encoder(), IK220

Encoder() talks to the IK220 PCI card of Heidenhain.

* = encoder( hhe9, position)
* = encoder( hhe9)                    position
* = encoder( hhe9, StaPort)           status register
* = encoder( hhe9, CancelRef)         cancel ref. sequence
* = encoder( hhe9, DoRef)             start reference sequence
* = encoder( hhe9, Init)              init encoder 
* = encoder( hhe9, offset, ival)      set offset [counts]
* = encoder( hhe9, conversion, xval)  set conversion factor
* = encoder( hhe9, offset)            get offset
* = encoder( hhe9, conversion)        get conversion

* = encoder( hhe9, p1)                0 increment
                                      1 EnDat   
                                      2 SSI         

* = encoder( hhe9, p2)                0 11 muApp      
                                      1 1Vpp          

* = encoder( hhe9, p3)                0 linear axis
                                      1 rotational axis

* = encoder( hhe9, p4)                0 positive 
                                      1 negative

The position is calculated by: pos = (encoder - offset)/conversion

A start sequence:

* = encoder( hhe9, p2, 0)   sets the card to current mode
* = encoder( hhe9, init)
* = hex(encoder( hhe9, staport)) -> 0x20   
* = encoder( hhe9)

A reference sequence:

 
!
! move near the reference mark
!
move mot1 0      
* = encoder( hhe9, init)
* = hex(encoder( hhe9, staport)) -> 0x20
* = encoder( hhe9, doref)
* = hex(encoder( hhe9, staport)) -> 0x4060
!
! move over the reference mark
!
move mot1 1  
* = hex(encoder( hhe9, staport)) -> 0xffffc024
* = encoder( hhe9, position)     -> some value

An encoder is calibrated in the following way (assume the encoder reads the monochromator rotation axis):

• The monochromator is calibrated. This defines the stepping motor position of the rotational axis. The calibration of the monochromator should be done the near energy that is later used for the measurements.

• The encoder is initialized and its conversion factor is set to 1 and the offset is set to 0.

  * = encoder( hhe1, conversion, 1)
  * = encoder( hhe1, offset, 0)
  

  This makes sense only when the encoder is used for the first time. Once the conversion factor is determined, we don't have to re-measure it.

• We scan the stepping motor and display the encoder reading.

• A linear fit to the data of the encoder reading gives the conversion factor and the offset. We use these values for the encoder:

  * = encoder( hhe1, conversion, conv)
  * = encoder( hhe1, offset, offs)