For testing plate & freeforms

• What was needed: A mobile scanning machine that can also be used to inspect complex plates and freeforms with air ultrasound
• Requirements: 100% lubrication and maintenance-free, many lines of freedom in movement, low weight, withstands high forces, high precision, compact, low backlash
• Products used: drylin® SLW-1660 with integrated dryspin® high helix lead screw made of stainless steel, robolink® RL-D-20 and RL-D-30 articulated drives, each with stepper motor, encoders and proximity switch
• Success for the customer: Complex shapes of the test objects require many degrees of freedom of movement. The bearings must be able to withstand high forces with a low dead weight and always guarantee sufficient precision. The designers therefore rely on spindle linear modules (SLW-1660) from the drylin® series with adjustable plain bearing clearance and articulated drives (RL-D-20 and RL-D-30) from the robolink® D series with stepper motor, encoders and proximity switch. The components are compact, suitable for industrial use and enable a modular machine design. According to engineers, the drylin® spindle has an astonishingly low, imperceptible backlash, so that precise measurements can be realised.

Non-destructive material testing: In order to couple ultrasonic waves into the material, a coupling agent is used in conventional ultrasonic testing methods. A special device technology makes it possible to dispense with this coupling agent, which means that testing with so-called airborne ultrasound is not only contactless, but new materials such as lightweight construction materials can also be tested.

One of the aims of the "IfUS" research project (funded by the BMBF) was to develop a transportable and flexible scanning machine for testing plate and complex freeforms with airborne ultrasound. The result was the "PortUScan 460". The scanner was to be as flexible, small, light and therefore mobile as possible while maximising the scanning area so that large or heavy objects could be inspected outside the laboratory with little effort. A certain robustness of the parts was required for possible industrial and outdoor applications.

Alternative bearing designs based on roller bearings, ball screws or metal worm gears were usually too massive and therefore too large and heavy, as they were intended for milling technology, for example. The weight of the scanner would have been excessively increased and the possible applications limited.

Complex shapes of the test objects require many degrees of freedom of movement so that the transducers are always guided at the correct distance and angle to the surface. The bearing must therefore be able to withstand high forces with a low dead weight and at the same time always guarantee sufficiently high measuring speed and precision. The drives also require the lowest possible backlash.

Four linear drives SLW-1660 with adjustable plain bearing clearance and dryspin®-high helix lead screw and two robolink® articulated drives RL-D-20 and RL-D-30, each with stepper motor, encoders and proximity switch, were used. igus® supplied the complete drive assemblies for the scanner. They are compact, suitable for industrial use and enable a modular design of the machine. This means that drives that are not required for an application can be quickly removed. Thanks to the plastic plain bearings, stainless steel spindles and IP68 protection class of the motors, dirt and moisture pose no problems. Adjustable plain bearings guarantee minimal bearing clearance and the dryspin®-spindle also guarantees astonishingly low, imperceptible backlash. This achieves very good precision for the measurement.