Title of Invention

A SAFETY INTERLOCK FOR RADIO REMOTE CONTROL.

Abstract

A safety interlock for radio remote control of a mobile equipment, like a crane, is provided comprising a programmable logic controller (PLC) for generating an output to represent the all command zero output (ANZ) to indicate that the motion commands are at zero. A plurality of normally closed (NC) auxiliary contacts of directional contacts are used for generating a directional relay zero (DRZ) signal representing that all directional contacts are at off position. Two contactors are provided to complete the interlock. The first contactor is a directional relay zero (DRZ) condition contactor and the second one an all command zero output condition contactor.

Full Text

FIELD OF APPLICATION The present invention relates to a safety interlock for radio remote control of a mobile equipment, like a crane. BACKGROUND OF THE INVENTION Safety is an important aspect of any mobile equipment. It becomes very critical when the equipment is operated remotely. In remote operation, in case of any failure, it should not lead to any motion for fail-safe operation. To ensure this, the control drop (Off) is interlocked with link failure, wrong data, watch dog, carrier detect and low battery. Link failure is the condition when the wireless communication channel between a transmitter and receiver is broken. This may be due to a weak signal generated from the transmitter unit or the distance between the transmitter and receiver is more than the range of the transmitter. The data from the transmitter unit is sent to the receiver unit in form of packets. Each packet consists of 8 bytes of the data. First byte and the last byte is the start byte and end byte. These values are fixed. The sixth and seventh byte is the checksum. In the receiving end the received data match along with checksum. If the data do not match the condition is known as wrong data. In addition to the main programmable logic controller (PLC) of the system there is a watchdog programmable logic controller (PLC) which monitors the health of the main programmable logic controller (PLC). In case this programmable logic controller (PLC) observes any abnormality in the main programmable logic controller (PLC) the control off circuit is activated. Carrier detect is an inbuilt feature of radio modules. When the receiver detects the carrier signal from the transmitter the carrier detect pin at receiver end goes high. The high and low of carrier detect pin indicates the presence or absence of carrier signal of transmitter at receiver end. The microprocessor circuitry inside the remote unit needs certain minimum voltage. This transmitter unit is powered with a rechargeable battery. When the battery voltage goes below a certain level the microprocessor circuitry may behave in an erratic fashion. This state of battery is known as Battery Low. It is expected that the above protection should stop the crane in case of failure of remote system. However, there is no feedback from the end operation i.e. direction and main contactor operation. In case, due to any reason, the direction contactor picks up without any motion command issued by the remote system the crane can start moving. Presently there is no system to prevent such situation. In such condition, operator can only stop the crane either by pressing control off, emergency or simply switching off the transmitter (switching off transmitter shall activate carrier detect and in-turn activate control off). SUMMARY OF INVENTION The main object of the present invention therefore, is to ensure that in the event of a failure, signals are generated indicating that all motion commands are at zero and that all the directional contacts are at off conditions. To achieve these and other objects, a programmable logic controller (PLC) is provided for generating an output to represent the all command zero output. The logic in the programmable logic controller (PLC) first checks whether any motion command has been received from the transmitter end. If there is no motion command of any of the drive this output will remain off or low. As soon as any motion command is given this will be on or high. For the other requirement, normally closed auxiliary contacts of directional contacts are used. In addition to this two contactors are used to complete the interlock. Directional contactors and normally closed (NC) contacts for long travel forward (LTF) motion, long travel reverse (LTR) motion, cross travel forward (CTF) motion, cross travel reverse (CTR) motion, main hoist hoisting (MHH) motion, main hoist lowering (MHL) motion, auxiliary hoist