fnal-ads, 4-mar-2009gaston gutierrez1 actuator test the idea of this presentation is to make sure we...

FNAL-ADS, 4-MAR-2009 Gaston Gutierrez 1

Actuator test

The idea of this presentation is to make sure we all have the same understanding about the actuator’s test. The series of tests proposed by ADS will satisfy the specs requirements, but we would like to propose a couple of additional tests.


Test stand capabilities

1. One fully operational actuator, with two universal joints and the control software.

2. A pneumatic system capable of ramping from -max_load to max_load in tens of seconds. max_load = 35 KN in most tests, except for a one time (irreversibility) test of max_load = ± 57 KN.

3. Rotary encoder read out at 20 Hz.

4. Readout of at least 4 linear encoders (resolution of 2.44 nm/bit) at 20 Hz.

5. Pneumatic load readout (?)


Actuator test

1. Total range

2. Linearity

3. Stiffness (separate for actuator and joints)

4. Backlash

5. Resolution

6. Maximum speed

7. Smoothness (related to ramp profiles)

8. Power dissipation

9. Temperature and humidity operating range

10. Actuator’s irreversibility (no power applied)

We are curious to know the following about the actuators:


Total range

1. With actuator at -28 mm issue a command to move to 28 mm at v = 1 mm/sec

2. Read rotary and linear encoders at 20 Hz

3. Repeat reversing direction and changing actuator’s load.

4. Plot linear vs. rotary encoder (translated into linear displacement)

ADS proposal (OK with FNAL)


Linearity

1. If there is no plan in place yet we would like to propose that the “Range test” be repeated for different velocities (and load) as to cover different part of the screw. Then a plot of the linear vs. rotary encoder (translated to linear distance) will measure the actuators linearity.

We have no specifications on linearity but we would like to know how linear the actuator is. If our understanding is correct ADS will need this to implement software corrections.


Stiffness

1. Cycle load from -35 KN to 35 KN (actuator under power but inactive)

2. Install linear encoders to measure both ends of the actuator and both ends of at least one universal joint.

3. Read rotary and linear encoders at 20 Hz

4. Plot load vs. linear encoders. Study in detail the zero load x-over point to make sure there no motion when the load reverses.

5. Repeat three times.



Backlash

1. We don’t know what the best way to measure backlash is, but something like the following will work. In different position of the screw we would take N step forward and N-1 steps backwards several times and monitor the behavior of the linear encoder. The step size can vary from 5 to 100 μm.

We have no specifications on backlash but we would like to know how much backlash there is.


Resolution-1

1. A sequence of steps of 100, 10, 5, 2, 1 and 0.5 μm and back is issued at three different test locations and with loads of 0, ±35 KN.

2. The rotary and linear encoders are read out and compared.


On top of the previous sequence we would like to propose a test that simulates the way the actuators are going to be used (see the following page)


Resolution-2

1. Very slowly change the actuator’s load from -25 to 25 KN.

2. Every time the linear encoder reaches certain value (like 5, 10, 20 and 100 μm) issue an actuator command to keep the actuator+joints length constant.

3. Compare the linear encoder readout with the expected value after the actuator stopped moving.

4. Repeat in different positions of the screw.


Maximum speed

1. Measure the minimum time it takes to complete a command to move a step of 150, 500 and 400 (about 40 arcsec tip/tilt equivalent) μm.

2. Repeat for three test locations.



Smoothness

1. There is no proposal to measure the motion smoothness and we don’t know what the best test is either. But since the main fear is excitation of hexapods resonances we can probably test two different ramps with two different frequency intervals (around 30 Hz) chopped off.

No proposal


Power dissipation

1. The actuator is commanded to step 20-50 μm every 100 sec.

2. We do not understand exactly how the power dissipation will be measured.

ADS proposal


Temperature and humidity ranges

1. Humidity will not be tested. The compliance is by design.

2. For temperature the actuator’s operation will be tested at room temperature and at -10 C. Power consumption test is repeated with zero load.

ADS proposal


Irreversibility

1. The load is cycled from -57 to 57 KN with the actuator in open loop conditions. The proposal only specifies a pulling load. Shouldn’t we also test the pushing condition?

2. The rotary encoder readings should not change.

ADS proposal

fnal-ads, 4-mar-2009gaston gutierrez1 actuator test the idea of this presentation is to make sure we...

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