GB2489427A

GB2489427A - Slack calculated from measurements of two opposing deflection forces and corresponding displacements

Info

Publication number: GB2489427A
Application number: GB201105069A
Authority: GB
Inventors: Richard Arthur Lindsay
Original assignee: MOTOMETRIX Ltd
Current assignee: MOTOMETRIX Ltd
Priority date: 2011-03-25
Filing date: 2011-03-25
Publication date: 2012-10-03
Anticipated expiration: 2031-03-25
Also published as: GB201105069D0; GB2489427B

Abstract

Tension (slack, sag or free play) in a span of a flexible member (e.g. motorcycle transmission chain or belt drive; cable, rope or tie-rod) is measured by sequentially applying increasing deflection forces to the member in two opposite directions perpendicular to its lengthwise axis; detecting when each force attains a pre-defined magnitude; electronically measuring the corresponding deflections; and calculating a function of these two distances (e.g. their absolute difference). Apparatus may include input (13, Fig. 1) and jaws 8 (comprising deflectors (6, 7, Fig. 1), compression spring (9, Fig. 1)) mounted to a fixed base (1, Fig.1) for movement along a common axis such that forward and reverse axial forces at the input act on the member via the deflectors. Deflection force sensors (18, 19, Fig. 1) may comprise micro-switches. Deflection distances may be measured by linear potentiometer (11, Fig. 3), LVDT, ultra-sonic or laser distance transducer.

Description

I

Measurement Of Tension Or Slack In Flexible Members This invention relates to apparatus for checking tension or slack in a span between supports of an elongate flexible member such as a cable, tie rod, chain or belt, particularly but not exclusively chain or belt drives used in motorcycle transmissions. For optimum efficiency such drives are required to be regularly adjusted to maintain a specified tension or slack. Slack is typically defined as a dimension for total lateral free play of the chain or belt at mid span in the plane of the drive. Similarly, whilst not a direct measure of tension in a member, its lateral deflection in response to a force at mid span is often employed as an indicative measure. The limits of such deflection or free play are defined by the sequential application of appropriate opposing deflection forces at the point of measurement, to take up slack and/or apply a specified force to the member. In practice, obtaining the required dimension using a measuring rule can be a very unwieldy and imprecise process due to inaccessibility, line of sight parallax errors and uncertainty regarding the pressure applied to the member when making the measurement. This approach and its limitations are exemplified in the case of a motorcycle chain, in Patent number JP2005140534.

Instruments are known that provide means to measure deflection in a chain.

Patent number DE 100 44 318 Al describes a device that applies and measures chain deflection by means of a jacking mechanism and display of associated displacement. However, this device does not measure between precise limits of free play, applying unidirectional lift to the chain from an imprecise starting position of static sag to a limit of free play for which there is no indication or control of applied force.

Other more complex instruments, such as that described in patent number US2005/0209034 Al, enable the unidirectional lateral stiffness of the chain or belt to be determined by providing means to measure the relationship between applied forces and resultant deflections. This approach is unsuitable for measuring slack in the chain or belt, which is commonly the specified parameter for assessing adjustment. In addition, many of the known devices are dedicated to, and in some cases physically integrated with, a specific transmission system, lacking the portability for wider application.

In summary the known devices lack the simplicity, flexibility and ease of use required for quick and convenient application by unskilled individuals in the course of routine setup or maintenance.

It is the purpose of this invention to provide an apparatus for measurement of tension or slack in a span between supports of a flexible elongate member comprising: means to apply a first deflection force of progressively increasing magnitude to the member, normal to its lengthwise axis at a specified point on the span; a first sensor to detect when the first deflection force attains a pre-defined magnitude; means responsive to an output of said first sensor to electronically measure and save to a microprocessor memory a first deflection comprising the current distance between said specified point and a fixed reference, and notify completion of this action; means to apply a second deflection force of progressively increasing magnitude to the member, co-axial and in the opposite direction to the first deflection force; a second sensor to detect when the second deflection force attains a pre-defined magnitude; means responsive to an output of said second sensor to electronically measure a second deflection comprising the current distance between said specified point and said fixed reference, notify completion of this action, and initiate a microprocessor control to retrieve from memory said first deflection and compute and display a function of said first and second deflections.

