Resolution Parameters: GearRatio

Description

This parameter is used to set the ratio of axis position to drive position for an axis.

Ratio

The ratio represents the physical transmission between a motor and the axis movement point (a slide, table, spindle, etc.). It should only need to be changed if the transmission changes. It must be set to a valid value for correct axis positioning to occur. The ratio functions are GetGearRatio and SetGearRatio.

The definition of ratio is:

axis position units / drive position units

This ratio is independent of the resolution of the feedback device attached to the motor, and of the default unit system for an axis. It is dependent on the axis units: being linear or angular.

Here is an example, where the drive position units on the SERCOS® drives are set as revolutions:

a lead screw is attached to the motor and moves the axis 2 inches/turn of the motor, so the ratio is set to inch(2) / rev(1).
A transmission moves a rotary table 1 turn for 10 turns of the motor, so the ratio is set to rev(1) / rev(10).

Imaginary Axis and Ratio

A servo drive does not control an Imaginary Axis. The drive position units must be encoder feedback counts. The axis position units can be any angular or linear units. The ratio should represent typical resolutions of position feedback devices. For example:

A ratio of: rev(1) / feedback count(65536)

A ratio of: mm(1) / feedback count(1000)

Remote Axis and GearRatio

The position feedback for a RemoteSetpoint is the feedback register for that axis. The 32-bit integer placed in the register is assumed to have feedback count units. The ratio is chosen to convert to the desired axis units. For example:

A ratio of: rev(1) / feedback count(10000)

A ratio of: mm(1) / feedback count(1000)

Associated Functions

The associated functions of this parameter are:

GetGearRatio which sends a read request for the actual ratio,
SetGearRatio which sends a write request for the new ratio.

These functions use, according to the language objects, the WRITE_CMD, READ_PARAM or WRITE_PARAM instructions.

Associated Language Objects

The table below presents the different language objects linked to the Accel parameter.

Object	Name	Function code	Instruction type	Description
%MFr.m.c.59	SCALE_NUMERATOR	-	READ_PARAM	Read command
%MFr.m.c.59	SCALE_NUMERATOR	-	WRITE_PARAM	Write command
%MFr.m.c.61	SCALE_DENOMINATOR	-	READ_PARAM	Read command
%MFr.m.c.61	SCALE_DENOMINATOR	-	WRITE_PARAM	Write command

%MWr.m.c.26	ACTION_CMD	1500	WRITE_CMD	Read command
%MWr.m.c.26	ACTION_CMD	2500	WRITE_CMD	Write command
%MFr.m.c.22	RETURN_CMD_2	-	-	Result of the read (Numerator).
%MFr.m.c.24	RETURN_CMD_3	-	-	Result of the read (Denominator).
%MFr.m.c.31	PARAM_CMD_3	-	-	Value to write (Numerator).
%MFr.m.c.33	PARAM_CMD_4	-	-	Value to write (Denominator).
%MWr.m.c.19	ERROR_CMD	-	-	Error report. See (WRITE_CMD Command: Programming Errors)