Cable grip tester

Abstract

A grip tester adapted for testing cable grips for a chair lift has a sprocket wheel mounted in proximity to the cable. The sprocket wheel has four axially extending notches across the perimeter of the wheel, each notch being profiled to receive a portion of the grips adjacent the cable-gripping portion of the grip as the grips pass by on the cable, the sprocket wheel being rotated a quarter turn by each grip. On one side, the sprocket wheel has coaxially secured to it a projecting two-tooth first member of a two part torque-friction device, the second four-tooth member being non-rotatably secured to a fixed support. The teeth of the friction device extend radially and are slope-sided. The non-rotatable member is adjustably spring-biased toward the first member for engagement of the respective teeth sides. A speed sensing wheel is biased against the top of the cable and each grip has a ramp-like track portion over which the wheel may travel. The wheel drives a tachometer generator which is electrically connected to a tachometer meter for operating a switch in the motor drive circuit of the lift for shutting off the lift when the tachometer senses a slowing of the wheel as it passes over the track portion of the grip.

Description

BACKGROUND OF THE INVENTION

This invention relates to testing for slippage of a grip device clamped to a linearly driven cable or rope where a load is carried or moved by means of the grip.

Prior art grip-testing devices have usually comprised tools or gauges for manually applying a measured pressure against the grip at some point along the path of travel of the load-carrying or load-pulling grip while the cable is at rest. Such devices are laborious and necessitate stopping of the grip-carrying cable or rope for the testing of each grip.

Other known grip testers involve a separately-driven car or rail-carried device at each point where the grip is tested which carry a device for exerting a back pressure on the grip and sensing for slippage of the grip as the cart is carried along with the grip and means for signalling slippage so that the travel of the cable may be stopped. Such devices are expensive, frequently get out of order, and are unreliable. They can also usually only be used at points where the cable is traveling in a horizontal path.

SUMMARY OF THE INVENTION

This invention contemplates rotatably securing a grip-engaging sprocket or wheel on a support adjacent to a cable or rope which supports or moves a load suspended from or connected to the cable by means of a grip device. This sprocket is removably secured adjacent a portion of the cable which moves linearly bringing a plurality of load bearing grips past the sprocket which is adapted to be turned or rotated by the passage of the grips.

The sprocket has an annular groove therearound in which the cable lies as it passes linearly. A plurality of angularly spaced notches extend laterally across the perimeter of the sprocket extending axially of the sprocket. Each notch is profiled to receive and to later release a portion of a grip as it passes by so as to turn the sprocket as the grip passes.

On one side of the sprocket, secured coaxially thereto is a first torque-friction member having at least one radially extending tooth, the tooth having ramp-like sloping sides. A second torque-friction member having more teeth than the first member and the teeth being radially extending and with sloping sides, is nonrotatably secured to the sprocket support coaxially with the first member. The second member is spring biased toward the first member for bringing the teeth into engagement and the spring pressure is regulatable.

As each passing grip rotates the sprocket, the sloping sides of the teeth engage until the high points of the engaged teeth pass one another. The torque-friction applied to the sprocket thus increases from zero until the passing point and then, the other sides of the teeth being engaged, the torque-friction device assists the sprocket in turning a portion of a full turn, leaving the sprocket in position to receive another grip in a succeeding notch.

Each grip has a ramp-like track portion lying along one side of the cable, for example the top. The track portion has a ramp gently sloped away from the cable to a high point and another ramp gently sloped toward the cable on the other side of the high point.

A speed-sensing wheel is biased toward the cable and adapted to rotate as it contacts the cable and, at intervals, the track portions of passing grips. The ramps of the track portion allow the sensing wheel to run along the cable and then along the grip track with minimal bouncing and minimal change in speed unless the grip slips.

If the grip slides along the cable as the torque-friction is applied or if it partially slips and moves along the cable, the wheel senses the change in rate and operates a signal. A tachometer generator may be operated by the sensing wheel to electrically operate a tachometer metering device which may be set to operate a switch if the sensing wheel slows from the speed of the moving cable. The signal may conveniently be an opening of the electrical circuit to the drive motor of the cable, which stops the cable for enabling repairs at once.

Alternatively, a second speed sensing wheel may also be employed to constantly monitor the speed of the cable. The second wheel may operate a second tachometer meter and the two tachometer meters may be connected so as to operate the signal if the two meters show a slowing of the speed of the grip.

An important object of the invention is to provide a device which can quickly be installed or removed from a support adjacent a linearly moving cable or rope carrying a plurality of grips each carrying a load, for applying a preset pressure resisting the passage of each grip together with sensing means for signalling any slippage of a grip.

