WO1994013892A1

WO1994013892A1 - Gas/liquid accumulator for a level difference measuring apparatus and apparatus for level difference measurement

Info

Publication number: WO1994013892A1
Application number: PCT/FI1993/000525
Authority: WO
Inventors: Marko Nuotio
Original assignee: Marko Nuotio
Priority date: 1992-12-07
Filing date: 1993-12-03
Publication date: 1994-06-23
Also published as: AU5468094A; FI626U1; FIU920716U0

Abstract

A gas/liquid accumulator (8) for a level difference measuring apparatus based on the measurement of the hydrostatic head of a liquid column and particularly intended for use in a piece of construction equipment, said equipment having its boom system (2, 4) equipped with a liquid-filled hose (14) extended between a point (6) separate from the boom of the equipment and the pivotal fastening joint of said attachment, one end of said hose being provided with a transducer (5) capable of measuring the hydrostatic pressure prevailing in said liquid-filled hose (14). The gas/liquid accumulator comprises a liquid compartment (9) communicating with said hose (14) and a gas compartment (10), said compartments (9, 10) being separated from each other by means of a resilient diaphragm (8c). The invention also relates to a level difference measuring apparatus utilizing said gas/liquid accumulator (8).

Description

Gas/liquid accumulator for a level difference measuring apparatus and apparatus for level difference measurement

The invention relates to a pressurized gas/liquid accumu- lator for buffering the fluid of the measurement circuit of a level-difference-measuring apparatus based on hydro¬ static head pressure measurement for use in construction equipment, particularly land excavators, underwater exca¬ vators and similar equipment, and to an apparatus for level difference measurement.

When using land excavators, underwater excavators and similar construction equipment, level measurement is con¬ ventionally performed by measuring the relative level with regard to a known reference level. Measurement of excavation level by conventional methods requires, besides the equipment operator, two additional workers with the task to perform the actual measurement at the site to be surveyed. The surveyed object is most fre- quently the base level of an excavation generally located below one of the excavator's working platforms, typically the ground level, while such measured level can also be situated above the working platform of the construction equipment. Using such a method, the level measurement is performed after the desired grading level is assumed to have been attained. One of the measuring personnel has to take into the excavation, or other site to be surveyed, a level marker stake to which a horizontally aligned, pre- marked level tag is fixed. Using a proper means, the second persons verifies that the stake is driven into the ground so that the level tag becomes to the same level with the corresponding tags of the other stakes driven to the ground. This procedure makes it possible to estimate the amount of corrective grading required to a desired result. Concurrently, multiple different technical means are known suited to implement the surveying measurement. Level-difference-measuring apparatuses applicable to construction machines such as excavators are based on either a combination measurement by means of one or multiple angular transducers and the hydrostatic head of a liquid column, by means of angular transducers alone or using measurement equipment which employ a laser beam to generate the reference plane. All these means measure the relative level with regard to a certain reference level.

Measurement systems based on an angular transducer and head measurement of a liquid column are generally implemented by placing the pressure transducer measuring the head of the liquid column as well as the angular transducer to the excavator shovel arm, to a certain distance from the pivot points of the arm. The liquid reservoir belonging to the system is correspondingly placed in the superstructure of the excavator, above the center of rotation of the excavator superstructure. Such a system is then arranged to compute the level difference to be measured from the indicated inclination of the shovel arm and head of the liquid column.

Systems based on angular transducers alone comprise, e.g., three separate angular transducers, one of which is placed in the excavator superstructure, the second to the main boom and the third to a suitable location on the shovel arm. The level different to be measured can then be computed from the angles of attitude indicated at these three locations.

Sites measured by means of a laser beam require a separate planar-radiating laser device, which can be located at the construction site, close to the working area. The laser beam then acts as the reference plane for the measurement. A detector, that is, a beam sensor and a device capable of indicating the relative level differ¬ ence are located aboard the construction equipment.