hoisting (AHH) motion, and auxiliary hoist lowering (AHL) motion are found in the crane drive panels. These contacts are activated when the respective motions are activated. Control relay zero (CRZ) contactor will be high if any of the two contacts directional relay zero (DRZ) or all command zero (ANZ) is high. The high condition of the relay indicates that in programmable logic controller (PLC) indicated by all command zero (ANZ) as well as in actual field indicated by directional relay zero (DRZ) none of the directional relay is activated. This means that neither the motion command has been sent by the user nor any motion command is being executed by the actual field contacts. The new interlock circuit does not put extra burden on contactor cost. For generating the directional relay zero (DRZ) contact the free auxiliary contacts of the directional relays can be used. Normally in cranes these contacts are not being used elsewhere and are therefore free. Similarly all command zero contact can be generated without any extra cost attached to it. The only contactor cost is of two additional contactors, directional relay zero (DRZ) contactor and all command zero (ANZ) contactor. Thus, the present invention provides a safety interlock for radio remote control of a mobile equipment, like a crane, comprising : a programmable logic controller (PLC) for generating an output to represent an all command zero output (ANZ) to indicate that the motion commands are at zero; a plurality of normally closed (NC) auxiliary contacts of directional contacts used for generating a directional relay zero (DRZ) signal representing that all directional contacts are at off position; and two contactors, a first directional relay zero (DRZ) condition contactor, and a second all command zero (ANZ) output condition contactor to complete the interlock. BRIEF DESCRIPTION OF THE ACCOMPANYING DRAWINGS: Figure 1 shows a schematic diagram of the interlock logic circuit. Figure 2 shows a schematic diagram of control power circuit. Figure 3 shows the programmable logic controller (PLC) of the present invention. Figure 1 shows the auxiliary contacts of the directional relays for the respective motion of long travel forward (LTF), long travel reverse (LTR), cross travel forward (CTF), cross travel reverse (CTR), main hoist hoisting (MHH), main hoist lowering (MHL), auxiliary hoist hoisting (AHH), auxiliary hoist lowering (AHL).These contacts are normally closed (NC) contacts. When none of the motion is activated, the directional relay zero (DRZ) contactor connected to it is high. Now as explained earlier the all command zero (ANZ) is the programmable logic controller (PLC) contact indication for no motion command received. If there is no motion command of any of the drive this output will remain off or low. As soon as any motion command is given, this will be on or high. Figure 2 shows in schematic form the control power circuit. In normal operation of the crane (manual operation) when control on is pressed the power will flow through control off (C-OFF), change over (CH), control on (COON), change over (CH), other interlocks to main contact (MC) coil. This will energize the main contact (MC) after the release of control on (C-ON) switch power will flow through control off (COOFF), change over (CH), main contact (MC), other interlocks to main contact (MC) coil. When system is changed over to remote operation change over (CH) contact becomes open and control off remote (C- OFF(R ) becomes closed. After control on (C-ON) is pressed power will flow through control off (C-OFF), control off remote (C-OFF(R), control relay zero (CRZ), control on remote (C-ON), other interlocks and main contact (MC). And after the release of remote control on button through control off (C-OFF), control off remote (C-OFF( R), control relay zero (CRZ), main contact (MC), other interlocks and main contact (MC). As we have seen from above that control relay zero (CRZ) will remain high as long as there is power flow through either directional relay zero (DRZ) or all. command zero (ANZ). In case any of the crane contact is high but system has not issued any command the control relay zero (CRZ) will drop which will in turn drop the main contact (MC) of the crane. Please note that control off (C-OFF(R ) and control on remote (C-ON (R ) indicate the control ON and control OFF of radio remote system. Figure 3 illustrates the PLC used in the present invention for generating an output to represent an all command zero (ANZ) to indicate that the motion commands are at zero. The PLC comprises a set of electrical contact having input and a separate set of