The cable may travel in an endless path or travel in one direction for a time and then travel in the opposite direction. The grips may be adapted for substantially permanent attachment to the cable, as in chair ski-lifts, or adapted for detachable attachment to the cable at each loading station and detached at the unloading station or may be detached and stored at their return to the loading station, as in some types of T-bar ski-lifts.

Recent local regulations for ski-slopes, however, include the requirement that each chair-lift grip must be tested for slippage at least once each week and, for this reason, the device of the present invention is peculiarly adapted for use with chair-lifts. Accordingly, another important object of the invention is to provide a device which can quickly be installed or removed from a support adjacent a chair lift cable for testing successively each chair-supporting grip by applying a preset pressure resisting the passage of each grip together with sensing means for signalling any slippage of a grip by stopping the lift when slipping is detected.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a plan view of a chair grip-engaging sprocket according to the invention, a grip and cable being shown fragmentarily;

FIG. 2 is a longitudinal sectional view of the chair-supporting grip of FIG. 1;

FIG. 3 is a fragmentary, diagrammatical, side-elevational view of a bull-wheel and bull-wheel support portion of a chair-lift, showing the grip engaging sprocket and a speed-sensing wheel as applied thereto;

FIG. 4 is an enlarged, side elevational view of the sprocket of FIG. 1 in grip-receiving position as viewed from a passing lift-chair, the cable being shown fragmentarily;

FIG. 5 is an enlarged side elevational view of the sprocket in maximum torque-frictional position as viewed from the support side, the grip being shown in end elevation and the cable being shown fragmentarily;

FIG. 6 is a fragmentary, edge elevational view of the sprocket, the torque-friction portion of the sprocket being viewed in the direction of the arrows 6--6 of FIG. 5;

FIG. 7 is a fragmentary side elevational view of the sprocket-supporting shaft and a portion of its support and showing the tension-adjusting mechanism for the torque-friction mechanism;

FIG. 8 is an end view, partly in section, of the mechanism of FIG. 7;

FIG. 9 is a diagrammatic view of the sprocket and speed sensing wheel and associated parts of FIG. 3, and showing one embodiment of electrical means for signalling slippage of a grip;

FIG. 10 is a view similar to FIG. 9, showing another embodiment of electrical means for signalling slippage of a grip.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

Referring to FIGS. 1--10 the grip-tester of the invention is shown adapted for use with a chair ski-lift having a cable 11. A known type of cable grip is shown at 12 for supporting a lift chair 13 in known manner.

Referring to FIGS. 1, 2, 3 and 5, the grip 12 has an annular journal portion 14 around which a bearing-like member 15 at the top of chair 13 (FIG. 3) may be clamped for supporting the chair from cable 11. From the journal portion 14, and integral therewith, a neck portion 16 extends, tapering outward to a hooked tooth 17 (FIG. 2) for embracing the chair side of cable 11.

A jaw member 18 has a tooth 19 for embracing the other side of cable 11, as seen in FIG. 2, and the jaw member extends over the tooth 17 and between spaced portions 20 of the neck to an annular portion 21. Portion 21 is threaded and the threaded end of a shaft 22 is threadedly and adhesively secured in the portion 21.

Shaft 22 extends slidingly through the center of the annular journal portion 14 to its other end which is threaded for carrying an adjusting nut 23 and a locknut 24. Nut 33 may be tightened on shaft 22 for compressing a heavy coil spring 25 around the shaft between appropriate washers 26 and 27 to provide cable gripping pressure between teeth 17 and 19.

A snap ring 28 is provided in an appropriate groove in journal portion 14 for retaining the bearing clamp 15 at the top of chair 13 in position. The weight of the chair and occupants serves to maintain the grip 16 projecting laterally from the cable 11.

Connected by ribs 29 (FIG. 1) to the grip 12 is an elongated track portion 30 which lies on top of cable 11 and passes over the top of jaw 18 at its center, as best seen in FIG. 2. The double-ramp side-elevational shape of the track portion is best seen in FIG. 5. The elongated portion 30 is common in grips for load bearing cables, the object, of course, being to distribute the load over a considerable length of cable. The double ramp-shape comprises a first ramp portion sloping gently away from the cable to a high point and then followed by a second ramp portion sloping gently from the high point back toward the cable. Such ramp like grip portions are common in cable constructions where the cable is carried on its supports between a support pulley and a hold down pulley as hereinafter described.

