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How Motion Works www.emersonct.com 23
5 How Motion
Works
5.1 Introduction
The SM-EZMotion module offers four different motion
object types. These four types are Jog, Home, Index, and
Gear. All motion objects run on what is called a Profile.
Only one motion object can run on a Profile at a time. For
applications that need to run multiple motion objects
simultaneously, the SM-EZMotion module has two
different Profiles. This will be discussed further in the
Summing Multiple Profiles subsection below.
This section will concentrate on how the different motion
objects work, and not on how they are configured using
PowerTools Pro. For more information on how to configure
the motion objects in PowerTools Pro, see “Configuring an
Application” on page 33.
5.2 Jog
Jog is a motion object that has Acceleration, Velocity, and
Deceleration, but no dedicated distance. The user pressing
a push button or foot pedal often controls jog motion. When
the user presses the Jog button, the jog accelerates up to
the jog velocity and continues to run at that velocity until the
user releases the Jog button. When the user releases the
Jog button, the jog decelerates from the Jog Velocity back
down to zero velocity (stopped).
Figure 32shows an example of a Jog profile.
Figure 32: Jog Profile Diagram
The distance traveled by a Jog is entirely dependant on the
duration that the Jog signal is held active. To accurately
control the distance the motor moves, an Index is the
preferred motion object type.
5.3 Home
Home is a motion object that has Acceleration, Velocity,
and Deceleration. A Home works by accelerating up to the
specified velocity until a reference signal activates. Once
the reference signal activates, the motor either begins to
decelerate to a stop immediately (called Calculated
Offset), or continues at the Home velocity and comes to a
stop a specified distance from where the reference signal
activated (called Specified Offset).
The Home is typically used to define a reference position
(or Home position) on a machine. This can be done in
several different ways depending on what type of Home
Reference is used. The Home Reference determines what
action or signal defines the Home position. The three types
of Home Reference supported by the SM-EZMotion
module are Marker, Sensor, and Sensor then Marker.
Following is a description of the three different Home types.
5.3.1 Home to Marker
Most motors used with the Unidrive SP have an encoder
mounted in the back end of the motor. This encoder is used
to feed positional data back to the Unidrive SP or
SM-EZMotion module for position control. Each encoder
has a special signal called the Encoder Marker Channel
that activates once every revolution of the motor. The
SM-EZMotion module can use this Marker as a reference
signal when executing a Home.
The Marker provides an extremely accurate means of
homing the system. The SM-EZMotion module will detect
a rising edge of the Encoder Marker signal every revolution
of the motor shaft. The Home routine begins by
accelerating up to the Home Velocity. The motor continues
at the Home Velocity until the Encoder Marker activates.
The motor then decelerates to a stop immediately, or
continues for a specified offset distance. Figures 33 and 34
show examples of the Home to Marker profile, with
calculated offset and with specified offset respectively.
Figure 33: Home to Marker Profile (Calculated Offset)
Velocity
Jog Accel
Jog Velocity
Jog Decel
Time
Jog.PlusActivate
Velocity
Home Accel
Home Velocity
Home Decel
Time
Home Initiate
Encoder Marker