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Positioning with external SSI encoder

Valid for S400, S600

Setup for external SSI position feedback

Setup must be done with a terminal software or with the setup software in the terminal screen page.

DIS switches software enable off
EXTPOS 1 Position feedback  => with external position encoder
GEARMODE 7 Selection of the measuring system => SSI
ENCMODE 2 Emulation mode of the ROD / SSI interface (with GEARMODE=7 always 2 with SSI encoder )
SSIGRAY 0 or 1 Data format according to SSI protocol 0=binary / 1=gray
SSIINV 0 or 1 Transmission of MSB (=0) first or LSB (=1) first
SSIMODE 0 Alarm bit at the beginning (=1) or at the end (=2) or none (=0)
SSIOUT x x = number of data bits +1
EXTMUL y

Internal factor:  y = sz / (encoder resolution in increments)
z = PRBASE ( Default 20, optional 16 )

Finish the setup with
SAVE saves parameters in the EEPROM of the servo amplifier
COLDSTART restarts the amplifier, required to enable parameter changes

It must be guaranteed that one revolution of the position controller set point produces one revolution of the position controller actual value. Possible procedures for the adjustment are described on page "Speed adjustment with external position feedback" described.

Parameter overview see page Parameters for SSI Interface.

Set reference point

A reference task (homing) is not required, because the SSI encoder is an absolute measuring system.

  • Move the servo axis after restart to the required zero position.
  • Read the actual position with the command PFB inthe terminal screen
  • Set ROFFS = -PFB
  • Save the parameters with SAVE and restart the amplifier with COLDSTART. PFB is now = 0.

Help with problems

  • check phase position !
  • check signal form of data and clock signals: should be similar to the above diagram. Number of data bits and clock bits can differ due to the software setup.
  • Start an external terminal software (e.g. HYPER TERMINAL). Setup: 9600 baud, 8 bit, 1 stop bit, no parity, no handshake
    • If your command looks like this: o -- >, then send the command PROMPT 133
    • Send the commands
    • You can evaluate the SSI data which have been received by the amplifier by the ASCII command M NEWSSI. The information is shown hexadecimal in LONG FAST format.
    • Example:
      • LONGFAST = 0x00FC1E44 => 16522820 DEZ
      • after about one encoder turn
      • LONGFAST = 0x00FC2E34 => 16526900 DEZ
      • difference is 4080 decimal, the set SSI encoder has 4096 bits. SSIOUT has been set correctly. Finish the check with the commands
      • MSG 1 and SAVE
  • Incorrect EXTMUL setting can result in wrong position monitoring