Precise packaging performance with digital servo-amplifiers

Paul Boughton

Located in Donzdorf near Stuttgart, Michael Hörauf Maschinenfabrik was founded in 1938. The company originally manufactured special machines for the paper processing industry.

Today the company has 340 employees and operates throughout the world, with a special focus on Asia, Europe and the USA. Its main business is the design and manufacture of casemakers, packaging machines for the manufacture of food wrappings, and aseptic filling machines for the sterile filling of packaging.
With 600 casemakers installed worldwide, Hörauf is one of the leading manufacturers in this segment of the market. Within the sector, the company specialises in the supply of single or small batches of casemaking machinery.
These machines are used to produce book casings -- front and rear boards with either hard or flexible spines. The three parts are joined together by covering material and the finished casing can have a variety of features such as insert flaps, title labels, fold-out plates and embossing. If there is no spine, a continuous casing is used. Binders are an example of this.
The casemaking machines are based on a modular design so that they can easily meet the different technical configurations demanded by users. Typical variations include machine size, type of adhesive used and covering materials. Card, paper, textiles, plastics and leather can all be used as covers, for example.
Production time for customised case making machines is about three months. However, delivery can be as short as three weeks for a prefabricated machine that has been adapted for a particular customer's requirements.
To work effectively, case making machines rely on precision movements, fast cycle times and exact positioning.
To begin with, the casings are fed into the hopper by hand, from a pre-stacking conveyor, or via a connected feeder machine. They are then continuously pushed down out of the hopper, and brought together extremely accurately with the covering material. Next, the casings are drawn off downwards from the non-stop case feeder and passed to the glueing cylinder with precise register accuracy. After this step, the casing is glued together with the board -- without any blistering -- in a rotary movement. Finally the cases are firmly pressed by the double pressing rollers and passed to the operator in stacks of a defined number. Continuous feeding from the case feeder ensures high machine efficiency.

The next generation

At a recent print media exhibition, Hörauf was due to present a new generation of case making machines. Against this background, the company's engineers set out to find optimally adjusted drive and control systems that could be integrated into their machines. In addition, the supplier of such components would have to be reliable and guarantee fast delivery of spare parts so that no users would suffer from production loss in the event of a breakdown.
Danaher Motion's Servostar600 series digital servo amplifiers and associated synchronous servo-motors were considered the ideal solution. They offered the performance range demanded by Hörauf, provided reserve capacity if needed, emitted low levels of heat, had a compact design and were easily integrated into the case making machines. In addition, they offered an open hardware and software architecture which Hörauf considered necessary to ensure versatility and a wide range of communication possibilities.
We know very well that our list of requirements covers a very broad spectrum. First of all the service systems must provide high performanceprecision and stabilityand secondly the amount of work involved for programmingsoftware developmentwiringindividual tests and commissioning times during the production of the casemakers must be reduced explained Roland Schmid, head of software development at Hörauf. Other criteria are the necessary integration capacity for the communication of control loops with the intelligent master PLCcompact design and the reliability of the supplier regarding service and support he added.
As well as these mainly technical requirements, the issues of profitability and service also played a significant role in the choice of supplier. Because Hörauf's sales are worldwide, any supplier's components from the automated production sector would also need to be suitable for use throughout the world.
Danaher Motion satisfied this requirement because its systems can be connected to all earthed industrial mains and comply with all CE and UL standards. Another important factor was that the supplier should be represented all over the world and therefore have extensive experience of the technical requirements in different countries. Hörauf felt that such a global presence and the fact that the systems used are standard products with very high production figures gives customers confidence that they can call on a reliable partner even in the event of problems or when spare parts are needed.

Danaher Motion was finally awarded the contract after a jointly defined pilot project had been completed to Hörauf's satisfaction. This project set specific targets for speed, clock rate, positioning accuracy, temperature and integration.
In terms of training, a two-day in-house course proved sufficient for Hörauf's engineers. Recent experience has shown that it is possible to find answers to almost any other query directly on the Danaher Motion website. In fact a systems expert from the company has only had to physically visit Hörauf once.

