oil Gear preamplifier via TB403 terminals 10 and

11. The signal is also subject to interruption by relay K404 and

is monitored by detector X402, which is explained in section

4.4.0.

Section 7 - The Measuring Circuits

7.0.0 The measuring circuits

The measurement of force is based on the response of four load

cells located under the loading frame lower platen. These cells

are connected as described in Gilmore manual section 7.1.

Subsequent to original delivery of these machines the Astrodata

amplifying system was replaced with an amplifying system mounted on a card and shown on Figure 7.0.0. This figure shows the load

cells, their power supplies, the load cell amplifiers and mixers,

and the output dividers. It is extracted from Gilmore drawing

D27142 sheet 2.

47

Figure 7.0.0 shows the parts that are discussed in this section

section of the manual. It starts with the load cells and ends

with a single output which is proportional to force.

7.1.0 The load cells

The method of connecting the load cells is given in Gilmore manual

section 7.1. The electrical equivalent of a pair of the cells as connected is shown in Figure 7.1.0 for the 200K machine. Location

and mounting details will be found in section 4.3 of the Gilmore

manual. Figure 7.1.0a shows the load cell orientation on the platen.

Figure 7.0.0 shows the details of the connection of all cells in

the machine.

Power supplies PS201 and PS202 serve the load cells and are dedicated to this one use. Potentiometers and switches shown on the drawing are used to calibrate or standardize the cells. These

parts are designated potentiometers R201 and R202, switches S210A

and S201B. These components are mounted on chassis 200.

Instructions for standardizing the load cells are given in the

Gilmore manual section 5.1.4.

7.2.0 The load cell amplifiers and mixer

The signal amplifiers, the mixer, and the power supplies for these

parts are mounted in a box attached to the loading frame. These

components are placed close to the load cells to minimize noise

problems. The minimum forces detected by the load cells

correspond to a 1/2 microvolt signal. The distance between the

console and the loading frame and the number of connecting lines

made close placement of the amplifiers mandatory if the lowest

range of the machine was to be used.

The single output line of these conponents carries an amplified

signal v^ose minimum is in the low millivolt range

Parts involved in this section are shown on Figure 7.0.0 and are identified as:

1. Power supply PS203.

2. Amplifiers AR-1, AR-2 and AR-3.

The output line has two destinations:

1. The remote console.

2. The range selection divider in chassis 200.

^9
/

50
I^ACH I NH2 PRONT

LOAD CELL UOCATIOW G.lUMOf^E- rv^ACHlNeS

51
7.3.0 Range selection

The manufacturer chose to use a single fixed gain wide range

amplifying system for the machines.

Range changing is accomplished by using a fraction of the

amplifier output for the higher loads. Figure 7.0.0 shows this

system. The signal input enters the system on TB202-1 terminal.

With the range changing accomplished, the signal output leaves the

system on the moving contact of switch S210-C,

A description of the divider and its use and adjustment is given

in Gilmore manual section 7.1, page 3^.

Section 8 - Maintain Load

8.0.0 Introduction

This section explains the electronics used in the maintain load

mode. This circuit is unusual in its relation to the drive

systems in that it bypasses the normal up and down relays. The

system is called when the function switch is in the maintain load

position, or it can be called by the remote console.

Figure 8.0.0 shows the circuits which are discussed. The function

switch is in the maintain load {position on this diagram.

8.1.0 Signal sources

A reference signal (which is entered as a percent of full scale

voltage reference) is given to the machine by the operator using

the preset load potentiometer. This signal enters operational

amplifier M210 by the path from the source potentiometer R503,

through TB501-5, TB401A and resistor R19.

The reference signal is compared with the retransmitting slidewire

RI03. The slidewire reports the percent of range position

actually in force on the machine. The slidewire signal enters

amplifier M210 from the source slidewire R103 by the path RB106-4,

TB401-1, S401B and resistor RI8.

8.2.0 The error signal

If these signals are equal in amplitude, amplifier M210 reports a zero output. If the signals are not equal, the amplifier delivers

52
53
a signal proportional to their difference, whose polarity will

show which input exceeds the other.

8.3.0 Reaction rate control

The output of amplifier M210 is not fed directly to the crosshead

servo control. It is entered into another operational amplifier

whose task is to mix two forms of rate control.

