GB2505932A

GB2505932A - Crane hoist rope pay-out system

Info

Publication number: GB2505932A
Application number: GB201216503A
Authority: GB
Inventors: Garry Richard Wright
Original assignee: Individual
Current assignee: Individual
Priority date: 2012-09-15
Filing date: 2012-09-15
Publication date: 2014-03-19
Also published as: GB201216503D0

Abstract

When a hoist is being raised a load cell amplifier is tared every 96mm of travel to zero the instrument to the current weight on the hook. When the hoist is being lowered, taring is inhibited. When the load cell detects a loss of 1 tonne of hook weight, a circuit enters a weight loss detected latched condition. Once the condition is set, it can only be reset by raising 240mm above the height at which the weight loss was detected. At this point the condition is reset regardless of the hook weight. With the weight loss detected condition set, the hoist can only lower to 756mm below the height at which the weight loss was detected. The hoist is free to raise and lower above this height. If the hoist is lowered to 756mm below the height at which the weight loss was detected, the circuit enters a disabled lower latched condition. From this point any further hoist lowering is inhibited until the disable lower latched condition is reset, this reset occurs concurrently with the weight loss detected condition reset, i.e. 240mm above the height at which the weight loss was detected.

Description

CRANE MOIST ROPE PAY-OUT SYSTEM

(Defence against ledge load leading to hang man's drop) Read in conjunction with sketch 1 (Electrical schematic)

DESCRIPTION

This logic provides a rope payout solution to prevent against ledge load fault sequences occurring for all types of industrial cranes. Electrical overhead travellers, dockside cranes, tower cranes etc. The logic described can be either hard-wired relay logic or PLC ladder logic, either method would utilise the same functionality.

Explanation of ledge load leading to hang-mans drop.

The free fall of an unstable or ledged' load that is still connected to the hook block of the crane is termed hangman's drop. Hangman's drop is caused by ledging a load whilst lowering and then continuing to payout rope in the lowering direction causing an accumulation of slack rope. Once the load topples from its edge position it is free to fill due to the accumulated slack ropc. On thc load falling and thc slack ropc bcing takcn up thc hangman's function is capable of Crane topple or collapse.

The logic system consists of the following components.

1. A signal conditioning amplifier /weigh system device.

Function: Continuously checks for a pre-deternilned weight loss of a load.

* Capable of reading an mv/Volt input signal generated from a standard wheat-stone-bridge load cell or a 4-2OmA signal.

* Has a remote tare function. (Taring: zeroes the instrument to the current load on the hook).

* Has a configurable trip output relay contact.

2. Pulse counter Ci Function: When enabled provide absolute monitoring with reference to a pre-determined distance of hoist rope paid out or paid in.

* CapaHe of monitoring 2 inputs A and B with the math function of A-B * Capable of accepting slow or fast frequency pulse inputs, pulse encoder, proximity sensor or Umit switches.

* Preset count function operates in count down mode.

* Has an auto reset function i.e. if pre-set to operate at 30 counts the counter will automatically recycle providing a puhe output every 30 counts.

* The output contact pulse duration must be configurable e.g. 0.05 to I second.

* Has a remote reset function. (Hard wired, reset back to pre-set count i.e. 30).

* Memory of last count on loss of power.

3. Timer (fleeting type) Function: Modifies a continuous signal to a pulse one-shot signal of a pre-detennined duration.

* A one shot device. On receiving an input signal an output relay contact energises for a preset time and then de-energises. The input must switch off and then back on in order to re cyde the timers fleeting function.

4. Latch relay Function: Provides stable logic that retains state on potential loss of power supply.

S

CRANE MOIST ROPE PAY-OUT SYSTEM

(Defence against ledge load leading to hang man's drop)

DESCRIPTION continued

* The relay must latch on seeing an input signal and remain latched until it receives an electrical input signal on its reset (unlatch) function coil.

* Resetting the latch is via a momentary input signal (typica'ly 0.5 seconds) applied to the reset coil.

5. Pulse encoder/proximity switch! limit switch.

Function: Provides an input pulse signal to the 3 off counters, giving a ratio of pulses to distance of rope payout. This can comprise of any of the following: * A pre-deteimined ratio for a geared wheel incorporating cams to operate a limit switch or limit switches.

* A pre-determined ratio for a geared whed incorporating a castle headed disc to operate a proximity switch or switches.

* A pulse encoder matched to meet a pre-determined ratio of pulses relating to distance of rope pay-out.

* A proximity sensor positioned to sense gear teeth on a suitable part of existing mechanical geanng / drivetrain. I.e. hoist banel drive.

Pre-requisites for this example: * Threshold trip is set for a load loss of It.

* Calibrate the signal conditioning trip amplifier or weigh system.

The signal conditioning trip amplifier or weigh system is calibrated to lOt. Depending on which system is used (weigh system or signal conditioning amp). The output trip relay is calibrated to trip at (energise at minus It) typical accuracy (3-5%) * The unit is configured for the tare command to operate from an external hard wired input.

Pre set Counters Cl, C2 & C3: * For al 3 counters each count is proportional to 12mm of hoist Hock travel.

* Cl set at "count down" 63 to 0 counts. Absolute lower (Raise input A -Lower input B). 63 counts equal 756mm of hoist rope pay-out.

* C2 set at "count down" 20 to 0 counts. Absolute lower (Lower input A -Raise input B). 8 counts equal 240mm of hoist rope pay-out.

* C3 set at "count down" 8 toO counts (Raise only). 8 counts equal 96mm of hoist rope pay-out.

* All are set to enable an output contact on reaching pre set count.

* All are set to enable the output contact for duration of 0.5 seconds.

* All are set to auto recycle on completing preset count.

* All are set to allow reset of count back to zero from external hard wired input.

