GB2187708A

GB2187708A - An apparatus for monitoring the forces acting during operation on a working cage

Info

Publication number: GB2187708A
Application number: GB08705589A
Authority: GB
Inventors: Rudiger Keuper; Hans Bronk
Original assignee: Pietzsch Ludwig & Co GmbH
Current assignee: Pietzsch Ludwig & Co GmbH
Priority date: 1986-03-14
Filing date: 1987-03-10
Publication date: 1987-09-16
Also published as: DE3608628A1; DE3608628C2; GB8705589D0; GB2187708B

Abstract

An apparatus for monitoring the forces acting in operation on a working cage (30) held by a carrying structure (1) at the head (15) of a cantilever comprises a supporting structure (2) which comprises a horizontal guide rod (3), a tie rod (6) parallel to the same, and a cross girder arranged between these members and into which a force measuring device (12) is incorporated. In view of the fact that the force acting in the cross girder depends exclusively on the magnitude of the load in the working cage rather than on the point of application thereof at the working cage (30), force measurement without any moments is warranted. This guarantees that the assembly composed of the cantilever and working cage is monitored reliably against any overloading or tilting. <IMAGE>

Description

SPECIFICATION An apparatus for monitoring the forces acting during operation on a working cage The invention relates to an apparatus for monitoring the loads acting during operation on a working cage held atthe head of a cantilever by means of a carrying structure.

Such a working cage usually is mounted at the end of a telescope-type cantilever such that it will always be held in horizontal position, regardless ofthe angular position of the cantilever. The cantilever in turn is mounted on a vehicle so as to be pivotable azimuthallyand in elevation.

To guarantee safe operation, care must betaken that the loading of the working cage will remain below a limit load which varies in response to the angular position and length of the cantilever.

It is the object ofthe invention to provide an apparatus of the kind specified initially which will warrant that the assembly composed ofthe working cage and the cantilever is monitored reliably.

To meetthis object it is provided, in accordance with the invention, thatthe working cage is supported at the carrying structure by a supporting structure which comprises a guide rod which is pivotably connected to the working cage and the carrying structure, a tie rod which is spaced vertically from the guide rod between the working cage and the carrying structure, and a cross girder which is disposed between the guide rod and the tie rod and pivotably connected to the same, and that a force measuring device is provided to measuretheforce acting in the cross girder.

Advantageously, the tie rod is rigidly connected to the working cage and comprises a supporting roller at its free end for supportwith little friction on the carrying structure.

Butting surfaces may be provided at the carrying structure and preferably be adjustable so asto contain the tie rod at the carrying structure as the working cage is eased or set down.

The force measuring device conveniently is a tension measuring linkto which strain gauges are attached, as known for exarnple from DE-PS 2618 359.

In the apparatus of the invention a pure tensile force always acts in the tie rod and this force is proportional to the loading of the working cage, regardless ofthe position ofthe load in the working cage. For this reason the force caused by the loaded working cage in vertical direction always can be determined clearly by the apparatus according to the invention. In further modification of the apparatus according to the invention the force thus measured is compared in a comparator with a memorised reference force determined on the basis ofthe admissible carrying capacity curves. If this reference force is exceeded by the force measured, an alaram or switch-off signal is released.

The mere force measurement free of any moments by means of the apparatus according to the invention as described, therefore, permitsthesafe and reliable monitoring of the machine during any operating condition. Specifically avoided is any tilting of the assembly comprising the working cage and the cantilever because of any displacement of the load on the working piatform without a change of the angular position and length of the cantilever.

The invention will be described further, by way of example, with reference to the accompanying drawings, in which: Figure lisa side elevation of an apparatus according to the invention; Figure2 is a diagrammatic illustration oftheforces acting in operation on the apparatus shown in figure 1; Figure3shows a modification of a detail offigure 1; and Figure 4 is a circuit diagram of an apparatus according to the invention.

In the embodiment ofthe invention shown in figure 1 the tip 15 ofthe cantilever of a telescope-type cantilever is connected by a swivel joint 16 and an intermediate flange 17 to a rotary cylinder 18 on which a carrying structure 1, including arms 19 and a carrier plate 20 is supported for pivoting about a vertical axis 21.

The carrying structure 1 is connected by a supporting structure, designated in general by reference numeral 2, to a support plate 22 for a working cage 30, which support plate extends parallel to the carrier plate 20.

The supporting structure comprises a pair of horizontal guide rods 3 (only one guide rod 3 is to be seen in the presentation of figure 1) and, belowthe same, at least one tie rod 6 which extends parallel to the guide rod 3 and is welded to the support plate 22.

At its free end the tie rod carries a supporting roller 7 for support on the carrier plate 20. The guide rod 3 is connected by a joint 4to the carrier plate 20 and by a joint 5 to the support plate 22.

