17.1 Integral and technological functions
17.1.3 Technology objects for motion control
The technology objects TO_Axis_PTO and TO_CommandTable_PTO are available in a CPU 1200 for controlling and monitoring stepper motors and servomotors with pulse interface.
The technology object TO_Axis_PTO (“Axis”) is the interface between the user pro- gram and the drive. The motion control statements in the user program process the technology object. The technology object TO_CommandTable_PTO allows you to create motion profiles for a drive that is controlled with TO_Axis_PTO.
In a CPU 1211C, 1212C and 1214C, a maximum of two TO_Axis_PTO technology objects can be configured, in a CPU 1215C a maximum of four technology objects.
A TO_Axis_PTO technology object requires a pulse generator in PTO mode. One 24 V output channel is required per drive; a signal board (SB) with a digital output channel must therefore be present for CPUs with relay outputs. An input channel with interrupt capability is required if a reference point switch is used.
Configuring the technology object TO_Axis_PTO
The Axis technology object requires an activated pulse generator in PTO mode.
You activate and configure the pulse generator in the properties of the CPU in the hardware configuration (see Chapter 17.1.2 “Pulse generator” on page 554).
The Technology objects folder in the project tree under the PLC station contains the technology objects. Double-click on Add new object to generate a new technol- ogy object. In the dialog window, select the Motion button and then TO_Axis_PTO.
The technology object stores the instance data in a data block whose number you can set. If the Add new and open checkbox is activated, the technology object is opened for configuration. Click OK.
A technology object is stored in the project tree in the Technology objects folder.
The axis contains the entries Configuration, Commissioning, and Diagnostics. Dou- ble-click on Configuration to open the configuration window (Fig. 17.5). In the working window, select the desired parameter range and enter the configuration data for the axis.
To control an axis in the user program, the statements referred to in Section “Pro- gramming the Axis technological axis” on page 559 are available.
Configuring the technology object TO_CommandTable_PTO
With TO_CommandTable_PTO you can configure a command table for a motion sequence. Double-click on Add new object in the Technology objects folder to create a new technology object. In the dialog window, select the Motion button and then TO_CommandTable_PTO. The technology object stores the instance data in a data
Fig. 17.5 Configuring the technology object TO_Axis_PTO
Fig. 17.6 Configuring the technology object TO_CommandTable_PTO
block whose number you can set. If the Add new and open checkbox is activated, the technology object is opened for configuration. Click OK.
To configure the command table, double-click Configuration in the project tree under the command table used. In the configuration window, enter the motion profile (Fig. 17.6).
For a motion sequence, the commands listed in Table 17.4 are available. Either
“Complete job” (the axis decelerates to a stop) or “Continue movement” (the axis maintains speed) can be configured as a completion of a positioning command.
The commands in the command table are implemented in the user program with the statement MC_CommandTable.
Programming the Axis technological axis
You control the Axis technology object and thus the drive with the user program using the motion control statements. The statements are available in the program elements catalog under Technology and Motion control. To call a statement, drag it with the mouse into the open block. Each call requires an instance data record, which can be either in a separate block (single instance) or – if the call is made in a function block – in the instance data block of the calling function block (multi- instance). Fig. 17.7 shows the calls of the motion control statements.
MC_Power enables and disables an axis for motion control.
MC_Reset resets all errors, and acknowledges all errors which can be acknowl- edged.
MC_Home sets a homing point, i.e. the (mechanical) positioning system of the axis is matched with the (logical) coordinate system in the controller.
MC_Halt aborts all movements and stops the axis.
MC_MoveAbsolute starts a positioning motion of the axis to an absolute position.
MC_MoveRelative starts a positioning motion of the axis relative to the start position.
Table 17.4 Commands for the motion control of a axis
Command Action
Positioning Absolute The axis is moved at the configured speed to the specified position.
Positioning Relative The axis is moved the specified distance at the specified speed.
Velocity Setpoint The axis is moved at the specified speed for the specified duration.
Hold The axis is stopped (only after a Velocity Setpoint command).
Wait There is a wait of the specified time between two commands.
Empty This command is used as a placeholder for any other command Separator This command separates different motion profiles in the command table.
MC_MoveVelocity starts the axis with the defined velocity.
MC_MoveJog starts the axis in jog mode for testing and commissioning.
MC_ChangeDynamic changes the dynamic settings of an axis of motion.
MC_CommandTable implements the commands configured in the command table as a motion sequence.
If a motion control statement is still being executed, it must not be interrupted by the start of the same motion control statement. You should therefore call a motion control statement only once in the user program.
Fig. 17.7 Calling the motion control statements in LAD representation Calls of the motion control statements
By assigning the AXIS parameter, you define the axis to be controlled by the motion control statements. At AXIS, specify the data block which was generated when configuring the technology object TO_Axis_PTO (Fig. 17.8). At the parame- ter CommandTable of the statement MC_CommandTable, create the data block that has been generated in the configuration of the technology object.