Delta RMC151 - Manual (Page 122)

RMC70/150 and RMCTools User Manual
In general, to move rotary axes, use the same motion commands as you would for linear
axes. When positions wrap on the axis, the RMC automatically accounts for it when calculating
target profiles, Position Error, etc.
When Should Rotary be Used?
If your machine has a rotary encoder, it does not necessarily mean the axis should be
defined as rotary. The application determines whether the axis should be defined as
rotary.
Typically, rotary applications are applications where the machine (motor, belt, etc.)
rotates through a position cycle and does not have endpoints of travel. That is, it is
possible for it continuously travel in one direction without needing to move the opposite
direction (it doesn't have to continuously travel in one direction, but it should be
possible). Typically, single-turn or multi-turn absolute encoders or incremental encoders
are used in rotary applications.
The Positive Travel Limit and Negative Travel Limit do not apply for rotary axes. If you
need positive and negative travel limits and you are using a rotary encoder, you should
set up the axis as linear.
Rotary Configuration Basics
For rotary axes, the counts per revolution must be a power of two, such as 1024, 8192,
etc. This typically means the encoder counter per turn must be a power of two.
The Position Unwind parameter defines the position range the axis will work in. The
Position Unwind parameter can be any positive non-zero value. It works together with the
Count Unwind and Position Offset parameters to scale the counts to position units.
For more details, see the Rotary Scaling topic.
Example 1:
Assume you have a 10 ft (120 in) long belt and an encoder. You wish to scale the axis for
inches. You would set the Position Unwind to 120. As the belt travels, the positions will go
from 0 up to, but not including, 120 in. The Count Unwind should be set to the number of
counts generated in 120 inches of travel.
Example 2:
Assume you have a motor with an encoder with 8000 counts per turn, and the encoder
turns 4 times per machine revolution. You wish to scale the axis for degrees. You would
set the Position Unwind to 360 and the Count Unwind to 32000 (8000 x 4). As the motor
turns, the positions will go from 0 up to, but not including, 360 degrees.
Rotary Motion Command Behavior
The sections below describe how commands behave on rotary axes:
• Rotary Motion with Absolute Position Moves
• Rotary Motion with Relative Position Moves
• Rotary Motion with Velocity and Gear Moves
• Rotary Motion with Open Loop Commands
Rotary Motion with Absolute Position Moves
This section applies to the following commands:
• Move Absolute (20)
• Quick Move Absolute (15)
• Time Move Absolute (23)
• Sync Move Absolute (13)
• Advanced Time Move Absolute (26)
• Move Absolute (I-PD) (28)
• Transition Rate (56)
102 Delta Computer Systems, Inc.