All such systems have a relatively complicated construc- tion and their mounting aboard construction equipment is cumbersome, because rigid mounting bases must be welded for, e.g., the angular transducers and also the vulner¬ able location of the pressure transducer necessitates its protection against heavy impact. Systems based on angular transducers alone or a combination of one or more angular transducers and head measurement of a liquid column for determining the level difference must always be calibrat¬ ed during their installation aboard the construction equipment.

Systems based on the use of a laser beam have the draw¬ back that the laser device with a dedicated power supply must be separately brought close to the site of measure¬ ment.

Furthermore, all these systems have the disadvantage that cabling to the transducers must be arranged on the moving main boom and shovel arm, which are suspect to dirt accumulation and frequent blows. Consequently, the system has a high probability of malfunction. Damage to the cable of a single angular transducer or a weak connection between the transducer and its cable makes the system give incorrect level difference information. Due to the complexity of conventional level measurement systems, their price tends to become quite high, which combined with their unreliable function has prevented a wider acceptance of these inherently necessary accessories.

It is an object of the present invention to achieve an apparatus capable of overcoming the drawbacks of prior- art techniques . The characterizing properties of the invention are disclosed in the annexed claims .

The implementation according to the invention offers a simpler construction and is thus appreciably more cost- effective to produce, more reliable in use and more straightforward to install than prior art systems. The installation work is also simplified therein that the present system need not be calibrated during its in- stallation, but rather, such calibration can be carried out while detached. Further, once calibrated the system can be transferred from one piece of equipment to another without the need for recalibration.

In the following the invention is examined by way of an advantageous exemplifying embodiment with reference to the annexed drawings in which

Fig. 1 shows an apparatus according to the invention installed on a piece of construction equipment,

Fig. 2 shows a sectional view of a gas/liquid accumula¬ tor for an apparatus according to the invention.

With reference to Fig. 1, a piece of construction equip¬ ment such as particularly an excavator with a wheeled undercarriage 15 is shown. The undercarriage 15 is adapted to support a frame (a superstructure) 16 of the excavator pivotally rotatable about a vertical shaft 6. An articulated boom system 2, 4 with pivotal joints is arranged in a conventional manner to the superstructure 16 of the excavator. The most distal section (shovel arm) 2 of the articulated boom system, at its distal end, carries a pivotally fastened shovel 3. The shovel is pivotally fastened to the arm by means of a pivot pin 1. The articulated boom system is movable in a conventional manner with the help of hydraulic cylinders 17, 18, 19. The excavator incorporates an apparatus for measuring level differences. Such an apparatus comprises a liquid- filled hose 14, which is mounted on the articulated boom system 2, 4 and the excavator superstructure 16. The hose end at the excavator superstructure side is provided with a pressure transducer 5, which is preferably located at the vertical axis 6 of the superstructure center of rotation. The other end of the hose 14 is connected to a pressurized gas/liquid accumulator 8. The gas/liquid accumulator 8 is advantageously adapted to within the pivot pin 1, which connects the main boom 2 to the shovel 3, or at least close to the pin. A central control unit 7 of the measurement system and a display unit 20 thereof are located in the cabin of the excavator.

With reference to Fig. 2, the construction of the gas/liquid accumulator 8 and for greater clarity a part of the pivot pin 1 are shown in a sectional view. The gas/liquid accumulator comprises a liquid compartment 9 and a gas compartment 10, separated from each other by a resilient diaphragm 8c. The liquid compartment 9 is connected to the liquid hose 14, advantageously via coupling elements 21, 22. The gas compartment 10 is pressurizable and sealable by means of a valve element 12. The gas/liquid accumulator 8 is advantageously comprised of three parts 8a, 8b, 8c, which are connected to each other by virtue of a suitable conventional manner.

