Using the SONY XC-55 Camera in Asynchronous Reset Mode with the IMAQ 1409

This article explains how to use the SONY XC-55 camera in asynchronous reset mode with National Instruments’ IMAQ 1409 device to acquire clear images of moving objects. It also includes an example program that illustrates asynchronous reset with the XC-55 camera.

Progressive Scan and Asynchronous Reset

Some industrial imaging and Web inspection applications involve acquiring images of fast-moving objects. In most cases, an external trigger produced by a photocell, proximity sensor, or a similar device starts the image acquisition.
Acquired images of moving objects are often blurred. Using triggered acquisition with a progressive scan camera is one way to produce an image that is not blurred. Progressive scan cameras, such as the SONY XC-55, eliminate the blur that results from motion because they acquire one full frame at a time. Moving images acquired using interlaced cameras often produce a motion-induced blur because they acquire the odd and even fields separately and then interlace them. Motion-induced blur occurs when the two fields are not acquired at the same time and the object is moving between the fields.

Triggering only the acquisition device while using the camera in free-running mode creates a variable delay between the time the acquisition board receives the trigger and the time the image is acquired. The delay occurs because the board has to finish acquiring the current frame before acquiring the triggered frame. Figure 1 illustrates this variable delay.





Because the delay is variable, depending on when the trigger occurs, the object does not appear at the same location on all the triggered images. Asynchronous reset cameras offer one solution to this problem. Asynchronous reset techniques help keep the motion device (a conveyor belt, for example) moving while acquiring the images on-the-fly. These techniques offer a way to introduce a vision system into an assembly line with very little modification of the environment.

When asynchronous reset cameras receive a trigger, they reset their CCD and immediately start the image acquisition, which ensures that the image is always taken at the same time after trigger assertion. In this case, the objects imaged appear at the same location in the image, which simplifies the preprocessing of the image—including locating the object under inspection and specifying the regions of inspection within the image.

Figure 2 illustrates the asynchronous reset principle.

Camera Switches Setup

This section explains how to set up the SONY XC-55 to run in asynchronous reset mode. See Figures 3 and 4 to locate the external and internal camera switches. See Tables 1 and 2 at the end of this section for a summary of the camera switch configuration.

Make the following modification to the external camera switches:

• Set the SIGNAL switch on the back of the camera to 1N (progressive scan).

Make the following modifications to the internal camera switches:

• Set switches S1-1 through S1-6 to OFF. These switch settings set the shutter speed to Normal.
• Set the S2 switch to the E position to select the asynchronous reset mode (also called trigger shutter E-DONPISHA II). This switch sets up the trigger mode.
• Set the S3 and S6 switches to OFF. These switches prevent the camera from outputting the HD and VD signals.
• Set the S4 switch to EXT. This switch allows the acquisition card to send the synchronization signals to the camera.
• Set the S5 switch to +. This switch corresponds to the trigger polarity.
  
  
  
  [+] Enlarge Image
  Figure 4: Internal Camera Switches (from SONY documentation)
  
  Summary: Camera Switches

  Tables 1 and 2 below summarize the camera settings.
  
  Table 1: External Switches
  
  
  
  Table 2: Internal Switches
  

  Cabling
  

This section discusses cabling and power supply requirements. Figure 5 shows the cable schematics for the SONY XC-55 and the IMAQ 1409.

Note: You can use the IMAQ-A6822 breakout box to easily prototype your cable.




Tables 3, 4, 5, and 6 outline the connection requirements for IMAQ 1409 loopback connections, connection from the IMAQ 1409 to the XC-55, external BNCs, and the power supply, respectively.

The IMAQ 1409 operates in external trigger mode. This mode requires that you provide the synchronization signals to the board. Since the 1409 generates these signals, it is necessary to loop them back to the corresponding inputs on the 1409.

Table 3: IMAQ 1409 Loopback Connections


[+] Enlarge Image



Table 4: Connection from the 1409 to the XC-55


[+] Enlarge Image



Table 5: External BNCs


[+] Enlarge Image



Table 6: Power Supply


[+] Enlarge Image

Note: To preserve the quality and signal-to-noise ratio of the analog video signal, National Instruments recommends a cable length less than 10 meters (~30 feet).

Interfacing with the IMAQ 1409

This section explains how to configure your software for asynchronous reset acquisition.
Before configuring your software, make sure to remove the W1 jumper on the 1409 device.