Timer T2 * Timer (fleeting type) * Output pulse signal set at 0.5 seconds.

Load and slings * 10 metre strops attached to hook block.

* St weight attached but landed at ground level.

CRANE MOIST ROPE PAY-OUT SYSTEM

(Defence against ledge load leading to hang man's drop)

Description of sequence.

1. Operator raises the St load off the ground.

2. Raise counter C3 decrements from 8 to 0 (96mm.) providing a weight loss of It has not been detected, the weigh system is tared by C3 to a reference of zero tonne. If raise confinues this cycle will repeat providing a weight loss of it is not detected.

3. When towering, on seeing a weight loss of It, WLR Weight loss Latch relay energises in turn energising timer T2 that provides a 0.5 second pulse, resetting counters Cl to 63, C2 to 20 &, & C3 to 8.

4. Each time -It latch relay WLR energises (latches) Lower is potentially restricted to 63 counts (756mm) via Lower dominant counter Cl. An absolute thwer count of 63 is achieved by the math function of the counter A-B Raise minus Lower.

5. if Raise dominant counter C2 achieves a count of 20 before Lower counter Cl achieves a count of 63, Raise Counter C2 will reset -it latch relay WLR providing a weight loss of It is no longer detected (Lower now unrestricted).

On resetting WLR Lower counter Cl will hold a value. CI will not be reset back to 63 until a weight loss of lt is again detected (Via T2.) 6. Each time -lt latch relay WLR energises Lower is potentially restricted to 63 counts (756mm). Once Lower counter CI reaches 0 counts, lower disable latch relay DLR energises (lower now disabled).

7. Lower can only be re-enabled by raising 20 counts above the initial enabling of the counter monitoring i.e. Raise counter C2 has to achieve countdown to zero from 63 + 20 = 83 (63 a 756mm bcing distancc lowcrcd off bcforc lower disabled. 20 a 240mm being the distance raised above the lower disable position.) On Raise counter C2 achieving 0 counts, C2 counter raise, resets lower disable relay DLR via reset relay Rl. Lower is now unrestricted providing weight loss of it remains undetected, otherwise lower is again potentially restricted to 756mm via lower counter CI.

8. For unusual load lift! turn operations, or for example lowering a long length of chain, it is Ukely that lower will be disabled due to a weight loss of It being detected and the allowance of 756mm of pay-out being exhausted. A key switch override is provided to give a policed' reset of the disable lowcr latch relay DLR. This provides a single shot of a further 756mm of pay-out on each operation of the spring return reset key.

Claims

CRANE MOIST ROPE PAY-OUT SYSTEM(Defence against ledge load leading to hang man's drop)CLAIMS* Provides the logic for building a rope pay-out system which can either be retro fitted as a standalone unit, incorporated into existing crane control systems, or included into new control system design.* Provides protection by limiting pay-out of rope on detecting a pre-determined weight loss of any load.* The rope pay-out system operates using absolute height positioning.* By re-constantly repeating the tare function at a pre-deterrnined rope pay-out distance in raise. Any load lifted is constantly updated ensuring full load weight has been captured.* The distance of height that the load must be raised before tare takes place is pre-settable,* The weight loss that triggers / enables the system is pre-settable.* The amount of rope pay-out before disabling lower is pre-settable.* The distance of height that the load must be raised above the point at which the thwer rope pay-out trigger operates in order to reset is pre-settable.CRANE HOIST ROPE PAY-OUT SYSTEM(Defence against ledge load leading to hang man's drop)CLAIMS1. Provides defence against ledging a suspended load leading to hang-man's drop, comprising of a weigh system, absolute height detection and rope pay-out restriction.
2. Limiting pay-out of rope on detecting a pre-determined weight loss of any load
3. Claim (1) Functionality of this system can be provided by either hard wired or software logic.
4. Weight loss detection is provided whilst raising a suspended load, taring its recorded weight to zero, and monitoring for a weight loss with reference to zero.
5. For claim (4) the value of weight loss required to trigger the absolute hoist block position monitoring is pre-settable, and defined by the user setting the weigh system trip output to the required weight loss.
6. For claim (4) continuous cycles of the tare command ensures that the applied load is suspended.
7. For claim (4) The continuous cycle firnetion of the tare command is pre-settable and defined by the user setting counter C3 output count value, this will be proportional to the hoist block distance of travel required.
8. For claim (4) on a weight loss being detected (weight loss signal being latched). The tare cycle is disabled until the weight loss latch is reset.
9. For claim (2) Counters monitor raise and lower relative to the hoist block position, providing absolute hoist block position.
10. For claim (9) Lower dominant counter Cl limits pay-out on a weight loss being *o..* detected. *.***
11. For claim (9) Lower dominant counter Cl limits pay-out on a weight loss being * :" : detected. This function of distance of rope pay-out is pre-settable and defined by the user setting the counter output count value; this will be proportional to the hoist block distance of travel required.*
12. For claim (11) on lower dominant counter Cl exhausting its pre-set value disable * r hoist lower latch signal is invoked.
13. For claim (9) Raise dominant counter C2 exhausting its pre-set value resets the : * weight loss latch signal, resets the disable hoist lower latch signal & tares the weigh system, providing the weight loss no longer exists.
14. For claim (13) if the weight lossremains, the weight loss signal re latches.
15. For claim (13) Raise dominant counter C2 resets the weight loss signal. This function of distance at which the hoist block is raised above the initial weight loss being detected, is pre-settable and defined by the user setting the counter C2 output count value, this will be proportional to the hoist block distance of travel required.
16. The Reset key function resets the disable hoist lower latch signal; this enables an additional allowance of rope pay-out as determined by the lower dominant counter Cl set value.
17. Each time a weight loss is detected the absolute hoist block position counters are reset to their initial pre-set count values.