Half Wave and PCM Control
Power supply of Electrified Monorail Systems is achieved with sliding bus bar systems, where normally 4 rails are provided L1, L2 & L3 for 3 phase power and PE ground. Dependent on the required number of commands more rails are required, implemented and used for command and message forwarding.
Even today this is the practise even though radio and WLAN transmission is regarded as state of the art - However the latter is unfortunately very restricted by many production plants due to several reasons such as:
- Interference with existing communication protocols.
- Interference from background or white noise emission for production equipment.
- Security of internal WLAN procedures.
- Design constraints of mechanical equipment and positioning of comms equipment.
From the outset LJU implemented a minimum configuration of rails:
One control / one message bar, no matter how many commands were required.
Full and Half wave signals form the basics of command structure.
LJU's PCM system can provide up-to 191 commands via one rail.
During the half-wave activation, commands are sent from the system controller to the trolley controller via full waves and half waves over a control rail.
- Drive at multiple speeds
- Release the brake separately (e.g. for mechanical adjustment of trolley at loading points)
- Slow down and stop with a slow-down photo-switch and anti-collision proximity switch
- Additional speed through magnetic switch
The trolley executes the actions (control commands) specified by the PLC and drives at the parameterized speeds V1, V2 (depending on the applicable control command) or releases the brake if needed. In addition, by activating a magnetic switch (evaluated by the controller), the speed is switched to another parameterized speed V3 in the controller, though the PLC specifies a different speed. If the switch is reset, the trolley once again drives at the PLC-specified speed. For anticollision protection there is a configurable proximity switch activating a ramped stop. (Click to magnify)
PCM-Command System (Puls-Code-Modulation)
The PCM command system represents an enhancement of the half-wave control. It has been developed by LJU in 1990 when the standard Half-Wave-system did not meet more variable control requests of customers. It allows a large number of commands to be transmitted over only one single control rail.
A command code is transmitted over this one control rail and is synchronized with one phase of the power rail. In the PCM command system, there are various LJU PCM modules that connect to the supervisory control system providing up to 191 different half wave patterns as commands to the drive controller. Some control commands are already predefined in the controller software (see right picture and table), however some can be adjusted and modified to provide flexibility for the end-user. Messages are transmitted by the trolley over the control rail as half-waves and full-waves and can be modified specifically for customers on request (e.g. completion messages for various movement sequences). Click on graphics to magnify.
The systems referred to above have proven reliable in production operations for more than 2 decades.
This is despite the increase in preference for bus communication systems in complex systems. Implementation of EMS into new build installations takes place with the installation of this so called "older" technology.
The reasons are:
- Flexibility - Increases ability for technology to be applied in many and varied applications.
- Reliability - Provides security in performance, maintainability and customer satisfaction
- Field Bus Interfaces for all systems Enables LJU systems to be implemented into modern facilities