7.8.12. Plugin class - Actuator

If you want to create a plugin in order to access piezo- or motor-stages, multi-axes-machines,… it is intended to derive your plugin class from ito::AddInActuator. Base idea of any actuator

The actuator interface has been developed with the following base ideas:

  • The actuator can consist of different axes. The first axis is indexed with the number 0. Create the read-only, integer parameter numAxis for the number of connected axes.

  • The plugin contains a set of parameters (like every other plugin), which can be set or get using the public methods setParam or getParam or the appropriate methods in Python.

  • emit the signal parametersChanged(m_params) if any parameter has been changed in order to inform the GUI about these changes.

  • Some of those parameters must be available, others are optional, but if you implement them, you should follow some rules concerning name and type of the parameter, and of course you can add an infinite list of further parameters (see below).

  • Every actuator is executed in its own thread.

  • Every actuator can have one configuration dialog and one dockable toolbox, that is directly included in the GUI of itom.

  • The current position of all axes should be stored in the vector m_currentPos, that is a member of class AddInActuator (bitmask of enumeration ito::tActuatorStatus.

  • The new target position for all axes must be stored in the vector m_targetPos, that is also a member of class AddInActuator.

  • The current status of all axes should be stored in the vector m_currentStatus (member of class AddInActuator).

  • Make sure at the initialization of your plugin that all three member vectors are initialized with the size of the numbers of axes.

  • Changes to the current status or position are signalled by the signal actuatorStatusChanged (class AddInActuator). This is usually emitted by calling sendStatusUpdate(…).

  • Changes to the target position vector is signalled by the signal targetChanged (class AddInActuator). This is usually emitted by calling sendTargetUpdate(). Connected toolboxes as well as further GUI elements are then informed about the changes.

  • Any GUI elements should only get live information about the position and status of the actuator by connecting to these signals (actuatorStatusChanged or targetChanged), since the communication to GUI elements must be executed across multiple threads.

  • Try to only connect to these signals if you really need this information, since the request of live-status and -position-information is time-consuming for certain motors. For example, a dock widget should only connect to these signals, if it is visible. This can be done by overwriting the slot dockWidgetVisibilityChanged of class AddInBase.

  • Methods like setPosAbs, setPosRel, setParam, calib or setOrigin should only execute their given task if the motor is not moving at this moment. This can be checked using the method isMotorMoving(), defined in AddInActuator by simply checking the appropriate status flags.

  • The method waitForDone (pure virtual method of class AddInActuator) has to be overwritten. This method continuously checks the moving status of all (moving) axes are returns if all requested axes reached their target position, reached a switch or if a time-out occurred. User interrupts are also checked within this function. In case of such an interrupt the axes status are set to interrupt as well and the method returns. If the hardware is able to give sophisticated live information about the current status and position of each axis, you can continuously adapt the values in the members m_currentStatus or m_currentPos; else you can to guess these values. Signal changes to these vectors using the methods sendStatusUpdate() or sendStatusUpdate(…). If the axes are asynchronously moved, the semaphore waitCond has to be released immediately before the loop waiting for the target position starts. Then the caller can directly continue working. In synchronous mode (default behaviour), waitCond is only released, if no requested axis is moving any more.

  • There is a slot requestStatusAndPosition(bool sendActPosition, bool sendTargetPos), defined in ito::AddInActuator. This slot is invoked e.g. by a toolbox or configuration dialog in order to force the actuator to directly emit the signals actuatorStatusChanged and/or targetChanged. The original caller is then immediately informed about the current status and position values. Overload this function if you want to update m_currentStatus, m_currentPos or m_targetPos before they are emitted to the caller. In the default implementation, they are emitted as they are. Programming steps

In order to program the actuator plugin, follow these steps:

  1. Create the header and source file for your plugin “MyActuatorPlugin”.

  2. Create the interface (or factory) class “MyActuatorPluginInterface”. For details about how to create such an interface class, see Plugin interface class.

  3. Create the plugin class “MyActuatorPlugin” with respect to the exemplary implementation, given in the next section.

    • Consider which internal parameters, that can be read and/or written by the user, your plugin has. Add these parameters in the constructor of your plugin to the m_params-vector.

    • Implement the init-method that gets the initial parameters, defined in the interface class.

    • Implement the methods getParam and setParam, which are the getter- and setter-methods for the internal parameters.

