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McLennan motors

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Freddie Akeroyd edited this page May 29, 2023 · 73 revisions

Wiki > The Backend System > Specific Device IOC Motor IOCs > McLennan

The McLennan motor is a controller that support multiple independent motors. It is often used at ISIS for rotation stages.

WARNING: Unlike many other motor controllers that remember settings through autosave the McLennan exclusively uses macros. This means for changing parameters in a persistent way you will need to change them in the IOC configuration rather than the motor details panel, otherwise they will get lost on IOC restart

Behaviour

Motor Resolution

The motor resolution is set with the MSTPn IOC macros and in units of steps/mm (same as in SECI/labview), this will be inverted by the IOC internally as the EPICS motor record MRES field uses the inverse mm/step.

Encoder Resolution

The encoder ratio rather than encoder resolution is set with the ERESn IOC macros, this is a string like 400/4096 and bears no direct relation to the EPICS motor record ERES. As the mclennan driver pretends to be open loop (no encoder present as per MSTA field) whatever mode it is running in, the motor record ERES is not actually used and is set to 0 in the st.cmd and will then display as the same value as motor record MRES when later viewed. So ignore the encoder resolution value displayed on the motor record screen.

The encoder ratio written M/E is providing motor_steps_per_revolution / encoder_steps_per_revolution, in SECI/labview this was referred to as Numerator / Demoninator. So actual_position_steps = encoder_steps_readback * encoder_ratio. For closed loop (encoder feedback) controller mode to work this ratio needs to be correct so that commanded_motor_steps_moved = encoder_steps_moved * encoder_ratio, if the ratio isn't right the motor will fail to get position leading to many retries and an error. It is possible to work out the ratio by e.g. going to motor console (PuTTY/hterm), doing a small MR relative move and comparing command position (CP) and actual position (AP). dbior command on an ioc window now shows these values, as does the QP command at the motor low level serial interface. The Raw encoder steps is IP or Input Position which is scaled by encoder ratio to give actual (AP) position. If encoder and motor move in opposite directions, add a minus sign to encoder ratio.

Velocity

The McLennan motor velocity is set with the VELOn IOC macros, the value set is in mm/second, same units as EPICS motor record uses.

Acceleration

The IOC macro ACCLn for acceleration is the the number of seconds under linear acceleration to reach maximum speed, the same convention as the EPICS motor record (The acceleration value on the device itself is the acceleration in units of step/s^2, this is calculated in the IOC as velocity divided by the product of the motor resolution and ACCL value).

Setting the motor position/offset

See Set the raw position of the motor without moving it

Homing

There are several homing modes on the McLennan set via the HOME macro. The choice of mode depends on the motor, modes 1 and 3 (constant velocity homes to limit switches) are controlled in software by SNL, others by controller HD (home to datum) command. Modes are:

  • 0: Controller does internal home to an external home signal (not normally used).
  • 1: Do a reverse constant velocity move (jog) until limit switch is hit, but do not zero the motor (this is deprecated)
  • 2: Do a hardware reverse direction search for a home signal and then zero the motor
  • 3: Do a reverse constant velocity move (jog) until limit switch is hit then zero the motor.
  • 4: Do a hardware forward direction search for a home signal and then zero the motor
  • 5: Move to forward limit, do a hardware reverse direction search for a home signal and then zero the motor
  • 6: Move to reverse limit, do a hardware forward direction search for a home signal and then zero the motor

The constant velocity move uses JVEL and is set to be a 1/10 of the normal velocity unless the macro is set to change it.

There is a special homing sequence for Vesuvio because it doesn't quite work until ticket 5739 is done

There is a special homing sequence for HRPD low temp sample changer because it doesn't quite work until ticket 5739 is done

The way this works in the code is that the motor driver send the correct home (or no home) dependent on the mode set in request_mode, for SNL then takes care of other moves.

Controller Switch settings

Rotary switch SW1 and SW2 give axis address, address is 10*SW1 + SW2

SW3

  • 1=ON 2=OFF gives serial baud 9600, see manual for other combinations
  • 3=OFF 7bit even parity, or 3=ON 8bit no parity
  • 4=OFF (no hardware flow control)
  • 5=ON (quiet command reply mode, required by EPICS driver)
  • 6=OFF
  • 7=OFF (rs232)
  • 8=OFF (no terminator for rs485)

SW4 controls encoder termination, with OFF=single ended (TTL), ON=differential pair (RS422). Not for us to change, leave to motion engineers.

