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T14900-3025: Tangent Actuator Replacement

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Document Number: T14900-3025, rev 1 of 20Procedure Title: Tangent Actuator Replacement

Additional information and tools

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This document is EAR99 controlled. Use or disclosure of this information is subject to the restrictions on the Title Page of this document.



ABOUT THIS PROCEDURE

IntroductionThis procedure describes how replace a Secondary Mirror Assembly (SMA) tangent actuator.

Hazard IdentificationHazards to people are indicated with one of three signal words: DANGER, WARNING, and CAUTION. Hazards to equipment and property are indicated with the signal word NOTICE. These words mean:

DANGER indicates a hazardous situation which, if not avoided, will result in death or serious injury.

WARNING indicates a hazardous situation which, if not avoided, could result in death or serious injury.

CAUTION indicates a hazardous situation which, if not avoided, could result in minor or moderate injury.

NOTICE indicates a risk of equipment or property damage

PERSONAL PROTECTION EQUIPMENT

The use of PPE is recommended when regulations or employer protocols require, or whenever appropriate. Safety glasses, safety shoes (steel toes) and gloves should be worn to protect personnel when operations warrant the use of these items to protect against injury. In addition, latex gloves should be considered to minimize contamination of critical surfaces from human hands.




TABLE OF CONTENTS

About This Procedure....................................................................................................................3

Introduction................................................................................................................................3

Hazard Identification..................................................................................................................3

Table of Contents..........................................................................................................................4

Actuator Replacement Safety........................................................................................................5

Glass Safety...............................................................................................................................5

Additional information and tools....................................................................................................6

Documents.................................................................................................................................6

Tools and Equipment.................................................................................................................6

Equipment Overview......................................................................................................................7

Procedure....................................................................................................................................10

Replacing a Tangent Actuator.................................................................................................10

Starting Conditions...............................................................................................................10

Procedure.............................................................................................................................10




ACTUATOR REPLACEMENT SAFETY

Replacing an actuator requires handling actuator assemblies, which are sensitive to damage by electrostatic discharge—always follow grounding procedures. It also requires working near the M2 glass; avoid accidental contact with the glass.

Glass SafetyMove and work carefully and deliberately when near the glass. Always be aware of your proximity to the glass, and how you or something you are working with might contact the glass. Think through potential ranges of motion of planned operations—for example, if a bolt suddenly releases, can the wrench impact the glass? A single mistake can cause catastrophic damage to the mirror that could in turn lead to serious injury or death of those working near it.

Always use caution when working near the glass. Operations that pose the greatest risk to the glass are identified with the signal word NOTICE and the heading RISK OF MIRROR DAMAGE. In addition to these warnings, it is important to remember that there is danger to the mirror throughout this entire procedure—always follow the recommendations below when working near the glass:

Remove jewelry

Use safety straps on eyeglasses

Remove loose items from shirt pockets

Tie back long hair

Tether tools to operators to prevent accidental drops

Apply temporary foam padding to tools or other objects that could contact the glass

Apply foam padding to non-optical surfaces that require protection in the event of

accidental drops

Use cloth barriers (foreign object catchers) to limit the travel of dropped tools, fasteners,

or other items, where appropriate.




ADDITIONAL INFORMATION AND TOOLS

DocumentsIn addition to this procedure, you will need the drawings and associated parts lists that are listed in Table 1.

Table 1: Identification of required drawings.

Document Number Description14900-1000 Secondary Mirror Assembly952-340 General Assembly/Cart Configurations14903-1000 Tangential ActuatorT14900-1016 Software Update for Actuator Replacement

Tools and EquipmentA list of tools needed to complete the procedure is included in Table 2.

Table 2: List of required tools.

