GB2220498A

GB2220498A - Force measuring apparatus

Info

Publication number: GB2220498A
Application number: GB8815918A
Authority: GB
Inventors: Edward Higgins
Original assignee: Crystalate Electronics Ltd
Current assignee: Crystalate Electronics Ltd
Priority date: 1988-07-05
Filing date: 1988-07-05
Publication date: 1990-01-10
Also published as: GB8815918D0

Abstract

Force measuring apparatus which is particularly suitable for use in weighing boats in conjunction with boat lifting equipment comprises a beam (1) secured to a bearing (2) supported on a structure (3) and capable only of rotation in one plane, about one axis (15), on the bearing (2). A force (4) of variable direction is applied to the beam (1) at a location (6) and a force-measuring transducer (9) cooperates with the beam (1) to counteract rotation of the beam when the force (4) is applied. The transducer (9) provides an output which is proportional substantially only to a single component (14) of the applied force (4), irrespective of the direction of application of the force (4), the component (14) being in a direction which extends from the location (6) where the force (4) is applied and which direction is in the plane of rotation of the beam (1) and normal to a line (16) passing from the location (6) through the axis of rotation (15) of the beam (1). The transducer (9) may be a tensile load cell (9) or a compressive load cell (19). In an alternative arrangement the beam (1) is pivoted at one end, the load is applied to the other end and a tensile or compressive load cell is provided intermediate the ends. <IMAGE>

Description

TITLE: FORCE MEASURING APPARATUS This invention relates to force measuring apparatus and particularly to apparatus for measuring a force in which the direction of application of the force relative to the apparatus is variable. The invention finds a particular, although by no means exclusive, application to weighing boats on boat lifts used, for example, in marinas. In such an application a boat is hoisted from the water on strops or cables which extend, from an elevated structure on either side of the boat, underneath the hull of the boat in the form of slings. Problems arise in trying to devise a means to determine the weight of the boat when slung on the strops or cables because the angle or direction of the strops or cables relative to the supporting structure varies according to the size of the boat and/or the height to which the boat is lifted from the water.When a force measuring arrangement is considered for mounting on the structure and incorporating a measuring transducer and mechanically connected to the strops or cables, difficulties occur in that due to the varying angle of the strops or cables, the measuring arrangement can be subjected to vertical, horizontal, lateral and rotational components of applied force.

It is an object of the present invention to overcame this problem by providing a force measuring arrangement which will react to and monitor only one specific component of the applied force while being unaffected by other components and also by the angle or direction of the applied force.

The present invention provides force measuring apparatus comprising: a beam secured to a bearing means on a support, the beam being constrained such that it is capable substantially only of rotation in one plane, about one axis, on the bearing means; means for applying to a predetermined location on the beam a force to be measured and whose direction of application relative to the beam is variable; a force measuring transducer cooperating with the beam in such a way as to counteract rotation of the beam when the force is applied, the transducer providing an output which is proportional substantially only to a single component of the applied force, the said component being in a direction which extends from the location on the beam where the force is applied and which direction is in the plane of rotation of the beam and normal to a line passing from the said location through the axis of rotation of the beam.

In one embodiment the beam is elongate and secured to the bearing means at a location, eg midway, between its ends, the force of variable direction of application is arranged to be applied at one end region of the beam and a transducer in the form of a tensile or compressive load cell is arranged to cooperate between the opposite end region of the beam and a relatively fixed support, the tensile or compressive load cell being suitably disposed so as to counteract rotation of the beam when the force is applied.

In a further embodiment the bearing means is provided at one end region of the beam, which is elongate, and the force of variable direction of application is arranged to be applied at the other end region of the beam, a transducer in the form of a tensile or compressive load cell being arranged to cooperate between the beam, at a region intermediate the end regions, and a relatively fixed support, the tensile or compressive load cell being suitably disposed so as to counteract rotation of the beam when the force is applied.

The transducer output is substantially independent of the direction of application of the force to the beam.

