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CRY (Cryo-payload R&D)
takafumi.ushiba - 19:17 Tuesday 24 November 2020 (15517) Print this report
Actuator efficiency measurement of new magnet

[Ushiba]

Since the new magnet for IM/MN was deliverred, I measured actuator efficiency with new magnets.
Measurement was done by using scales and micrometer stages as usual.
However, during the measurement, I found that cans of PDs for photosensor has magnetism and MN magnets makes some force between them.

Attached fig1 and 2 shows the force when the current is off.
X-axis represents the position of the magnets surface measured from the coil surface (positive sign means the magnets enter the coil).
To see these graph, MN actuator makes some force even though no current was applied to the coil.

Attached fig 3 and 4 shows the force of Im actuator and MN actuator when I applied the current (100mA for IM and 10mA for MN).
Blue dots show the raw data and red dots show the subtruction of the background measured as fig 1 and 2.
From the result of fig 3 and 4, new actuator efficiency was calculated as 0.055N/A for IM and 1.1N/A for MN, which is 20% and 10% larger than my estimation but probably fine.

We need to consider how to treat the force between Mn magnets and cans of PDs.

Images attached to this report
Comments to this report:
takafumi.ushiba - 17:45 Thursday 26 November 2020 (15536) Print this report

I measured actuator efficiency with old (used during O3GK) magnets to confirm that this issue is only related to new magnets.
Measurement method is same as before and unfortunately force between the MN magnet and cans of PD was observed even with the old magnet.

Attached is the actuator force with 100mA and force without current, respectively.
We can clearly see the force without applying the current to the coil (of cource absolute force value is smaller than new one because of the magnet size but still large).

Images attached to this comment
takafumi.ushiba - 9:45 Wednesday 02 December 2020 (15575) Print this report

I measured the force between magnets on MN and cans of PDs in more wider range (see attachment).

We considered to use the other best position for coil-magnet actuator to keep the distance between magnet and PD larger.
However, even if we use the other best position, the force is roughly 5 times smaller but still remains.
So, we need to consider another option.

One possible solution is to separate actuator coils and photosensors (PSs).
Since the cryopayload have many dummy coil bobins to keep their symmetry, it is not so difficult to separate coils and PSs.
Another solusion is to redesign the coil bobins but it will take long time.
So, Ithink it is not suitable for current tough schedule.

Images attached to this comment
takafumi.ushiba - 19:19 Monday 07 December 2020 (15596) Print this report

To design new coil-magnet actuator, I measured force between new magnet (larger than current one) and PD.
Followings are the result (see figure 1, scale can be measured 1mg ~ 0.01mN).

Magnet position from PD force [mN]
-63.5 -0.010 (limited by scale resolution)
-58.5 -0.010 (limitedd by scale resolution)
-53.5 -0.05
-48.5 -0.11
-43.5 -0.19
-38.5 -0.29
-33.5 -0.59
-28.5 -1.01
-23.5 -1.47
-18.5 -1.91

From this result, PD and magnet should be roughly 60 mm apart.
So, we need to set new coil as shown in attached figure 2.

Now, we check if the space is enough to do so or not.

Images attached to this comment
shinji.miyoki - 19:52 Monday 07 December 2020 (15597) Print this report

We need to check of the lower resonance frequency of long lods for a magnet. 

It could be another obstacle for control.

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