Name Requirement Use

Torque wrenches

2.5-2.9 in-lbs ILC (electronics) cable connectors128-141 in-lbs (10-12 ft*lbs) Tangent keeper washer bolts122-184 in-lbs. (10-15 ft*lbs) Link turnbuckle lockout bolts307-340 in-lbs (26-28 ft*lbs) Flexure clamp bolts545-602 in-lbs (45-50 ft-lbs) Actuator mounting bolts

ILC/Actuator shunt box

Drain stored charge; prevent ESD damage to telescope electronics




EQUIPMENT OVERVIEW

A list of the main parts and assemblies referenced in the procedure are included in Table 3. Images of these items are also included below.

Table 3: Identification and description of main components.

Name Drawing NumberM2 Mirror Cell Assembly 14900-1000Cell Weldment 14907-3000M2 Mirror 14901-1000M2 Mirror Mount Pads 14901-3001Tangent Actuator Assembly 14903-1000

Figure 1: M2 Mirror Cell Assembly




Figure 2: M2 Cart

Figure 3: Cell Weldment




Figure 4: Tangent Actuator on Cell Assembly

Figure 5: Tangent Actuator with Tangent Actuator Link and Tangent Actuator Base



Tools and Equipment

PROCEDURE

Replacing a Tangent ActuatorStarting Conditions

Make sure all the following conditions are met before beginning actuator replacement:

A tangent actuator has been identified for replacement

The M2 control system has been placed in “Enable” via the Engineering Users Interface

(EUI) and remains in open-loop operation once the system transitions to Enable. A

trained operator for the M2 control system is required for this procedure. Reference

T14900-1001 on starting up the EUI and Controller.

The SMA is supported in a configuration that allows access to the actuator to be

replaced (such as on the M2 cart)

If the glass M2 (not the surrogate mirror) is installed in the Mirror Cell, Harris recommends performing this procedure with the Outer Aperture Ring and mirror cover installed on the Cell. This helps protect to the mirror against accidental damage by hand tools being used on the tangent actuator.

Procedure

1. Rotate SMA to the desired orientation for actuator replacement. SMA may be supported in

the M2 Cart or the telescope for this operation. Refer to the M2 Cart User’s Manual for Cart

rotation procedures, or Telescope procedures for Telescope movement and SMA

preparation.

NOTE

Harris recommends that tangent actuators be replaced on the M2 Cart with the M2 facing up or down. Replacing a tangent actuator with the M2 in the horizon-pointing orientation is possible but it more difficult to de-load the actuator. Further guidance is provided below.

2. Ground operators (via wrist straps) before removing replacement actuator from protective

packaging. Ground fixture before setup.

Failure to follow grounding protocols may result in damage to SMA electronics by electrostatic discharge



Tools and Equipment

3. M2 Controller Operator : Using the rigid body position view on the EUI, record the θZ

position of the mirror. You will need this value later.

4. M2 Controller Operator : Using the Actuator Control view of the EUI, select all tangent

actuators EXCEPT the actuator to be replaced. Move all selected actuators simultaneously

in small increments to offload the actuator to be replaced. If the actuator to be replaced is

under tension (positive load), extend the remaining tangents in small increments. If the

actuator to be replaced is under compression (negative load), retract the remaining

tangents in small increments. Target a force of 0 ± 100 N, except in the horizon-pointing orientation (see NOTE). After offloading, power down the system. Reference T14900-1001

EUI Manual for instructions on powering down.

NOTE

It is not possible to completely offload actuators A2, A3, A5, or A6 with the SMA in the horizon-pointing orientation. Doing so will cause the remaining actuators to exceed their force limits before the actuator to be replaced can be completely offloaded. If attempting tangent actuator replacement in the horizon-pointing orientation, stop offloading when any tangent actuator exceeds a load magnitude (positive or negative) of 6005 N to avoid triggering a load limit fault.

RISK OF MIRROR DAMAGEThe tangent actuator ILCs saturate at a load of 6,850 N (positive or negative), and cannot measure more force than this, even if more force is applied. The tangent actuators are capable of producing more force than the ILCs can measure, and are capable of damaging the mirror. To prevent this, tangent actuators are force-limited through software. If the software force limit is changed, the actuators could damage the mirror, and the system would not detect the excessive force. DO NOT increase tangent force limits above 6,670N, and immediately stop mirror movement if and tangent actuator reports a load in excess of 6,670 N (positive or negative).



