At least four steps are necessary to capture a single image from a Balluff device. These steps are explained with the help of source examples from ImpactControlCenter.

Step 1: The Device Needs To Be Initialized

// Get a pointer to the first device found
mvIMPACT.acquire.DeviceManager devMgr = new mvIMPACT.acquire.DeviceManager();
mvIMPACT.acquire.Device pDev = devMgr.getDevice( 0 );
 
// initialise it(this step is optional as this will be done automatically from
// all other wrapper classes that accept a device pointer):
pDev.open();

Note: You HAVE to keep a reference to at least one instance of mvIMPACT.acquire.DeviceManager as long as you want to work with devices! When the last reference gets destroyed by the garbage collector all devices will be closed automatically!

Step 2: Request The Acquisition Of An Image

// create an instance of the function interface for this device
// (this would also initialise a device if necessary)
mvIMPACT.acquire.FunctionInterface fi = new mvIMPACT.acquire.FunctionInterface( pDev );
// send the request for one image down to the driver
fi.imageRequestSingle();

A live acquisition (running inside a thread function) could be implemented as follows:

ContinuousCapture.java:

import mvIMPACT.acquire.*;
 
//-----------------------------------------------------------------------------
public class ContinuousCapture
//-----------------------------------------------------------------------------
{
    //=============================================================================
    //=== Static member functions =================================================
    //=============================================================================
    static
    {
        try
        {
            System.loadLibrary( "mvIMPACT_Acquire.java" );
        }
        catch( UnsatisfiedLinkError e )
        {
            System.err.println( "Native code library failed to load. Make sure the 'mvIMPACT_Acquire.java' library can be found in the systems search path.\n" + e );
            System.exit( 1 );
        }
    }
 
    //-----------------------------------------------------------------------------
    public static void main( String[] args )
    //-----------------------------------------------------------------------------
    {
        DeviceManager devMgr = new DeviceManager();
        Device pDev = mvIMPACT.acquire.examples.helper.DeviceAccess.getDeviceFromUserInput( devMgr );
        if( pDev == null )
        {
            System.out.print( "Unable to continue! " );
            mvIMPACT.acquire.examples.helper.DeviceAccess.waitForENTER();
            System.exit( 1 );
        }
 
        System.out.println( "Initialising the device. This might take some time..." );
        try
        {
            pDev.open();
        }
        catch( ImpactAcquireException e )
        {
            // this e.g. might happen if the same device is already opened in another process...
            System.out.println( "An error occurred while opening device " + pDev.getSerial().read() +
                                "(error code: " + e.getMessage() + ")." );
            mvIMPACT.acquire.examples.helper.DeviceAccess.waitForENTER();
            System.exit( 1 );
        }
 
        CaptureThread captureThread = new CaptureThread( pDev );
        captureThread.start();
        mvIMPACT.acquire.examples.helper.DeviceAccess.waitForENTER();
        captureThread.terminate();
        try
        {
            captureThread.join();
        }
        catch( Exception e )
        {
            System.out.println( e.getMessage() );
        }
    }
}

CaptureThread.java:

import mvIMPACT.acquire.*;
 
public class CaptureThread extends Thread
{
    //=============================================================================
    //=== private static member variables =========================================
    //=============================================================================
    private static final boolean isWindows_ = System.getProperty( "os.name" ).startsWith( "Windows" );
 
    //=============================================================================
    //=== private member variables ================================================
    //=============================================================================
    private Device pDev_;
    //private ImageDisplayWindow window_; // Windows only but there is no such thing as #ifdef in Java!
    private boolean terminated_ = false;
 
    //=============================================================================
    //=== public constructor ======================================================
    //=============================================================================
    //-----------------------------------------------------------------------------
    public CaptureThread( Device pDev )
    //-----------------------------------------------------------------------------
    {
        pDev_ = pDev;
        //window_ = new ImageDisplayWindow( "mvIMPACT_acquire sample, Device " + pDev.getSerial().read() );
    }
 
    //=============================================================================
    //=== public member functions =================================================
    //=============================================================================
    //-----------------------------------------------------------------------------
    public void run()
    //-----------------------------------------------------------------------------
    {
        if( isWindows_ )
        {
            System.out.println( "\n\nSince you are running on a Windows platform you could use the display module belonging to this SDK. To try this simply remove the comments wherever the 'window_' variable is used. As Java does not support something like '#ifdef' we did not come up with anything smarter. Suggestions welcome!!!\n\n" );
        }
 
        // establish access to the statistic properties
        Statistics statistics = new Statistics( pDev_ );
        // create an interface to the device found
        FunctionInterface fi = new FunctionInterface( pDev_ );
 
