WO1999035462A1

WO1999035462A1 - Monitoring arrangement for a multi-element boom

Info

Publication number: WO1999035462A1
Application number: PCT/AU1999/000009
Authority: WO
Inventors: David Thiel; Sulaiman Thompson; Barry Blakeway
Original assignee: Griffith University
Priority date: 1998-01-12
Filing date: 1999-01-12
Publication date: 1999-07-15
Also published as: AUPP130498A0

Abstract

A monitoring arrangement for a multi-element boom (4) consist of a fixed inclinometer (14) that provides a reference signal and a further inclinometer (11-13) associated with each element (5-7) of the boom (4). The further inclinometers provide signals proportional to the angle of the boom element to the horizontal. A processor means uses the length of each boom element and the inclinometer signals to calculate the position of the end of the boom (7). The arrangement is usefully applied to backhoes by placing the processor means and fixed inclinometer in the cabin. A display provides a continuous indication to the operator of the position of the bucket of the backhoe.

Description

"MONITORING ARRANGEMENT FOR A MULTI-ELEMENT BOOM"

FIELD OF THE INVENTION

THIS INVENTION relates to a depth monitor and in particular to an

electronic device that is well suited to digging machines to provide an

operator with precise information on the depth and slope of a hole as it is

dug.

BACKGROUND TO THE INVENTION

Precise monitoring of hole depth and slope during digging is required

in many situations. The simplest method of achieving this is for a person to

periodically check the depth with a measuring device while the hole is being

dug. This approach is both slow and dangerous for the person making the

measurement. It is preferable if the measurements can occur concomitantly

with the digging process.

Laser based devices have been used to measure depth and slope for

trench digging however this technology suffers considerably from excess

vibration and dust. These problems necessitate frequent cleaning and

realignment. Laser based systems are also expensive and therefore

unattractive in many situations.

Another manner of achieving depth monitoring is described in United

States patent number 3997071 assigned to Laserplane Corporation. This

patent describes a method and apparatus for indicating effective digging depth of a backhoe in which a trigonometric equation is used to calculate the lowest point of the backhoe bucket from a knowledge of the length of the booms and a measurement of the relative boom angles. The relative boom angles are determined from transducers that produce electrical signals

proportional to the angular displacement of the transducer shaft relative to the body. In order to use such an arrangement the transducers must be

suitably mounted on a pivot axis of each boom. Such an arrangement is

difficult to realise in practice because of problems associated with mounting

the transducer. Furthermore, compounding inaccuracies in the transducers

result in unacceptable errors in the system.

An alternate arrangement of depth monitoring has been described by

Bachmann et al in United States patent number 4491927 assigned to The

Digger Meter Corporation. The Bachmann system utilises a pair of inclinometer sensors on the boom and dipper stick of a digging machine to

electrically measure the angle of inclination of these elements relative to the

horizontal and calculates the depth in similar manner to Laserplane. The

inclinometer sensors are pendulous mechanical devices that fail in the

rugged environment of a digging machine.

None of the known prior art systems provide slope information as well

as depth information. Furthermore, the known systems are insufficiently

robust to be reliable in rugged applications. OBJECT OF THE INVENTION It is an object of the present invention to provide a system of

instrumenting a multi-element boom to determine the depth and slope of an

end of the boom.

It is a further object of the invention to provide a robust system for

depth and slope monitoring of a multi-element boom.

It is a yet further object to provide the public with an economic

alternative to known depth monitoring systems.

Further objects will be evident from the following description.

DISCLOSURE OF THE INVENTION

In one form, although it need not be the only or indeed the broadest

form, the invention resides in a monitoring arrangement for a multi-element

boom comprising : an essentially fixed, reference inclinometer for providing a reference

signal;

a plurality of further inclinometers arranged one per boom element;

a processor means for calculating the position of an end of the multi¬

element boom using a trigonometric equation having as inputs the length of each boom element and processed signals from the inclinometers; and display means for displaying the position of the end of the multi¬

element boom.

In preference, the inclinometers are micromachined semiconductor accelerometers providing output signals proportional to the angle of the accelerometer from the horizontal. The accelerometers suitably provide an output signal proportional to the sine of the angle of the accelerometer from

the horizontal.

The reference inclinometer, processor means and display means may suitably be incorporated in a control unit.

In preference the display unit displays the position of the end of the multi-element boom in terms of displacement and slope.