Exact controls and positioning

Although mechanical and structural improvements had already helped to increase the productivity of the casemakers before Danaher Motion's involvement, a considerable increase was nevertheless noticed when the new servo system was used.
The handling of these components was also very easy due to the intuitive operation in areas such as parameter definition. The free software supplied gives support for individual configurability in the location. The operating software, which is compatible with Windows95/98/NT, has oscilloscope functions and offers direct access to all relevant control parameters of the Servostar 600. The controllers can be adjusted to the optimum settings with just a few parameters and simple instructions. If several interconnected servo amplifiers are used, the software also allows the simultaneous display of the dialogues to adjust the control parameters. The front panel of the servo amplifier offers two-key operation and a three-digit LED display.
Many control functions and movements, including jolt-free movements, can be carried out directly without additional programming. With a bandwidth of more than 1200Hz and a cycle time of 62.5µs, the current controller is the heart of the servo amplifier. Motor-specific default values from the database integrated in the amplifier can be used for the adjustments. The parameters from the integrated database make it easy to adjust the system to the mechanical needs of the respective system. Setpoint ramps and dead band are adjusted by a speed controller working at a cycle time of 62.5µs.
The integrated position control offers a cycle time of 250µs and enables a large number of applications to be carried out without additional NC functions. Up to 180 motion blocks can be stored. 16 types of homing and four position registers are available. The definition of speed profiles, absolute and relative movements and linking of motion tasks are possible. The adjustment options for jolt limitation are also worth mentioning. Monitoring windows can also be set up for afollow up errors' and the aInPosition' signal. The electronic gearbox of the digital servo amplifier has 24v and 5v encoder input points and an adjustable transmission. The servo amplifier receives the position setpoint from an incremental angle sensor, the encoder, and controls the position of the drive shaft synchronously with this guidance signal.

Fast configuration

Hörauf has also had a positive experience with the preparation of configuration programs for the servo systems. The aim here is to configure the drives in accordance with movement profiles demanded by the company's structural design department. In the past, these tasks were always very time-consuming. But now exact configuration data are available in a very short time. This is reflected in the exclusion of error sources, the reduction of the number of tests -- and ultimately in the precision of the machines and shorter commissioning times.
The default values already show excellent control reactions as well as high performance and dynamics. Because of the simple user interfacewe can quickly make adjustments in the control actionswe need fewer test cycleswe noticeably reduce the commissioning costs and we can increase the throughput times in production noted Schmid.
Synchronous servo-motors from the DBL/DBK series and the new AKM motors from Danaher Motion also contribute to flexibility. These rotary motors have proved their reliability as a result of their quality, smooth running characteristics and high stability under excess loads.
In conjunction with the Servostar600, the motors are perfectly suited to positioning tasks which place high demands on dynamism and stability. This is further enhanced by properties such as a highly dynamic action due to the integrated neodymium permanent magnets, good heat dissipation without forced ventilation and the fact that the motors are maintenance-free due to their brushless operation. Standardised flange and shaft dimensions enable the gearbox to be fitted without problems; the motors of the DBK series, being short motors, are particularly suitable for mounting in restricted spaces.

Optimum communications

The Servostar600 has a wide range of interfaces: the integrated CANopen connection, other optional fieldbus interfaces, an interface to the multi-vendor step motor control and an interface for master-slave operation.
Several servo amplifiers can be interconnected with the aid of the master-slave interface, so the slaves (up to 16) follow the position setpoint of the master. If several servo amplifiers are linked together via a fieldbus, the parameters for the entire group can be set with a PC and the operating software without a master, and the group can then be taken into operation.
Two connectors for the intermediate circuit voltage simplify the connection between the intermediate circuit and the individual controllers. In addition, some wiring work is avoided because the mains filter and brake resistance are already integrated.
Hörauf's specifications included the integration of a SERCOS interface to guarantee optimum communication between the digital servo amplifiers and the control units in the casemakers. This request was met with the standardised SERCOS extension card. This permits the transmission of setpoint and actual values with different cycle times (1 to 65ms) with an additional interpolation of the setpoint values within the drive. A synchronisation to µs accuracy ensures exact and fast multiple control.
The transmission is carried out with a pre-selectable rate of two or four MBaud via fibre optic cables that are immune to interference, and the transmission process complies with the SERCOS standard according to ICE61491.
Transmission rates of these magnitudes permit sufficiently short PLC cycle times, while the available functions simplify programming considerably. This applies to the setup functions such as reference movements and measuring functions, positioning functions such as digital speed or position control and a data transfer function. These transfer functions include the reading and writing of control parameters and diagnostic data and a pre-selectable scaling function for setpoint and actual values.

Achieving 85 cycles per minute

The well-established BDM20 casemaker has now been followed by the BDM Universal and BDM Speed. The high-speed BDM Speed casemaker achieves 85 cycles per minute in the production of casings, folders, ring binders and game boards. Casemakers of the BDM Universal type, with a speed of 60 cycles per minute, can produce not only this range of products, but also pocket calendars, wall calendars and padded photograph albums.
We had to work very hard at the DRUPA2004 exhibition to present the further innovations and technical advantages associated with the BDM Universal und BDM Speed casemakers explained Reinhold Gallasch, head of electronic development at Hörauf. In this respectthe tried and trusted digital servo amplifierssynchronous servo-motors and ac servo-motors from Danaher Motion again proved their capabilities. We are pleased that our wishes are being taken into account in the further development of these external components he concluded.

Dipl-Ing Metin Han is Sales Engineer with Danaher Motion, Bretten, Germany, tel +49 (0) 7252-9739040,
fax +49 (0) 7252-9739055, email m.han@danahermotion.net

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