GB2350688A

GB2350688A - Weighing device for a refuse vehicle

Info

Publication number: GB2350688A
Application number: GB0012221A
Authority: GB
Inventors: Adair Egbert Avon Lloyd Taylor; James Matthew Henderson
Original assignee: Egbert H Taylor and Co Ltd
Current assignee: Egbert H Taylor and Co Ltd
Priority date: 1999-05-29
Filing date: 2000-05-19
Publication date: 2000-12-06
Anticipated expiration: 2020-05-19
Also published as: GB0012221D0; DE10026288A1; GB9912486D0; FR2794239A1; GB2350688B

Abstract

A weighing device comprises an arm (12) for lifting a load, and a sensor (16) in the arm on the neutral bending axis thereof. The sensor (16) is adapted to measure strain in the arm (12) and thus the load carried by the arm. The invention is particularly applicable to container lifting devices of refuse vehicles.

Description

1 2350688 WEIGHING DEVICE This invention relates to a weighing device, and

particularly though not exclusively to a weighing device for refuse containers.

Refuse is generally deposited in containers, and collected for disposal by refuse vehicles. Container size varies from about 140 litres for domestic use, to about 1200 litres for commercial use. Containers are typically lifted by the refuse vehicle and upended over the vehicle body for emptying, before being returned to ground level.

It has been proposed to charge consumers by the weight of refuse disposed. GB 2270170 discloses an example of a load cell mounted on the container lifting mechanism of a refuse vehicle. Such a load cell can weigh the full container as it is lifted from the ground, and the empty container as it is returned to the ground. A simple mathematical subtraction indicates the weight of refuse emptied from the container, and in conjunction with a bin identification system enables an individual charge to be generated for the consumer.

Existing load cell systems have several disadvantages. In particular, a means of compensating for the moment applied by the container to the lifting arms is necessary. This is because the distance from the lifting arms to the centre of gravity of the container may vary, usually due to a variation in bin type or non-uniform weight distribution of refuse within the container. Typically existing systems are truly accurate to about 10 kg. This is wholly unsuitable for light domestic refuse. A system accurate to 1 kg or better is necessary.

Since many types of container are in general use. it may be found that individual weighing is not possible, or is not accurate for certain container types. Furthermore, many different kinds of bin lifting mechanisms are in use. These generally require specialised modification to accommodate a load cell, and this can be rather expensive. An additional difficulty is that few vehicle fleets consist of one kind of vehicle/lifting 2 mechanism, and accordingly use of a common type of weighing device is often precluded.

What is required is a weighing device that can be adapted to almost all kinds of refuse vehicle and lifting mechanism, is relatively easy to fit using non- specialised techniques, is inexpensive, and is not affected by the kind of refuse container being emptied, or the attitude of the vehicle (whether the vehicle is tilted on the road).

According to a first aspect of the invention there is provided a weighing device comprising an arm for raising a load and a sensor on the arm for sensing shear force in the arm as the load is lifted, the sensor being positioned substantially on a neutral bending axis of the arm.

By positioning the sensor on the neutral axis of the arm, tensile or compressive loads 15 generated in the arm as the load is lifted will not have a significant effect on the shear force sensed by the sensor.

Preferably, the sensor is located in a hole formed in the arm. The hole can easily be drilled in a lifting arm of an existing refuse bin emptying mechanism on a refuse vehicle making it possible to retrofit the sensor. The sensor is preferably an interference fit in the hole, although a form-locking arrangement is also possible.

The sensor is preferably arranged in a circuit for sampling the output of the sensor and for calculating the load being lifted by the arm. The circuit may be arranged to sample the output at a given position or at given positions of the arm. The sensor may take the form of a strain gauge.

Typically a container lift mechanism comprises two spaced arms extending from the rear of a refuse vehicle, and onto which the container is latched. In such a case, each arm may have a sensor thereon and the outputs of the sensor may be averaged or summed in the circuit to provide an accurate calculation of the load.

3 Preferably the weight of the container is zeroed on the upstroke, the negative value on the downstroke immediately indicating the loss of weight and hence contents discharged.

A typical lifting arm consists of a tube of square or rectangular section. The sensor may be fitted in one side of the tube, but in a preferable arrangement a hole is formed through the beam on the neutral bending axis so as to pass through opposite walls of the tube. A sensor may be fitted in each opposite side wall so as to eliminate torsional loads on the arm. For example the sensor outputs may be summed, and if torsion is present, the lower strain at one side of the arm will be countered by the higher strain at the other side. Thus the torsion error may be eliminated.