The processor means suitably includes analogue to digital conversion

means for converting analogue signals from the accelerometers to digital

form suitable for processing in the processor means.

The monitoring arrangement for a multi-element boom may further comprise input means for setting a desired displacement and slope. An alert

means suitably alerts an operator when the set displacement and slope are

reached. The control unit may also include memory means associated with the

processor means. The memory means may store boom element length data

for a number of commercially available booms. The storage means may also

store calculated data from the processor means.

In a further form, the invention resides in a method of monitoring the

position of an end of a multi-element boom including the steps of :

positioning the end of the multi-element boom at a reference location

and recording a zero value; setting a desired displacement and slope; moving the multi-element boom; reading the output signals of inclinometers associated with each element of the multi-element boom;

determining in a processor means the displacement and slope of the

end of the multi-element boom by reference to the zero position; and

displaying the displacement and slope on a display means.

The step of determining the displacement and slope of the end of the

multi-element boom is suitably performed by reference to a look-up table.

Alternatively, the step may be performed by calculation of functions defining

a trigonometric relation between elements of the multi-element boom. In preference the method may further include the steps of :

setting a desired displacement and slope; and providing an alert if the displacement and slope equal or exceed the

set displacement and slope.

BRIEF DETAILS OF THE DRAWINGS

To assist in understanding the invention preferred embodiments will

now be described with reference to the following figures in which :

FIG 1 is a schematic of a typical digging machine fitted with the

monitoring arrangement; FIG 2 is a schematic of a sensor unit;

FIG 3 is a schematic of a control unit;

FIG 4 depicts the front of the control unit of FIG 3;

FIG 5 is a vector diagram of the digging machine of FIG 1 ; and

FIG 6 is a flowchart of the operation of the monitoring arrangement. DETAILED DESCRIPTION OF THE DRAWINGS In the drawings, like reference numerals refer to like parts.

Referring to FIG 1 , there is shown a schematic of a digging machine, generally indicated as 1. The digging machine is of the type having a body

2 movable across the ground on wheels 3. A multi-element boom 4 extends

from the body 2. In the embodiment shown the multi-element boom 4

consists of a near arm 5, far arm 6 and bucket 7.

The near arm 5 is pivotable with respect to the body 2 at pivot 8.

Similarly, the far arm 6 is pivotable with respect to the near arm 5 at pivot 9. The bucket 7 is pivotable with respect to the far arm 6 at pivot 10. It will be

appreciated that the digging machine described is just one version of a class of machines that employ multi-element booms. In fact, the invention can be

applied to any multi-element boom and is not restricted to digging

implementations, although it is envisaged by the inventor that this will be the

primary application.

Each element 5, 6, 7 has a respective sensor unit 11 , 12, 13 mounted

thereon. A fourth sensor unit 14 is mounted on the body 2 inside a control

unit 15 which is described in detail below.

Each sensor unit 11 , 12, 13, 14 has the same structure. Schematic

detail of sensor unit 11 is shown in FIG 2. Sensor unit 11 comprises an accelerometer 16 and conditioning element 17. The accelerometer 16 is a micromachined semiconductor device, such as Analog Devices ADXL05JH,

that provides an analogue output signal on signal line 18. The output signal

is proportional to the sine of the angle the accelerometer makes with horizontal. Signal line 18 carries the analog signal to the control unit 15 for

processing. The accelerometer is very robust and can withstand prolonged

vibration and intense mechanical shock.

The conditioning element 17 includes power supply regulation, DC

offset adjustment and a low pass filter to remove vibration effects. Power is

supplied to the conditioning element 17 on power line 19. The conditioning

element 17 ensures a stable voltage is supplied to the accelerometer 16 so

that an accurate signal is provided to the control unit 15 on signal line 18.

The control unit 15 is mounted on the body 2. In diggers having a

cabin 20, such as shown in FIG 1 , it is convenient to mount the control unit within the cabin. In any event, the control unit 15 is mounted so as to be

easily visible to the person operating the digger. Referring now to FIG 3, the

control unit 15 consists of a processor means 21 , such as a microcontroller,

a power supply 22, a display means 23, associated memory means 24 and

input means 25. As mentioned above, an accelerometer 14 is mounted in the

control unit 15 to provide an absolute reference point on the machine 1

which is independent of the slope of the ground or the inflation of the tyres.

An input means 25 is provided for the operator to interface with the control

means in the manner described below. A reset switch 26 may optionally be

provided.