    • Implement the motor-specific methods, including waitForDone Actuator plugin class

A sample header file of the actuator’s plugin class is illustrated in the following code snippet:


#include "../../common/addInInterface.h"

#include "dialogMyMotor.h"
#include "dockWidgetMyMotor.h"

class MyMotor : public ito::AddInActuator

        ~MyMotor() {};  /*! < Destructor*/
        MyMotor();/*! < Constructor*/

        ito::RetVal waitForDone(int timeoutMS = -1, QVector<int> axis = QVector<int>() /*if empty -> all axis*/, int flags = 0 /*for your use*/);

        friend class MyMotorInterface;
        const ito::RetVal showConfDialog(void); /*!< Opens the modal configuration dialog (called from main thread) */
        int hasConfDialog(void) { return 1; }; /*!< indicates that this plugin has got a configuration dialog */

    public slots:
        //! get/set parameters
        ito::RetVal getParam(QSharedPointer<ito::Param> val, ItomSharedSemaphore *waitCond = NULL);
        ito::RetVal setParam(QSharedPointer<ito::Param> val, ItomSharedSemaphore *waitCond = NULL);

        //! init/close method
        ito::RetVal init(QVector<ito::Param> *paramsMand, QVector<ito::Param> *paramsOpt, ItomSharedSemaphore *waitCond = NULL);
        ito::RetVal close(ItomSharedSemaphore *waitCond);

        //! calibration for single or multiple axis
        ito::RetVal calib(const int axis, ItomSharedSemaphore *waitCond = NULL);
        ito::RetVal calib(const QVector<int> axis, ItomSharedSemaphore *waitCond = NULL);

        //! current axis position is new zero-position
        ito::RetVal setOrigin(const int axis, ItomSharedSemaphore *waitCond = NULL);
        ito::RetVal setOrigin(const QVector<int> axis, ItomSharedSemaphore *waitCond = NULL);

        //! Reads out status request answer and gives back ito::retOk or ito::retError
        ito::RetVal getStatus(QSharedPointer<QVector<int> > status, ItomSharedSemaphore *waitCond);

        //! get current position of single or multiple axis (in mm or degree)
        ito::RetVal getPos(const int axis, QSharedPointer<double> pos, ItomSharedSemaphore *waitCond);
        ito::RetVal getPos(const QVector<int> axis, QSharedPointer<QVector<double> > pos, ItomSharedSemaphore *waitCond);

        //! move one or more axis to certain absolute positions (in mm or degree)
        ito::RetVal setPosAbs(const int axis, const double pos, ItomSharedSemaphore *waitCond = NULL);
        ito::RetVal setPosAbs(const QVector<int> axis, QVector<double> pos, ItomSharedSemaphore *waitCond = NULL);

        //! move one or more axis by certain relative distances (in mm or degree)
        ito::RetVal setPosRel(const int axis, const double pos, ItomSharedSemaphore *waitCond = NULL);
        ito::RetVal setPosRel(const QVector<int> axis, QVector<double> pos, ItomSharedSemaphore *waitCond = NULL);

        //! if this slot is triggered, the current status and position is emitted (e.g. for actualizing a dock widget)
        ito::RetVal RequestStatusAndPosition(bool sendActPosition, bool sendTargetPos);

        //ito::RetVal requestStatusAndPosition(bool sendCurrentPos, bool sendTargetPos); //!see notes above

    private slots:
        void dockWidgetVisibilityChanged( bool visible ); /*!< this slot is invoked if the visibility of the dock widget has changed */

The corresponding source file should start with something like this:


#include "yourHeaderFile.h"

//implement your code here Signalling the current position and status of any axes

Each actuator has the possibility to signalize the target position, the current position and the current status of each axis. Then its own toolbox or other widgets or slots (general: listeners) can be connected to the corresponding signals in order to be informed about the current activity. The base class ito::AddInActuator provides the necessary structures for this:

1. The vector m_currentPos must be initialized to a length corresponding to the number of axes and contains the current position of every axis using the units stated below. Whenever the actuator registers a change of any current position, the corresponding value should be changed as well. Listeners are finally informed about this change by calling the method


The argument false means that not only a change of the current status happened, but also a change of any current position. This method internally emits the signal actuatorStatusChanged.

  1. The vector m_targetPos must also be initialized to a length corresponding to the number of axes. Whenever a positioning operation starts, set the target value of specific axes to the new target value and call


    that finally emits the signal targetChanged.

  2. The status of every axis is stored in the vector m_currentStatus. Each item in this vector with a length corresponding to the number of axes, contains an OR combination of the enumeration ito::tActuatorStatus. Whenever the status of any axis changes, change its status value, too and use sendStatusUpdate(true/false) in order to also emit the signal actuatorStatusChanged.

The enumeration ito::tActuatorStatus contains the following values that are grouped by specific mask values:

The moving flags contain flags about the current moving status of any axis (bits containing to this group are contained in the mask ito::actMovingMask):

  • ito::actuatorUnknown: The current status of this axis is unknown

  • ito::actuatorInterrupted: The movement of this axis has been interrupted and no further commands followed

  • ito::actuatorMoving: The axis is currently moving (or is supposed to move)

  • ito::actuatorAtTarget: The axis reached its target position (this is the default value)

  • ito::actuatorTimeout: A timeout occurred during the movement of this axis

The status flags inform about the general status of any axis (bits containing to this group are set in the mask ito::actStatusMask):

  • ito::actuatorAvailable: This axis is available (usually set)