        // Send all requests to the capture queue. There can be more than 1 queue for some devices, but for this sample
        // we will work with the default capture queue. If a device supports more than one capture or result
        // queue, this will be stated in the manual. If nothing is mentioned about it, the device supports one
        // queue only. This loop will send all requests currently available to the driver. To modify the number of requests
        // use the property mvIMPACT.acquire.SystemSettings.requestCount at runtime or the property
        // mvIMPACT.acquire.Device.defaultRequestCount BEFORE opening the device.
        int result = TDMR_ERROR.DMR_NO_ERROR;
        while( ( result = fi.imageRequestSingle() ) == TDMR_ERROR.DMR_NO_ERROR ) { };
        if( result != TDMR_ERROR.DEV_NO_FREE_REQUEST_AVAILABLE )
        {
            System.out.println( String.format( "'FunctionInterface.imageRequestSingle' returned with an unexpected result: %d(%s)", result, ImpactAcquireException.getErrorCodeAsString( result ) ) );
        }
 
        mvIMPACT.acquire.examples.helper.DeviceAccess.manuallyStartAcquisitionIfNeeded( pDev_, fi );
        // run thread loop
        Request pRequest = null;
        // we always have to keep at least 2 images as the display module might want to repaint the image, thus we
        // cannot free it unless we have a assigned the display to a new buffer.
        Request pPreviousRequest = null;
        int timeout_ms = 500;
        int cnt = 0;
        int requestNr = acquire.getINVALID_ID();
        while( !terminated_ )
        {
            // wait for results from the default capture queue
            requestNr = fi.imageRequestWaitFor( timeout_ms );
            pRequest = fi.isRequestNrValid( requestNr ) ? fi.getRequest( requestNr ) : null;
            if( pRequest != null )
            {
                if( pRequest.isOK() )
                {
                    ++cnt;
                    // here we can display some statistical information every 100th image
                    if( cnt % 100 == 0 )
                    {
                        System.out.println( String.format( "Info from %s: %s: %s, %s: %s, %s: %s", pDev_.getSerial().read(),
                                                           statistics.getFramesPerSecond().name(), statistics.getFramesPerSecond().readS(),
                                                           statistics.getErrorCount().name(), statistics.getErrorCount().readS(),
                                                           statistics.getCaptureTime_s().name(), statistics.getCaptureTime_s().readS() ) );
                    }
                    //window_.GetImageDisplay().SetImage( pRequest );
                    //window_.GetImageDisplay().Update();
                }
                else
                {
                    System.out.println( "Error: " + pRequest.getRequestResult().readS() );
                }
                if( pPreviousRequest != null )
                {
                    // this image has been displayed thus the buffer is no longer needed...
                    pPreviousRequest.unlock();
                }
                pPreviousRequest = pRequest;
                // send a new image request into the capture queue
                fi.imageRequestSingle();
            }
            //else
            //{
            // Please note that slow systems or interface technologies in combination with high resolution sensors
            // might need more time to transmit an image than the timeout value which has been passed to imageRequestWaitFor().
            // If this is the case simply wait multiple times OR increase the timeout(not recommended as usually not necessary
            // and potentially makes the capture thread less responsive) and rebuild this application.
            // Once the device is configured for triggered image acquisition and the timeout elapsed before
            // the device has been triggered this might happen as well.
            // The return code would be -2119(DEV_WAIT_FOR_REQUEST_FAILED) in that case, the documentation will provide
            // additional information under TDMR_ERROR in the interface reference.
            // If waiting with an infinite timeout(-1) it will be necessary to call 'imageRequestReset' from another thread
            // to force 'imageRequestWaitFor' to return when no data is coming from the device/can be captured.
            // System.out.println("imageRequestWaitFor failed (%d, %s), timeout value too small?", requestNr, ImpactAcquireException.getErrorCodeAsString(requestNr));
            //}
        }
        mvIMPACT.acquire.examples.helper.DeviceAccess.manuallyStopAcquisitionIfNeeded( pDev_, fi );
 
        // stop the display from showing freed memory
        //window_.GetImageDisplay().RemoveImage();
 
        // In this sample all the next lines are redundant as the device driver will be
        // closed now, but in a real world application a thread like this might be started
        // several times an then it becomes crucial to clean up correctly.
 
        // free the last potentially locked request
        if( pRequest != null )
        {
            pRequest.unlock();
        }
        // clear all queues
        fi.imageRequestReset( 0, 0 );
    }
 
    //-----------------------------------------------------------------------------
    public void terminate()
    //-----------------------------------------------------------------------------
    {
        terminated_ = true;
    }
}

Note: Images supplied to the user are locked for the driver. So if the user does not unlock the images, a permanent acquisition won't be possible as sooner or later all available requests will have been processed by the driver and have been returned to the user.

See also: Step 4.

Step 3: Wait Until The Image Has Been Captured

int requestNr = fi.imageRequestWaitFor( timeout_ms );

Step 4: Unlock The Image Buffer Once The Image Has Been Processed:

if( fi.isRequestNrValid( requestNr ) )
{
  // processing, displaying whatever
  fi.imageRequestUnlock( requestNr );
}

Note: ImpactControlCenter acquires images with the help of a capture thread. In order to avoid performance losses, the image buffer is locked during either the live or single image acquisition.

So after displaying the image the unlock is necessary!