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Investigating Optical Online Quality Inspection of Cutting Knifes in a Wood chipper.


I investigated the possibilities to introduce methods of machine vision for the inspection of cutting knives in a Wood Chipper. So that energy and time can be saved that was wasted in stopping the Wood Chipper for every inspection.


Stepper Motor with 200 steps, 1 step=1.25um.

Stepper Motor Controller 8SMC1-USBhF

Lumenera Camera


Laser Light Q-6413 Coherent, Canada.

Software Tools:

NI Labview 2009

Visual Studio Express

Matlab 7.8.0 (R2009a)

The Challenge:

  • Development of an experimental setup for illumination and image capture of a rotating cutting knife that are rotating at the speed of 45 m/s andexposure time for camera is 10us. These experiments are preferable conducted onthe experimental wood chipper shown in Figure 1 but with consideration of afull scale wood chipper.
  • Development of machine vision algorithms for theanalysis of condition of cutting knifes.

The Solution:

Working of the Project:

Our first challenge wasto capture the images of moving knifes from the camera at every step of themotor. So we wrote the Labview program for controlling the stepper motor withhelp of Controller 8SMC1-USBhF. Our program was moving the stepper motor fromcurrent position to the destination position with required speed as well asrequired step size. Speed and Step size of the motor can be varied at run time.

Then our next challengewas to synchronize the stepper motor with luminera camera. We wrote theseparate program for the camera in Visual studio express. Then we generated theexecutable file of the c-program for the camera and used it in the labviewprogram of the stepper motor. That was taking 7 input parameters Width, Height,Exposure time, gain, xoffset, yoffset and name of the image. So my steppermotor and camera was synchronized and moving the required number of steps andproducing the bmp image of knifes for every step and storing it into ourallocated path.

Our next problem was howto illuminate the cutting knifes for that we used two approaches. 1stapproach was to use the sheet of LEDS i.e. SCHOTT HB-LED Lightline. So wearranged the setup in the position that provide us the best images that can beused for our analysis in cutting knifes. So we gathered that images and tookthe mean of all the images. Then applied our machine vision algorithms usingMatlab and plotted the result with respect to the expected result for differentexposure times. And we checked the error between obtained and expected result.We tried to keep the exposure time as low as possible because it will increaseblurring in the images as the speed of motion is 45 m/s. Our 2ndapproach was by using laser triangulation technique that will give us the 3-Dimage of the object. 2nd approach is under progress.

Benefits of usingLabVIEW and NI tools:

Labview was very beneficial for us in completing this project dueto its user friendly graphical programming environment we haven’t took too muchtime in bringing our stepper motor in running condition with the requiredaccuracy. Its resemblance with the flow chart and highlighted executionimpressed me.  Its integration with ourhardware devices and provided built-in libraries for creating virtualinstrumentation was very helpful for successfully completing this project.  Its ability to execute or launch otherWindows–based applications from within Vis was ideal for my project that helpedus in synchronizing the camera with our stepper motor. With the System Exec VI,we executed a system-level command line i.e. DOS command that can include seveninput parameters supported by our camera.


Figure1. Experimental wood chipper at Mid Sweden University labs


Figure2. Front Panel of the Inspection Control Panel

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Benefits gained using LabVIEW and NI tools

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Good Luck, Jessica in Austin, TX.