Engineering Notes by Oriental Motor

Simplified Position Control for Index Tables Operating in Absolute Coordinates

[fa icon="calendar"] Jan 4, 2019 7:56:17 PM / by Johann Tang

Johann Tang

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 90° 180° 270° 360° 450° 540° 630° 720° 810° 900°

Since the same index positions repeat after 360 degrees, the actual position 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)

Manage 360° coordinates better by converting to absolute coordinates instead of steps

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 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.

Use the Wrap Function to reset position counter when appropriate

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 setting flow chart

Here we show you a screenshot of the dedicated MEXE02 support software where it contains the Wrap parameter settings.

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 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

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.

  Bonus: Learn the various types of Wrap positioning operations you can do with this video tutorial.

MEXE02 Support Software AZ Series Wrap Positioning Operation for Indexing

For more information about the Wrap Function, please refer to page 40 of the 
AZ Series Functions Manual
*The DG II Series is the hollow rotary actuator version of the AZ Series.

Product Highlight: DG II Series Rotary Actuators

  • Low profile
  • AC and DC versions available
  • 60/85/130/200 mm frame sizes
  • Built-in absolute position sensor
  • Permissible torque up to 50 Nm (440 lb-in)
  • Moment load up to 100 Nm (880 lb-in)
  • Thrust load up to 900 lbs (408 kg)

Learn More

Watch More Videos

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The Wrap Function is also available with other products from Oriental Motor that use the AZ Series hybrid controlled stepper motors, such as linear slides, linear cylinders, compact cylinders, and rack and pinion lift and gripper systems.

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Topics: Stepper Motors, Absolute Positioning, Linear & Rotary Actuators, VIDEOS, Software, Application Examples

Johann Tang

Written by Johann Tang

Johann Tang is a Product Specialist at Oriental Motor USA Corp. with over 15 years of knowledge and experience supporting applications of various types of electric motors, gearheads, actuators, drivers, and controllers.