Waldkirch / Donaueschingen, November 2008 – The TTK70 linear measurement system is currently the most compact motor feedback system with a HIPERFACE® interface on the market. Its magnetic functional principle, long measurement lengths and very high resolution open up numerous potential uses for absolute position detection, e.g. on linear motors. SICK STEGMANN is the world’s only producer that can currently offer drive producers both rotative and linear motor feedback systems with integrated HIPERFACE® interface.

The TTK70 was developed in response to a trend towards direct drive technology, particularly in high-tech applications, because unlike rotative drives – whose movement is ultimately “linearised” – they offer considerably greater precision, speed, dynamism, rigidity and regulatory quality. While mechanically coupled systems (such as spindles or toothed belts) are increasingly being replaced by linear drives, the regulatory circuits of machines often still retain a HIPERFACE® infrastructure for data transmission from the “old rotative” times. The TTK70 linear motor feedback system combines the above-mentioned drive and communication aspects, and thus takes into account the trend towards direct drive technology, particularly in high-end applications.

Magnetic and absolute: the functional principle

The TTK70 linear measurement system consists of an “absolute” reading head and a 10 mm wide and up to 4,096 mm long magnetic tape as a reference. Compared to optical linear systems, the magnetic functional principle offers considerable advantages regarding price, immunity to contamination, and availability. The rugged metal housing of the reading head (including the plug connector) is hardly larger than a matchbox. It is therefore the smallest system of its kind currently on the market. It is specified for a maximum operating distance of 0.4 mm between the tape and the TTK70 sensor head, which contains the latest sensor and evaluation technology. The sensor circuit board aligned on the measurement level is equipped with Hall sensors on two parallel tracks. Their arrangement corresponds to the division of the magnetic tape into an incremental and an absolute component. In order to calculate the absolute position value during operation, the reading head first detects the absolute starting position via Manchester coding when the linear motor starts, and then determines all further actual drive positions via the increments on the magnetic track or sine/cosine signals.

Data transmission in HIPERFACE® standard

The values thus formed by the TTK70 are transmitted to the higher-ranking evaluation electronics of the linear drive via the asynchronous semi-duplex HIPERFACE® interface. The motor feedback system’s power supply is provided via two of the eight wires. Two more wires are required for the bi-directional, bus-enabled parameter channel via which, among other things, the absolute position data are transferred to the governor in digitalised form. The two remaining pairs of wires form the real-time process data channel. Sine-shaped increment signals are transferred via these in analogue form and interpolated in the governor. Thanks to HIPERFACE®, an interface standard is available for all common servo-drives covering all applications with just one type of signal cable. Another advantage is the possibility of autonomous initialisation of the drive system through the use of an electronic type label in the motor feedback system.

High accuracy and resolution, very good tolerance behaviour

As a result of the analogue transmission of the sine-shaped incremental signals with a pole or period length of 1 mm as well as, for example, 10-bit interpolation, the TTK70 achieves a very high resolution of 1 µm. System accuracy of < 10 µm is also an excellent value. In addition, the measurement system is ideally equipped for the high speeds that are common in direct drive technology. Thus the TTK70 can generate and transmit sine/cosine output signals at speeds of up to 10 m/s. In adjustment and commissioning terms, the measurement system offers very good tolerance regarding alignment of the sensor head to the magnetic tape. This considerably simplifies mounting and commissioning, and optimises availability during operation of the linear unit.

TTK70 of interest for numerous applications

Linear drives will increasingly contain the TTK70 measurement system as ready-to-connect solutions. This will be advantageous for a range of machines and applications, including eroding machines, handling systems in semiconductor production, assembly and placement machines, vertical lifting systems, pick & place applications in electronics production or the food industry, measurement and inspection machines, labelling plants, or multi-axle gantry systems.