DCP-Interface (Drive Control and Position)

Cost reduction by databus between frequency inverter and elevator control System

Cost pressure in elevator industry is con-tinuously increasing.

By buying cheap (i.e. not price favourable) units (control Systems, incremental encoders, power Converters) it is partially tried to achieve an acceptable covering of costs. For designing as well as assembly these units must then be connected with the other components at a high amount of work and costs in such a way that a satisfactory operational behaviour is obtained for the elevator installation.

It has always been the philosophy of the Loher AG at Ruhstorf that the components used for elevator installations require to be coordinated. Only then an effective and optimum correlation of the units, also under cost aspects, is possible; e.g. data of the units "Shaft copying" - "Control system" - "Power Converter" and "Central monitoring System" must be easily interchangeable.

Loher does no longer consider the frequency inverter only as a power device which feeds the motor, but as a unit to be integrated into the overall installation by an optimum communication.

It must be made easier for the customer to decide which one of the units can be used together without a lot of engineering (program adaptation, wiring etc.). His responsibility (at least in part) as to the compliance with TRA, EN 81, directives acc. to VDEW and EMC has to be reduced and taken by the respective component manufacturers.

Loher already made a decisive step in this direction by developing the DCP-Interface (Drive Control and Position) and the appropriate communication protocol.

The DCP-Interface and the communication protocol were developed and laid open to the public in cooperation with a German control system manufacturer Böhnke + Partner. It allows an optimum integration of Loher's frequency inverter DYNAVERT L into the control sequence. Thus a quasi-standardized Operation is possible for everybody!

Coupling to the elevator control System is made via the RS 485-Interface, which allows at low expenditure the transmission of high data rates even over large distances by means of a twisted and shielded two-wire line. A high immunity to interference as well as a low emission level is achieved.

Loher's DCP-protocol allows a transmission of the position set values and the Position actual values as well as the exchange of all important Information Signals and messages, and that simply, favourably priced and immune to interference (EMC) via the RS 485.

The control system works as master, the DYNAVERT L frequency inverter works as slave.

Various modes of Operation can be realized:

• Operation mode 1: Travel with a con-stant stopping distance corresponding to the conventional travel commands (com-mands as previously, but transmission of speed Signal via RS 485).
• Operation mode 2: Floor-to-floor travel at a variable stopping distance.
• Operation mode 3: Travel at a variable distance.

Operation mode 3 offers Optimum advantages to the user. At this Operation mode the control system passes the value of a requested travel distance in "mm" to the DYNAVERT L frequency inverter. The travel distance can also be changed even during the travel. The distance covered and the actual position of the car (= position actual value) is measured by the absolute encoder and signalled via the control System to the frequency inverter. During acceleration, travel and deceleration up to the stop, the car follows a travel profile optimally calculated in the DYNAVERT L frequency inverter for the respective travel distance. This ensures a maximum of riding comfort, shortest possible travel times by Optimum speed and a levelling position accurate to the millimetre with direct levelling.

The frequency inverter continuously monitors the most important operating conditions. Irregularities or faults are identifiable via the DCP-interface. A local fault analysis is no longer required, but can for instance directly be made by the extemal service centre.

With an adequately equipped control system, the information transfer can even take place without a data- or telephone line. By means of a mobile phone e.g. the DYNAVERT L event memory can be read via the control system and DCP-interface. This memory Stores the last 30 events at the moment of a fault. Therefore a diagnosis is possible everywhere and at any time!

Compared with conventional elevator installations, there are considerable advantages for the manufacturer of the installation and for the Operator by an optimum combination of position Signal (absolute encoder), control system and frequency inverter using the DCP-Interface with the DCP-Communication protocol:

• communication via interface at no relay
• independence as to various floor-to-floor distances
• shaft tags are no longer required
• signal propagation times of the control system do no longer affect the levelling Position
• time- and position-optimized direct levelling (no additional setting on the frequency inverter required)
• high data security (EMC)
• Optimum data exchange (transmission of all Signals, actual/set value, position Signal)
• less expenditure for assembly (saving up to approx. 50 %)
• less commissioning times (saving up to approx. 60 %)
• incremental encoder on motor can be deleted (saving up to approx. 20 %)

The DCP-Communication protocol developed by Loher is a free protocol, which means available for all users!

By using adequately coordinated components the elevator manufacturer cannot only offer a technically perfected and high-quality installation, but also saves a lot of time and trouble (consequently also money) as to the adaptation of different Systems.

The possibility to use price favourable (because coordinated) components or even to delete various components (e.g. incremental encoder) helps to save money.

Not only with respect to the DCP-Interface but also by the development of the "DYNAVERT L-KOMPAKT" frequency inverter integrating all units required for frequency inverter-operation, as for instance mains fuses, mains choke, EMC-Filters, motor filter, brake chopper and even the brake resistor (up to L 75), Loher shows a way like under technical and also commercial aspects a price favourable, technically perfected and high-quality drive unit for elevator installations is realizable!

Walter Schmidtmayer
(Translated by Loher AG)