New GalilPVT Software Released

Galil's newest mode of motion is PVT (Position, Velocity, Time). This mode allows arbitrary motion profiles to be defined by position, velocity and time individually on all axes. This motion is designed for systems where the load must traverse a series of coordinates within time constraints and with no discontinuities in velocity. Taking advantage of the built in buffering, the user can create virtually any profile including those with infinite path lengths. GalilPVT is a developer's tool for using the PVT mode of motion on the DMC-40x0 series motion controller. PVT is one of Galil's more sophisticated modes of motion, and the GalilPVT software tool allows the user to visualize the planned trajectory prior to sending the data to the controller. GalilPVT is offered as a free trial, with saving data disabled. The full version allows the user to save the output data of the software.

GalilPVT aides PVT motion design with the following features:

• Open PVT data in CSV and DMC formats
• Open Contour data in CSV and DMC formats
• Convert Contour data to PVT data
• "Segment View" display of each PVT point as it would be commanded by the user including elapsed time, total distance, incremental position, velocity, and incremental time. Segment data can be edited.
• "Kinematics View" display of controller internal calculations on a profile-by-profile basis including distance, velocity, acceleration, and jerk.
• Graphing capability
• Multi-axis graphing of Position, Velocity, Acceleration, and Jerk vs. time
• Single axis graphing of up to two data sets, e.g. Position and Velocity vs. time
• Two axis position vs. position graphing for coordinated motion planning
• "Motion Summary" providing timing, and maximum velocity, acceleration and jerk throughout the move.
• Stream capability to connect to a controller and stream an arbitrarily long segment list to a DMC-40x0.

To highlight some of the features of PVT and GalilPVT, a simple example will suffice. Suppose the motion requirements of an application are the following:

1. Start from rest and move in 1 second to a position of 1000000 counts.
2. Return to the origin in 1 second.
3. Smoothness in motion is paramount.

We can do this in many ways, three methods are outlined below.

1. Position Relative

The Position Relative (PR) mode of motion is excellent for specifying position targets. The inputs to this mode of motion are speed (SP), acceleration (AC), deceleration (DC), and relative position (PR). A trapezoidal or triangular velocity profile is used to attain the target position. By maintaining a triangular profile, we minimize the magnitude of acceleration. PR mode is not designed, however, to provide a motion within a given time, so some calculations are necessary to guarantee our 2 second round trip.

From the kinematic equations for constant acceleration:

With initial velocity and acceleration zero, we can find that the first acceleration phase, which must traverse 500,000 counts in 0.5 seconds, yields an acceleration of 4,000,000 counts/s/s. Symmetry yields a deceleration of the same value. We calculate the speed from the velocity function as 2,000,000 counts/s.

The code in Table 1 demonstrates this triangular profile. Figure 1 shows a plot of the profile. Notice that the velocity profile (yellow) has a discontinuity (sharp point) at the position curve Inflection points. This can cause roughness and vibration in the motion profile.

Figure 1: Graph of Triangular Velocity Profile for Position Relative Mode

2. Contour Mode

A mode of motion that is better suited to time-based position targets is the contour mode. In this mode, position targets are specified for a particular time interval and the controller linearly interpolates position between these target points. No external calculations are required by the user to ensure the time interval. The code in Table 2 shows a Contour Mode program and Figure 2 shows a graph of the velocity profile. Notice that the position waveform is triangular, and the velocity waveform is square. Acceleration and deceleration are infinite between changes in velocity. In this instance, the contour mode is worse than the position relative mode with respect to velocity smoothness.

Table 2: Program for Contour Mode

Figure 2: Graph of Square Velocity Profile for Contour Mode

3. PVT Mode

PVT mode is quite easy to specify in this example, and maintains smooth velocity. Table 3 shows the program and Figure 3 shows the resulting velocity profile. Notice that both position and velocity are smooth curves, leading to the smoothest possible motion.

Table 3: Program for PVT Mode

Figure 3: Sinusoidal Velocity Profile of PVT Mode

GalilPVT Software helps with this example by providing visualization of the motion prior to actually profiling it, and provides helpful motion statistics. Example Screen shots of the GalilPVT software are shown in Figures 4, 5, and 6.

For more information about Galil's new GalilPVT software please visit http://www.galilmc.com/products/galilpvt.php.

Figure 4: Tabular PVT data in GalilPVT


Figure 5: Motion Summary from GalilPVT


Figure 6: Position and Velocity Profile Generated from GalilPVT

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