Ship stabilization-multra control system - K-160

AJOURNAI OF NSTUMEPtT ENGINEERING.

ARCHEF

JULY

1963

MUIRHEAD

OURNAL OF INSTRUMENT ENGINEERING

R.J.STANLEY

I I A'J k.i.

.

,

EDITOR

Published by MUIRHEAD & CO. LIMITED BECKENHAM KENT ENGLAND

Telephone: Beckenham 4888 Telegrams and Cables: MUIRHEAD BECKENHAM THE MUIRHEAD GROUP

CANADA

MUIRHEAD INSTRUMENTS LIMITED

CT. BRITAIN MUIRHEAD & CO. LIMITED

ADDISON ELECTRIC COMPANY LIMITED ADDISON CHEMICAL LIMITED ITALY

MUIRHEAD ITALIANA s.r.l. U.S.A.

MUIRHEAD INSTRUMENTS INC. ADDISON ELECTRIC COMPANY INC.

IN THIS ISSUE

SHIP STABILIZATION -

Page 19

MULTRA CONTROL SYSTEM - K-160

by J. Bell, M.Sc., M.I.E.E., M.R.I.N.A.

WEATHER CHARTS FOR SHIPS AT SEA

Back Cover

Reprinted from RACAL REVIEW

THE FRONT COVER

The front cover depicts a Leander' class frigate, one of the latest additions to the Royal Navy. These vessels are being equipped with stabilizers incorporating the latest in con-trol systems the Muirhead K-160 MULTRA Concon-trol System described in this issue.

Illustration by G. F. Campbell,A.M.R.1.N.A..based on a photograph by courtesy of the Admiralty, Department of the Chief of Naval Information.

SIZE 18 SYNCHRO RECEIVER INDICATOR

The Size 18 Synchro Receiver Indicator described in the January 1963 issue of Technique is now in production in two versions, types 18M23A1 and 18M23A2 for 400 c/s and 60 c/s respectively.

Details are given in the relevant Data Sheet which is available on request.

VOLUME Il NUMBER 3

SHIP STABILIZATION - MULTRA CONTROL SYSTEM

K-160

by J. Bell, M.Sc., M.LE.E., M.R.I.N.A..n

Introduction

The present production stabilizer equipment

known as the D-769 Compensated Control has been in use for a number of years with relatively small modifications. Some points have arisen, however, which justify a revision of the design while still using in principle the same control. The size and weight of the control equipment

have been dictated in the previous design by

the requirement that the gyroscopic units should be capable of sufficient mechanical output to operate the Magslips and succeeding hydraulic

amplifiers without a significant error. The forces

involved are not large but a gyro wheel of the order of 20 lb in weight is necessary to obtain the momentum required to provide an output, after mechanical differentiation, of the order of 01 oz in to operate a Magslip.

lt was desired to make a control equipment

using modern synchro type control elements

and also to reduce the bulk and weight of the control equipment. Such a step involved neces-sarily the use of amplifiers before application to control existing types of hydraulic relay. In order to provide, in the new design, the same

degree of reliability which has hitherto been

enjoyed by the users of control equipment, it was considered desirable that the amplifiers

should be of the transistor type and the design

provides in the most vital portions of the control

equipment, interchangeable amplifiers so that

should a fault develop even in these very

re-liable units, a simple interchange by selection can be made to maintain the equipment in an operating condition.

The new form of the control equipment uses

the same functions of the vessel's motion as

previously, viz, roll angle, roll velocity and roll acceleration. Helm control and natural list are also features of the new control. The fin

feed-back which was hitherto employed has been

omitted. This feedback had been found to be a ready means of adjustment of the sensitivity of

the compensated control. By this means the sensitivity of the whole equipment could be altered without having to make mechanical

adjustments on the gyro

control linkages.

With the introduction of amplifiers in the new

control a suitable potentiometer can be used

to obtain varying sensitivity settings in a simple manner. Fig. i is a schematic diagram of the

system.

No. FN

Fig. 1. K. 160 Stabilizer Control

*EngJneerIng Consultant, Mu rhead & Co. Limited.