According to a second aspect of the invention there is provided a refuse vehicle having a container-lifting linkage thereon, the linkage incorporating a weighing device according to the first aspect of the invention or any of the consistory clauses relating thereto. The arm may comprise a container-lifting arm of the linkage.

According to a third aspect of the present invention there is provided a method of fitting a strain gauge to a lifting arm of a refuse vehicle, the method comprising the steps of determining the neutral bending axis of the lifting arm; fonning a hole in the lifting arm substantially on the neutral bending axis; and fitting a strain gauge to the hole, wherein the strain gauge is adapted to sense shear stress in the arm. Preferably the strain gauge is fitted as a push or interference fit which is sufficiently close to ensure effective transmission of lifting forces from the arm to the strain gauge.

Such a method is a convenient and inexpensive way of fitting a load sensor to a wide 3 )0 range of lifting arms of refuse vehicles.

4 Where the arm is a hollow beam, the method preferably includes the step of forming a hole through the beam, and fitting a strain gauge from the exterior into both sides of the beam.

According to a fourth aspect of the present invention there is provided a method of weighing refuse contained in a container lifted by a lifting arm of a refuse vehicle, the method comprising the steps of.

providing a sensor on the neutral axis of the lifting arm, the sensor being adapted to sense shear stress in the lifting arm; lifting a container containing refuse with the lifting arm; obtaining a first reading from the sensor on upward movement of the lifting arm; obtaining a second reading from the sensor on downward movement of the lifting arm; and comparing the second reading and the first reading to obtain a value indicative of the weight of refuse in the container.

The first and second readings may be taken at the same position. The value may be determined from continuous monitoring of the output of the sensor. Spaced strain gauges may be provided on either side of the neutral axis of a hollow beam and the outputs of the gauges summed; this arrangement eliminates the effect of torsion on the beam.

Other features of the invention will be apparent from the following description of a preferred embodiment shown by way of example only, in which:

Fig. 1 illustrates in schematic elevation, the rear side of a refuse vehicle, lifting mechanism and refuse container; and Fig.2 illustrates a schematic installation of a shear stress sensor according to the invention.

Figure 1 illustrates the rear part of a typical refuse vehicle 10 having the usual box like body 11 adapted to receive refuse through an opening at the upper rear edge thereof A linkage 12 is operable under the action of telescopic rams (not shown) to raise a refuse container 13 from the ground. At an appropriate height, a secondary mechanism (not shown) rotates the container until it is upended over the refuse opening, whereupon the container contents fall into the body 11. The container is then pivoted back to the upright condition, and lowered to the ground.

Various mechanisms for gripping the container 13 are known, and the linkage 12 can have a wide variety of configurations. However at least one pivoting arm is usually provided to lift the container from the ground.

Pivoting arms may be arranged in horizontal pairs across the rear of the refuse vehicle to permit two or more small containers to be lifted independently. These independent lifting arms can usually be coupled to permit one large container to be lifted.

Figure 2 illustrates a transverse section through a typical pivoting arm 12, in this case a generally square section hollow steel tube. The tube has a neutral bending axis 14 approximately coincident with the middle of the beam, and about which the beam is neither in tension nor in compression. As is well understood, in practice, the upper side of the beam is in tension whereas the lower side is in compression, but on the neutral axis neither positive nor negative tensile stresses are experienced. The exact position of the neutral axis can be determined using well known empirical techniques.

The arm 12 has a hole 15 drilled into one side thereof. on the neutral axis. and a cylindrical strain gauge 16 is pressed into the hole as an interference fit. The strain gauge is shown somewhat enlarged for reasons of clarity. A degree of interference is necessary in order for the strain gauge to experience shear stresses imposed on the arm 12, but the interference should not be so great as to require excessive fitting force. A suitable interference fit is for example H7 on the standard scale.

The strain gauge 16 is coupled by a lead 17 to an electronic display and recording device 18 of any suitable kind.

6 A strain gauge suitable for pressing into the hole 15 is described in GB 2305729A, but other constructions of strain gauge are possible.

By fitting the strain gauge on the neutral axis of the lifting arm 12, tension and compression effects can be minimised or even eliminated. The beam shear stress thus measured can be truly representative of the load carried by the arm 12.

The strain gauge may be retained in the arm by the interference fit, but is alternatively retained by some other means, such as epoxy cement 19 in order to separate measuring and retention functions.

