GB2316668A

GB2316668A - Elevation limiting safety device for excavator arm

Info

Publication number: GB2316668A
Application number: GB9717881A
Authority: GB
Inventors: Robert Wilson
Original assignee: Individual
Current assignee: Individual
Priority date: 1996-08-24
Filing date: 1997-08-26
Publication date: 1998-03-04
Anticipated expiration: 2017-08-26
Also published as: GB2316668B; GB2316668A8; GB9717881D0

Abstract

A system for limiting the maximum height of an excavator arm 9, preferably the dipper arm 9 of a backhoe 2, the excavator comprising a body 4 to which the arm is pivotally linked and a hydraulic cylinder 16 for raising or lowering the arm. A check valve 21 in the hydraulic fluid supply system for the cylinder blocks the supply of fluid depending on either the presence or absence of a control signal. The system comprises means for generating a signal 19, detector means for detecting the signal 20, and control means responsive to detection of the signal to send the appropriate control signal to the check valve. Preferably the signal generating means comprises a light source 19 mounted on a mast 18 on the roof of the excavator and the detector means comprises a light detector mounted on the arm. The arm cannot be raised above the level of the beam of light from the light source. Alternatively, an arcuate steel plate (23, Fig 3) mounted on the arm and one or more proximity detectors (24, Fig 3) mounted in a fixed position relative to the arm adjacent the plate. As the arm is raised the plate pivots until it is no longer adjacent a detector, in which case, an alarm may sound and the check valve is activated to prevent further raising of the arm.

Description

EXCAVATOR ARM ELEVATION LIMITING SYSTEM Field of the Invention This invention relates to a system for limiting the elevation of an excavator arm, especially the dipper arm.

Background to the Invention Excavators working under overhead power lines are set a safe working height which allows sufficient clearance beneath the power lines to prevent the occurrence of arcing, since this would be extremely dangerous, and probably fatal, for the excavator operator. A particular example of this is work carried out on or adjacent to an overhead electrified railway. A difficulty with such work is that it is difficult for the operator to gauge the correct working height in relation to the excavator arm, and it is often tempting to exceed the safe working height limit in order to finish a piece of work more quickly.

In order to overcome this difficulty, it has been proposed to fix limiting devices to diggers, especially in the case of the type of machine known as a backhoe loader, having an excavating bucket pivotally mounted on a dipper arm which is itself pivotally mounted on a lifting arm, in turn pivotally mounted on the chassis of the excavator. In one known limiting device, a chain is attached between the lifting arm and the dipper arm, the length of the chain determining the available working height of the dipper arm. Such devices are relatively easily attached by welding attachment points to the respective arms. While such devices can provide a simple indication to the operator that he has attempted to elevate the dipper arm too far, the tensile force which can be applied to the chain can be very high, and this can lead ultimately to failure of the attachment points or their welds, or of the chain itself.

If failure occurs, two dangers arise. Firstly, the dipper arm is again free to be elevated to an unsafe proximity to the overhead power lines, and secondly, the failed metal parts can be propelled at high velocity in the region of the excavator, constituting a danger to workers nearby and possibly to the operator himself.

Similar problems occur with other devices having extendible arms which are required to work within height restrictions, for example cranes.

Summary of the Invention According to the invention, there is provided a system for limiting the elevation of an excavator arm, the excavator comprising a body section to which the arm is pivotally linked, a hydraulic cylinder for raising or lowering said arm, means for selectively supplying hydraulic fluid to said cylinder to raise the arm, and a check valve responsive either to the presence or to the absence of a control signal to block the supply of hydraulic fluid to the cylinder, the system comprising means for generating a signal, detector means for detecting the signal, and control means responsive to detection of the signal to send said control signal to the check valve.

The means for generating a signal may comprise optical means for projecting an optical signal, the detector means detecting the optical signal.

The signal generating means may comprise a plate, the detector means comprising at least one proximity sensor. Advantageously, three proximity sensors are provided. The plate is suitably steel. The plate may be arcuate. Preferably, the plate is mounted on the dipper arm and the or each proximity sensor is mounted on the lifting arm.

Alternatively, the plate may be mounted on the lifting arm and the or each sensor may be mounted on the dipper arm.

