Resolver Scaling

Defining the Valid 16-bit Position Range

For general scaling information, see the Scaling Overview topic.

Because the RMC uses 16-bit positions, positions must all fit within a range of 65,536 position units. Because position units are user definable, this range does not limit most applications. See the section below on defining position units.

For resolver axes, the Coordinate Limit parameter is used with the Scale parameter to define the position range. If the Scale parameter is positive, then the position range extends from the Coordinate Limit value (which would normally be negative) up to the Coordinate Limit + 65535. If the Scale parameter is negative, then the position range extends from the Coordinate Limit value (which would normally be positive) down to the Coordinate Limit – 65535. The following chart summarizes this concept:

Scale	Min. Position	Max. Position
³ 0	Coordinate Limit	Coordinate Limit + 65535
< 0	Coordinate Limit – 65535	Offset

Translating to Position Units

Before the translation from counts to position units begins, the Count Offset is applied to the counts. This means that the value of the Count Offset is subtracted from the Counts before they are displayed or processed in any way. For a full discussion on the use of the Count Offset setting, see Resolver Configuration.

The following formula summarizes the translation from transducer counts to Actual Position units:

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As described above, the Count Offset configuration setting has already been subtracted from the Counts field before using this formula. If the Actual Position overflows the valid 16-bit position range due to excessive travel of the axis, the position will wrap around to the opposite extreme shown in the table of the minimum and maximum positions above.

Notice that the Scale can hold values from -32768 to 32768, but 16-bit signed numbers are limited to -32768 to 32767. Therefore, enter a scale of 32768 as 0; the RMC will interpret it as 32768.

Calculating the Scale and Count Offset

Follow these steps to calculate the Scale and Count Offset parameters:

Determine the Scale
Each revolution of the resolver generates 65536 counts. To calculate the Scale parameter, determine how many position units there are in one turn of the resolver.

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The sign of the Scale is positive if the counts and the position units increase and decrease together. The sign is negative if the counts and position units move in opposite directions.

You can use the Resolver Calibration Tool to assist with this step. To access it, on the Tools menu, click Resolver Calibration Tool.

Select the Coordinate Limit
In most cases, the Coordinate Limit can be set to -32768 (for a positive scale) or 32767 (for a negative scale). This will allow position units to go from -32768 to 32767, which is the same range as most PLCs use for 16-bit numbers.

You can pick other values for the coordinate limit if you wish to specify a different range of valid position units.

You can use the Resolver Calibration Tool to assist with this step. To access it, on the Tools menu, click Resolver Calibration Tool.

Set the Count Offset
Move the axis to a known position and issue a Z command with the current desired position for the Command Value. This will change the Count Offset parameter such that the Actual Position will indicate the current position.

The Count Offset value must be stored in non-volatile memory in order to read the correct position the next time the RMC powers up. Use the Update Flash command to store the parameters to non-volatile memory.