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Operating modes

Mode 1 - Switch on / restart mode

When the ACC2-3 is switched on the start up sequence is as follows:

1.  A one-second delay while the power supply rails stabilise.  During this time the STOP signal is applied.

2.  After STOP is released the internal interface will be inhibited.

3.  The configuration switches on the back panel will be read and the necessary internal setups made.

4.  The rack connection is tested.

5.  The port lids will be checked and if an open lid is detected and datum mode is selected.

6.  Dependent on the result of step 5, either mode 2 or mode 6 will be entered.

When a K reset command, reset switch or external reset is applied, the sequence is the same except that it starts from step 2.

Mode 1 is a transitional state.

Mode 2 - Main software nucleus mode

This is the normal operating mode of the software.

In mode 2 the ACC2-3 can accept input in the form of a direct command, an error signal, or a port lid movement.

Depending on the type of input, the appropriate operating mode is selected: direct command (mode 5), error (mode 4) or change cycle (mode 3)).

Mode 3 - Change cycle mode

Change cycle (mode 3) is entered from mode 2 whenever a rack infra-red beam is broken.  Depending upon which beam is broken first, the ACC2-3 decides whether to perform a pick-up or put-down.

The sequence of operation is as follows (error conditions are given in italics):

1.  ACC2-3 waits for a beam to be broken.

2.  An infra-red beam is detected.

# Q (CR)(LF) is sent indicating that the first beam has been broken

# ACC2-2 decides whether to pick up or put down

3.  The infra-red beam detection is debounced.

Q6 Excessive Entry Speed

Cycle Error LED is ON

Entry speeds greater than 60 mm/sec (2.36 in/sec) are not permissible

4.  Within 100 µs of the first beam being broken

# Touch probe is inhibited (conventional) PPOFF and PDAMP override applied (PICS)

# Change cycle LED is ON

# Probe Active LED is OFF

5.  Depending upon screwdriver position, ACC2-3 decides whether it is necessary to move the screwdriver to mate with the incoming head

Motor reverse takes 0.95 seconds maximum, and the quill has 11.9 mm (0.46 in) left to travel. Entry speed must be restricted to 5 mm/sec (0.196 in/sec) if reversal is necessary.

If the operator is confident that the screwdriver will ALWAYS be in the correct position, the entry speed can be as high as 60 mm/sec (2.36 in/sec), provided the touch probe does not trigger when its body contacts the lid.

6.  Both beams are broken within 10 seconds

Q3 Lid Time-out

Cycle Error LED is ON

Both beams not broken within 10 seconds

7.  ACC2-3 sends P0(CR)(LF) indicating that the probe is parked and the screwdriver is in the correct position

8.  ACC2-3 waits for a G message or starts the preset time delay for stand-alone operation. Its internal status is P0.

Q4 G Not Received Error

Cycle Error LED is ON

The ‘G' was not received within 10 seconds

9.  G is received or time delay complete

10.  Lock / unlock is performed within 3.25 seconds

Q1 Lock Mechanism Error

Lock Error LED is ON

Mechanism is not in the required position. The ACC2-3 has assumed that the mechanism is jammed and aborts the move.

11.  G0 is sent indicating that lock / unlock has been successfully completed

12.  Both beams are made within 10 seconds

Q3 Lid Time-out Error

Cycle Error LED is ON

Both beams not made within 10 seconds

13a.  If a successful pick-up was performed:

# Touch probe is enabled after a 1.5 second delay (conventional) PPOFF and PDAMP override released (PICS)

# Probe Active LED is ON (conventional)

# Sends Y0

13b.  If a successful put-down was performed:

# Touch probe left disabled (conventional) PPOFF and PDAMP override applied (PICS)

# All rack LEDs are OFF

# Sends Z0

14.  Software return to main software nucleus (mode 2)

Additional errors

a)  If ACR1 overtravel is detected at a time during this procedure the change cycle is abandoned and error mode (mode 4) is entered.

b)  If a stop command is applied (from another unit) during a change cycle, then the cycle will be aborted.  If this happens during a blade move, the blades will return to the unlocked position before error mode (mode 4) is entered.