In one application the flexible elongate member is a chain or belt supported by, and configured to transmit rotation between, sprockets or pulleys and the means to apply the first and second deflection forces act in the plane of, and at a specified point on a span between, adjacent sprockets or pulleys.

In further applications the flexible elongate member comprises a cable, rope or tie-rod spanning fixed ends In a preferred embodiment, means to apply first and second deflections comprise a base fixable relative to the supports of the span, deflection means engageable with the member mounted for bi-directional translation along an axis of the base, an input for applying a displacement to the apparatus mounted for translation along said axis between first and second stops acting to limit movement between the input and the deflection means.

Optimally outputs of said first and second sensors are produced in response to defined forces applied between the input and the respective stops.

In one embodiment, spring means act between the base and the deflection means to maintain the base in contact with a fixed point with respect to the supports of the span and allowance is made for the force applied by the spring means in determining said defined forces.

A transducer reactive to said outputs provides signals commensurate with the displacement of the deflection means from a reference position with respect to the base. An indicator provides notification of said outputs.

Typically the indicator produces audible and/or visual alerts and may comprise a piezo-electric sounder and/or a Light Emitting Diode.

In preferred embodiments the indicator provides uniquely identifiable notification of outputs resulting from forces applied between the input and each of the stops.

Usually said function is the absolute difference between signals produced when forces are applied between the input each of said stops, and the means to determine the absolute difference comprise a microprocessor.

In a preferred arrangement the microprocessor is set to accept and process signals produced by successive application of force between the input and each of said stops. Further the microprocessor may be set to register an error condition if the magnitude of either of said signals is outside defined limits.

In any embodiment means to display said function may comprise an LED or Liquid Crystal numeric display.

In one arrangement of the preferred embodiment deflection means may comprise first and second dellectors slidably co-joined for relative movement along said axis, each having a dependant clamping face normal to the axis and co-aligned to provide moveable jaws to captivate and apply bi-directional displacement to the member, and a spring acting between the deflectors to provide a clamping force to the jaws and first and second stops act between the input and the first and second deflectors respectively.

In an alternative arrangement the deflection means comprise a single deflector having a magnetic interface to attach and provide bi-directional displacement to the chain or belt and said stops act between the input member and the single deflector.

In either of these arrangements each stop may comprise an abutment slidably attached to the input member to contact the deflection means at a pre-defined position of the input member on the deflection means and a pre-loaded spring acting to resist displacement of the abutment with respect to the input unless the force of said contact exceeds a pre-defined magnitude.

Alternatively each stop may comprise an abutment slidably attached to the deflection means to contact the input at a pre-defined position of the input on the deflection means and a pre-loaded spring acting to resist displacement of the abutment with respect to the deflection means unless the force of said contact exceeds a pre-defined magnitude.

Said pre-defined magnitudes related to the first and second stops may differ in accordance with the static weight of the span of the member.

Sensors may comprise a micro-switch responsive to said displacement of the abutment.

In the preferred embodiment the transducer may comprise a linear potentiometer, LVDT, rack and pinion and rotary potentiometer or ultra-sonic or laser distance transducer.

The following is a description of a specific embodiment of the invention, reference being made to the accompanying drawings in which: Figures 1, 2 and 3 are side and front and cross sectional views respectively of the apparatus Figures 4 and 5 are partial views of a motorcycle transmission, illustrating the apparatus applied to a motorcycle chain and imparting first and second deflections respectively Figure 6 is a flow chart illustrating the microprocessor workflow for a preferred embodiment of the invention, in which: F1, F2 = first and second deflection forces Fa, Fb = pre-defined threshold forces for sensors (16) and (17) respectively 51, 52 = first and second deflections n, J = temporary control variables Figures 1 to 3 depict an apparatus for measuring tension or slack in a span of an elongate flexible member comprising a base (1), a telescopically engaged extender (2) and clamp (3) providing variable extension of the base along its principal axis AA, a first deflector (4) slidably mounted on the base and a second deflector (5) slidably mounted on the first deflector, each deflector constrained to move parallel to said principal axis. The first and second deflectors have dependant protrusions (6 and 7 respectively) that function in combination to provide moveable jaws (8) to captivate and displace the member. A compression spring (9) acts between the deflectors to maintain a light clamping force between the jaws and a limit stop (10) restricts the maximum opening of the jaws. A linear potentiometer (11)is attached to the first deflector and connected to the base to measure relative axial displacement.

