van Rooij Electronics Design & Software Engineering

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The iAVS-TI32 Smart Camera has a lot of build in features. One of them is encoder-less laser triangulation! As explained earlier, a Smart Camera has a lot of capabilities. One of them is measuring in 3D. Although the iAVS-TI32 can measure 3D features with the method of stereo vision, it's mostly used in laser triangulation applications. The camera measures the deformation of a laser line and interprets this deformation as changes in object distance, such as height differences. But a camera image is only 2 dimensional and in this case it measures only in the YZ plane. The third dimension is added by measuring multiple YZ plane 'slices' separated in time, thus creating a 3D volume of measurements. The timing of the YZ-plane slice acquisition needs to be carefully controlled to give the third dimension its proper unit, e.g. mm. This precise timing is typically controlled by the use of an encoder. The encoder measures distance travelled and generates YZ-plane acquisition 'triggers' at set intervals of e.g. 1mm.

Encoder-less laser triangulation

Enter the programmable timer. A programmable timer sets of a trigger at pre-programmed intervals. Typically, this interval is fixed, like every millisecond or so. But they can also generate pulses with varying intervals leading to an interesting application: encoder-less laser triangulation! When an encoder is capturing a linear motion profile, it generates trigger pulses with a fixed interval. The speed of the motion determines the exact time interval, but it remains fixed thereafter. So if we know the motion speed in advance, we can program a timer to trigger at the corresponding intervals and hence at the desired spatial axis resolution.

What about non-linear motion?

When a motion axis is driven by a servo motor, e.g. a robot axis, the motion profile is often a rather complex curve typically having multiple accelerations, decelerations and speeds. Although the motion is non-linear, it's repeatable, meaning that the form of the curve is often know in advance. By measuring this curve one can determine the various trigger moments required and hence the way the programmable timer needs to be programmed. One such calibration method is having the camera measure a reference object with fixed timer trigger intervals. The reference object will then look distorted, due to the non-linear motion profile. The timer can now be re-programmed by computing the corrections required. An expensive and fragile encoder can be omitted from the system, leading to more cost effective and flexible solutions for the end user.

Contact us for personalized advice on how to benefit from Smart Cameras in your application!