Gearing - Emerson EZMotion User Manual

6.4

Gearing

The Gear motion profile is used to slave the motion of the motor to the motion of a master axis at a specified ratio. Gearing is often
referred to as "electronic line shafting" or "electronic gearing". To gear a follower axis to a master axis, a ratio (called the gear ratio)
must be specified. The Gear Ratio defines the relationship between the master and follower motion.
The ratio is calculated as follows:
The ratio is the number of follower distance units to move the motor per master distance unit of travel. Follower Distance Units are
configured on the User Units view. Master Distance Units are configured on the Master Setup screen.
The gear ratio can be positive or negative and is a signed 32-bit parameter. The resolution of the parameter is determined by the
number of decimal places configured for the Master Velocity Units on the Master Setup screen.
By default, gearing does not use acceleration or deceleration ramps with respect to the master encoder. This means that once
gearing is activated, peak torque is available to try to achieve the specified gear ratio. Therefore, if the master axis is in motion when
gearing is activated, the control loop will attempt to achieve the programmed ratio within one update without programmed
acceleration. Analogously, when gearing is deactivated, the motor will use peak torque to bring the motor to a stop without a
deceleration ramp.
Acceleration and Deceleration ramps can be enabled by the user. If enabled, the Accel and Decel ramps are specified in units of
Follower Units / Velocity Time Base / Acceleration Time Base. Note that this is a Realtime ramp. Therefore, the time that it takes to
reach the programmed ratio depends on how fast the master is traveling when gearing is activated.
Figure 54 demonstrates that the faster the Master Velocity, the longer it will take to reach the programmed ratio. If the Master Axis is
not moving when gearing is initiated, then the follower locks into its programmed gear ratio instantly (no acceleration time required).
Figure 54:
The GearRatio can be changed on the fly (while gearing is active and in motion), but acceleration or deceleration must be enabled to
use ramps to achieve the new ratio. If gearing accel and/or decel ramps are not enabled, the motor will attempt to achieve the new
ratio in one trajectory update.
42
Gear Ratio =
Velocity
Gear Accel Rate
MV
3
MV
2
MV
1
Gear
Initiate
T < T < T = The greater the master velocity (MV) the
1 2 3
longer it takes to accelerate to the Gear Ratio.
Gear Acceleration Diagram
www.controltechniques.com
# of Follower Distance Units
1 Master Distance Unit
Programmed
T T T
1 2 3
Time
EZMotion User/Programming Guide
Revision: A8