  • ito::actuatorEnabled: This axis is enabled and can be driven (usually set, but there are drivers that allowing disabling selected axis)

Axes that have got any reference or end switches can signal related status information using the switches flags. All bits belonging to this group are set in the mask ito::actSwitchesMask divided into ito::actEndSwitchMask and ito::actRefSwitchMask):

  • ito::actuatorEndSwitch: This bit is set if any (unknown) end switch was reached

  • ito::actuatorLeftEndSwitch: This bit is additionally set if the left end switch was reached

  • ito::actuatorRightEndSwitch: This bit is additionally set if the right end switch was reached

  • ito::actuatorRefSwitch: This bit is set if any (unknown) reference switch was reached

  • ito::actuatorLeftRefSwitch: This bit is additionally set if the left reference switch was reached

  • ito::actuatorRightRefSwitch: This bit is additionally set if the right reference switch was reached

You can either manually set the necessary bit-combination of moving, status and switch flags for signalling the right status of the axis. There are three methods defined in ito::AddInActuator that simplify this process:

setStatus(int &status, const int newFlags, const int keepMask = 0)
setStatus(const QVector<int> &axis, const int newFlags, const in keepMask = 0)

Use this methods to the set the status of one or multiple axis. The parameter newFlags should contain an or-combination of all flags that should be set. The status flags are then set to this value (hence, old values are overwritten). If you want to keep the current bit values of a certain group, pass the specific mask as argument keepMask. For instance, if you want to the status of the second axis to actuatorMoving without changing the status flags, use the following command:

setStatus(m_currentStatus[1], ito::actuatorMoving, ito::actStatusFlags)
# this command will set all bits of the switches mask to 0!

The equivalent command for multiple axis, requires a vector with axes-indices as first argument. This example does the same for the first and third axis:

QVector<int> axis;
axis << 0 << 2;
setStatus(axis, ito::actuatorMoving, ito::actStatusFlags)

The similar commands replaceStatus

replaceStatus(int &status, const int existingFlag, const int replaceFlag)
replaceStatus(const QVector<int> &axis, const int existingFlag, const int replaceFlag)

can be used to replace one status flag by another one without changing the other bits. If the bit corresponding to the existingFlag is set, it is set to zero and the bit of the replaceFlag is set to 1. In the following example, the flag of the first axis is set from moving to atTarget:

replaceStatus(m_currentStatus[0], ito::actuatorMoving, ito::actuatorAtTarget)

After using one of these functions to set the current status, call sendStatusUpdate to emit the signal actuatorStatusChanged such that connected listeners can for instance visualize the current status. Interruption of movement

It is possible to implement an interrupt button in the toolbox of the actuator that becomes active once at least one axis is moving. Once the button is clicked it must directly call the thread-safe function setInterrupt() of the actuator plugin (If the toolbox inherits from ito::AbstractAddInDockWidget call its method setActuatorInterrupt().

In the method waitForDone regularly check if the interrupt flag has been set, using the actuator’s method isInterrupted(). If this method returns true, set the moving state of all moving axes to ito::actuatorInterrupted and return with an appropriate return value, like:

return ito::RetVal(ito::retError, 0, "movement interrupted");


Once isInterrupted() returns true, the internal interrupt flag is reset to false. Therefore consider to call this function to reset the interrupt flag if desired (e.g. at the begin of the next movement). Parameters and Unit Conventions

In order to have a unified behaviour of all actuator plugins, respect the following unit conventions. That means, the plugin should store related parameters using these conventions, such that getParam and setParam returns and obtains values using these units. Internally, it is sometimes necessary to convert these units to the units required by the interface of the real actuator device.

  • Length values in mm

  • Angles in degree

  • Velocity in mm/sec or degree/sec

  • Acceleration, deceleration in mm/sec^2 or degree/sec^2

Implement the following mandatory parameters in the map m_params:

  • “name”: {string | readonly}

    name of the plugin

  • “numaxis”: {int | readonly}

    number of connected axes

  • “async”: {int, [0,1]}

    If 1: asynchronous movement. Methods like setPosAbs or setPosRel only start the movement and immediately return. Hence, the waitCond in waitForDone is directly released before the loop waiting for the end of the movement is executed. If 0: synchronous movement (default). setPosAbs and setPosRel block until the end of the movement, hence, waitCond in waitForDone is only released at the end of the movement. Since waitForDone always is running during the movement, the plugin thread is blocked and no further commands can be executed, even in asynchronous mode.

If desired implement the following optional parameters in the map m_params:

  • “speed”: {double or doubleArray}

    Desired speed for the axes. If double, the speed holds for all axes, else the doubleArray must have the same length than the number of axes, holding the axis specific speed values. Make sure, that it is not possible to set an array of another length in setParam.

  • “accel”: {double or doubleArray}

    Acceleration values (similar to speed)

  • “decel”: {double or doubleArray}

    Deceleration values (similar to speed)