Reference Point

Introduction

An incremental encoder does not measure the position but supplies a number of pulses proportional to a movement.In order for this movement to be transformed into a position, a known value must assigned to a particular point on the axis (usually chosen as 0).This operation is called setting a reference point.An axis which has been given a reference point, is classed as referenced.

Reference Point Field

The Reference point field defines the type and direction of the reference point (only when an incremental encoder has made the position measurement).

The type is defined by using 2 source detection inputs :zero marker input and cam input.

Possibilities	Approach speed (1)	RP Speed	Icon
short cam (2) and zero latch, + direction	F	F	(3)
short cam (2) and zero latch, - direction	F	F/8	(3)
Short cam (2), + direction	F	F	(3)
Short cam (2), - direction	F	F/8	(3)
Long cam (2) in stop and zero latch, + direction	F	F/8	(3)
Long cam (2) in stop and zero latch, - direction	F	F/8	(3)
Long cam (2) in stop, + direction	F	F/8	(3)
Long cam (2) in stop, - direction	F	F/8	(3)

(1) F is the speed programmed in the instruction in automatic mode or the speed FMANU (defined in the adjustment screen) in manual mode.This speed can be modulated by the SMC coefficient.

(2) Only short cam reference points can be used when the machine is of infinite type.

(3) The icon illustrates the reference point.

Reference Point Command

The reference point command is given:

in automatic mode, by instruction code 14:reference point,
in manual mode, by the SETRP command:manual reference point.

Forced Reference Point

There is also a forced reference point mechanism:

G62 command in Auto mode,
RP_HERE command in Manu mode.

This method of setting a reference point forces the position to a specified value.This operation does not entail any movement and does take account of the type of RP selected.

Reference Point Short Cam

The following table provides a detailed description of short cam reference points :

Type	Short cam / zero latch		Short cam only
Direction	+ Direction	- Direction (1)	+ Direction	- Direction (1)
Icon
Movement Zero latch Cam

(1) or start on cam

Reference Point Long Cam

The following table provides a detailed description of the long cam and zero latch reference points:

Type	Long cam in stop / zero latch
Direction	+ Direction (2)		- Direction (2)
Start	Start off cam	Start on cam	Start on cam	Start off cam
Icon
Movement Zero latch Cam

The following table provides a detailed description of long cam only reference points:

Type	Long cam in stop
Direction	+ Direction (2)		- Direction (2)
Start	Start off cam	Start on cam	Start on cam	Start off cam
Icon
Cam Movement

(2) defines the place on the machine where the cam is situated.

TSX CAY •2 and TSX CAY 33: Zero Latch Presence Monitoring

Reference point short cam monitors the presence of the zero latch along the length of the cam.

During a short cam type of reference point setting, in + direction or – direction, with zero latch, if all the cam is covered without detecting any zero latches, the axis stops at the output of the cam and an error is signaled.The axis goes into a non-referenced state.