GB2213969A

GB2213969A - Data communication system

Info

Publication number: GB2213969A
Application number: GB8730121A
Authority: GB
Inventors: John Bicknell
Original assignee: Era Technology Ltd
Current assignee: Chelton CTS Ltd
Priority date: 1987-12-24
Filing date: 1987-12-24
Publication date: 1989-08-23
Anticipated expiration: 2007-12-24
Also published as: GB8730121D0; GB2213969B

Abstract

A data communication system provides communication between a plurality of controlled equipments (1) (powered by synchronised a.c. power signals) and respective remote controllers (3). The period of one a.c. power cycle is notionally divided into a plurality of time slots and each equipment and its associated controller is assigned one or more of these time slots. A microprocessor (5) at the equipment times the appropriate delay between a synchronisation signal and the respective time slot. The synchronisation signal may be derived from the a.c. power signal. Data, including an identification signal, is then transmitted to the associated controller. The controller having received the data from the equipment then re-transmits the identification signal and transmits command data. If data is not received within a certain time by either the equipment or the controller an indication of failure is generated. <IMAGE>

Description

Data Communication System This invention relates to a data communication system and is particularly useful for providing command signals from a controller to a controlled equipment and data signals from the controlled equipment to the controller.

There are many industrial applications in which a number of controlled equipments are to be controlled by respective remote controllers, such as in the control of overhead cranes. In this application cranes are conventionally controlled by respective manually-operable controllers which are connected to the crane motor controls via a hanging umbilical cable. These cables can provide adequate two-way communication but are expensive to install and are unwieldy where very high cranes are concerned. It would be desirable to control overhead cranes, for example, using a form of wireless communication, but steps then have to be taken to ensure that the receivers do not suffer interference from extraneous signals, and particularly from signals from adjacent cranes or controllers.

Viewed from one aspect, there is provided a data communication system for communicating data between controlled equipments and respective remote controllers, comprising means associated with each equipment for receiving a common synchronisation signal, means for timing respective transmission time slots following said synchronisation signal, means for transmitting respective identification signals in said time slots, and :eans associated with said controllers for identifying said identification signal and for transmitting data in response thereto.

Preferably the common synchronisation signal is supplied on a common line to the controlled equipments.

Conveniently the synchronisation signals may be derived from a common a.c. power signal signal or synchronised power phases.

Viewed from another aspect, the invention provides a data communication system for communicating data between an a.c. powered equipment and- a remote controller, comprising means associated with the equipment for deriving a synchronisation signal from the a.c. power signal, means for timing a transmission time slot following said synchronisation signal, means for transmitting an identification signal in said time slot, and means associated with said controller for identifying said identification signal and for transmitting data in response thereto.

The invention takes advantage of the fact that a synchronised a.c. signal is available to a plurality of powered equipments and so they can employ this as a synchronising signal. Because the remote controller responds to identifying a received identification signal, it does not need to be provided with synchronisation signals. Preferably the means for timing a transmission time slot comprises a settable input device, such as wire or diode links or a thumbwheel switch which may be set to define a unique time slot within an a.c. power cycle during which a particular equipment will transmit. The settable device preferably also defines the identification signal which is transmitted and the associated remote controller may be provided with a similar settable device to assign it to the particular powered equipment.

Preferably the communication system is a twoway communication system arranged to transmit data from the powered equipment to the controller and command signals from the controller to the powered equipment.

Preferably the system comprises infra-red transmitters and receivers. These are readily available at low cost and have the advantage over radio links, for example, of not causing electromagnetic interference.

An embodiment of the invention will now be described by way of example and with reference to the accompanying drawings, in which Fig. 1 is a schematic view illustrating the environment in which a communication system according to the invention may be used; Figure 2 is a block diagram of a practical implementation of a data communication system according to the invention; Fig. 3 is a timing diagram illustrating the operation of the apparatus of Fig. 2; Fig. 4 is a flow chart illustrating the steps performed in the controlled equipment of Fig. 2; and Fig. 5 is a flow chart illustrating the steps performed in the remote controller of Fig. 2.

Referring to the drawings, the data communication system may be used to provide data communication in a situation in which a plurality of controlled equipments 1 powered by synchronised a.c. power signals on line 2 are to be controlled by respective remote controllers 3. A typical application will be in the remote control of overhead cranes in which each controlled equipment 1 will be an overhead crane and its associated motors and electrical control equipme and each controller 3 will be a hand-held remote controller. In such applications it is required that each controller 3 should only communicate with its associated controlled equipment 1. Overhead cranes may be typically 100 metres from their associated controllers and so there is clearly a danger of signals from one controller interfering with the operation of another controlled equipment.The present invention overcomes this in a simple and reliable manner.

The invention employs duplex infra-red links between the controllers and the controlled equipment and operates to communicate operational data (such as fault indications) from the controlled equipment to the controller for display at the controller, and control commands from the controller to the controlled equipment.

Referring now to Fig. 2, communication apparatus at controlled equipment 1 comprises a microprocessor 5 for following a procedure described below, a synchronisation circuit 6 arranged to receive the a.c. power signal and to derive a synchronisation signal therefrom and to supply it to the microprocessor 5. A settable device 7, e.g. a thumbwheel switch, provides a settable address (identification signal) and time slot assignment which is used for controlling the time at which the apparatus transmits and for setting the transmitted identification signal which may be reognised by an associated controller 3. The microprocessor 5 controls the transmission of signals via Manchester encoder 8 and optical transmitter 9 and the reception of signals via optical receiver 10 and Manchester decoder 8. Received command signals are provided by interface 11 to activators of the controlled equipment 1, e.g. for controlling conventional motor contactors.