In use the strain gauge is calibrated after fitting using known weights. Typically the shear stress in the lifting arm 12 will be recorded at a predetermined lift angle, for example when the arm is horizontal, both on the up and down stroke. This may be initiated by e.g. a reed switch or inclinometer. Alternatively, electronic sampling techniques may continuously monitor the output of the strain gauge in order to calculate the load imposed by a container.

Where arms are provided side by side to operate in pairs, two strain gauges may be provided, one in each arm. The output of such gauges may be surnmed or averaged in any known manner in order to determine container load.

The advantage of the present invention is that the strain gauge can be easily retrofitted at low cost and minimal inconvenience to any refuse vehicle having a lifting mechanism incorporating a pivoting arm. Many types and configurations of arms are known, but the invention is readily adaptable to them all. All that is required is the drilling of a small hole on the neutral axis, which is a very low stress area in any event. A fleet of refuse vehicles of different types can be retrofitted with the same weight sensor and thus operators need not become familiar with several kinds of sensing equipment. Furthermore, the sensor is easily replaced should a malfunction occur.

7 The location of the sensor is not susceptible to contact damage, and the recording device can be located in any suitable place, or even in the vehicle cab. A printer may be provided for instant generation of bills. The lead 17 can be secured by cable ties in any suitable place.

Each refuse container may be fitted with a unique indentifier to permit automatic generation of bills. A container identification device may be fitted to the rear of the refuse vehicle, this device recognising and logging the identity of a container by means of a passive indentifier on the container. This identifier may be a bar code, an electrical device activated by radio emissions from a transponder, or some other suitable device. The container or address may of course be logged manually, for example via a keyboard.

A container identification system may also enable the weighing system logic to identify whether one large container, or two small containers are being lifted. Such a dual lift capability is common. In the latter case the containers will be separately logged and weighed, whereas in the former case the load indicated by the sensors will be summed.

As will be apparent from Fig.2, the hole 15 may be easily drilled entirely through the arm 12 by simply extending the stroke of the drill. Another sensor may easily be fitted in this additional hole, and by summing the outputs of the sensors, torsional effects on the arm, in the direction indicated by arrow 21, may be eliminated. Such an arrangement is particularly advantageous in cases where offset or unbalanced containers are to be expected.

The invention is especially useful because it can be fitted to any reasonably accessible part of the arm 12. Furthermore, the fitter may be provided with a jig to suit the relevant arm so that the hole is drilled precisely on the neutral axis. A reamer may be used to accurately finish the hole to the precisely required size so as to achieve the desired interference fit of the sensor.

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Claims

1. A weighing device comprising an arm (12) for raising a load and a sensor (16) on the arm (12) for sensing shear force in the arm as the load is lifted, the sensor (12) being positioned substantially on a neutral bending axis of the arm (12).

2. A device according to claim I wherein the sensor (16) is located in a hole (15) formed in the arm (12).

3. A device according to claim 2 wherein the sensor (16) is an interference fit in the hole (15).

4. A device according to claim 3 wherein said sensor (16) is retained in said hole (15) by a form locking shape.

5. A device according to any of claims 2-4 wherein said hole (15) is a through hole.

6. A device according to claim 5 wherein said arm (12) is tubular.

7. A device according to claim 5 or claim 6 wherein a sensor (16) is provided in each end of said hole (15).

8. A device according to any preceding claim wherein said sensor is a strain gauge.

9. A refuse vehicle having a container-lifting linkage thereon, the linkage incorporating a weighing device according to any preceding claim.

10. A vehicle according to claim 9 wherein said arm (12) comprises a container-lifting arm of the linkage.

11. A vehicle according to claim 9'or claim 10 and further including means responsive to said sensor (16) to determine the load on said arm (12).

12. A method of fitting a strain gauge to a lifting arm of a refuse vehicle, the method comprising the steps of deten-nining the neutral bending axis of the lifting arm; forming a hole in the lifting arm substantially on the neutral bending axis; and fitting a strain gauge to the hole with a push or interference fit sufficiently close to ensure effective transmission of lifting forces from the arm to the strain gauge.

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13. The method of claim 12 wherein the hole is a through hole and a strain gauge is fitted from the exterior into both ends of said hole.

14. A method of weighing refuse contained in a container lifted by a lifting arm of a refuse vehicle, the method comprising the steps of.

15. A method according to claim 14 wherein the first and second readings are taken at the same position of said arm.

16. A method according to claim 14 wherein said sensor is monitored continuously during upward and downward movement of said arm.

17. A method according to any of claims 1416 wherein said lifting beam is provided with sensors on either side thereof, the outputs of the sensor being summed to 20 determine the weight of refuse in said container.