The output of M210 is fed via switch S401K to potentiometer R414

whose arm will now represent a linear fraction of the error

signal. This fraction voltage is fed through switch S401L and

resistor R21 to amplifier MI8OA. This is now the error signal

modified to drive amplifier MI8OA at a lower rate than the full

signal out of M210. i

The tachometer TG102 monitors the movement of the slidewire drive

and produces a signal which is proportional to the rate the

slidewire is changing and whose polarity shows the direction in

which the slidewire is moving. This signal is also fed to MI8OA.

The path is through TB105-5, TB403-1, resistor R23 (on card X404),

switch S401C and resistor R22.

At balance point both signals discussed above are zero.

8.4.0 Servo control drive

The output of MI8OA is presented to the servo control motor input

through switch S401I.

S401D and S401E are the normal input switches to the servo motor

controller. The normal speed control potentiometer R415 is still

in this circuit. It can serve if desired to modify further the

speed with which the system will try to maintain a load.

8.5.0 Cross reference

Maintain load operation is discussed in Gilmore section 5.3, which

provides additional insight into this system and defines the

proper use of the controls.

Section 9 - The Indicating Circuits

9.0.0 The indicating circuits are covered in detail in the Gilmore

manual section 7.1.

54
The diagrain has been redrawn to aid in understanding the system.

Figure 9.0.0 shows the circuits.

Section 10 - Velocity mode feedback control system

10.0.0 Introduction

This section contains the open loop frequency response

characteristics of the Manual node (velocity control node) of the

200 000 Ibf Gilmore testing machine. No other modes were investigated. The tests were performed witn no test sample in

the machine.

Open loop phase and gain responses to different sinusoidal

frequencies are plotted as a Bode plot.

One ordinate is plotted as 20 log

v input"^^ other

ordinate is plotted as phase shift in degrees. The abscissa is

plotted as the frequency in Hz.

There is no measurable difference between the responses in the

High speed mode and in the Medium speed mode. Since there is no measurable difference between High & Medium speed modes only the

High and Low speed modes are plotted.

10.1.0 Description and results of tests

Six tests were performed on the Gilmore machine. In test number

3, ^, and 5 the methods were found to be in error. The tests were repeated in test number 6.

Test number 1 (Figures 10.1. OA and 10.1. OB) is of the outer loop

(loop number 1 on block diagram Figure lO.O.lC). The loop 'was broken at TB 406 terminal number 11 (Figure 6.0.0). The input was applied through R3 to the P65AU operational amplifier, and the

response was taken from TB 406 terminal 11 which is connected to

the Machine Tachometer output.

The curves of Figures 10.1. OA and 10.1. OB show that the low

frequency open-loop gain is the same for both High and Low speed

modes. The responses of these modes are different at higher

frequencies. There appears to be a pair of complex poles at about

4 hertz (u/ =12.5), because the gain plot shows peaking somewhere

between 2 and 4 hertz. The natural frequency , ^ ^ = ^ tx of

these poles is approximately 4 hertz. The actual resonant

frequency is cv„\//-;^ /^.^ where zeta, /' , is the damping ratio.

Zeta cannot be determined exactly with the data points shown; more

55
56
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57
S33H93G Ni 3SVHd

58
59
points would be needed to find zeta,^^t^ , and the resonant

frequency.

Zeta appears to be different for High and Low speeds. High speed

appears to have a lower zeta (more peaking), and therefore the

machine will be more likely to overshoot when in the High speed

mode

Test number 2 (Figure lO.l.OD) is of the velocity stabilization

loop (loop number 2 on Figure lO.l.OC). This loop was broken at

R2 on board X40^ (Figure 6.0.0). The input was applied through

R2, and the response was taken from the terminal from which the

lead of R2 was disconnected (Command Servo Tachometer output).

This plot shows a pole at about 2 hertz. For normal operation

this loop is closed, and the closed loop response has a pole at

about 8 hertz. This frequency is high compared with the

frequencies of interest of loop number 1.

Test number 6 (Figure lO.l.OE) is of the synchronization loop

(loop number 3 in Figure lO.l.OC). The loop was broken at

terminal number 1 of the Oil-Gear preamplifier (Figure 6.0.0).

