Motion PT

The “Motion – PT” dialogue allows you to program a positioning path described through a series of points. Each point specifies the desired Position and Time, i.e. contains a PT data. Between the points the built-in reference generator performs a linear interpolation.

In the PT mode the load/motor is controlled in position. A PT sequence must begin when load/motor is not moving.

The PT mode is typically used together with a host, which sends PT points via a communication channel. Due to the interpolation, the PT mode offers the possibility to describe arbitrary position contours using a reduced number of points. It is particularly useful when the motion reference is computed on the fly by the host, like for example, in vision systems. By reducing the number of points, both the computation power and the communication bandwidth needed are substantially reduced optimizing the costs. When the PT motion mode is used simultaneously with several drives/motors having the time synchronization mechanism activated, the result is a very powerful multi-axis system that can execute complex synchronized moves.

Upon reception, each PT point is stored in a reception buffer. The reference generator empties the buffer as the PT points are executed. The drive/motor automatically sends warning messages when the buffer is full, low or empty. The buffer full condition occurs when the number of PT points in the buffer is equal with the buffer size. The buffer low condition occurs when the number of PT points in the buffer is less or equal with a programmable value. The buffer empty condition occurs when the buffer is empty and the execution of the last PT point is over.

•	The PT buffer size is programmable and if needed can be substantially increased. By default it is set to 7 PT points.

•	The buffer low condition is set by default when the last PT point from the buffer is read and starts to be executed

•	After the execution of the last PT point from a sequence the drive/motor keeps the last reference position, waiting for the next PT commands.

•	The PT mode requires the drive/motor to be setup for position control. Otherwise, in the Motion view, the button opening this dialogue will not occur.

The “Motion – PT” dialogue was specifically created to help you quickly evaluate, in advance, a PT sequence of points. The included graphical plot shows you the interpolated trajectory allowing you to check the results. Moreover, you can execute the whole sequence of PT points and check your application behavior before implementing the PT handshake on your host.

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One by one, by setting for each point its Position and Time values. Both are relative to the beginning of the PT motion. Select the measuring units from the list on the right. The graphical tool included, will automatically update the evolution of the position after each point change. A red spot, indicates the active point. Use buttons: Remove, Update, Insert, << and >> to navigate between the PT points and modify them.

•	With Import From File to insert a set of PT points previously defined. The file format is a simple text with 2 columns separated by space or tabs representing from left to right: position and time values. The number of rows gives the number of PT points

Check Host address and set your PC/host address if the drive/motor is connected via CANbus with your host. The host address is where the PT messages regarding buffer status are sent.

Remark: By default, the host address is initialized with the same value as the drive/motor address, plus the host bit set. This causes to send the PT messages via RS-232 link.

Check Clear PT Buffer to erase all the previously stored points from the PT buffer. Use this option each time when you initiate a new PT motion. Uncheck this option if the execution of the PT points was interrupted and you want to resume the execution of the remaining points.

Select Generate new trajectory starting from actual values of position and speed reference if you want the reference generator to compute the PT motion path starting from the actual value of the position reference (the speed reference is always considered zero). Select Generate new trajectory starting from actual values of load/motor position and speed if you want the reference generator to compute the PVT motion starting from the actual value of the load/motor position. When this option is used, the position and speed reference are updated with the actual values of the load/motor position and speed. Use this option for example at recovery from an error or any other condition that disables the motor control while the motor is moving. Updating the reference values leads to a “glitch” free recovery because it eliminates the differences that may occur between the actual load/motor position/speed and the last computed position/speed reference (before disabling the motor control).

Remark: In open loop control of steppers, this option is ignored because there is no position and/or speed feedback.

Choose Execute Immediate to start the programmed motion immediately when the motion sequence is executed. Check Then wait until motion is completed if you want to postpone the start of the following motion until this programmed motion is completed.

Remark: Verify the motion complete condition parameters. If these are incorrectly set, you may never reach the motion complete condition:

▪	0 = sets motion complete when the reference generator has completed the trajectory and has arrived to the commanded position

If these parameters have not been set previously, check their default value. Reset the drive/motor and using the command interpreter get their value.

Choose Execute On event to start this new motion when a programmable event occurs. Click Change Event to select the event type or Edit Event to modify the parameters of the selected event (see Events for details).

OK: Close this dialogue and save the motion sequence in your motion sequence list.

Cancel: Close this dialogue without saving the motion sequence in your motion sequence list.