Tools and Equipment

5. If in the horizon-pointing orientation, complete offloading of the actuator to be replaced

manually using its turnbuckle:

a. M2 Controller Operator : Using the Detailed Forces View, record the load in the link

to be replaced. You will need this value later.

b. One at a time , loosen turnbuckle lockout bolts and then retighten to 5-7 ft-lbs (60-

84 in-lbs) before loosening the next bolt (Figure 6).

c. Attempt to rotate the turnbuckle by hand. If it cannot be rotated, repeat step (b) with

a lower retightening torque. DO NOT LOOSEN ALL BOLTS SIMULTANEOUSLY.

d. Once the turnbuckle can be rotated by hand, rotate it slowly while the M2 Controller Operator calls out remaining load in the link. Rotate the turnbuckle to reduce load in

the link to 0 ± 400 N

Figure 6: Turnbuckle lockout bolts

6. Remove and save the tangent keeper washer bolt and flat washer (items 48 and 49 of

14900-1000) and the large keeper washer (item 16 of 14903-1000).

7. Remove and save the actuator-end flexure clamp bolt (item 24 of 14903-1000) (Figure 7).

8. Remove and save the mirror-end flexure clamp bolt (item 7 of 14903-1000) (Figure 7)..



Tools and Equipment

Figure 7: Flexure clamp bolts.

9. Connect the shunt box (Figure 8) to and certified ESD grounding location.



Tools and Equipment

Figure 8: Shunt box

10. Disconnect the cables of the old actuator from the associated ILC. Remove cables from

ports J1, J2, and J3. (Figure 9)

Figure 9: ILC Ports.

11. Connect old actuator’s cables to the actuator shunting ports of the shunting box (Figure 8)

for a minimum of 1 minute to dissipate stored charge. After shunting, disconnect from shunt

box and protect cable ends with ESD-safe bagging. NOTE: It is still important to protect the



Tools and Equipment

old actuator’s electronics from damage by ESD, even though it is being replaced—the

assembly may be refurbished and returned to service.

12. While one person supports the weight of the actuator at the flexure block end (DO NOT SUPPORT BY LINK), remove the six bolts and washers that mount the actuator to the cell.

Move actuator directly outward from the mirror until the link comes off of the tangent pad

boss. After removal, store actuator.

Actuator assembly weight is approximately 50 pounds. Use caution to avoid dropping it as bolts are removed.

Figure 10: Tangent actuator mounting bolts (3 of 6 have already been removed.)

13. Move the new actuator into position, aligned to the outer holes and temporarily install 3 bolts

and washers (Figure 11).

14. Connect the shunt box ILC shunting cables to ports J1, J2, and J3 of the tangent actuator

ILC. Leave connected for a minimum of one minute to dissipate stored charge.



Tools and Equipment

15. Connect new actuator’s cables to the actuator shunting ports of the shunting box (Figure 8)

for a minimum of 1 minute to dissipate stored charge. After shunting, disconnect from shunt

box and connect to matching cables on ILC.

16. Torque the jack screws in the connectors to 2.5-2.9 in-lbs.

17. M2 controller operator : power on the system in open-loop mode.

18. M2 controller operator : record the raw telemetry force value from the new actuator.

19. M2 controller operator : Load configuration data (encoder and load cell sensitivities, and

load cell bias) as described in T14900-1016.

Figure 11: Installation of tangent actuator on outer hole pattern

20. Install the new tangent actuator:

a. Verify that tangent link turnbuckle clamping bolts are loose to allow link adjustment.

b. M2 controller operator : Verify that the new actuator is at its center of travel (+/-

0.05 mm). Move to center if necessary

c. Have one person support the weight of the actuator at the actuator end (do not support by link) while a second person removes the 3 mounting screws and

washers that hold the actuator in the outer hole position (Figure 11).



