WO1990005288A1

WO1990005288A1 - Tension meter

Info

Publication number: WO1990005288A1
Application number: PCT/GB1989/001342
Authority: WO
Inventors: Ian John Osborne
Original assignee: Transmission Developments Co. (Gb) Limited
Priority date: 1988-11-10
Filing date: 1989-11-10
Publication date: 1990-05-17
Also published as: GB8826332D0

Abstract

A tension meter for determining the tension in belt (B) of transmission drive or a conveyor belt including a body (10), an elongate touch probe (14) projecting from the lower surface of the body. The touch probe (14) is coupled to a transducer (18) which detects any longitudinal displacement of the probe (14) from the extended position of the probe. The tension meter further includes a load cell comprising a ring (26) strain gauges (1, 2, 3 and 4), the strain gauges (1, 2, 3 and 4) being connected to a computer to compare pre-programmed belt characteristics with the belt being tested.

Description

TENSION METER

This invention relates to a tension meter for measuring the tension in power transmission or conveyor belting.

Various methods are known for determining the tension in a transmission or conveyor belt. In one method, the belt is deflected using a spring balance and the distance through which the belt is deflected is measured with a ruler for a given force required to produce that deflection as read from the spring balance: the tension is then determined by reference to a table of theoretical values. This method requires two measurements to be made simultaneously with relatively inaccurate equipment of low repeatability. In another method, the distance between the centres of two opposite pulleys around which the belt is trained can be elongated by a measured amount to provide a pretension in the belt: by knowing the belt stiffness the value of pretension is predetermined. However this method does not take account of tolerences in the components and cannot be used to measure the tension in a previously installed belt.

Tension meters are also known which cooperate with an installed belt and include a load cell which is loaded under a deflection of the belt and provides an output indicative of the tension in the belt. However these tension meters [e.g. US patent 3572110] require the belt to be threaded through them between a pair of guide rollers which contact one face of the belt and a shoe which contacts the other face of the belt, the shoe being offset relative to the rollers to produce a deflection of the belt and being coupled to the load cell. In accordance with this invention, there is provided a tension meter comprising a body having a first positional means projecting therefrom, a touch probe projecting from it at a spaced interval from the first positional means, and a load cell probe projecting from it at a position -intermediate the first positional means and touch probe, the load cell probe being coupled to a load cell.

In use of this tension meter, it is applied by hand to one face of a belt the tension of which is to be determined, so as to produce a small deflection of the belt and the output of the load cell is indicative of the tension in the belt, for a belt of given characteristics and given belt geometry. The first positional means may be a simple stop in order to provide the correct geometry between the load cell probe and the touch probe. In this instance the load cell preferably projects beyond a ^• line joining the outer ends of the stop and the touch probe.

However, the first positional means may also be a touch probe such that two readings may be taken with the load cell probe over a known length of belt in conjunction with the two touch probes either side of the load cell. The two readings may be averaged to provide a single determination of belt tension which is less affected by operator error in use of the machine. In the second case of two touch probes the load cell and the touch probes are in line and the load reading taken on depression on one and then both touch probes by a predetermined amount to provide the correct belt geometry.

In particular, the meter may be applied to the belt with just the stop touching the face of the belt, then the body of the meter is turned, using the stop as a pivot, until the laod cell probe presses against the belt. The user continues to turn the meter body, keeping the stop pressed against the belt and so that the load cell probe deflects the belt, until the touch probe makes contact with the same face of the belt. At this instant a reading of the load cell output is taken and, from a knowledge of the belt characteristics and belt geometry, the belt tension is determined.

In a preferred embodiment, the touch probe is displaceable and coupled to an electrical transducer which responds at the instant the touch probe is displaced by contact with the surface of the belt. This electrical transducer and the load cell are connected into an electrical circuit which is triggered by the sensed displacement of the touch probe to take a reading of the load cell ouput at that instant. In the preferred embodiment, the output from the load cell is passed to a handheld computer [e.g. an Psion organiser] which responds to the triggering output from the displacement transducer to record the load cell output, and further to compare the measured load with a theoretical value for the belt and belt geometry in question so as to provide an indication of whether the belt is under or over tension.

In a second preferred embodiment, each touch probe is displaceable and is coupled to an electrical transducer which responds to the displacement to the belt surface as the load is applied. Each electrical transducer and the load cell are connected into an electrical circuit which is triggered by the' sensed displacement of the touch probe to take a reading the instant each probe is displaced from the belt by the required amount. In this embodiment, each output from the load cell is passed to a hand held computer [e.g. a Psion organiser] and the average of the readings is computed and thereafter the average measured load is compared with a theorectical value for the belt and belt geometry in question to provide as indication of over or undertensioning of the belt.

Preferably the load cell comprises a ring which is loaded across its diameter when probe is loaded. Strain gauges attached to the ring provide the electrical output from the load cell. The load cell probe transmits the tension of the belt to the load cell. However in order that the probe does not alter the belt characteristics, it is preferred that it does not move or only moves a small amount e.g. up to 5 microns when transmitting to the load cell the belt tension to be tested.

The present invention will now be described by way of example only and with reference to the accompanying drawing, in which:

Figure 1 is a longitudinal section through the body of a tension meter in accordance with this invention; and

Figure 2 is a longitudinal section through a body of a tension meter in accordance with an alternative embodiment of this invention;

Figure 3 is a diagram of an electrical circuit to which the load cell and touch probe transducers of the tension meter body are connected.