Preferably, the or each sensor detects the presence of plate while the dipper is within a safe working height. Where three sensors are provided, the control means initiates the following sequence upon detection of signals from the proximity sensors: 1) When the first sensor ceases to detect the plate, a warning signal is switched on, thereby warning the operator that the dipper arm is approaching maximum height. The warning signal may be visual or audible.

2) When the second sensor ceases to detect the plate, the check valve is closed, preventing the dipper arm from lifting further.

3) When the third sensor ceases to detect the plate, which only occurs if the check valve fails to close, the vehicle is immobilized.

Preferably, the third sensor also switches a warning signal.

The warning signal may be an audible or visual alarm.

The control means may be comprise at least one relay, and preferably at least one relay for each proximity sensor.

The optical means is preferably mounted on the body of the excavator, for example on the operator's cab, with the detector means being mounted on the excavator arm, although the opposite arrangement, with the optical means on the excavator arm and the detector means on the body of the excavator, may be used as an alternative.

The optical means may be arranged to project the optical signal in a horizontal arc sufficient to encompass the range of movement of the arm, with the control means being arranged to send the control signal as soon as the optical signal is detected. Alternatively, the optical signal may be projected over a spherical angle encompassing the range of working movement of the excavator arm, the control means being arranged to hold the check valve open while the control signal is present and to close the check valve in the absence of the control signal.

The optical signal may be provided by a solid state laser device emitting a continuous or intermittent output, the detector being responsive only to light of the wavelength emitted by the laser.

Alternatively, in order to avoid the risk of false signals arising from ambient light, the optical signal may be modulated with an identifying code, the detector means comprising means for discriminating the code in the light detected.

Preferably, the check valve is mounted directly on the cylinder, and may serve the additional function of locking the cylinder in the event of an excessive load being placed on the arm.

In the case of an excavator of the backhoe type, the detector means is preferably mounted on the dipper arm, in such a position that it comes into line-of-sight alignment with the optical means as soon as the dipper arm elevates relative to the lifting arm. The optical means is preferably mounted on a support mast on the roof of the cab of the excavator, and is suitably mounted in such a manner as to be adjustable in elevation so as to permit the maximum working height of the excavator arm to be set on site according to the height of the overhead power lines, and other local circumstances. Typically, this can be carried out by elevating the arm to its safe working limit, and then adjusting the elevation angle of the optical means so that its signal is detected by the detector means, and then locking the optical means in position.

Since the system of the invention prevents the arm being elevated excessively by stopping the supply of hydraulic fluid to the elevating cylinder, there is no risk of damage to the limiting device if the operator fails to remember the working limit for the location. The system is simple to install on existing excavators, and is easy for the operator to set up in the individual locations.

Brief Description of the Drawing In the drawings, which illustrate exemplary embodiments of the invention: Figure 1 shows a side elevation of an excavator having an elevation limiting system according to one embodiment of the invention; Figure 2 shows a side view of part of a backhoe shown in Figures 1 and3; Figure 3 shows a side view of an excavator having an elevation limiting system according to another embodiment of the invention, and an exploded view thereof; and Figure 4 shows a block diagram of a control system of the elevation limiting system according to one embodiment of the invention.

Detailed Description of the Illustrated Embodiment The drawing shows a typical excavator of the 'backhoe loader' type, having an hydraulically driven front loader bucket arm 1 and a backhoe 2, described hereinafter in more detail. The excavator has a main chassis 3 mounting the operator's cab 4 and the engine 5. The main chassis 3 is supported by main wheels 6 and steerable wheels 7.

The backhoe 2 consists of a lifting arm 8 and a dipper arm 9 pivotally linked together, the dipper arm in turn pivotally mounting a bucket 10. The lifting arm 8 is mounted on a carriage 11 which is slidably mounted on transverse mounting rails 12 between extendible supporting legs 13, with hydraulic rams being provided to slide the carriage.

A hydraulic lifting cylinder 14 extends between the carriage 11 and a bracket 15 on the lifting arm 8 to raise and lower the arm, while another cylinder 16 extends between the bracket 15 and the dipper arm 9 to rotate it relative to the lifting arm. Yet another cylinder 17 controls the movement of the bucket 10.