Mode 4 - Error mode

This mode is entered if:

  • an error occurs in the change cycle
  • the system is switched on without the rack being connected
  • an overtravel error occurs
  • an invalid command is received
  • a command is received while the system is busy
  • an external STOP is received

Error mode messages

Error messages sent are as follows:

Lock mechanism error(LME)

Q1 (CR) (LF)

Lid time-out error


Q3 (CR) (LF)

G message not received 


Q4 (CR) (LF)

Command not accepted


Y5 (CR) (LF) *

Excessive entry speed 


Q6 (CR) (LF)

Invalid command


Y7 (CR) (LF) *

Rack overtravel error


X8 (CR) (LF)

Rack not connected


R9 (CR) (LF)

Lock operation aborted


YA (CR) (LF) *

Change cycle aborted


YB (CR) (LF) *

*  The first character of these messages indicates the state of the system before the error occurred.  Other responses are possible such as Q5, ZB etc.

In the case of CNA (Command Not Accepted) or INC (Invalid Command), the appropriate reply –5 or –7 is given, and the system returns to what it was doing.

In the case of LCA (Lock Cycle Aborted) the screwdriver blades will be returned to unlocked positions its status reported –0 and the system returns to the main software nucleus (mode 2).

The CNA reply is given in response to a valid command, received when the system is performing another task (ie the system is busy). The INC response is given in reply to a command that is not recognised by the system.

For all remaining errors the following actions occur:

  • Rack motor is stopped
  • Change cycle disabled
  • Datum mode (mode 6) disabled
  • Touch probe overridden to look like open probe (conventional) stop applied (PICS)

To recover from an error:

  1. Remove the problem.
  2. Ensure ACR1 is not overtravelled.
  3. Move the quill from the ACR1.
  4. Ensure no lids are open.
  5. Press RESET button / apply external reset 'Direct command mode' (mode 5) can be entered on receipt of a CMM message.  However, unless this is a K message, error mode (mode 4) will be re-entered after processing this command.

LED errors

The type of error is also visually displayed using the ACC2-3 and ACR1 LEDs as shown in the following table:


LED off

LED on

















Change cycle
Probe active
Cycle error
Lock error
















Rack ready
Rack active◊ *◊ *
Lock error
Overtravel error

*  These LEDs are ON so that a unique display is given for each error.

— Present mode or status.

There is no display for CNA, INC or LOA because these errors do not cause the unit to stay in error mode.

During error mode only the following commands are available:

  • Front panel reset
  • External reset
  • C, H, J, K, R, S, V, W, Y, and Z commands

Mode 5 - Direct command mode

There are 15 commands which the CMM can send to directly command system actions.

The ACC2-3 can receive commands and reply to them while it is in any operating mode except switch on / restart (mode 1).  When the command has been processed, the ACC2-3 returns to the mode it was in before the command was received unless that command was a K, in which case a restart is performed.

Mode 5 is a transitional state.

There are two main operating modes of the system: main software nucleus mode (mode 2) and datum mode (mode 6).

Mode 6 - Datum mode

Datum mode is used for the alignment and datuming of the ACR1. It is necessary because the datum probe must be active for part of the procedure and the port lids must be held open without causing the Change cycle to start.  Neither of these actions is allowable in mode 2.

Datum mode can be selected and de-selected in two ways:

  • By using the direct commands D (select datum mode) and K (reset)
  • Manually by pressing the RESET switch (or applying the external reset) while a port lid is held open, or closed to reset

Datum mode is subdivided into datum mode 1 and datum mode 2.

Datum mode 1 is selected by opening any or all of the port lids while the system is in datum mode. In datum mode 1 the CMM probe is active and the change cycle inhibited, this allows the port positions to be probed.

Datum mode 2 is selected when all the port lids are closed and while the system is in datum mode. In datum mode 2 the datum probe is enabled and the CMM probe disabled, this allows the probe head autojoint to be aligned and its position to be determined.

The system status characters are:

K0 (CR) (LF) for datum mode 1

L0 (CR) (LF) for datum mode 2

System status

The system status can also be determined from the LEDs on the ACC2-3 and the ACR1 (see following table).


LED off ♦
LED on ◊
LED flashing ‡


LEDDatum mode 1Datum mode 2
Change cycle
Probe active
Cycle error
Lock error


LEDDatum mode 1Datum mode 2
Rack ready
Rack active