Structural details

The roll angle gyro consists of a pendulously

mounted assembly of a size 18 servomotor

driving a 083 lb flywheel. The assembly is borne

in gimbals specially designed (when suitably

mounted on shock absorbing mountings of

accepted type) to resist shock in accordance

with the strict requirementsofthe Royal Navy. For commercial use, shock mountings are not necessary. The general design of the gyroscope is similar to that which has been used for some years in our D-993 Roll Recorder.

The roll velocity measuring gyroscope con-sists of a flywheel of approximately 4 lb weight mounted on its own bearings and driven by a

size 18 servomotorthrougha hysteresis coupling.

This is substantially the same design as has been used for some years in the D-768 Gyro

Controlled Hydraulic Relay.

The roll acceleration is measured by differen-tiating the movement of the roll velocity

gyro-Fig. 2. Gyro Unit wi/i, covers removed

20

scope by meansofa servo, and the acceleration term thus derived is rather more precise than

that given by the mechanical differentiation used in the previous control. The method of

producing the acceleration signal is quite simple.

A servo follows up the precession of the roll

velocity gyro and the speed of the servomotor therefore corresponds to the rate of precession.

The rotational speed of the motor is considerably

higher than the precessional speed of the gyro

and it can be applied directly to driving an induction generator whose output voltage at every instant, therefore, represents the roll

acceleration. The signal generated is small and

requires a stage of amplification before applying

it. in common with the other signals, to the control chain. Willi simple harmonic motion

of say ten seconds period and ±2 degrees roll. the lag in the velocity function is approximately

8° and the lag in the derived acceleration

function is 17° more. For larger angles

of

ROLL VELOCITY LINK ACCELERATION OUTPUT AMPLIFIER X4 HINGE PIN

Str.,

VERTICAL KEE PING GYRO LINK SERVO & SY N CH RO TRAY AMPLIFIERS XI X2 X3 POWER TSUPPLY ._SENSITIVITY

ACCELERATION DASH POT VELOCITY DA 5H PO T ROLL VELOCITY GYRO VERTICAL KEEPING GYRO f,

Fig. 3. Mechanism Unit

movement the angular lag of each function is

less.

While the control functions are generated in accordance with the movement of the vessel,

the actual amount of each control must be

selected according to some theoretical

justi-tication and also in accordance with experience gained in practice. [t is therefore necessary to

have some ready arrangements by which a

suitable fraction of each control function may be selected and then added to the others to con-stitute the whole control function.

Transducers and Summation

For the roll angle and roll velocity functions,

synchro type elements known as Linvars are

operated directly by the gyroscopes. These are

of the size iI (1 I in external diameter) and

similar sized synchro elements are used in the acceleration and natural list servos. The Linvar has the characteristic that it gives an a.c. output voltage proportional to the angle through which its rotor is moved from a zero position. Each Linvar and also the output from the acceleration amplifier and the helm transmitter (if fitted) is

applied to a potentiometer having nine tappings.

The output windings are all electrically isolated from each other and from earth. They can there-fore be connected in series and added (or

sub-tracted) directly according to the sign of the

function each represents. The output from this summated circuit is applied via an adjustable attenuator to an amplifier which energizes the

output transformer of the control equipment.

Four outgoing parallel windings are provided

21

on the output transformer each of which is

capable of energizing through a phase-conscious

rectifying system, a D-696 Hydraulic Relay

whose mechanical output is capable of operating

the V.S.G. pump required to actuate a stabilizer

fin.

Adjustments

The equipment is designed to be applied to ships

having natural rolling periods of from 7 to

30 seconds. The velocity gyro can be provided

with any one of three sets of centralizing springs

to match the characteristics of the particular

vessel in which it is being fitted and also, the gear ratio in the acceleration servo is selected to suit the period of the vessel. These changes are not operational but are made when installing

the equipment in a given vessel. To prevent

parasitic oscillation in the acceleration servo,

two dashpots are used which are filled with

silicone oil giving a minimum change of damping

with temperature. The adjustment of the

dam-ping in the dashpot for the velocity gyro is

just short of critical. This gives the minimum

of time lag without oscillation. The second

dashpot is adjusted to give a degree of damping in the mechanical coupling operating the input transducer to the acceleration servo. While the original Compensated Control equipment in-cludes a master hydraulic relay unit driving a bank of transmitters, this stage is eliminated in the new control. The signal for up to four fins

is passed directly from the gyro unit to the

hydraulic relays associated with each fin. The fin follow-up system employs electrical reset