contacts for the outputs. The way in which the input signals are processed can be programmed into the device, through an arrangement called the read only memory (ROM). The programming is conventionally known as the "Ladder Logic", and typically comprises of the arithmetic operators [+/-/*/Exp/Log etc) and logical operators [If/And/Nand/Or/Nor etc]. In the present invention, the PLC logic comprises of processing the Long/Cross/Hoist increments sent by the Radio Remote Control device. Each time that a signal is received it changes the contact status of Long/Cross/Hoist Zero in the PLC. The Outputs comprise the All Zero Motion (ANZ) contact. The signal progresses in the sequence LTZ ? CTZ ? MHZ ? AHZ ? Cont1? OnDelay Timer? ANZ. The delay circuits implement calls to an internal clock, and the specific time [3 Sec], is coded into the program. The circuit is very simple and easy to implement. The circuit only uses free auxiliary contacts of the directional relay and two additional contactors. This improves the safe working condition of remote control cranes. As in this circuit the feedback is taken directly from the main output, any fault in between, generated from any intermediate circuit shall force the system to trip and put the equipment in to the fall safe condition. This is the crane is prevented from moving without any directional command. In case such a condition occurs the circuit trips the control power preventing any further motion in any direction. WE CLAIM 1. A safety interlock for radio remote control of a mobile equipment, like a crane, comprising: - a programmable logic controller with a set of electrical contacts having the inputs, and a separate set for the outputs, generating an output to represent an all command zero output (ANZ) to indicate that the motion commands are at zero; - a plurality of normally closed (NC) contacts for long travel forward (LFT) motion, long travel reverse (LTR) motion, cross travel forward (CTF) motion, cross travel reverse (CTR) motion, main hoist hoisting (MHH) motion, main hoist lowering motion (MHL), auxiliary hoist hoisting (AHH) motion and auxiliary hoist lowering (AHL) motion of directional contacts used for generating a directional relay zero (DRZ) representing that all directional contacts are at off position; and a first directional relay zero (DRZ) condition contactor, and a second all command zero (ANZ) output condition contactor to complete the interlock. 2. The safety interlock as claimed in claim 1, wherein said plurality of normally closed (NC) contacts are for long travel forward (LTF) motion, long travel reverse (LTR) motion, cross travel forward (CTF) motion, cross travel reverse (CTR) motion, main hoist hoisting (MHH) motion, main hoist lowering (MHL) motion, auxiliary hoist hoisting (AHH) motion, and auxiliary hoist lowering (AHL) motion are found in the crane drive panels. 3. The safety interlocks as claimed in claims 1 and 2, wherein free auxiliary contacts of the directional relays can be used for generating the directional relay zero (DRZ) contact. 4. The safety interlock as claimed in the preceding claims, wherein said all zero motion (ANZ) output of the PLC can be programmed to make it off delay. 5. The safety interlock as claimed in claim 4, wherein said PLC output is provided with a delay of three seconds. 6. A mobile equipment for example a crane incorporating a safety interlock for radio remote control as claimed in claim 1. A safety interlock for radio remote control of a mobile equipment, like a crane, is provided comprising a programmable logic controller (PLC) for generating an output to represent the all command zero output (ANZ) to indicate that the motion commands are at zero. A plurality of normally closed (NC) auxiliary contacts of directional contacts are used for generating a directional relay zero (DRZ) signal representing that all directional contacts are at off position. Two contactors are provided to complete the interlock. The first contactor is a directional relay zero (DRZ) condition contactor and the second one an all command zero output condition contactor.

Documents:

652-kol-2004-granted-abstract.pdf

652-kol-2004-granted-claims.pdf

652-kol-2004-granted-correspondence.pdf

652-kol-2004-granted-description (complete).pdf

652-kol-2004-granted-drawings.pdf

652-kol-2004-granted-examination report.pdf

652-kol-2004-granted-form 1.pdf

652-kol-2004-granted-form 18.pdf

652-kol-2004-granted-form 2.pdf

652-kol-2004-granted-form 3.pdf

652-kol-2004-granted-form 5.pdf

652-kol-2004-granted-gpa.pdf

652-kol-2004-granted-reply to examination report.pdf

652-kol-2004-granted-specification.pdf