Interface 11 also receives indications of fault conditions, such as the operation of an overcurrent trip, for transmission via optical transmitter 9.

The controller 3 is of similar construction but does not include a synchronisation circuit and is additionally provided with a keyboard 15 and display 16. Specifically, controller 3 includes microprocessor 17, settable device 18, Manchester encoder/decoder 19, optical transmitter 20 and optical receiver 21.

The microprocessor 17 follows the routine described below to display on display 16 data received from the controlled equipment 1 having the same address as that set on device 18, and operates to transmit in response to identifying the correct address command signals input on keyboard 15.

Fig. 3 illustrates the timing of the transmission operations of the communication apparatus at the controlled equipments 1 and of the controllers 3.

The period of one a.c. power cycle is notionally divided into a plurality of separated time slots 30. For example, there may be sixteen controlled equipments and sixteen corresponding time slots.

Each controlled equipment and its associated remote controller is assigned one (or more) of these time slots by means of the number set on the devices 7 and 18. Each microprocessor 5 times an appropriate time from the supply of the synchronisation signal from synchronisation circuit 6 and then commences data communication operations. This timing may be performed using a conventional crystal oscillator associated with the microprocessor and because of the possible variations in crystal frequency and also transmission delays it may be desirable to leave a guard period 31 before each transmission commences.

The controlled equipment then proceeds to transmit its identification signal 32 (e.g. a four-bit binary code) followed by operational data 33. The controller 3 which recognises the transmitted identification signal then responds by transmitting the identification signal and any command signals as indicated at 34.

The identification signal may be preceded by idle bits if necessary. The controlled equipment assigned to the next time slot 30 then performs the same operations at 35, again after a suitable guard period.

With 16 two-way links, a typical signalling rate of 300k baud would allow approximately 160 bits to be transmitted in each direction in each cycle.

Fig. 4 shows the steps carried out in microprocessor 5. First of all in step 40 the microprocessor acquires from interface t1 any operational data to be transmitted.

Then at step 41 it awaits the provision of a synchronisation signal (e.g. zero crossing) from synchronisation circuit 6. When this has been received the microprocessor times the appropriate delay in step 42 until the time slot assigned by device 7, including any guard period. Thereafter the assigned identifier and the acquired operational data are transmitted in step 43 via encoder 8 and transmitter 9. The microprocessor 5 then determines whether the appropriate identification signal is received from controller 3 within a first time period (step 44). If so, the following received data is permitted to be used as command data (step 45) and the process repeats. If no valid identification signal is detected at step 44 a test is performed at 46 to see if a second, longer period has expired.

If not, the microprocessor makes a further attempt to communicate with the controller 3 by returning to step 41. If the second period expires this indicates failure of the link and this is reported at step 47. This step may cause the equipment to stop and enter a standby mode.

At the controller 3 the procedure of Fig. 5 is followed. At step 50 the keyboard is scanned for any manually-input control commands. At steps 51 and 52 it is determined whether a signal has been received and if not whether a timeout period has expired. If so, this indicates failure of the link and this is reported on display 16 at step 53. Step 54 checks for the receipt of a valid identification signal. If this is not received within the period of step 52 the fault is again reported at step 53.

The receipt of a valid identification signal within the timeout period permits operational data to be received and displayed at step 55 and thereafter the identification signal and input command signals to be transmitted at step 56.

It may be seen that each controlled equipment 1 repeatedly transmits at least its identification signal and monitors the return of an acknowledgement, and each controller 3 checks for the receipt of a valid identification signal and provides a warning if this is not received. Thus the invention provides a communication system which, although simple, is highly reliable and not prone to interference.

Claims

Claims:

1. A data communication system for communicating data between controlled equipments and respective remote controllers, comprising means associated with each equipment for receiving a common synchronisation signal, means for timing respective transmission time slots following said synchronisation signal, means for transmitting respective identification signals in said time slots, and means associated with said controllers for identifying said identification signal and for transmitting data in response thereto.

2. A data communication system according to claim 1 wherein said common synchronisation signal is supplied on a common line to the controlled equipments

3. A data communication system according to claim 1 or 2 wherein said synchronisation signal is derived from a common a.c. power signal.

4. A data communication system according to claim 1 or 2 wherein said synchronisation signal is derived from synchronised power phases.

5. A data communication system for communicating data between an a.c. powered equipment and a remote controller, comprising means associated with the equipment for deriving a synchronisation signal from the a.c. power signal, means for timing a transmission time slot following said synchronisation signal, means for transmitting an identification signal in said time slot, and means associated with said controller for identifying said identification signal and for transmitting data in response thereto.

6. A data communication system according to claim 5 wherein said means for timing a transmission time slot comprises a settable input device, which may be set to define a unique time slot within an a.c.

power cycle during which a particular equipment will transmit.

7. A data communication system according to claim 6 wherein said settable device defines the identification signal which is transmitted.

8. A data communication system according to claim 5, 6 or 7 wherein said remote controller is provided with a settable device by which it may be assigned to a particular powered equipment.

9. A data communication system according to any preceding claim arranged to transmit data from a powered equipment to a controller and command signals from said controller to said powered equipment.

10. A data communication system according to any preceding claim comprising infra-red transmitters and receivers.

11. A data communication system substantially as hereinbefore described with reference to the accompanying drawings.