Milligram precision

Particularly in the case of small and micro components with sensitive bearings, absolute concentricity over the lifecycle of the device is one factor that cannot be underestimated. After all, the ­higher the speed and non-symmetrical weight, the greater the forces involved. Alongside vibrations, this leads to increased strain on the bearings and thus to premature wear and tear.

Micro Präzision Marx GmbH in Erlangen offers a horizontal balancing machine for testing the quality of small components that is specifically geared to the needs of such test subjects. Registering the slightest imbalance also means that the measuring pressures are very small, which is why every element within such test procedures must be adjustable to a high degree of precision. This is the only way to capture accurate data. With this in mind, the Erlangen-based balancing experts rely on FAULHABER motors for their drives.

Universal means special

There are many small rotating parts that have to be balanced: from rotors inside small motors and micromotors to ­ventilator drums and special rotating test mounts. This gives rise to a broad range of different shapes, sizes and speeds. The problem starts with even the "simple" rotors of electric motors, also known as armatures. Whilst wire-wound DC ­armatures made of dynamo sheet are non-magnetic, the armatures of modern, brushless DC-Drives definitely require an antimagnetic testing device. Eddy ­currents caused by ill-positioned metal parts also impair the testing procedure. This is where specialist expertise is called for. After all, these small parts require the highest degree of balancing precision, down to an accuracy level of a tenth of a milligram. The particular shape of the ­balancing machine is designed to deal with all possible types of test pieces, while special controls ensure the test conditions are exactly the same for every test piece within a product line. After all, every ­two-gram rotor of a micro turbine ­running at 400,000 rpm must be able to be ­balanced perfectly every single time. ­Highly accurate oscillation sensors ­combined with precise evaluation provide a solid basis for accurate readings. It is clear that such measurements can only be as accurate as the driving motor permits. Synchronisation, high speed and very good adjustability are the key things here.

Test drive is also crucial

Tests like these therefore require a drive that is reliable, capable of consistently high speeds and able to be adjusted to a particular revolution profile. The drive specialists at FAULHABER came up with a brushless DC-Servomotor of 35 mm ­diameter to meet these requirements. Preloaded ball bearings guarantee ­particularly quiet running. 90 Watts of power ensure highly dynamic perfor­mance for quick acceleration and braking. A high resolution encoder inside the motor housing and a programmable ­positioning and speed control complete the drive. Apart from its power supply (24 V DC), the standard features of this drive include an analogue input, an error output and an RS232 interface. The start module of the balancing device controls the direction of rotation and speed of the drive via these interfaces. These functions are ­complemented by a motor start/stop and speed display. The servo drive can ­accelerate test pieces to speeds of 40,000 to 80,000 rpm during the measuring ­process. Modern, brushless DC-Servo­motors now offer a whole new range of options for the miniaturisation of ­measuring and testing devices. Depending on the user requirements in each case, standard drives, modified versions or ­custom drives for a maximum level of ­system integration may be the right option.