The memory means 24 is used to store calculated data from the

processor means 21. It can also be used to store standard boom element

lengths for a number of commercially available multi-element booms. The monitoring arrangement can be easily installed on a multi-element boom by selecting the appropriate pre-stored setup information.

Cable 27 provides power to the accelerometers 11 , 12 ,13 and carries

signals from the accelerometers back to the processor means 21. The

processor means 21 includes a multiplexed analogue to digital converter that

converts the analogue signals from the accelerometers to digital signals able

to be processed by a microprocessor in the processor means.

A schematic of the front of the control unit 15 is shown in FIG 4. The display means 23 is a multi-element display providing a read-out of the

current depth and slope. The depth and slope are calculated from a

knowledge of the length of each boom element and the signals from each

accelerometer.

In operation, the digger is manoeuvred and the bucket is positioned

on the ground at the place digging is to commence. Power is applied to the

control unit by working switch 25a and the processor means 21 sequentially

steps through a set-up procedure. The position is zeroed by working the set switch 25b. The display then automatically steps to a depth selection mode.

The displayed depth is changed with change switch 25c. When the desired depth is displayed the set switch 25b is worked and the display steps to a

slope selection mode. The displayed slope is changed with change switch

25c until the desired inclination of, say, a trench is displayed. The set switch

25b is again worked and the control unit 15 enters an operation mode in

which the depth and slope is continuously displayed on the display 23.

A suitable alert can be displayed when the set position is reached. For instance, the display may flash or an audible alarm may sound. The calculations required for determining the depth and slope are

best described by reference to FIG 5 which provides a vector diagram of the

digger of FIG 1. It is conventional for angles below the horizontal to be

considered as positive and angles above the horizontal to be considered as

negative. The near arm 5 has a length of R₁ and makes an angle X with the

horizontal plane though pivot 8. The pivot 9 between the near arm 5 and the

far arm 6 is at a distance L, and a height H., from the pivot point 8 and are

calculated by :

H^ F^ Sin X L, = R, Cos X

The far arm 6 has a length of R₂ and makes an angle of Y with the

horizontal plane through pivot 9. The pivot 10 between far arm 6 and bucket

7 is at a distance L₂ and height H₂ from the pivot point 9 and are calculated by :

H₂ = R₂ Sin Y

L₂ = R₂ Cos Y

Similarly, the end of the bucket 7 can be calculated by :

H₃ = R₃ Sin Z L₃ = R₃ Cos Z

The end of the bucket can then be easily calculated as being at a

depth D and position P being :

D = H, + H₂ + H₃ P = L, + L₂ + L₃ The depth D is displayed at the control unit. The slope S is calculated

by S = P/D, and also displayed at the control unit. If desired the angle from

the pivot point 8 to the end of the bucket can be calculated as tan^"1S.

Although the above calculations can be made in the processor means

21 , the inventor has found that the use of a look-up table is preferable to

calculating the trigonometric functions. The look-up table is stored in

memory means 24 and is programmed for each specific machine to which

the monitoring arrangement is applied.

The use of a micromachined semiconductor device such as Analog

Devices ADXL05JH facilitates the use of look-up tables because the sine of

the angle is output directly. Since the lengths of each element of the multi¬

element boom are fixed and known a look-up table can be constructed that

is specific to the particular multi-element boom and provides the depth and

slope for each set of accelerometer readings. If other forms of inclinometer

are used it may be necessary to calculate the trigonometric functions in the

micro-controller thereby adding significantly to the computing power and

time required.

As mentioned above, the accelerometer 14 provides an absolute

reference. The reference signal R can be recorded and subtracted from the

signals X, Y and Z to compensate for minor movements of the digging machine 1 while digging. It will be appreciated that during the digging

process the digging machine will move slightly due to the load applied to the

boom. In particular, the pivot 8 may get lower as the digging machine 1 sinks

slightly into the ground. The reference signal R compensates for this lowering of the pivot point 8. Such compensation is not available in known prior art systems.

The flowchart of FIG 6 summarises the operation of the monitoring

arrangement for a multi-element boom. The unit is switched on by the switch 25a at the control unit 15. The display 23 of the control unit 15 shows the set

depth and the message, "C for change; S for set". If the displayed depth is

correct the operator presses the set button 25b, if not the depth is changed

until it is correct and the set button is pushed. The set slope is then

displayed and a similar procedure is followed to set the desired slope.

