New-Tech Europe | April 2018

need to be tightly controlled; even slightly different focal lengths lead to inaccurate 3D measurements. A common method with which to avoid loose lens elements is to glue them to the barrel. This production method solves the problem of loose and moving lens elements under shock and vibration, or simple movement. Just the same, it can introduce problems under wide temperature ranges, or for the long-term stability of the system; it is not a perfect solution. The thermal expansion coefficient of the glue cannot be ignored, and neither can its aging performance be ignored under the heat cycling that it will endure over the years of installation. Testing Parameters Aside from all design theory, lenses must be tested tomeet specifications during the prototyping phase. C-mount lens manufacturers test their lenses and either share the information automatically, or on request. In many cases, board mount lens manufactures possibly test their lenses for shock and vibration. Usually, this type of testing is performed at the request of the customer and their customers' specifications. Historically, a primary estimate of the lens stress performance (shock and vibration) can be supplied based on the design parameters and design experience. Generally, a test of the complete stereo vision system is advisable, especially if shock, vibration, or temperature changes are expected in the field. Previously, it has been mentioned that there can be interactions between the different components in a system, like lenses and mount materials. The vibrations that a lens experiences in a camera system are very different from that experienced in testing

Figure 4: Lens with tilted or loose lens elements (i.e., Elements 2 and 4).

the lens alone. A complete camera system is much heavier than an M12 mount lens, for example, and exhibits widely different vibrational and shock behavior. Additionally, the camera housing can amplify or attenuate the shock and vibrations introduced into the system. Factors for Consideration There is a wide variety of stereo vision systems, and no one rule applies to all of them. Here are some key factor to consider: The ambient temperature range to which the stereo system will be exposed The amount shock and vibration to which the stereo system will be exposed The degree of movement to which the stereo system will be exposed The internal size of the system; that is, the dimensions of both the baseline and focal lengths The setup and environmental

factors of an application must be reviewed, properly designed, and have had complete testing. Then, camera manufacturers and vision system engineers can be confident in the selection of an optimal lens for a stereo vision system. The more components in a stereo vision system, the greater the risks of imprecision, and the greater the effort required for error correction to achieve a desirable result. Therefore, lenses that are so important in one-camera vision systems, are even more critical in stereo vision systems. Shop References: Computar: Ruggedized “R” series Fujinon: “4D high resolution performance”, shock and vibration data Kowa: anti-vibration, high shock “V” series Sunex: athermalized lenses

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