A mast 18 is fixed to the roof of the cab 4 and carries a laser device 19 (for example incorporating an infra red laser) arranged to project a beam of light in a plane represented by the broken line over an arc encompassing the range of movements possible with the arm. A detector 20 is mounted on the dipper arm 9 in such a position as to be in sight of the laser device 19 only when both the lifting arm and the dipper arm are at least partially elevated. A check valve 21 is mounted between the cylinder 16 elevating the dipper arm and the hydraulic supply thereto, the check valve being operable in response to an electrical control signal from a controller (not shown) receiving signals from the detector 20.

In use, the angle of elevation of the beam from the laser device 19 is set so that as soon as the dipper arm is elevated to its maximum desired elevation, the detector receives the beam and causes the check valve to close, thereby preventing any further contraction of the cylinder and thus further elevation of the dipper arm.

Referring now to Figures 2 to 4, the same reference numerals used in Figure 1 are used in Figures 2 to 4 where like parts are represented.

It can be seen from Figure 3 that an arcuate plate 23 made from steel is mounted on the dipper arm 9 so that when hydraulic cylinder is extended, thereby lifting the dipper arm 9, plate 23 moves past the proximity sensors 24, 25, and 26. Each of the proximity sensors 24 to 26 is individually connected to connection box 28.

The manner of operation of the system for limiting the elevation of the excavator arm 2 is best described with reference to Figures 3 and 4.

As hydraulic ram 16 is retracted so the height of dipper arm 9 is increased. The plate 23 moves past the first proximity sensor 24 which changes the signal received by the control box 29. Upon receiving the change in signal, the control box 29 causes visual alarm 30, which may be an LED to be activated, indicating to the operator that the dipper arm 9 is approaching maximum height. The visual warning remains on until dipper arm 9 has been lowered so that proximity sensor 24 detects the presence of plate 23. If the visual warning signal 30 is ignored, when arcuate plate 23 moves past the second proximity sensor 25, the signal received form sensor 25 changes, deenergizing the hydraulic solenoid valve 21 which is held open whilst the arm 2 operates within a safe height. De-energizing the valve 21 closes the valve and stops flow of oil to the hydraulic ram 16. The valve 21 is so arranged that, when de energized, it will only permit hydraulic fluid to flow out of the ram 16 thereby only permitting lowering of dipper arm 9.

If hydraulic valve 21 fails to close, the dipper arm 9 will continue to rise until the plate 23 moves past the third proximity sensor 26. when plate 23 has moved past proximity sensor 26, the signal received by the control box 29 from the said sensor changes and activates an immobilizes 32 which immobilizes the vehicle by turning off the engine. Until the dipper arm 9 is lowered below the safe height, so that all three proximity sensors can detect the presence of plate 23, the vehicle's engine may not be restarted. Immobilizes 32 may incorporate an audible alarm.

The purpose of visual alarm 30 is to warn the operator that the critical height is being reached.

Control box 29 houses electrical relays which enable the switching of the proximity sensors 24 to 26 to control the warning devices 30 to 32.

The control box has a three-position switch which is preferably key operated. In the first position, the vehicle and the system are switched off, the key may be removed, and the vehicle is disabled. In the second position, the vehicle is switched on, but the system of the invention is switched off. In the third position the vehicle is switched on, and the system of the invention is switched on, thereby restricting the height to which the dipper arm 9 may be raised.

The control box 29 comprises 4 relays, the relays being powered via the proximity sensors 24 to 26.

The first relay is energized by proximity sensor 24. Whilst energized, the first relay is held open, but in the absence of a signal from proximity sensor 24, the relay is de-energized causing the relay to close thereby activating the audible alarm.

The second relay is energized by proximity sensor 25. The relay is connected to the solenoid of hydraulic valve 21 which is normally held open, the contacts of the relay being closed. When the plate 23 moves past proximity sensor 25, the second relay is de-energized, thereby closing the hydraulic valve 21.

The third and fourth relays are both energized by proximity sensor 26. The third relay is normally held open and is connected to an audible alarm, so that when plate 23 moves past sensor 26, the alarm is activated.

The fourth relay has a pair of voltage free contacts which are used to interrupt the vehicle's support system, e.g. the fuel solenoid. The fourth relay is adapted to fail safe, stopping the engine if the dipper arm 9 is raised so high that plate 26 passes proximity sensor 26.

