Issue 5/2007


09/02/07

DCP ... A true success story

Dipl.-Ing. Jörg Hellmich, Peter Gerstenmeyer, B. C. Sci.

This article is intended to point out the advantages, diversity and flexibility of the open DCP (drive control and positioning) standard used in the elevator industry. It will, however, not go into extensive detail or require any comprehensive theoretical background on the reader’s part. This article is to provide decision- makers assistance in achieving an objective picture of the technology and its advantages.
Category: Issue 5/2007
Posted by: Editor

The history

At the mid-1990s two companies – Böhnke + Partner GmbH Steuerungssysteme in collaboration with Loher GmbH – developed a serial process to link the elevator controls with the inverter.
The first DCP specification, with the DCP_ 01 and DCP_02 standards, was created in 1996 and they were presented, ready forgeneral use, at the 1997 interlift. These standards were made available to the public and were then, over the year, implemented by additional manufacturers in their components.
In parallel to this, talks were conducte with a number of manufacturers, the aim being to improve the protocols for the various applications found on the market. These were to be described in the new DCP3 and DCP4 versions of the protocol; they were to replace entirely the “old” DCP_01 and DCP_02 protocols. Here the DCP4 offers both the inverter and the controls sufficient latitude to draw upon and offer various services, depending on what any given application might demand. Even the simplest embodiment offered significant advantages for the user.
One of the first implementations of DCP3 and DCP4 appeared at the start of 2001 through cooperative efforts among three companies: Kollmorgen, Böhnke + Partner and Ziehl-Abegg. Most of the other makers of inverters and controls quickly followed suit, changing over to DCP3 and DCP4, then implementing additional services.
In recent years a DCP user group has come into existence. Fifteen companies around the world participate and they and their components provide active support for the open DCP standard.
The motivation to adopt DCP 
DCP is a specification, embodied in both protocols and hardware, for the creation and management of a serial connection between the elevator controls and the frequency inverter. The objective is to exchange all the required control commands and information between both components. A shielded RS-485 link (in two-conductor technology) is used for this purpose; it replaces entirely the previous parallel connector lines.
Many elevator industry control and inverter makers have for several years now employed DCP as a standard offering the user the flexibility needed to adapt an elevator to the needs and requirements found in any of the most widely diverse settings. In this regard, DCP not only supports the elevator installer in time-optimized commissioning. It also offers the elevator user maximum convenience and comfort in regard to selecting the ideal travel speeds, stopping at the destination at accuracy inside a fraction of an inch, and eliminating a time-consuming creep travel phase when approaching the destination landing.
The major benefits DCP offers during an elevator’s life cycle are explained in greater detail in the following paragraphs.
A small dose of DCP theory
The DCP specifications, in existence for some years now, defi ne the scope of the functions in several chapters, each of which is independent from the others.
The serial application given preference by DCP, involving the conventionally employed interfaces between the elevator controls and the inverter, represents only one aspect here. The entire DCP specification covers a far greater scope of functions.
The first and simplest expansion stage is represented by DCP3. Here the inverter is driven in the conventional fashion but the commands are interchanged, serially, using the secured DCP communication. The commands are transmitted to the inverter components by the elevator controls before the start of travel, drawing from a selection of distinct travel commands. No longer is it necessary to adjust magnets in the hoistway to effect the required set-up work and speed-dependent adaptation of deceleration paths. Instead, this can be done conveniently and flexibly at the elevator controls in the machine room.
DCP4 represents the second and far more complex expansion stage for the specification. It is based on the same communications layer as DCP3 but here a process utilizing an analysis of the remaining path is applied. In this case the inverter itself, having received information on the desired travel path, can select the ideal and fastest travel speed.
An intelligent, dynamic process ensures flexible response to additional intermediate stops. DCP defines two differing but very similar processes for this purpose. They are hidden for the elevator builder and represent no appreciable difference for the elevator user.
In addition to the two differing expansion steps already mentioned – DCP3 and DCP4, the specification incorporates several mutually independent expansions that significantly extend the scope of the functions available. At the same they time offer numerous benefits when compared with the conventional link.
The DCP specification provides for all the event memory reports to be transferred from the inverter to the elevator control system. A time stamp and landing information are applied here and stored so as to be resident in the control system’s non-volatile event memory. This provides operating and maintenance personnel with a chronological output of all the events that have occurred, providing assistance in the analysis, identification and rectification of malfunctions. When the elevator is linked to a remote data transmission system the maintenance company can obtain an overall picture of the entire installation whenever required.
Setting up, parameterizing and running diagnostics on the inverter can be effected, as desired, either at the inverter itself or at the man-machine interface (MMI) available at the elevator controls. To do this, the inverter’s entire user interface is transferred to the elevator controls and displayed there in the same way as at the inverter itself. This advantage comes to bear particularly where access to the inverter components is difficult – the machine- room-less elevator being mentioned as just one example here. Connecting a remote data transmission system also enables remote control of the inverter using the MMI at the elevator controls.
The DCP specification can also score points in another discipline since further supplementary information can be exchanged between the two communications parties.
The parametrization and monitoring of up to three user-definable speeds makes it possible, for instance, to report attaining maximum approach speed (0.8 m/s) and leveling speed (0.3 m/s) and any overspeeding. The appropriate responses can then be carried out by the elevator controls.
Operating on the basis of an intelligent exchange of information, the DCP also makes possible energy-saving rescue trips when running on an emergency power source, thus protecting that source from overloading.
What practical advantages result for the elevator builder and final users when DCP is installed?
The practical world – Advantages for elevator installers
  • Quick setup and commissioning for elevator controls and the inverter, since tedious adjustment work can be carried out using the DCP communication capabilities
  • Automatic adjustment of deceleration paths for the particular travel speed
  • Automatic selection of ideal travel speed for any given travel paths and distances between floors
  • Transmission of the inverter’s event reports and comparison with those at the elevator controls
  • Improved fault analysis with the chronological depiction of all the event reports received
  • Complete control and parameterization of the inverter using the MMI at the elevator controls
  • Complete support of data transmission and remote maintenance
  • Monitoring of up to three user-definable speeds
  • Active support of intelligent rescue trips powered by the back-up electrical supply
The practical world – Advantages for the user
  • Automatic selection of the ideal travel speed reduces travel and waiting periods
  • Position-dependent speed selection guarantees improved ride comfort
  • Stopping accuracy down to the millimeter, regardless of the travel speed
  • Direct approach to the destination landing without a time-consuming creep travel phase (direct floor approach)
  • Dynamic and intelligent procedure for serving intermediate stops
The outlook
DCP can in the meantime look back on a long and successful history but it has by no means become dated.
At www.kollmorgen.de you will find the DCP specification ready for gratis download. A comprehensive survey in the preface to that specification gives information on all the participating companies and manufacturer support provided for all the available components.

 

   

 

5/2007

^ Top