The input was applied to terminal 1 and the response was taken

from the wire removed from terminal 1 (Command Servo Synchro

Receiver). The signal at the point where the loop was broken is

phase synchronous 60 hertz. The input used was amplitude

modulated on a 60 hertz carrier. The carrier was obtained from a socket on the control panel. A block diagram of the test

instruments used is shown in Figure 10.1. OF.

The Bode plot for test number 6 (Figure lO.l.OE) shows an integrator (1/s) with vriiat appear to be complex poles at about 4

hertz. The closed loop response has a corner at 0.55 hertz and

the complex poles at about 4 hertz. This loop (loop 3) has the

dominant poles that appear in the outer loop (loop 1) response.

As a test of the experimental results the open loop response of

loop 1 will be compared with the responses from loops 2 and 3.

The open loop responses of loops 2 and 3 ar'e known, so the closed

loop responses can be calculated. The close loop responses of 2,

3, H , and 1/S connected in cascade should correspond closely

with the open loop response of loop 1.

60
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Loop 1 open loop response

Si- .S 6KZ/T

5 - Z

Loop 2 open loop response

where G2 = 3.

Gz Hz

Loop 2 closed loop response = = ^

Loop 3 ppen loop response

where = 3.6.

S

Loop 3 closed loop response = ^ , - —e -? /

Cascade H^, ~- , closed loop 2, and closed loop 3 and

compare this to the open loop response of loop 1.

s.z _ H. i y/7G£

S-^'s.V (Si- IGJT)(Si2L)

6^
There is very close correlation between the dominant poles on both

sides of the equation. This shows that the closed loop response

of loop 3 has the dominant pole observed in the open loop response

of loop 1. The complex poles were left out of the exercise above

because they cannot be determined quantitatively from the few data

points on the graphs.

10.2.0 Conclusions

The conclusions that can be drawn about the possible optimization

of the servo system are as follows:

The machine has conservative parameters (large phase margin and

large gain margin) when there is no sample in the machine. These

parameters change with a sample in the machine, and thus the

machine will require different optimization for each sample.

Optimization will require many tests of the response of the

machine for each sample. If the machine is to be used to test one

kind of material, it may be cost-effective to optimize. If the

machine is to be used to test non- identical samples, optimization

will not be worthwhile.

As it is adjusted now, the machine is intended to work on the

worst-case sample. This means the response is slower than it

could be with optimization, but the conservative parameters assure

that the machine will not oscillate with any sample.

USCOMM-NBS-DC 65
NBS-lUA (REV. 7-73)

U.o. Ut"l . KJr \^\JrnTn

,

BIBLIOGRAPHIC DATA

SHEET

1. PUBLIC ATION OR REPORT NO.

NBSIR 75-773

2. Gov't Accession

No.

3. Recipient's Accession No.

4. TITLE AND SUBTITLE

Report on Characteristics of Three Universal

Force Testing Machines

5. Publication Date

6. Performing Organization Code

7. AUTHOR(S)j^^

C, Palasky, J. E. Malcolm and W, H. Appleton

8. Performing Organ. Report No.

9. PERFORMING ORGANIZATION NAME AND ADDRESS

NATIONAL BUREAU OF STANDARDS

DEPARTMENT OF COMMERCE

WASHINGTON, D.C. 20234

10. Pro)ect/Task/Work Unit No. 4460112

11. Contract/Grant No.

M. Sponsoring Organization Name and Complete Address (Street, City, State, ZIP)

Mechanics Division

Institute for Basic Standards

National Bureau of Standards

13. Type of Report & Period Covered

Final

14. Sponsoring Agency Code

15. SUPPLEMENTARY NOTES

16. ABSTRACT (A 200-word or less factual summary of most significant information. If document includes a significant

bibliography or literature survey, mention it here.)

Three universal testing machines at the National Bureau of Standards have been

analyzed in detail. Information developed in the study is organized in this

manual which provides a better understanding of the theory, structure, and

operation of the machines, an improved basis for maintenance, a clear and

logical set of schematic drawings, and other data that supplement the

manufacturer's documentation.

17. KEY WORDS (six to twelve entries; alphabetical order; capitalize only <he first letter of the first key word unless a proper name; separated by semicolons)

Automatic control; constant loading; force machine; load cell; mechanical testing;

velocity feedback

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