In a particular application an elongate beam is disposed substantially horizontally and a substantially vertical component of the applied force is measured. Such an application may, for example, be in respect of weighing a boat in a hoist arrangement in which one or more strops or cables pass underneath the boat hull in the form of a sling and over pulleys on an elevated structure at either side of the boat, each pulley being connected to the end of a beam of a said force measuring apparatus provided on the elevated structure at either side of the boat, the beam of each force measuring apparatus being disposed substantially horizontally and the output from the force measuring transducer on each measuring apparatus being proportional only to the substantially vertical component of the applied force.This component of the applied force is measured to provide an indication of the weight of the boat and is independent of the angle at which the strops or cables connect, by means of an appropriate pulley, to the beam of each measuring apparatus.

Stop means may be provided, adapted to cooperate with the beam to limit rotation of the beam and thereby serve as a safety device.

The force measuring transducer is suitably of well-known construction, incorporating electrical strain gauge devices and providing an electrical output proportional to the component of applied force being measured. Transducers in the form of well-known load cells for compressive or tensile force measurement may conveniently be provided.

The invention is now described by way of example with reference to the accompanying drawings in which: Figure 1 represents a partly-sectioned view of force measuring apparatus according to the invention; Figure 2 represents a sectional view of an alternative to the force measuring apparatus of Figure 1.

Referring to Figure 1, force measuring apparatus is provided which is suitable, for example, for use in weighing boats in conjunction with boat lifting equipment. The apparatus comprises a beam 1 secured at a position (eg midway) between its ends to a bearing 2. The bearing 2 is supported on a structure 3. The beam 1 is constrained by the bearing 2 such that it is capable substantially only of rotation in one plane (as represented by the plane of the paper in Figure 1), about one axis 15 (which is perpendicular to the plane of the paper in Figure 1), on the bearing 2. A force 4 to be measured and whose direction of application relative to the beam 1 is variable, as indicated by arrows 5, is applied to an end region of the beam 1 at a predetermined location 6. The force 4 in the embodiment illustrated is applied by way of a cable or strop 7 which passes over a pulley arrangement 8. The pulley arrangement 8 is secured to the location 6 on the beam 1 in such a way that it is able to swivel to accommodate changes in angle of the cable or strop 7. A force measuring transducer in the form of a tensile load cell 9 is secured between the opposite end 10 of the beam 1 and a fixed supporting structure 11 and has a force measuring axis 17. The construction of such a load cell 9 is well known to those skilled in the art.Such a load cell 9 incorporates known strain gauge devices and provides an electrical output which will change in proportion to the magnitude of a tensile force to which the load cell 9 will be subjected if the end 10 of the beam 1 is caused to be deflected in a direction which tends to move it away from the fixed supporting structure 11. The load cell 9 is secured at its ends to the structure 11 and the end 10 of the beam 1 by way of spherical bearings 12 and 13 and counteracts rotation of the beam 1 about the bearing 2 when the force 4 is applied.

Regardless of the direction at which the force 4 is applied, the load cell 9 will provide an output which is proportional only to a single component 14 of the applied force 4. This component 14 is in a direction which extends from the location 6 on the beam where the force 4 is applied. The direction of component 14 is also in the plane of rotation of the beam 1 and normal to a line 16 passing from the location 6 through the axis of rotation 15 of the beam 1. In the construction shown in Figure 1, the force measuring axis 17 of the load cell 9 is parallel to the component 14 of the force being measured. Stop members 18 are provided as safety devices to limit rotation of the beam 1, eg in the event that fracture of the load cell 9 occurs.

In a particular application, the force measuring apparatus of Figure 1 is used to weigh boats in a boat lift or hoist arrangement. One such measuring apparatus is provided on an elevated structure (not shown) at either side of a boat and a cable or strop 7 (Figure 1) is passed underneath the hull of the boat, in the form of a sling, and over a pulley 8 secured to the end of the beam 1 of each measuring apparatus. The beam 1 of each force measuring apparatus is disposed substantially horizontally. As the boat is hoisted from the water, the angle of the cable or strop 7 changes and hence the direction at which the force 4 (resulting from the weight of the boat) is applied to the end of the beam 1.Regardless of this, the load cell 9 on each force measuring apparatus will always only measure the component 14 of the applied force 4 (which in this case is in a vertical direction) and provide an accurate indication of the weight of the boat.