Referring to Figure 1 of the drawings, there is shown a body 10 of a tension meter for determining the tension in a belt B of a transmission drive or of a conveyor belt. The body 10 comprises a generally rectangular block of metal e.g. aluminium. A stop 12 is fixed to the body 10 adjacent one of its ends, projecting from the lower face of the body. An elongate touch probe 14 is mounted in a socket 16 adjacent the opposite end of the body 10 and also projects from the lower surface of this body. The touch probe 14 is coupled to a transducer 18 which detects any longitudinal displacement of the probe 14 from the extended position of the probe which is shown in Figure 1.

A load cell probe 20 is mounted to a stem 22 at a position intermediate the stop 12 and touch probe 14, the load cell probe 20 projecting from the lower face of the body slightly further [typically although not essentially by 1.6mm] than a line joining the outer extremities of the stop and touch probe. A chamber 24 within the body 10 houses a ring 26 to which the inner end of stem 22 is fixed. Strain gauges 1, 2, 3, 4 are fixed to the ring 26 adjacent its junction with stem 22, strain gauges 1, 2 lying along the inner periphery of the ring and strain gauges 3, 4 lying along the outer periphery of the ring. Electrical leads L from the strain gauges pass through the body 10 to its outer surface as shown.

In use of the tension meter, the body 10 is applied by hand to the outer face of the belt B. First the user rests the stop 12 on the belt surface, then he turns the body 10 using the stop 12 as a pivot, until the load cell probe 20 presses against the belt. Continuing to turn the body 10 in this manner, keeping the stop 12 pressed against the belt surface produces a small deflection of the belt and soon the touch probe 14 comes into contact with the belt surface. Immediately that displacement of the touch probe 14 is sensed by the transducer 18, a reading of the load cell output is taken.

In Figure 2, like features shown in Figure l are designated with the same numerals. The embodiment of Figure 2 shows a second elongate touch probe 15 mounted in a socket 17. The touch probe 15 projects from the lower surface of the body 10 and once again detects any longitudinal displacement of the probe 15 from the extended position to the desired position [typically although not essentially 1.6mm] offset from the level of the load cell. In use of the tension meter, the body 10 is applied by hand to the outer face of the belt B such that the touch probe

14 and 15 and the load cell probe 20 all touch the belt surface at the same level. Continuing to press the body 10 on to the belt causes first one of the touch probes 14 or

15 and then the other touch probes 14 to retract. As each of the touch probes is displaced by a preselected amount and preset amount of preferably 1.6mm and is sensed by the transducer, a reading of the load cell is taken providing two readings in close succession. Figure 2 shows the touch probes 14, 15 at the position taken at the moment of the reading of the load cell displaced by a distance d. The dotted lines show the touch probes in an extended position, as at rest.

Referring to the circuit diagram shown in Figure 3, the strain gauges 1, 2, 3, 4 are connected in an electrical bridge circuit the output of which is passed to an interface connector 30. The displacement transducer 18 is connected to a threshold comparator stage 32 having its output also connected to the interface connector 30. A handheld computer [e.g. a Psion organiser] is coupled to the interface connector: at the instant that an output is provided by the comparator stage 32 [indicating displacement of- the touch probe], this is used by the computer as a trigger to record the output at that instant from the load cell. The handheld computer is preprogrammed with data in respect of the belt characteristics and belt geometry [e.g. size and spacing of the pulleys around which the belt is trained] , so that the computer is able to compare the measured load cell output with theoretical values applicable to the belt and belt geometry in question, and indicate whether the belt is under tension or over tension.

In the case of the second embodiment the handheld computer averages the two readings of the load cell which is then compared with the preprogrammed characteristics of the belt and belt geometry as described.

It will be appreciated that the tension meter which has been described is simple and straightforward to use by hand, requiring application of the body 10 against just one surface of the belt of which the tension is to be determined.

It should also be appreciated that although the present invention has been described used in conjunction with handheld computer, it can also be used with its own internal calculating microprocessor and display system in order to give an absolute value for belt tension.

In addition the present invention may be used in conjunction with other computers such as mainframe, micro and PC's in order to provide the necessary calculation and if required comparative function.

Claims

1. A tension meter comprising a body having a first positional means projecting therefrom, a touch probe projecting from the body at a spaced interval from the first positional means, and a load cell probe projecting from the body at a position intermediate to the first positional means and the touch probe, the load cell probe being coupled to a load cell, the load cell being moveable such that the load cell is capable of determing displacement applied thereto.

2. A tension meter as claimed in claim 1 wherein the first positional means comprises a touch probe in order to provide a touch probe either side of the load cell probe.

3. A tension meter as claimed in claim 1 or claim 2 wherein the touch probe is displaceable and is coupled to an electrical transducer which responds instantly as the touch probe is displaced on contact with a surface, the electrical transducer being connected to the load cell such that it is capable of triggering electrical circuit by the sense displacement of the touch probe in order to take a reading of the load cell at that instant.

4. A tension meter as claimed in claim 3 further including computation means capable of responding to the output from the electric circuit to compare the measured load with the predetermined value for a particular surface to provide an indication of tension within the surface.

5. A tension meter as claimed in claim 1 or claim 2 having two touch probes each of which is displaceable and each of which is coupled to an electical transducer capable of responding to the displacement of the surface as load is applied to a surface.

6. A tension meter as claimed in claim 5 further including an electrical circuit connected to the load cell capable of being triggered by the displacement of the touch probe to take a reading the instant each probe is displaced from any surface by a required amount, the output from the load cell being passed to ^' computation means capable of averaging the readings and comparing the readings with a theoretical value for the particular surface in question.

7. A tension meter as claimed in any one of the preceding claims wherein the surface of which the tension is to be measured is a belt.