Stage motor moves using the PMAC device

Notes on PMAC coordinate system and motors

In a PMAC, motors that should move in a coordinated fashion ware put into the same coordinate system that can run a motion program. Motors that should move independently of each other should go into a separate coordinate system. A coordinate system is established by assigning axes to motors. The axes allocations defined for the chip stages set up are:

#1->X
#2->Y
#3->Z

When an X-axis move is executed, the #1 motor will make the move.

When running chip collections, the stage motors are moved via the PMAC device in a couple of different ways.

1. In most cases, the {x,y,z} motors are moved by sending a command to the PMAC as a PMAC_STRING.

   • Using a JOG command J:{const}, to jog the motor a specified distance from the current position. For example, this will move motor Y by 10 motor steps: python      yield from bps.abs_set(pmac.pmac_string, "#2J:10")

   • The hmz strings are homing commands which will reset the encoders counts to 0 for the axis. All three motors are homed by sending the string: #1hmz#2hmz#3hmz. In the plans this is done by triggering the home move: python       yield from bps.trigger(pmac.home)

   • Another pmac_string that can start a move has the format !x..y... This is a command designed to blend any ongoing move into a new position. A common one through the serial collection code is !x0y0z0, which will start a move to 0 for all motors. python      yield from bps.trigger(pmac.to_xyz_zero)

2. The stage motors can also be moved directly through the existing PVs ME14E-MO-CHIP-01:{X,Y,Z}, for example:

   yield from bps.mv(pmac.x, 0, pmac.y, 1)https://github.com/DiamondLightSource/mx-bluesky/wiki/Serial-Crystallography-on-I24#cs_reset-custom-chips
   

Notes on the coordinate system for a fixed-target collection

CS_MAKER: Oxford-type chips (Oxford, Oxford-Inner, Minichip)

Generally, the first step before a chip collection is to create the coordinate system. This is done by first selecting the 3 fiducials on the and then clicking the Make co-ordinate system button. This button runs the cs_maker plan, which computes the correct pmac_strings to assign axes values to each motors.

Theory for this computation

Rx: rotation about X-axis, pitch
Ry: rotation about Y-axis, yaw
Rz: rotation about Z-axis, roll
The order of rotation is Roll->Yaw->Pitch (Rx*Ry*Rz)
Rx           Ry          Rz
|1  0   0| | Cy  0 Sy| |Cz -Sz 0|   | CyCz        -CxSz         Sy  |
|0 Cx -Sx|*|  0  1  0|*|Sz  Cz 0| = | SxSyCz+CxSz -SxSySz+CxCz -SxCy|
|0 Sx  Cx| |-Sy  0 Cy| | 0   0 1|   |-CxSyCz+SxSz  CxSySz+SxCz  CxCy|

Skew:
Skew is the difference between the Sz1 and Sz2 after rotation is taken out.
This should be measured in situ prior to expriment, ie. measure by hand using
opposite and adjacent RBV after calibration of scale factors.

The plan needs information stored in a few files:

• The motor directions are stored in src/mx_bluesky/i24/serial/parameters/fixed_target/cs/motor_directions.txt. The motor number multiplied by the motor direction should give the positive chip direction.

• The scale values for x,y,z, the skew value and the sign of Sx, Sy, Sz are all stored in src/mx_bluesky/i24/serial/parameters/fixed_target/cs/cs_maker.json

• The fiducials 1 and 2 positions are written to file when selecting the fiducials (Setting fiducial 0 instead sends a homing command directly to the pmac_string PV)

NOTE. The motor_direction.txt and cs_maker.json files should only be modified by staff when needed (usually when the stages have been off for awhile).

CS_RESET: Custom chips

When using a Custom chip, open the Custom chip edm and before doing anything else click the Clear coordinate system button. This will ensure that any pre-existing coordinate system from pre-vious chip experiments is wiped and reset.

This operation is done by the cs_reset plan, which sends instructions to the PMAC device to assign coordinates to each motor via the following pmac_strings:

"#1->10000X+0Y+0Z"
"#2->+0X-10000Y+0Z"
"#3->0X+0Y-10000Z"