Furthermore, when the control box is in the off position, the contacts of the fourth relay are open thereby interrupting the vehicle's support system. Hence, the system also acts as an anti-theft device.

The system of the invention may be used on other devices comprising an extendible arm which is capable of extending above a required height.

Claims

1. A system for limiting the elevation of an excavator arm, the excavator comprising a body section to which the arm is pivotally linked, a hydraulic cylinder for raising or lowering said arm, means for selectively supplying hydraulic fluid to said cylinder to raise the arm, and a check valve responsive either to the presence or to the absence of a control signal to block the supply of hydraulic fluid to the cylinder, the system comprising means for generating a signal, detector means for detecting the signal, and control means responsive to detection of the signal to send said control signal to the check valve.

2. A system according to Claim 1, wherein the means for generating a signal comprises optical means for projecting an optical signal, the detector means detecting the optical signal.

3. A system according to Claim 2, wherein the optical means is mounted on the body of the excavator, with the detector means being mounted on the excavator arm.

4. A system according to Claim 2, wherein the optical means is mounted on the excavator arm and the detector means on the body of the excavator.

5. A system according to any of Claims 2 to 4, wherein the optical means is arranged to project the optical signal in a horizontal arc sufficient to encompass the range of movement of the arm, with the control means being arranged to send the control signal as soon as the optical signal is detected.

6. A system according to any of Claims 2 to 4, wherein the optical signal is projected over a spherical angle encompassing the range of working movement of the excavator arm, the control means being arranged to hold the check valve open while the control signal is present and to close the check valve in the absence of the control signal.

7. A system according to any of Claims 2 to 6, wherein the optical signal is provided by a solid state laser device emitting a continuous or intermittent output, the detector being responsive only to light of the wavelength emitted by the laser.

8. A system according to any of Claims 2 to 6, wherein the optical signal is modulated with an identifying code, the detector means comprising means for discriminating the code in the light detected.

9. A system according to Claim 3, or any of Claims 5 to 8 when dependent on Claim 3, wherein the detector means is mounted on the dipper arm, in such a position that it comes into line-of sight alignment with the optical means as soon as the dipper arm elevates relative to the lifting arm.

10.A system according to Claim 9, wherein the optical means is mounted on a support mast on the roof of the cab of the excavator.

11.A system according to Claim 10, wherein the optical means is mounted in such a manner as to be adjustable in elevation.

12.A system according to Claim 1, wherein the signal generating means comprises a plate, the detector means comprising at least one proximity sensor.

13.A system according to Claim 12, comprising three proximity sensors.

14.A system according to Claim 12 or 13, wherein the plate is formed from steel.

15.A system according to any of Claims 12 to 14, wherein the plate is arcuate.

16. A system according to any of Claims 12 to 15, wherein the plate is mounted on the dipper arm and the or each proximity sensor is mounted on the lifting arm, or the plate is mounted on the lifting arm and the or each sensor is mounted on the dipper arm.

17.A system according to any of Claims 12 to 16, wherein the or each sensor detects the presence of plate while the dipper is within a safe working height.

18.A system according to Claim 13 or any of Claims 14 to 17 when dependent of Claim 13, wherein the control means initiates the following sequence upon detection of signals from the proximity sensors: a) when the first sensor ceases to detect the plate, a warning signal is switched on, thereby warning the operator that the dipper arm is approaching maximum height.

b) When the second sensor ceases to detect the plate, the check valve is closed, preventing the dipper arm from lifting further.

c) when the third sensor ceases to detect the plate, which only occurs if the check valve fails to close, the vehicle is immobilized.

19) A system according to Claim 18, wherein the third sensor also switches on a warning signal.

20) A system according to Claim 18 or 19, wherein the warning signals are audible and/or visual.

21) A system according to any of Claims 12 to 20, wherein the control means comprises at least one relay.

22) A system according to Claim 21, wherein the control means comprises at least one relay for each proximity sensor.

23) A system according to any preceding claim, wherein the check valve is mounted directly on the cylinder.

24) A system according to any preceding claim, wherein the check valve serves the additional function of locking the cylinder in the event of an excessive load being placed on the arm.

25) A system for limiting the elevation of an excavator arm substantially as described with reference to, or as shown in, the drawings.