Configuration Files

1. Copy the Sony XC-55(1409).icd file into the <NI-IMAQ>\Data folder, and the Sony XC-55(1409) support.txt file into the <NI-IMAQ>\Camera Info folder.

2. Launch Measurement & Automation Explorer (MAX). Expand the Devices and Interfaces branch of the tree view. Expand the IMAQ PCI/PXI-1409 branch of the tree view. Right-click Channel 0. Select Camera>>Sony>>Sony XC-55. Click Save and exit Measurement & Automation Explorer.

Note: Because asynchronous reset mode requires that you provide the trigger signal and the synchronization signals to the camera (external lock mode), image acquisition within Measurement & Automation Explorer is not possible.

In order to acquire images in asynchronous reset mode, both the IMAQ 1409 and the camera must receive the trigger. The input trigger connects to the IMAQ device, which generates the trigger signal sent to the camera. This setup allows you to specify the length of the trigger pulse in order to set the exposure time. (In external trigger mode, specifying the length of the trigger pulse sent to the camera sets the XC-55 exposure time.)

The IMAQ device generates the horizontal (HD) and vertical (VD) synchronization signals the camera needs. The HD signal is generated on one of the pattern generation lines of the IMAQ 1409 (Control Line 0), as specified in the configuration file.

The VD signal is generated on another line (External Trigger 3) and is synchronized with the trigger signal, as shown in figure 6.


When acquiring images of moving objects, decreasing the exposure time (increasing the shutter speed) ensures that the resulting images are not blurred. Decreasing the exposure time decreases the amount of light that the CCD sensor can integrate. To compensate for the short exposure time and still get a well-contrasted image, provide a more intense lighting or use a strobe light at the time of the image acquisition. The strobe light can also control the exposure time, in which case the sensor exposure time can be set to the maximum.

Because the acquisition device is capable of outputting a signal that corresponds to the start of a frame (TRIG 1), it can be useful to illuminate the object by firing a strobe light when the frame is acquired.

Computing Exposure Time

This section explains how to compute the correct exposure time for your application.

To compute the exposure time needed for your application, you need to know the following parameters:

• Horizontal resolution of your camera (example: 640 pixels)
• Horizontal field of view (example: 100 mm)
• Speed of the moving object (example: 150 mm/s)
• Acceptable blur - defines the maximum blur that is acceptable in the image (example: < 1 pixel)
  
  The shutter speed needed for the application corresponds to the time needed for the object to move the number of pixels specified by the blur. Figure 7 demonstrates how to compute exposure time.
  
  Figure 7: Computing Exposure Time
  
  In the example, the Exposure Time needs to be less than: 1 x 100 / (640 x 150) = 0.00104 s = 1.04 ms.

  Example Program
  

This section includes a sample program that demonstrates an asynchronous reset acquisition.

This example shows how to control the camera's shutter speed and how to perform an asynchronous reset acquisition with an IMAQ 1409 and a SONY XC-55 camera. You can either provide an external trigger to trigger the acquisition, or the IMAQ device can generate a signal to trigger the acquisition (internal trigger). The internal trigger mode allows you to test the example without having to provide an external trigger signal to the board.

This example is implemented using a state machine. In the first frame, IMAQ Create allocates the memory for the images.

1. The Idle state waits for a click on the Start button.

2. In the Start state, shown in Figure 8 below, IMAQ Init is called to initialize the board. Then, the subVI XC-55 Asynchronous Reset Manager generates all the signals. Inside this subVI, IMAQ Generate Pulse is called twice to create the shutter and VD pulses, which control the camera's shutter and asynchronous reset, respectively. Additionally, IMAQ Trigger Drive is called to output a strobe signal (synchronized with the Frame Start signal) on one of the output lines.

3. Next, IMAQ Configure List configures the buffer list, which contains one buffer. IMAQ Start starts the acquisition.

4. In the Acquire state, shown in Figure 9 below, IMAQ Copy provides a copy of the image currently being acquired. IMAQ WindDraw displays this image in an image window.




5. The Stop state, shown in Figure 10 below, calls XC-55 Asynchronous Reset Manager to stop generating the pulses. IMAQ Close.vi is called to shut down the acquisition.



To download the source code for this example, refer to the related link below.

Related Links:
Using the SONY XC-55 Camera in Asynchronous Reset Mode with the IMAQ 1409

Reader Comments | Submit a comment »