A marker band (12) on the base aligns with the bottom of the first deflector when the potentiometer is at mid stroke. An input (13) is mounted to the second deflector to slide thereon parallel to the principal axis between stops (14) and (15). Sensors (16) and (17), comprising micro-switches (18) and (19) in parallel with compression springs (20) and (21), act between the input and the stops. Springs (20) and (21) are preloaded by means of tie rods (22) and (23) to resist actuation of their associated micro-switches unless the force applied between the input and the second deflection member exceeds said preload. A switched battery power source (24), microprocessor (25), piezo-electric sounder (26) and Liquid Crystal alphanumeric display (27) are housed within the input.

By way of example, application of the apparatus to the measurement of free play in a motorcycle chain will now be described with additional reference to figures 4 and 5. The apparatus is attached by means of the lightly spring-loaded jaws (8) at an appropriate point on the lower span of the chain, its principal axis normal to the chain and in the plane of the sprockets. The linear potentiometer is set to mid stroke by aligning the marker band (12) with the bottom of the first deflector and the telescopic extender (2) is set to contact a fixed reference surface, typically the ground, and clamped by clamp (3). Whilst maintaining the telescopic extender in contact with the reference surface a steadily increasing displacement is applied to the input (13) to extend the apparatus and deflect the chain until the deflection force exceeds the preload applied to spring (20), whereupon micro-switch (18) is activated and, under the control of microprocessor (25), sounder (26) emits a single beep and the displacement registered by linear potentiometer (11)is automatically monitored and recorded in memory.

A steadily increasing reverse displacement is then applied to the input, initially compressing spring (9) until limit stop (10) is engaged, retracting the apparatus and deflecting the chain. When the deflection force exceeds the preload applied to spring (21), micro-switch (19) is activated and, under the control of microprocessor (25), sounder (26) emits a double beep and the further displacement registered by linear potentiometer (11) is automatically monitored.

The saved displacement is recalled from memory and the absolute difference between the recalled displacement and said further displacement is computed and output to display (27).

The associated microprocessor program flow represented in Figure 6, incorporates process steps and checks that simplify application of the apparatus. At the commencement of the operating cycle the input stage counter n is set to unity and the control variable J, identifying sensors that have been engaged, to zero. A prompt to commence application of the nth deflection force is displayed and sensors (16) and (17) are continuously monitored until one sensor is activated, whereupon the current value of J is interrogated.

If J has not been previously set by activation of the other sensor: it is assigned a value associated with said one sensor and the output of the linear potentiometer (11) is acquired. If the output lies within a defined working range of the potentiometer it is recorded in memory and a first stage notification generated in sounder (26). Input stage counter n is set to 2, and when the displacement force has been reduced and both sensors are again in an inactivate state, the sequence returns to the prompt for application of a deflection force.

If J has been previously set by activation of the other sensor: the current output of the linear potentiometer (11) is acquired. If the current output lies outside a defined working range of the potentiometer, an error message is displayed and the process is aborted. If the current output lies within a defined working range of the potentiometer, the saved output is recalled from memory and the absolute difference between the recalled output and said current output is computed and displayed. A second stage notification is generated in sounder (26), signifying completion of the process.

Thus the process is independent of the order in which chain defiections are applied, tolerant of repeated defiections in one direction and responsive only to the first occurrence of alternate defiections. It also provides checks that the working range of the displacement transducer is not exceeded, for example if the telescopic member (2) has been incorrectly adjusted.

