Simplified Position Control for Index Tables Operating in Absolute Coordinates (VIDEO)

With recent trends focusing on improving engineering efficiency, many products have been developed to specifically help shorten design cycles for machine automation. Part of improving efficiency is making products easier to use, so additional time and resources can be spent elsewhere. This post describes an example of a product feature that can make index table applications less complex to manage.

Rotary index table

APPLICATION EXAMPLE: rotary index table that rotates a fixed distance repeatedly in the same direction. A motorized rotary actuator is installed below the index table.

Product video below shows another application example of a syringe dispensing application with a rotary actuator.

For an index table that rotates a fixed distance repeatedly in the same direction, position management can be difficult since the internal position counter value keeps increasing. Since position values are often step counts based on the motor's resolution, some mathematical calculations needs to be included to convert the step count to degrees before the operator can understand where the table is actually facing.

For example, let's say we are positioning 90 degrees at a time with a motor that has a basic step resolution of 200 steps per revolution, or 1.8° per step. The position counter value will look like this:

Steps	0	50	100	150	200	250	300	350	400	450	500
Degrees	0°	90°	180°	270°	360°	450°	540°	630°	720°	810°	900°

Since the same index positions repeat after 360 degrees, the actual positon coordinates within 360° have to be calculated.

Actual Position = Current position in degrees - (360 x number of revolutions travelled)

For 900°, the rotary table have rotated more than 2 revolutions, so the formula will be:

Actual Position = 900° - (360° x 2) = 180° (from home position)

For positioning management of index tables, it is easier to monitor the table position if the position count value can be reset to 0° once it passes 360°. For the above example, the position values can be converted to only 0°, 90°, 180°, and 270°. Position count value conversion won't be necessary, which make lives a little bit easier for control engineers. Other functions, such as Wrap Proximity Positioning and Wrap Absolute Positioning, can be used to make position control and management even easier.

CHALLENGE: Manage 360° coordinates easier by converting to absolute coordinates for index tables

SOLUTION: Use the Wrap Function to reset the position counter to 0 when the table passes 360°

The Wrap Function automatically reset the current position counter value to 0 when the motor output shaft exceeds a set value. For example, when the "Wrap Setting Range" is set to "1 rotation", the position counter value automatically resets to 0 when the motor shaft exceeds 360° from the home position.

Wrap function graph

Here we show you the section of the dedicated MEXE02 support software where it contains the Wrap parameter settings to resolve the above challenge.

Left Menu:

MEXE02 wrap menu

Center Window:

Wrap function setting-1

The circled parameters are changed from their default values to make this possible.

Initial Coordinate Generation & Wrap Coordinate Setting	To use the wrap function, select manual setting. Setting range: ABZO sensor or manual
Initial Coordinate Generation & Wrap Setting Range (rev)	Sets the wrap range. The command position returns to 0 when the motor has rotated for the number of times set here. Setting range: 5 to 655,360 (1=0.1 rev)
Initial Coordinate Generation & Wrap Range Offset Ratio (%)	Set the offset ratio of the wrap range. Setting range: 0 to 10,000 (1=0.01%)
Wrap Setting	Enable or disable
The Number of the RND-ZERO output in wrap range	Sets the number of times to turn the RND-ZERO output ON in the wrap range. Setting range: 1 to 536,870,911 divisions

Here's a video showing you how to set up the Wrap Function parameters for Oriental Motor's rotary actuators by using the MEXE02 support software.

For more information about the Wrap Function, please refer to page 39 of the
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*The DG II Series is the hollow rotary actuator version of the AZ Series.