When the desired depth and slope have been set the monitoring arrangement is zeroed by placing the extremity of the multi-element boom

at a start point and setting the position as zero. The processor means 21 then loops through a programme to read each sensor in turn and calculate

the distance and height according to the method described above. When the

calculated depth and slope reach the set points an alarm sounds to alert the

operator of the multi-element boom. If the set slope and depth have not been

reached the programme loops through a further set of readings and

calculations.

Programming of set slope and depth information facilitates automatic

operation of the multi-element boom. The main purpose of an operator is to

ensure that the correct task is performed by, for example, the digger. The

monitoring arrangement can be interfaced with a control system to remove the necessity of the operator.

It will be appreciated that the monitoring arrangement for a multi- element boom has been described with reference to a digging machine for convenience and need not be limited in its application. Furthermore, the

accelerometers have been described as operating in one plane although

devices are available that provide signals indicative of movement in two or

even three planes. The monitoring arrangement can therefore be

implemented for determining the position of a multi-element boom in three

dimensions. For implementation in three dimensions it is necessary to make

two angle measurements using inclinometers as described. The

measurement of angle in the horizontal plane may conveniently be made

using, for example, a magnetic compass. As the look-up tables become more complex for the three dimensional case it is appropriate to calculate the trigonometric functions.

Throughout the specification the aim has been to describe the

preferred embodiments of the invention without limiting the invention to any

one embodiment or specific collection of features.

Claims

CLAIMS 1. A monitoring arrangement for a multi-element boom comprising :

an essentially fixed, reference inclinometer for providing a reference signal;

a plurality of further inclinometers arranged one per boom element;

a processor means for calculating the position of an end of the multi-element

boom using a trigonometric equation having as inputs the length of each

boom element and processed signals from the inclinometers; and

display means for displaying the position of the end of the multi-element boom.

2. The monitoring arrangement of claim 1 wherein the inclinometers are

micromachined semiconductor accelerometers providing output signals proportional to the angle of the accelerometer from the horizontal.

3. The monitoring arrangement of claim 2 wherein the accelerometers

provide an output signal proportional to the sine of the angle of the

accelerometer from the horizontal.

4. The monitoring arrangement of claim 1 wherein the reference

inclinometer, processor means and display means are incorporated in a control unit.

5. The monitoring arrangement of claim 1 wherein the display unit

displays the position of the end of the multi-element boom in terms of

displacement and slope.

6. The monitoring arrangement of claim 1 wherein the processor means includes analogue to digital conversion means for converting analogue

signals from the accelerometers to digital form suitable for processing in the processor means.

7. The monitoring arrangement of claim 1 further comprising input

means for setting a desired displacement and slope.

8. The monitoring arrangement of claim 7 further comprising an alert

means for alerting an operator when the set displacement and slope are reached.

9. The monitoring arrangement of claim 1 wherein the control unit further

includes a memory means associated with the processor means.

10. The monitoring arrangement of claim 9 wherein the memory means stores boom element length data for a number of commercially available booms.

11. The monitoring arrangement of claim 9 wherein the memory means

stores calculated data from the processor means.

12. The monitoring arrangement of claim 1 wherein the processor means

calculates the position of the end of the multi-element boom in three

dimensions using a trigonometric equation having as inputs the length of

each boom element and processed signals from the inclinometers, said

signals being proportional to an angle of the inclinometer from horizontal and an angle of rotation of the inclinometer.

13. A method of monitoring the position of an end of a multi-element

boom including the steps of :

positioning the end of the multi-element boom at a reference location and recording a zero value; setting a desired displacement and slope; moving the multi-element boom;

reading the output signals of inclinometers associated with each element of the multi-element boom;

determining in a processor means the displacement and slope of the end of

the multi-element boom by reference to the zero position; and

displaying the displacement and slope on a display means.

14. The method of claim 13 wherein the step of determining the

displacement and slope of the end of the multi-element boom is performed by reference to a look-up table.

15. The method of claim 13 wherein the step of determining the displacement and slope of the end of the multi-element boom is performed by calculation of functions defining a trigonometric relation between

elements of the multi-element boom.

16. The method of claim 13 further including the steps of :

setting a desired displacement and slope; and

providing an alert if the displacement and slope equal or exceed the set

displacement and slope.

17. A monitoring arrangement for a multi-element boom as herein described with reference to the drawings.