Claims

Claims 1. An apparatus for measurement of tension or slack in a span between supports of a flexible elongate member comprising means to apply a first deflection force of progressively increasing magnitude to the member, normal to its lengthwise axis at a specified point on the span, a first sensor to detect when the first deflection force attains a pre-defined magnitude, means responsive to an output of said first sensor to electronically measure and save to a microprocessor memory a first deflection comprising the current distance between said specified point and a fixed reference, and notify completion of this action, means to apply a second deflection force of progressively increasing magnitude to the member, co-axial and in the opposite direction to the first deflection force, a second sensor to detect when the second deflection force attains a pre-defined magnitude, means responsive to an output of said second sensor to electronically measure a second deflection comprising the current distance between said specified point and said fixed reference, notify completion of this action and initiate a microprocessor control to retrieve from memory said first deflection and compute and display a function of said first and second deflections.
2. An apparatus according to claim 1 for measurement of tension or slack in a span between supports of a flexible elongate member wherein the member is a chain or belt supported by, and configured to transmit rotation between, sprockets or pulleys and said means to apply a first deflection force act in the plane of, and at a specified point on a span between, adjacent sprockets or pulleys.
3. An apparatus according to claim 1 for measurement of tension or slack in a span between supports of a flexible elongate member wherein the member is a cable or rope spanning fixed ends.
4. An apparatus according to claim 1 for measurement of tension or slack in a span between supports of a flexible elongate member wherein the member is a tie rod spanning fixed ends.
5. An apparatus according to any of claims 1 to 4 wherein means to apply first and second deflections comprise a base fixable relative to the supports of the span, deflection means engageable with the member mounted for bi-directional translation along an axis of the base, an input member for applying a displacement to the apparatus mounted for translation along said axis between first and second stops acting to limit movement between the input member and the deflection means.
6. An apparatus according to claim 5, wherein outputs of first and second sensors are produced in response to defined forces applied between the input member and the respective stops.
7. An apparatus according to claim 6 in which spring means act between the base and the deflection means to maintain the base in contact with a fixed point with respect to the supports of the span and allowance is made for the force applied by the spring means in determining said defined forces.
8. An apparatus according to claim 6 or 7 wherein a transducer reactive to said outputs provides signals commensurate with the displacement of the deflection means from a reference position with respect to the base.
9. An apparatus according to claim 8 wherein the transducer comprises a linear potentiometer or LVDT.
1O.An apparatus according to claim 8 wherein the transducer comprises a rack and pinion and rotary potentiometer.
11.An apparatus according to claim 8 wherein the transducer comprises an ultra-sonic or laser distance transducer.
12.An apparatus according to claim 8 wherein an indicator provides notification of said outputs.
13.An apparatus according to claim 12 wherein the indicator produces audible and/or visual alerts.
14.An apparatus according to claim 12 wherein the indicator comprises a piezo-electric sounder and/or a Light Emitting Diode.
15.An apparatus according to claim 12 wherein the indicator provides uniquely identifiable notification of outputs resulting from forces applied between the input member and each of the stops.
16.An apparatus according to claim 5 wherein said function is the absolute difference between signals produced when forces are applied between the input member and said first and second stops respectively.
17.An apparatus according to claim 16 wherein means to determine said absolute difference comprises a microprocessor.
18.An apparatus according to claim 17 wherein the microprocessor is set to accept and process signals produced by successive application of force between the input member and each of said stops.
19.An apparatus according to claim 18 wherein the microprocessor is set to register an error condition if the magnitude of either of said signals is outside defined limits.
20.An apparatus according to claim 5 wherein the deflection means comprises first and second deflection members slidably co-joined for relative movement along said axis, each having a dependant clamping face normal to the axis and co-aligned to provide moveable jaws to captivate and apply bi-directional displacement to the chain or belt, and a spring acting between the members to provide a clamping force to the jaws and first and second stops act between the input member and the first and second deflection members respectively.
21.An apparatus according to claim 5 wherein the deflection means comprises a single deflection member having a magnetic interface to attach and provide bi-directional displacement to the chain or belt and said stops act between the input member and the single deflection member.
22.An apparatus according to claim 20 or 21 wherein each stop comprises an abutment slidably attached to the input member to contact the deflection means at a pre-defined position of the input member on the deflection means and a pre-loaded spring acting to resist displacement of the abutment with respect to the input member unless the force of said contact exceeds a pre-defined magnitude.
23.An apparatus according to claim 20 or 21 wherein each stop comprises an abutment slidably attached to the deflection means to contact the input member at a pre-defined position of the input member on the deflection means and a pre-loaded spring acting to resist displacement of the abutment with respect to the deflection means unless the force of said contact exceeds a pre-defined magnitude.
24.An apparatus according to claim 22 or 23 wherein said pre-defined magnitudes related to the first and second stops differ in accordance with the static weight of the span of the member.
25.An apparatus according to claim 22 or 23 wherein sensors comprise a micro-switch responsive to said displacement of the abutment.
26.An apparatus according to claim I wherein means to display said function comprises an LED or Liquid Crystal numeric display.