PT2006_475e,_New SSI Rotary Encoder with hollow shaft

Pepperl+Fuchs GmbH – Königsberger Allee 87 – 68307 Mannheim Please quote the following contact information when publishing: Tel.: +49 621 776-1111, Fax: +49 621 776-27-1111, www.pepperl-fuchs.com, [email protected] Editorial contact: Irmtraud Schmitt (extension: -1215, fax: -1667), [email protected]

A popular interface combined with a practical style of mounting:

New SSI Rotary Encoder with hollow shaft In the field of absolute value encoders the SSI Interface (Synchronous Serial Interface) is a much discussed option for the connection of angle of rotation encoders to control systems. A World of automation without such devices would now be unthinkable, because in many applications the transfer technology - firmly established between the field bus and parallel connection - is the preferred option. It has certainly been reason enough for Pepperl+Fuchs Drehgeber GmbH to combine the favoured SSI Interface with the novel “Hollow shaft“ method of installation in a new absolute value encoder. In view of the diversity of choice, in addition to the basic data, such as resolution and scanning principle, questions concerned with the data interface, type of mounting and housing size have an increasingly critical impact on the selection of absolute value encoders for specific applications. In principle, customer thinking is always oriented towards the most cost-efficient solution. But depending on the available automation structures, plant parameters, design specifications, etc., the optimum communication concept and the fastest and most suitable style of mounting are frequently a compromise between technical and commercial arguments. As regards the electrical connection, the colourful mix of the many field bus versions, including for example the Synchronous Serial Interface (SSI), is proving to be remarkably persistent. The reasons for this are partly historical, but not least based on technical requirements.

From parallel data transfer, through SSI and on to the field bus Absolute encoders with field bus connection are attracting considerable attention at the moment in the specialist press. The specialists themselves - Pepperl+Fuchs Drehgeber, Tuttlingen – also include corresponding sensors in their programme, with integrated interfaces for Profibus, Interbus, CANopen, DeviceNet, AS-Interface and Ethernet. The advantages are clear: All the participating elements are connected to the same bus cable and the benefits are greatest in the case of complex systems with branches and many sampling points, with the resulting savings in

Page 1 of 5

cabling. In addition, self-intelligence and extended functions for diagnosis and parameter assignment via the bus bring with them further rationalisation. The absolute opposite of this is the original method of parallel data transfer, which also has its place. It is useful in highly dynamic applications, where the serial transfer via the bus is too slow, for example in filling plant, printing machinery and generally on drive controls with high real time demands. The disadvantage is that the parallel connection technique requires a separate control data line for each bit, which drives up costs and restricts cable lengths. In the further development of the absolute value encoder towards higher resolution, this is associated with ever more expensive, susceptible cabling, requiring many binary input channels on the control side.

The golden middle course: SSI Interface The SSI Interface is established between parallel connection and field bus technology. It offers a standardised method for the communication of absolute encoder position values via a serial RS422 connection. As opposed to parallel data transfer SSI provides an essential simplification in at least two aspects: It enables large distances of up to several hundred metres to be economically bridged and only four cables are required in total for the clock signal and data – irrespective of the resolution. In comparison with the field bus there are no overheads involved for bus management, the administration of participating items and address assignment. Because it is a point-to-point connection, the whole bandwidth is always available for a sensor, which is a very important selection criterion for real time applications. The clock pulse provided by the control system is used to synchronise the data transfer between the absolute value encoder and the higher-level system. When a bundle of pulses is sent the sensor responds by sending the position data. In this way the point in time and speed are determined exactly. In this way time-synchronised control and regulatory processes are achievable with baud rates up to 2 Mbaud. Other advantages of the interface are the favourably priced construction with only a few conventional components, the galvanic isolation of the encoder by the control through the optocoupler and the reliable acquisition of data using the cyclic Gray-Code.

Hollow shaft encoders are the home favourites There are also rationalisation possibilities on the mechanical side. For example, in various projects encoders with standard dimensions enable their easy replacement by other resolution and interface versions. Therefore in Europe the 58 mm diameter housing format has become established as an important standard. Page 2 of 5

The desire for a more rational coupling of drive shaft and encoder led years ago to the development of hollow shaft versions. Because of the persistent pressure on costs a long-term trend towards this efficient, economically priced and space-saving mounting principle can be discerned. In the connection of conventional solid shaft encoders with the drive shaft a so-called shaft coupling is unavoidable. It evens out any shaft offset and suppresses shocks and vibration, which can never be completely eliminated and would otherwise lead to the destruction of the sensor. On the other hand, hollow shaft encoders are fitted and fixed directly on the drive shaft and twisting of the shaft is prevented by means of a torque support. Since they are carried completely on the shaft, they are able to follow all the motions of the shaft without problem. Expensive coupling designs are completely avoided in this case, which also leads to a more compact design.

New hollow shaft encoder features SSI The new absolute value encoder AHS58/AHM58 from Pepperl+Fuchs Drehgeber GmbH combines the favoured SSI Interface with the novel “Hollow shaft“ style of mounting in a standard 58 mm diameter housing. It is a single-turn version with a resolution of up to 16 bits, i.e. one revolution is subdivided into 65536 angular steps; this is currently the typical maximum resolution on standard construction types. The single-turn model is supplemented by a multiturn encoder with an additional 14 bit multiturn resolution to provide an overall resolution of 30 bits. The device, which is equipped with a 12 mm diameter through-going hollow shaft, can be used in any arbitrary position on the drive shaft, in contrast to versions with a blind hole hollow shaft. A torque support/bracket, or clamping ring can be used to provide the fixing. Hollow shaft diameters of 11, 10 and 8 mm are also possible by using a special reducing sleeve. The micro processor-controlled sensor has two function inputs, between which the customer can choose: One for reversing the direction of counting and one for calling up the zero setting function. The SSI-Interface supports data transfer rates up to 2 Mbaud and the data format is either the Gray-Code or the Binary-Code. The sensor housing is optionally of aluminium or highgrade steel and constructed to provide protection class IP65. The robust mechanical components are designed for speeds up to 3000 revolutions per minute. The AHS58/AHM58 operates on 10...30 V DC and at -40...+85°C and is supplied with either a 12-pin round plug connector or a 1 m long connection cable.

Page 3 of 5

Authors:

Dipl.-Wirtsch.-Ing. Yvonne Grabowski Product Manager at Pepperl+Fuchs Drehgeber GmbH, Tuttlingen Division Factory Automation Dipl.-Ing (FH) Volker Paroth Technikredaktion LOGOS

Characters:

6.408 without spaces

Characters Summary: 502 without spaces Pictures:

Picture 1: No. 54_1244_01 Picture 2: No. 54_0374_03

03/2006 For publication free-of-charge

Page 4 of 5

Picture 1: (Caption: Hollow Shaft Encoder AHS58/AHM58) This new absolute value encoder combines the much-favoured SSI interface with the interesting “Hollow shaft” construction in a 58 mm standard housing.

Picture 2: (Caption: An assortment from the encoder family) Hollow shaft encoders play an increasingly important role in all encoder product categories, from absolute value encoders for the hazardous area, through standard versions and on to the economically priced incremental encoders.

Page 5 of 5