The gas/liquid accumulator 8 according to the invention is characterized in that the physical dimensions of the liquid compartment 9 and the gas compartment 10 in the direction of the resilient diaphragm 8c are essentially greater than in a direction perpendicular to said resi- lient diaphragm. The gas compartment 10, which serves for the pressurization of the liquid compartment 9 to a pressure essentially above the ambient pressure, has a multiple volume compared with the volume of the liquid compartment 9. The liquid hose 14, which preferably is made of a high-pressure hose, is continued within the gas/liquid accumulator as a liquid channel 11, which exits into the liquid compartment 9 at a point which is essentially located on an axis aligned orthogonal to the surface of the resilient diaphragm 8c at the diaphragm center point. This arrangement avoids measurement errors that could be caused by the rotation of the gas/liquid accumulator 8 about said center axis aligned orthogonal to the surface of the resilient diaphragm and passing through the diaphragm center point.

The small volume of the liquid compartment 9 and the large area of the resilient diaphragm 8c are advantageous to the function of the apparatus, because such an ar¬ rangement reduces the movement of the resilient diaphragm 8c caused by thermal expansion to a very low value, which is advantageous to the behaviour of the volume of the gas compartment 10, since pressure changes are kept small by this arrangement. Small displacement of the resilient diaphragm 8c is also advantageous in the sense that thus the actual elastic behaviour of the resilient diaphragm 8c need not fulfill any strict requirements.

As the end of the pivot pin 1 of the attachment 3 in construction equipment conventionally forms an outward projection, the end of the gas/liquid accumulator 8 of the apparatus according to the invention is designed to incorporate a recess 13, whose shape is compatible with the end of the pivot pin. Thus, the gas/liquid accumu¬ lator 8 can be mounted very close to the wall of the boom 2. This arrangement makes the additional projection at the pivot pin 1 on the wall of the boom 2 insignificant to the operation of the equipment. The recess 13 can be shaped to be compatible with the requirements of the mounting point, or even omitted if, e.g., the pivot pin end is not of an outward projecting type, or for any other similar reason.

The minimal significance of the extra outward projection caused by the gas/liquid accumulator is further greatly accentuated by the fact that a wide variety of construc¬ tion equipment are in use today based on fastening of attachments by means of quick-connects. In these cases, merely the projection of the quick-connect assembly from the boom wall generally is appreciably larger than that caused by the gas/liquid accumulator 8 according to the invention.

The fastening arrangement of the gas/liquid accumulator 8 according to the invention is implemented in any conventional manner so that rapid detachment or sideways rotation of the accumulator is facilitated to aid the removal of the pivot pin 1. Further, a separate storage space can be adapted to the boom 2 of the construction equipment, close to the pivot pin 1, suited to accommo¬ date the accumulator 8 when detached. In some types of construction equipment the gas/liquid accumulator can be installed permanently. Such a case is, e.g., a boom of relatively large width made from two parallel beams, whereby the accumulator can be installed coaxially with the axis of the pivot pin in the center of the forked structure without forming any obstacle, because in such cases two short pivot pins are conventionally employed.

The gas/liquid accumulator can be fabricated as an integral part of the pivot pin 1 or other type of joint particularly when the attachments 3 used are known be provided with quick-connects only. Thus a pressurized gas/liquid accumulator 8 could be located entirely to within the pivotal joint 1, which connects the arm of the boom 2 of the construction equipment to the attachment 3 , so that the center point of the resilient diaphragm 8c is located on the axis passing through the center of rota¬ tion of the joint.

Pressurization of the system according to the invention can also be implemented by means of an entirely or par¬ tially separate gas compartment or even using a pressur¬ izing medium other than a gas. The separate gas compart¬ ment and the apparatus according to the invention could in this case be placed, e.g., to the interior of the arm of the boom 2. Then, the separate gas compartment and the apparatus according to the invention are advantageously connected to each other by means of a hose. By this arrangement, the apparatus according to the invention could be designed with a yet slimmer shape.