Tools and Equipment

d. Move the actuator into position:

i. Have one person support the actuator at the flexure block end while a second

person slides the mirror end onto the tangent pad boss. Move the actuator in

place to align with its 6 mounting holes. Position flexure block to be parallel

to outside edge of mounting flange on cell. NOTE: Mirror-end flexure clamp

bolt (Figure 7 & Figure 13) is not installed at this time. Rotate turnbuckle (by

hand) if necessary to allow actuator to be installed.

ii. Once in place on the tangent pad boss, rotate turnbuckle to develop a

compressive load of 40-400 N in the actuator.

e. Install and lightly tighten the 6 actuator mounting bolts (Figure 10).

f. One at a time, remove the six actuator mounting bolts, apply thread locking

compound, reinstall and torque per 14900-1000 note 6.2.

g. Install the flexure clamp jack bolt into the actuator end flexure clamp (952-340 item

30) and tighten until clamp can be slid freely on pin in flexure block.

h. Position link radially: slide the link radially on the boss and pin in the flexure block so

that:

i. It is fully on the tangent boss (Figure 13)

ii. It is not contacting the sides of the flexure block cavity (Figure 14).

iii. The two clamps are aligned without being forced into position or stuck by

friction.

iv. If these conditions cannot be met, loosen the 6 actuator mounting bolts and

reposition the flexure block. After finding a suitable position, first snug all

bolts, then remove one at a time, apply thread locking compound, and torque

per 14900-1000 note 6.2.

i. Apply thread locking compound to, install, and torque the mirror-end flexure clamp

bolt (Figure 7) per 14900-1000 note 6.17.

j. Verify that actuator-end clamp is still not contacting inside of flexure block. Remove

mirror-end clamp bolt and return to step (g) if contacting.

k. Remove the jack bolt from the actuator-end flexure.



Tools and Equipment

l. Apply thread locking compound to, install, and torque the flexure-block-end flexure

clamp bolt (Figure 14) per 14900-1000 note 6.17.

m. One at a time, remove turnbuckle clamp bolts (Figure 12), apply thread locking

compound, reinstall, and hand-snug.

n. Rotate turnbuckle by hand to develop 50-150 N of compression in the link.

o. Working in an alternating diagonal pattern, torque turnbuckle clamp bolts to 50% of

minimum torque specified by 14900-1000 note 6.18

p. Repeat the pattern, torqueing turnbuckle clamp bolts to the full torque specified in

14900-1000 note 6.18.

q. M2 controller operator : if the mirror is pointing up or down (on the M2 Cart) move tangent actuator as required to reduce load developed by turnbuckle tightening

to ±30 N (offset from bias of each actuator). Acceptable ranges (telemetry values

from EUI) given below. The ideal load for each link is the middle of the given range,

at which point the telemetry value is equal to load cell bias, meaning there is zero

actual load in the link.

A1 A2 A3 A4 A5 A6

min max min max min max min max min max min max

-14N 46N -162N -102N -34N 26N -60N 0N -39N 21N -59N 1N

r.

s. M2 controller operator : if the mirror is NOT pointing up or down, move tangent

actuator as required to achieve the same load (±20 N) as recorded in step (5.a)

above.

t. Apply thread locking compound to mirror-end retaining bolt, install washers and bolt,

and torque per 14900-1000 note 6.18. Reference Figure 15.

u. M2 Controller Operator : Using the Actuator Control view of the EUI, select all

tangent actuators and move them in small increments to return the system to the

same θZ position recorded in step (3) above. Note: X mm tangent movement =

X/1780.2 radians θZ)

v. M2 controller operator : Put the system in Manual Enable and then begin closed

loop control to allow the forces to settle.



Tools and Equipment

Figure 12: Turnbuckle clamp bolts

Figure 13: Clamp must be entirely on tangent pad boss



Tools and Equipment

Figure 14: Clamp must not contact sides of flexure block cavity.

Figure 15: Mirror-end retention washers and bolt.

End of: Replacing a Tangent Actuator .

End of document.