Across girder 10, 11,12 is arranged between the guide rod 3 and the tie rod 6. It is composed of forks 10 and 11 each welded to the guide rod 3 and the tie rod 6, respectively, and of a tension measuring link 12 which is articulated between the forks. The tension measuring link is ofthe design described in detail in German patent 26 18359. The tensile force is measured and transformed into a voltage by means of strain gauges (not shown ) which are mounted in a central bore of the tension measuring link so as to be protected from outside influences ofthe surroundings. Acable 24 supplies powertothe tension measuring link 12 and also transmits the electrical voltage output signal from the tension measuring link 12to the outside.

When the working cage 30 is loaded, the supporting roller 7 rests on the right end surface of the carrier plate 20, as shown in figure 1. In the case of the embodiment according to figure 1,supporting surfaces 8 and 9 are connected firmly to the carrier plate 20 to fix the supporting roller 7 and thusthetie rod 6 to the carrier plate 20 when the working cage 30 is eased or set down.

Figure 3 shows a preferred embodiment ofthis arrangement. Reference numeral 25 designates a support surface of hard, wear-resistant metal mounted on the carrier plate 20 for support ofthe supporting roller 7. The surfaces 8 and 9 are adjustable in the direction of the tie rod 6 and transversely ofthe same by means of screw-connectable stops 26,27.

Figure 2 shows the relationships offorces ofthe apparatus according to figure 1. In the area ofthe working cage a constant weight FG acts in the centre of gravity ofthe working cage. This force FG is superposed in operation by vertical forces (not shown) which may be applied by persons or loads in the range 1 R. A pu re tensi le force FM is effective in the tension measuring link 12 symbolized in figure 2 buy a tie rod, and this tensile force is independent ofthe points of application of force exerted by the vertical weights in the range of the working cage 30.

A horizontal force and a vertical force Ay act at the point of joint 4, whereas a pure horizontal force B, in a direction normal to the supporting surface atthe carrier plate 20, acts on the supporting roller 7 in the point of support.

It may be seen that, by varying the distances a, b, the transmission ratio may be varied between the overall weight applied in the range of the working cage 30 and the tensile force FM acting in the cross girder 12: the force FM which is effective in the cross girder 12 rises as the distance a becomes greater and the distance b becomes smaller. In this manner a desired sensitivity of the measurement of thetensile force in the cross girder 12 may be realised bythe appropriate selection of a and b.

Figure 2 makes it clearthat the force FM measured always is proportional to the resultant of all weights in the range oftheworking cage, regardless oftheir points of application. In other words, the arrangement described makes it possible to obtain a measurement which is free of any moments of the vertical forces.

Such measurement is advantageous as compared to a measurementwhich depends on moments because in that case any displacement of the load in the area of the working cage 30 may lead to an increase ofthe actual vaiue and thus to the surpassing of the reference value because of the increase ofthe lever arm involved, without a change having taken place in the magnitude of the load and the angular position and/or length ofthe cantilever.

Figure4isacircuitdiagram showing the processing of force measurement signals obtained by an apparatus according to figure 1. Block 12 represents the tension measuring link 12 of figure 1.

The voltage output signal u is amplified to a value U in an amplifier31 and compared in a comparator 32 with a reference value S. If the amplified actual value U is smaller than the reference value S, a green lamp 33 is actuated and operation is permitted by a switch element 34. If, on the other hand, the amplified actual value U reaches or exceeds the reference value S, a red lamp 35 is released and operation is switched off bya switch element 36.

Claims

1. An apparatus for monitoring the loads acting during operation on a working cage held by a carrying structure at the head of a cantilever, characterized inthattheworking cage (30) is supported at the carrying structure (1) by a supporting structure (2) which comprises a guide rod (3) which is pivotablyconnectedtotheworking cage (30) and the carrying structure (1), a tie rod (6) which is spaced vertically from the guide rod between the working cage (30) and the carrying structure (1), and a cross girder (10,11,12) which is disposed between the guide rod (3) and the tie rod (6) and pivotably connected to the same, and in that a force measuring device (12) is provided to measure the force which is effective in the cross girder (10,11,12).

2. The apparatus as claimed in claim 1, characterized in thatthetie rod (6) is rigidly connected to the working cage (30) and comprises a supporting roller (7) at its free end for supportwith little friction on the carrying structure (1).

3. The apparatus as claimed in claim 2, characterized in that butting surfaces (8,9) are provided to fix the tie rod (6) atthecarrying structure (1) as the working cage (30) is set down.

4. The apparatus as claimed in claim 3, characterized in that the butting surfaces (8,9) are adjustable.

5. The apparatus as claimed in one of claims 1 to 4, characterized in that the force measuring device is a tension measuring link (12) to which strain gauges are attached.

6. The apparatus as claimed in one of claims 1 to 5, characterised in thattheforce measured bythe force measuring device (12) is compared in a comparator with a reference force memorised, and in that an alarm or switch-off signal is released if this reference force is exceeded.

7. Apparatus for monitoring the loads acting during operation on a working cage constructed and arranged substantially as herein specifically described with reference to and as shown in the accompanying drawings.