The gas/liquid accumulator 8 of the apparatus according to the invention can also be mounted so that the part 8c would abut the end of the pivot pin 1 of the attachment 3, while the part 8a would correspondingly remain as the outer part. Using this arrangement, the liquid channel 11 communicating with the liquid compartment 9 could be omitted and the liquid hose 14 of the level measurement circuit could be connected to the liquid compartment 9 through the wall of the part 8a at an axis, which is aligned orthogonal to the surface of the resilient dia¬ phragm 8c and passing through the diaphragm center point. However, the width of the gas/liquid accumulator 8 becomes herewith larger by the length of the hose connec¬ tion, thus increasing the risk of mechanical damage.

For those versed in the art it is obvious that the inven¬ tion is not limited to the exemplifying embodiment described above, but rather, can be varied within the scope of the annexed claims .

Claims

1. A gas/liquid accumulator (8) for a level difference measuring apparatus based on the measurement of the hydrostatic head of a liquid column and particularly intended for use in a piece of construction equipment, said equipment having its boom system (2, 4) equipped with a liquid-filled hose (14) extended between a point (6) separate from the boom of the equipment and the pivo- tal fastening joint (1) of said attachment, one end of said hose being provided with a transducer (5) capable of measuring the hydrostatic pressure prevailing in said liquid-filled hose (14) , c h a r a c t e r i z e d in that the gas/liquid accumulator comprises a liquid com- partment (9) communicating with said hose (14) and a gas compartment (10) , said compartments (9, 10) being separ¬ ated from each other by means of a resilient diaphragm (8c) .

2. A gas/liquid accumulator as defined in claim 1, c h a r a c t e r i z e d in that the physical dimensions of said liquid compartment (9) and said gas compartment (10) in the tangential direction of said resilient diaphragm (8c) are essentially larger than in the orthogonal direction to said diaphragm.

3. A gas/liquid accumulator as defined in claim 1 or 2 , c h a r a c t e r i z e d in that the volume of said gas compartment (10) employed for pressurizing said liquid compartment (9) to a pressure essentially above the ambient pressure is larger by a multiple to the volume of said liquid compartment (9) .

4. A gas/liquid accumulator as defined in any foregoing claim 1 - 3, c h a r a c t e r i z e d in that a liquid channel (11) acting as an extension of said hose (14) of said level measurement circuit exits into said liquid compartment (9) along an axis aligned orthogonal to the surface of the resilient diaphragm (8c) and passing through the diaphragm center point.

5. An apparatus for measuring level difference, said apparatus being particularly suited for use in a piece of construction equipment equipped with at least one articulated boom (2, 4) or similar extension, to which boom (2) is pivotally fastened an attachment (3), said measurement apparatus comprising a liquid-filled hose

(14) or equivalent element which is adapted in conjunc¬ tion with said articulated boom (2, 4) and is extended in the equipment between a point (6) separate from the boom and the pivotal fastening point (1) of said attachment and has one end of said hose (14) provided with a trans¬ ducer (5) capable of measuring the hydrostatic pressure prevailing in said liquid-filled hose, and a data pro¬ cessing unit (7) to which said transducer is connected, and a display unit (20), c h a r a c t e r i z e d in that the pressure-measuring transducer (5) is adapted to that end of the hose (14) which is separate from the boom (4) and that the other end of the hose (14) is connected to a gas/liquid accumulator (8) comprising a liquid com¬ partment (9) communicating with said hose (14) and gas compartment (10), said compartments (9, 10) being separ¬ ated from each other by means of a resilient diaphragm (8c) .

6. An apparatus as defined in claim 5, c h a r a c - t e r i z e d in that said gas/liquid accumulator (8) is arranged to the construction equipment so that the center point of the resilient diaphragm (8c) is located on the axis passing through the center of rotation of the pivotal joint (1) which connects the boom (2) of the construction equipment to the attachment (3) .