Image sensor acquisition, Triggering and Sending results

• 1. Introduction
• 2. Grab sensor images
• 3. Hardware trigger
• 4. Sending results
• 5. Other examples scripts

1. Introduction

We have to modifiy our script to fit the real constraints of our application:

• We have to get images from the sensor and not from an image file.
• We have to acquire images on hardware trigger
• We need to send the result to the process (PLC)

Let's start with the first topic.

2. Grab sensor images

There is a specific HALCON Image Acquisition Interface for the VC-Z camera. The file is called 'hAcqVC-Z.so'. You can check if it is present in /usr/lib/ folder in the camera:

We can see some other files:

HALCON Files	Descriptions
hAcqFile.so	HALCON Image Acquisition Interface for virtual acquisition of image files
hAcqVC-Z.so	HALCON Image Acquisition Interface to grab image from the sensor directly with 'grab_image'
libhalcon.so	This binary file contents every HALCON processing operators
libhalconc.so	HALCON C Interface
libhalconcpp.so	HALCON C++ Interface
libhdevenginecpp.so	HDevelop Engine Interface for C++ application

We can connect to the sensor by open_framegrabber() with the interface 'VC-Z' instead of the 'File' interface:

open_framegrabber('VC-Z', 1, 1, 0, 0, 0, 0, 'default', -1, 'default', -1, 'default', 'default', 'default', -1, -1, AcqHandle)

That is all! The images grabbed by 'grab_image_async()' will come from the sensor.

A complete documentation of the 'VC-Z' Image Acquisition Interface is available here.

3. Hardware trigger

We can enable the hardware trigger by this simple line:

set_framegrabber_param(AcqHandle, 'external_trigger', 'true')

Now when there is no hardware trigger, a timeout could happens. We have to manage this behaviour around the 'grab_image_async()' call.

try
  // Grab image only when a rising edge comes in the input TrigIn line
  grab_image_async(Image, AcqHandle, -1)
catch (Exception)
  // By default the timeout is 5sec (you can change it with the parameter 'grab_timeout')
  // if there is no hardware trigger during this delay,
  // you will get an exception with the error code 5322 (for timeout)
  // It is a normal behaviour, continue to wait a hardware trigger...
  continue
endtry

No image is taken until a rising edge happens on TrgIn.

4. Sending results

In HALCON we can handle TCP or UDP or serial communication. Have a look a the HALCON reference documentation on this topic. In our example we propose to establish a TCP socket connection between the camera and a small terminal on the HOST PC called 'TeraTerm' as a TCP client.

So we have to modify our script in order to manage a TCP communication. At first, we create a TCP server in order to accept a client connection:

// Socket connection
Protocol := 'TCP4'
Timeout := 5.0
// Open a listening socket
open_socket_accept (4660, ['protocol','timeout'], [Protocol,Timeout], AcceptingSocket)

And then we are waiting for an incoming connection from a client:

// Wait for an incoming connection, use the timeout of the
// AcceptingSocket
dev_error_var (Error, 1)
dev_set_check ('~give_error')
OpenStatus := 5
NbTry := 0
Socket := []
while (OpenStatus != 2 and NbTry < 3)
    socket_accept_connect (AcceptingSocket, 'auto', Socket)
    OpenStatus := Error
    NbTry := NbTry + 1
endwhile
dev_set_check ('give_error')

We are waiting for a client connection 3 times during the timeout of 5 sec, so we have 15 sec to establish the connection with a client otherwise the 'Socket' variable will be empty and no result will be sent after the processing step:

// Send result
if(Socket != [])
    send_data (Socket, 'z', msg + ' ', [])
endif

Have a look at the complete source code at the end of this page. We can launch the script in the camera:

/usr/bin/hrun ./tutorial_1_03.hdev -p ./procedures/

And we have 15 seconds to connect a TCP client to receive results. For example we use 'TeraTerm' client with this settings:

When the connection succeeds, a result is sent to the TCP client at each rising edge on the TrigIn line:

That's all! Our first real application is done, congratulations!

5. Other examples scripts

There are some other scripts to illustrate the VC-Z HALCON acquisition interface:

• VC-Z_simple.hdev : A simple example to show the usage of the interface. There is some processing to detect circular shapes. The images can be seen on a X-Server.
• VC-Z_external_trigger.hdev : A example of acquisition with an external hardware trigger.
• VC-Z_parameters.hdev : Lists all parameters of a device and log them in the console and in a txt file.
• VC-Z_subsampling_partialscan.hdev : A example of acquisition with a subsampling and an ROI on the sensor.
• VC-Z_CaptFPS.hdev : A example to measure the max FPS for a series of image height resolutions.
• VC-Z_simple_color.hdev : A simple example to grab color images.

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You can get the complete source code here.

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Next section: Additional tips: Strobe, Flipping image and color processing.