Instead of providing a tensile load cell 9, a compressive load cell could be located in position 19 between the end 10 of the beam 1 and a separate support 20.

Figure 2 shows an alternative arrangement to the force measuring apparatus of Figure 1. In Figure 2, parts fulfilling the same or similar functions to those in Figure 1 are given the same reference numerals as in Figure 1. In Figure 2 the beam 1 is secured at an end region to bearing 2 on a supporting structure 3, the beam 1 being arranged to rotate about the bearing 2. The force 4 to be measured, and which is of variable direction of application, is applied to the opposite end region of the beam 1 at location 6. A force measuring transducer in the form of a compressive type of load cell 19 is provided between an intermediate region of the beam 1 and a support structure 20 and counteracts rotation of the beam 1 when the force 4 is applied.Instead of the compressive type of load cell 19, a tensile load cell 9 could be provided secured between the beam 1 and a support 11 and again counteracting rotation of the beam 1. In substantially the same way as described with respect to the embodiment of Figure 1, the load cell 9 or 19 in Figure 2 will provide an output proportional only to the component 14 of the applied force 4 and independent of the direction of application of the applied force 4.

It is to be understood that the expression 'beam' used in the foregoing description is not limited to uniform elongate structures but is intended to refer to any uniform or non-uniform structure of a shape such as to be capable of being arranged for rotation in one plane, about one axis, on a bearing means and capable of receiving an applied force as described and a force measuring transducer for counteracting rotation of the structure, as described.

Claims

1 Force measuring apparatus comprising; a beam secured to a bearing means on a support, the beam being constrained such that it is capable substantially only of rotation in one plane, about one axis, on the bearing means; means for applying to a predetermined location on the beam a force to be measured and whose direction of application relative to the beam is variable;; a force measuring transducer cooperating with the beam in such a way as to counteract rotation of the beam when the force is applied, the transducer providing an output which is proportional substantially only to a single component of the applied force, the said component being in a direction which extends from the location on the beam where the force is applied and which direction is in the plane of rotation of the beam and normal to a line passing from the said location through the axis of rotation of the beam.

2 Apparatus according to Claim 1 in which the beam is elongate and secured to the bearing means at a location between its ends, the force of variable direction of application is arranged to be applied at one end region of the beam and a transducer in the form of a tensile or compressive load cell is arranged to cooperate between the opposite end region of the beam and a relatively fixed support, the tensile or canpressive load cell being suitably disposed so as to counteract rotation of the beam when the force is applied.

3 Apparatus according to Claim 1 in which the bearing means is provided at one end region of the beam, which is elongate, and the force of variable direction of application is arranged to be applied at the other end region of the beam, a transducer in the form of a tensile or compressive load cell being arranged to cooperate between the beam, at a region intermediate the end regions, and a relatively fixed support, the tensile or compressive load cell being suitably disposed so as to counteract rotation of the beam when the force is applied.

4 Apparatus according to any preceding Claim in which the beam is elongate and disposed substantially horizontally, a substantially vertical component of the applied force being measured.

5 Apparatus according to Claim 4 for use in respect of weighing a boat in a hoist arrangement in which one or more strops or cables pass underneath the boat hull in the form of a sling and over pulleys on an elevated structure at either side of the boat, each pulley being connected to the end of a beam of a said force measuring apparatus provided on the elevated structure at either side of the boat.

6 Apparatus according to any preceding Claim in which stop means is provided, adapted to cooperate with the beam to limit rotation of the beam and thereby serve as a safety device.

7 Apparatus according to any preceding Claim in which the force measuring transducer incorporates electrical strain gauge devices and provides an electrical output proportional to the component of applied force being measured.

8 Force measuring apparatus constructed and arranged substantially as hereinbefore described with reference to the accompanying drawings.