NATURAL LIST SERVO ACCELERATION SERVO ROLL ANGLE L INVAR

Fig. 4. Servo and Synchro Tray

ROLL VELOCITY LI NVAR

as hitherto, the resetting signal being derived from a size 23 synchro operated mechanically by the stabilizer fin through a limited angle to

give substantially linear response. The input

controlling the hydraulic relay at any moment

is the difference between the control and the

resetting signals. The desired cut-off ratio can

be arranged by making the sensitivity of the initial stages of amplification such that full

control of the hydraulic relay output is obtained with say one quarter of the maximum signal. This represents a 4 I cut-off ratio.

As stated above in connexion with the output

from the gyro unit, the signal is taken to a

phase-conscious rectifier in the relay unit and

the output from thìs is connected to the operating coil of a D-459-A Differential Electromechanical

Relay. This relay is polarized with d.c. and

responds proportionally both in sense and

mag-nitude to the d.c. current applied. The relay

armature is capable of a high frequency response

(20 c/s) and moves only ± I degree which is

adequate to operate the pilot valve of the

hy-draulic relay.

Construction and Layout

Referring again to the functional diagram of

the complete equipment (Fig. I) the details

shown within the chain dotted area are all

con-tained in the gyro unit which is illustrated in Fig. 2. The upper portion of the case houses

the mechanical unit comprising the two gyros and ancillary equipment and is shown in greater

detail in Fig. 3. The mechanical unit can be

made accessible by partly withdrawing it from

22

the case on the slides provided for this purpose.

Immediately below the mechanical Unit is

the synchro and servo tray, also illustrated in

Fig. 4. The servomotor and Linvar elements are all readily identifiable and it will be seen that this unit is also removable for servicing

after uncoupling the two mechanical links shown

in Fig. 2. In the lower section of the case are

three identical transistor amplifiers X1, X2 and X3 operating respectively the main output, and

the natural list, and acceleration servos. The

components are mounted on the inside surfaces of a metal boxlike structure which is hinged at

the four corners so that the amplifier may be

opened out flat for servicing as shown in Fig. 5.

To the left of these amplifiers is the emitter

follower amplifier X4 which provides the

accel-eration signal at the power level required for

application to the acceleration potentiometer.

The power supplies are located below the amplffiers and in the lowest part of the case

under separate cover is the sensitivity unit. This unit is arranged to open outwards on the hinge

pin shown in Fig. 2 and conceals at the rear the terminals for connecting up to the ship's

wiring.

Stabilizer Operation

The output transformer is shown in Fig. I

connected to one fin, and the remaining three output windings, which can be used to operate

similar fins, are shown unconnected. The addition

of the signals in the four potentiometers repre-senting roll angle, roll velocity, roll acceleration and helm is readily seen. Numerous details have

been omitted for the sake of clarity but the principles of operation and essential

adjust-ments are all given. The transmitter CX2 may

be operated by the helm according to any

desired law, it is normal, however, that small movements of helm of up to say 5° either side do not affect the control, and linear signals are derived for increasing helm from this point to give maximum stabilizing power at full helm, or say 80% of full helm by the use of a suitable

cam.

Switching is arranged so that the natural list function can be brought into operation or not

as desired, by switching Out the servomotor

MO1 and Linvar L1.

The velocity gyro operates the Linvar L.1

directly to give the roll velocity signal and also

provides the input to the acceleration servo

through the damping coupling D. Control of the

overall sensitivity of the system is provided in an

attenuator prior to the input to amplifier X1

and the control of fin angle in response to signals

can be adjusted by means of the potentiometer associated with the resetting transmitter CX1.

With the adjustment normally provided, full

fin angle, that is full stabilizer control, can be

obtained for a roll angle of 2° to 4°, a roll

velocity of 0'4°/sec to 1 '6°/sec and a roll

acceleration of 012°/sec2 to 2°/sec2. The sensi-tivity of the control is such that the fin, which normally has say 25° of movement either way

from its zero position, is controlled within

approximately I degree of its true position, A check point is provided on the sensitivity panel by means of the switch marked 'Normal'

and 'Test'; by this means it is arranged that

an output is given, when the switching is set to 'Test', equivalent to full defiexion of the stabil-izing fins irrespective of the input functions of

the control. The test confirms that the final

amplifier X1 and the output circuits are in

order; should amplifier X1 fail, this test would

reveal the fault and the amplifiers X2 or X3

Fig. 5. änsistor Amplifier (unfolded)

23

could be substituted in turn to establish normal working of the output transformer. In the event

of a failure of the amplifier in position X2 or X3 the control would be deficient in either

natural list or acceleration but would still operate

on the roll velocity function which is the major

control function providing roll damping.