Configuring axes

When configuring a particular axis, an axes.cmd file is required in C:\Instrument\Settings\config\[INSTMACHINE]\configurations\mclennan. See the the motion control pages for additional details. It is often desirable to set up a number of axes depending which controller, and which axis is in use. There are specific environment variables set up to let you do this. The following example shows a stretching rig set up on MOT0201 and a linear sample changer on MOT0101:

$(IFMTRCTRL1)$(IFAXIS1) dbLoadRecords("$(AXIS)/db/axis.db","P=$(MYPVPREFIX)MOT:,AXIS=STACK:LIN,mAXIS=MTR0101")
$(IFMTRCTRL2)$(IFAXIS1) dbLoadRecords("$(AXIS)/db/axis.db","P=$(MYPVPREFIX)MOT:,AXIS=STRETCH:LIN,mAXIS=MTR0201")

You can see the environment variables being used at the start of the line. The available variables are:

  • IFMTRCTRLn: The line is run if the controller number for the motor is n where n is between 1 and 24. This corresponds to the MTRCTRL IOC macro.
  • IFAXISn: The line is run if the axis number for the motor is n where n is between 1 and 8. This corresponds to the AXISn=yes IOC macro.

Note that the equivalent IFNOT... environment variables also exist but are typically of less use.

Also note that the two environment variables combine as an and operation when used in this form. That is, the line will only execute if both conditions are met. There is currently no way to combine the environment variable with an or operator.

Reset on move

The IBEX McLennan driver is set to send a reset command on any request to move. This is intended to clear errors (e.g. tracking abort) and avoid the need for power cycling that would clear the position.

Reset on stop

The IBEX McLennan driver sends the following sequence of commands when a stop is requested:

STOP
RESET
STOP

The first stop will stop the motor as part of the normal operation and the 2nd and 3rd command will have no effect. If the motor enters an error state during a move, the first stop will have no effect and the 2nd and 3rd command will stop it. The first command is necessary since the 2nd and 3rd commands will not cause it to stop under normal operation.

Creep Speed CS for home to datum

Quick note on this learnt from SECI; It appears that the SC command which set the speed for HD (home to datum) may be limited in it range. We don't think it can be set faster than the normal speed and maybe be limited to 400. Investigate when and if we need this.

Setup, Trouble Shooting and Usage

The McLennan now prints its current mode of operation (moving, homing, Idle, tracking abort etc) and any error messages to the IOC log file/ioc command window screen.

Setting up the unit

When starting the unit:

  1. Start the controller
  2. Start/restart the IOC (so that it can send the motor and encoder resolutions to the controller)
  3. Home the device

I've booted up a McLennan and can't get it moving (properly)

Check the MCLEN IOC log file for error messages and also examine output from dbior and dbior * 1 typed at the IOC console window.

If it doesn't move at all try using the macros for an axis number other than 1 (e.g. 2 or 3) in the ibex GUI. The axis to be driven by the buttons on the front panel are set by a position dial inside the mclennan crate, so you may not be be trying to control the correct axis id.

If it moves a short distance and stops it may be going into Tracking abort. A tracking abort means the encoder and motor step counters have got further apart than expected during the move, this could be due to:

  • The encoder and motor resolutions are incorrect/incompatible, so "expected" and "actual" position are diverging. The first thing to do is to restart the McLennan hardware and then the IOC so that the values are resent. If this does not fix it then check the settings are correct.
  • you are trying to accelerate or move too quickly, or possibly move too slowly, meaning there is a time lag between the motor pulses being sent and the motor response. Try changing these parameters. See end of this page if you need to change the tracking abort window.

McLennan moves but doesn't stop at desired position

If the McLennan moves but does not stop at the position you requested it could be that the encoder and motor resolutions have not been sent to the controller or are incorrect. This must be done whenever the unit is restarted and is done by restarting the IOC.

Homes are very slow

In homing modes 1 and 3, the McLennan homes via SNL and uses JVEL as it's speed. JVEL defaults to VELO/10 if not set, so try increasing the jog speed and see if this speeds up homes

In other homing modes, the McLennan uses an internal homing routine. This uses the "creep speed" which IBEX now does set as of https://github.com/ISISComputingGroup/IBEX/issues/4815. If you need to manually make homing faster, do the following:

  • Set HVEL macro to an appropriate speed for homing via IBEX configuration macros
  • Restart the IOC

Note that the creep speed for the PM600 at least is limited to 800 steps per second. We cater for this in the motor record and set it to the HVEL value if lower than 800 and otherwise set it to 800.

Mclennan does not communicate

Most McLennans have 2 RS232 ports, for daisy chain in&out. The out port is required to have an rs-232 terminator installed in it, this looks similar to a null modem and bridges two pins. If this terminator is not installed the mclennan will not communicate at all using any comms settings.

Office McLennan Settings

The office McLennan need the following:

  1. No Null terminator or gender changer (if using a straight-through male-female cable from a PC)
  • Note: If the mclennan has two ports (for daisy chaining), the out port MUST have an RS232 terminator in it. This looks similar to a null modem and bridges two serial pins. If this is not present, the motor controller will not communicate.

