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Tactile Probe: BLDC Motor Applications

Many machined surfaces are subjected to a quality inspection once the manufacturing process has been completed. In some cases, for example, the texture of the work-piece surface is assessed this is also referred to as roughness measurement. A new mobile measuring device that can be used in situ now enables completely new operating procedures.

Adjustable adapters enable the inspection of a large number of products with just one basic unit. The heart of the compact measuring device is the tactile probe. Its vibration free operation in measuring mode and gentle positioning on and removal from the measuring surface is essential for optimal measurement. Micro-drives in the measuring device ensure a sensitive and vibration-free feed, so that even the smallest irregularities can be reliably detected. Measuring devices for surface roughness measurement are usually rather large. In addition to an evaluating computer and a feed device for spatial adjustment, a tilting mechanism is also required. Therefore, in the past the measuring object has always been brought to the measuring device rather than vice versa. Breitmeier Messtechnik GmbH (BMT) from Ettlingen takes a different approach. Its new Mini-Profiler can easily be brought to the measuring object, as well as offering exceptional versatility thanks to adapters that can be adjusted to the specific task. This saves time and money during production. In order to give this micro device best-in-class precision and vibration resistance, FAULHABER a company specializing in miniature drive systems was invited to join the team involved in developing the drive solutions for lowering the tactile probe and controlling the measurement feed.

Precision and durability.

The state of the art, or rather the state of standardization, currently only includes tactile devices. The small-sized roughness measuring devices currently available therefore usually use a skidded probe. However, devices with a reference plane offer better results. For this reason, the miniature devices developed by BMT, only around the size of a matchbox, use a reference plane probe and integrated feed. During development a particular emphasis was placed on practicability in a production environment, with the result that the device can be easily adapted to a multitude of very different measuring tasks by means of work-piece specific adapters. What is more, these tiny devices boast the same technical specifications as their large scale counterparts. For evaluation purposes, the data acquired in situ are transferred to a PC via USB connection and processed by the extensive software provided. For instance, the version with 25 mm measuring section is capable of detecting "dominant waviness". On the hardware side, two versions with 12.5 and 25 mm measuring section are available. An optional purge air unit prevents impairment of measurement, as well as protecting the device itself, even in dusty or aerosol-containing environments. An internal program sequence controls the tactile probe movement and the feed. Crucial factors for selection of the drive were the minimal space available, an extremely uniform feed rate, the longest possible operating time per battery charge and durably robust design. Taking account of these points, a brushless penny motor from FAULHABER was chosen for the task.

Precise compact drive.

 The drive in a measuring device must be designed in such a way that it does not interfere with data acquisition during operation. In this case, the inherent vibration must therefore be minimized, and at the same time the uniformity of movement must be at the highest level. A simple control, minimal energy consumption in the typical battery voltage range and a long service life are therefore essential for this task. The miniature drives in the device are responsible for lifting the tactile probe and for the actual feed. The electronically commutated drives that meet these criteria allow continuous movement at both low and high feed rates thanks to the integrated gearhead (here around 750 : 1; the standard range extends from 17 : 1 to 1800 : 1). At the same time the torque, at approx. 5 mNm on the output shaft, is more than adequate for the application. Operating voltages of four to six volts with an input current of under 30 mA allow long operating times. The plastic and metal housing and the combination of ball and plain bearings mean minimal weight (under three grams), a small starting torque and long operating times. Integrated analog Hall sensors feed the control precise information on the rotor position for commutation and position detection.


To learn more about this measuring device visit Breitmeier Messtechnik GmbH at