Other equipment associated with the control includes a master operating switch at the ship's bridge and a control panel housing fuses,

selec-tor switch, stabilizer 'On-Off' switch and the

controlled roll unit, etc.

Special Features

For some vessels requiring to be operated with

full stabilizing power over a range of ship speed,

the operating fin angle must be reduced as the

speed is increased to avoid overstressing the

fin shaft. This adjustment is provided by a

servo fed with a voltage corresponding to ship speed and it regulates, according to any desired law, the signal voltage which is passed to the

fins.

An additional feature which can be incor-porated is 'Controlled Roll' by which a

sinu-soidal signal generated by a synchro is injected

into the signal circuit and the vessel is constrained

to roll a predetermined amount. The Controlled Roll feature is useful for exercises in Navy

vessels. While rolling in this way the stabilizer

is still in operation and will operate against

additional roiling due to wave action, Neither of these functions are shown in the operational diagram Fig. 1.

The operational speed of the fins must be

related

to the vessel's

characteristic rolling period and it is normal to provide that the fins will execute their full travel from hard over in one direction to hard over in the other direction in approximately 15% of the rolling period of the vessel. The sensitive controls including the hydraulic relay unit must respond more rapidly,

hence introducing no sensible lag and leaving the maximum speed of the fin movement dependent only on the higher power fin servo. The first example of this equipment has now been fitted in one of HM. Frigates, has proved successful and has been accepted.

By way of comparison the dimensions and

WEATHER CHARTS FOR SHIPS AT SEA*

Better In formation for Navigation

Weather chart recording at sea (RACAL RL\ Il W, JULY). now plays an important part in modern navigation. A growing number of shipowners, particularly those plying in bad weather routes

and carriers in the fruit trade, are installing radio facsimile units. By relating the ship's

course to the overall weather situation, great

savings can be made in steaming time and

losses due to damaged cargo are cut.

The RACAL RA 17 receiver is ideal for this purpose due to its precise calibration and high stability. The recommended installation uses the MUIRHEAL) (Mufax) D-649 18 in Continuous Roll Weather Chart Recorder.

The RACAL receiver and MUFAX recorder make it possible to receive the latest actual and

forecasted weather charts transmitted from any of the score or so facsimile radio stations. The

* R'prinr'd from R A CAL REVI E W 111th tile ¡terni issiopt of the publishers, Raca! Eleclronics Ltd.

weights of the earlier system and the MULTRA Control System are given below, where it will be seen that the new equipment occupies less than one third the volume and is less than half the weight of the D-769 Compensated Control. A further economy of space and weight accrues from the omission of the retransmission unit.

ease of operation of the RA 17 suits it ad-mirably for these transmissions. The MUFAX is continuously recording and requires little at-tention; it is extremely robust and receives charts at any of the universally-used speeds (60, 90 and 120 r.p.m.). This arrangement can be

adjusted to accept the latest German LF

transmission.

The receiver and chart recorder can be

operated by the navigating officer to enable him

to obtain high-quality charts depicting the

latest meteorological situation exactly as com-piled by highly-skilled forecasters at a major Weather Centre on land. Furthermore,

accu-rate charts are available without the

time-consuming and costly business of decoding morse signals and chart plotting.

ABRIDGED CATALOGUE

A revised edition of the abridged catalogue for Muirhead precision electrical instruments has recently been issued and

is available on request.

The copyright of all articles in this journal is strictly reserved, bat the material may be reprinted without permission provided definite acknowledgment is made to Mairhead & Co., Limited, the publishers

8M 039168 _{Printed in England}

TYPE _{DIMENSIONS VOLUME WEIGHT}

MULTRA Control System

K-160 (Bulkhead mounted) 26 in high X 16 in wide x 9 in deep 243 eu ft 107 lb D-769 Compensated Control