Use following IOC macro setting:

  1. BAUD 9600
  2. BITS 8
  3. AXIS3 yes (all others no)
  4. MODE3 CLOSED
  5. ACCL3 1
  6. VELO3 0.5
  7. ERES3 400/4096
  8. MSTP3 4000

getting debug output/information

console to IOC and type dbior for basic information. For extended information pass a higher report level to dbior e.g. dbior * 1 (you need the * as the first argument is the driver name and the second the debug level)

converting values from labview

if you need to convert a previous SECI/labview mclennan ini file, these are usually found in c:\labview modules\Drivers\Mclennan PM600\INI Files on the NDX computer. A file will have an entry like:

[M0]
Name = "Mclennan Newport"
Enabled = TRUE    
Units = "deg"
Com Port = 7 
Axis Address = 1    
Baud Rate = 9600    
Data Bits = 8    
Parity = 0    
Stop Bits = 10    
Acceleration = 40000    
Velocity = 10000    
Motor steps per unit = 8000.000000    
Encoder counts per unit = 1000.000000    
Correction Gain = 70    
Window = 50    
Creep Speed = 5000    
Creep Steps = 0    
Settling Time = 0    
Jog Speed = 10000    
Control Mode = 4    
BackOff Steps = 0    
Deceleration = 40000    
Upper limit = 180.000000    
Lower Limit = -180.000000    
Enable State = 1    
KF = 0    
KP = 10    
KS = 0    
KV = 0    
KX = 0    
Numerator = 8.000000    
Denominator = 1.000000    
Homing Method = 2    
Homing Speed = 10000    
Home Offset = 0.000000    
Apply Home Position = TRUE    
Home Position = 0.000000    
Apply Home Offset = FALSE

Calculate the appropriate MCLEN IOC macros as follows:

  • Axis Address = 1 and Enabled = TRUE so we set AXIS1=yes and then set other macros with a suffix of 1
  • Name = "Mclennan Newport" so we set NAME1 = Mclennan Newport
  • Motor steps per unit = 8000.000000 so we set MSTP1 = 8000 (which will lead to an EPICS motor record MRES of 0.000125)
  • Encoder counts per unit = 1000.000000 this is not used directly, but see comment on Numerator and Denominator below
  • Velocity = 10000 this is in steps per second, so we divide by motor steps per unit to get units per second (10000 / 8000), VELO1 = 1.25
  • Acceleration = 40000 this is in steps / s^2, we divide velocity by acceleration (10000 / 40000) to get the acceleration time ACCL1 = 0.25
  • Units = "deg" so we set UNIT1 = deg
  • Jog Speed = 10000 so like velocity above we divide by steps (10000 / 8000) to get JVEL1 = 1.25
  • Upper limit = 180.000000 is already in proper units so set DHLM = 180.0
  • Lower Limit = -180.000000 is already in proper units so set DLLM = -180.0
  • Homing Speed = 10000 so divide by motor steps (10000/8000) to get HVEL1 = 1.25
  • Numerator = 8.000000 and Denominator = 1.000000 refer to the encoder ratio components so we set ERES1 = 8/1 (This should be the equivalent numeric ratio to Motor steps per unit/Encoder counts per unit which is true here as 8000 / 1000 == 8 / 1 )
  • Home Position = 0.000000 IOC always applies a dial home position of 0, if labview value is non-zero set OFST1 IOC macro to this value
  • Control Mode = 4 in labview 4 is "closed loop stepper" so set CMOD1 = CLOSED (if labview was 1 that means "open loop stepper" so would set CMOD1 = OPEN. We don't currently handle other values and they are not used at ISIS as far as we know)
  • Homing Method = 2 for labview 0=none; 1=home signal+; 2=home signal-; 3=reverse limit,home signal+; 4=forward limit,home signal-;5=reverse limit;6=forward limit. So for labview 2 we set IOC HOME1 = 2 after examining the Homing section above for equivalent ibex modes.

Some labview values do not currently have macros and get IOC defaults. Edit MCLEN IOC st-motor-init.st if you need to temporarily change them and then create a ticket to add a proper IOC macro

  • Window = 50 this is the end of move check window before an internal mclennan retry, it is set to a IOC calculated default value. It is a bit like the retry deadband of the motor record, but done at the controller. If a moves plus retries completes and is still outside this Window, an error will be signalled. You can edit st-motor-init.st to change this directly (restart IOC afterwards) and then create a ticket to add a permanent macro.
  • Correction Gain = 70 this is equivalent to the IOC default PCOF = 0.7 for a stepper motor
  • Creep Steps = 0 number of steps to approach final position at the slower Creep speed in the final phase of a move
  • Creep Speed = 5000 only important for us if Creep Steps > 0 as this is temporary set to HVEL during a home so does not now affect homes.
  • Settling Time = 0 how long motor readback must be within Window of requested position at end of move
  • BackOff Steps = 0 used for backlash correction

Some mclennan values were not covered in labview but exist in MCLEN IOC st-motor-init.st

  • Tracking window - a parameter used to determine if a TRACKING ABORT should be signalled, it is the max allowed difference between current and requested position during a move (also known as the following error). This may get triggered by a motor being told to move/accelerate quicker than it can, or move too slowly and so stalling, or an incorrect encoder ratio so motor and encoder get out of step.
  • Not Complete/Time-Out time - the max time at end of a move for any settling/auto corrections etc. to take place, otherwise triggers a NOT COMPLETE/TIMEOUT ABORT
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