10 years DCP – an interface gained acceptance!

by Dipl.-Ing. Bernd Roeckerath, BÖHNKE + PARTNER GmbH

Within the last 50 years of the history of technique there were a huge number of trailblazing ideas and inventions which were rather non-spectacular in the moment of birth: so it was e.g. as the programmer Ray Tomlinson just for fun combined two existing data-transfer-protocols for to send the first e-mail which should explain his new created @ sign. Or the American Vint Cerf whos idea of the TRCP/IP-protocol, that became indispensable, came up during a foam bath. As he had no suitable paper for first notices to the communication protocol he used the backside his hearing aids manual. Similar to that it could have happened in 1995 to software engineer – let’s call him Max.

Max, active at the controller system manufacturer Böhnke + Partner GmbH in Bergisch Gladbach, found him self faced with the challenge for the umpteenth time to link a brand new inverter system with an existing lift controller system. The gateways at inverters were such multifaceted as the branch it self – each inverter producer treasures his own style – here a tiny signal to stop the lift more smoother, there a little terminal to drive the programmer into the final madness!

In the end the task formulation for an inverter is simple: it just has to switch the motor on or off in the right moment, or to turn left or right. Regarding the technique for controllers all the inverters are the same. While celebrating the lunch break with a hearty German card game to Max came up the bang idea: a universal connection must be found – serial, not parallel as usual. There is no information about the end of the card game, but the idea was drafted outright: A standardised protocol with only the most important information to interchange between inverter and controller, completely basing on 2-wire connection. In the end a serial RS-485 data protocol should replace the conventional parallel terminal operation. Max was looking for a partner to realize this new interface.

With company Loher he found an enterprise which was innovating enough to deal with this idea. The joint protocol description was a paper of just 5 DIN-A4 pages. Both of the companies attached importance to make it accessible to all related companies in this field. This happened in the beginning of 1996 on a symposium which was organized by Loher on the castel Schloss Neuburg where its name was introduced: DCP (Drive Control + Position). So things came into motion: within the following month further manufacturers of inverter converged and integrated this simple interface mostly by means of an additional interface board to their units.

On the other hand the producer of lift controllers were not so enthralled, more refusing as – a competitor is better to criticise than to support. To adapt an interface protocol from a competitor – no way to think about. But that this finally worked, even with a certain time lag, confirms that the general idea was appropriate. Due to intensive brainstorming and lively discussions of all involved persons further features could be added. So 2 modes of operation became established

• DCP 01    replaced the parallel operation by a serial operation, and
• DCP 02    enabled the additional transmission of travelling ways to the inverter

It became proven that this specifications were absolute sufficient for simple applications. On high speeds and little landing distances there was no comfortable travel to achieve without an exact parameterization. Beside that at the end of the 90th the trend in this branch was to get shorter time of installation so there was no time left for experimenting.

From this gained experiences with DCP 01/02 at the beginning of 2001 arose the desire for a customizing of the protocol. Also here Max was in the frontline and discussed a practice-oriented handling of the protocol, further steps of options became integrated. So the transmission speed became doubled and the telegram extended by several bytes. This new step got specified in the DCP 03 protocol. Consequently DCP 03 was the further stage of DCP 01.

But the potential of the DCP protocol was by far not yet exhausted. In the meantime the use of absolute value encoders (AWG) became standard and had ousted the dated incremental encoder. With this technology finally it was possible to realize an old vision which was not to practice with DCP 02. With linking the inverter to the controller the unique needed parameterization should be performed only inside the inverter, as it accomplishes the management of the motor in the end. The rest implies it self, parameterizations in the controller should not more be needed. This was defined by the protocol step DCP 04. The precept is to describe quickly but the realization is very complex. The following graph is to illustrate that

Displayed is a travel of 6 landings (3m floor distance and 1 m/s speed):
The controller delivers cyclical (all 10 ms) permanent the calculated remaining way (red curve) till to the next stop, the inverter delivers the needed brake way to the next stop (green curve) from its calculated travel curve. If both ways are the same the controller has to decide to stop at the next landing or not. If yes the remaining way will be not extended and the travel will end at this floor in case a landing call was set. Is there no landing call the controller extends the way and increases the floor counter to the next landing, which will be considered by the inverter’s calculation of the new brake way. That sounds very simple but the inverters effort for calculation is immense.

However the advantages are obvious: on high speeds the phase of acceleration till to the nominal speed may not get neglected, the controller must consider this. Receives within this phase an achievable landing call it can be dispatched without problems. This makes an essential improvement of the availability of the lift, especially for group controllers. At present DCP 04 in use for systems with a speed of 4 m/s and more. Max is preparing a regarding project in China in this times.

DCP lives and is used by nearly all drive suppliers, even hydraulic fabricators became convinced by DCP: the BeriPAC^® system, designed as a machine roomless lift from the Swiss company Bucher is controlled by DCP 04.

Just a few of the German controller makers are still missing, but abroad DCP is accepted already for a longer time, as it was to see on the Interlift this year. On a meeting of different German controller makers the company Kollmorgen was so kind to agree to attend the DCP protocol and to be the contact partner for all (PGerstenmeyer@Kollmorgen.de) because there are existing different descriptions which are not quite correct in all positions.

And how it will continue? Basing on the good experiences with DCP Max again is one step ahead. In our networked world the field of lift technique has an enormous back-log demand. So in this times Max is busy to network with the latest lift standard “CANopen-Lift” anything that’s in reach of his fingers: Lift controllers, lift doors, encoders, landing calls, car panels, and of course inverters.

Max is still playing cards during is lunch break – his fellows are worrying about further interruptions of the games.