Referring to FIGS. 3, 4, 5 and 6, a novel sprocket or notched wheel 31 is rotatably supported adjacent the cable 11. In FIG. 3, the sprocket 31 is shown supported on the support 32 for the bull wheel 33 and rotatable on a shaft 34. Preferably the bull wheel is the driving wheel for the cable and, as the lower portion of the hill is nearest to the electrical supply lines and nearest to storage sheds etc., the lower bull wheel is preferred. Bull wheel 33 has a drive gear 35 secured thereto and gear 35 is driven by a gear or gears, not shown, which in turn are driven by an electric motor M (FIGS. 9 and 10) carried by support 32.

The ends of the sprocket shaft 34 are supported in cantilever fashion by conventional framework, not shown, carried on support 32 and removable therefrom. This location is advantageous because of the cable support pulley 36 and hold down pulley 37 spring-biased toward the cable 11, but it may be located at any tower or portion of the lift having a support pulley and hold-down pulley where oscillation of the cable is minimal. Hold-down pulley 37 may travel over the grip track 30.

It will be apparent that a second pair of support and hold-down pulleys, like pulleys 36 and 37, may also be provided on the other side of sprocket 31, as viewed in FIG. 3, if necessary to ensure non-oscillation of cable 11 as it passes the sprocket.

Referring to FIGS. 1, 4 and 5, the sprocket 31 comprises a wheel-like member centrally apertured at 38 for shaft 34 and having a relatively deep annular groove 39 (FIG. 1) therearound in which the cable 11 is accommodated, as shown. A plurality of transverse notches 40 in the perimeter extend axially of the sprocket across the sprocket edge defined by chairside, teeth-like flange sections 41 and similar but narrower and shorter flange sections 42 on the other side of the sprocket for loosely guiding on cable 11. Four notches 40 is the preferred number as will hereinafter appear.

As best seen in FIG. 1 each notch 40 is profiled to receive, and later release neck portions 16 of grips 12 as they successively pass carried on cable 11. As seen in FIG. 1, the notch 40 between flange sections 41 taper outwardly from the chair side of the sprocket toward groove 39 to loosely accommodate the neck portion 16 of the grip. Between flange sections 42 there need be no taper, the notch being wider to accommodate the tooth-19-end of the grip.

As best seen in FIG. 4, the trailing edge 43 of each flange section 41 at any point along notch 40 is straight and parallel to a radius of the sprocket. The other or leading edge of the next flange section is angularly relieved from the point 44 radially outward of the sprocket to aid in the release of the grip therefrom as will hereinafter be apparent. The notches 40 are all of the same depth between flange sections 41 and 42 but, due to the configuration of the grips 12 between tooth 17 and the annular portion 21 of the jaw member, the chair side of the annular groove 39 may have a rounded flange 45 (FIG. 4) across each notch for added strength.

As shown in FIGS. 5 and 6 the side of sprocket 31 facing the bull wheel support 32 has an annular projecting member or portion 46 having at least one and preferably two projecting teeth with radially extending high points 47 and having sides sloping downward to low points 48 therebetween as best seen in FIG. 6.

Referring to FIGS. 7 and 8, another annular member 49 is secured on sprocket shaft 34 by a pin 50 through a slotted hole 50a in the shaft so as to be axially movable on the shaft. Member 49 has four teeth with high points at 51 and low points at 52 and, with member 46, serves as a torque-friction device.

A coil spring 53 around shaft 34 biases the member 49 against member 46 and the bias pressure is controlled by an adjusting nut 54 threaded on shaft 34 and bearing, with washer 55, against the other end of spring 53. This end of shaft 34 is secured to a portion 56 of the framework secured to the bull wheel support 32.

Referring to FIG. 4, it will be apparent that, when a grip 12 carried on cable 11 approaches the sprocket 31, its neck portion 16 engages the trailing side 43 of the flange section 41 adjacent a notch 40. Torque-friction is at first minimal as the sprocket 31 starts to rotate since the high points 47 of the teeth on member 46 are at the low points 52 between two of the teeth of member 49. As the sprocket is rotated by the passage of the grip, the torque-friction is increased as the teeth of members 46 and 49 engage and the resistance of the torque friction device increases to a maximum when the high points 47 pass the high points 51. At this point the grip and sprocket are in the relative positions shown in FIG. 5.

After the sprocket passes this position, the grip is released from notch 40, the engagement of the sides of the teeth members 46 and 49 aiding, instead of resisting, the turning of the sprocket. The shape of notch 40 prevents interference with this release.

By inspection of FIG. 4, it will be seen that when a grip 12 carried on cable 11 engages the trailing edge 43 of a flange 41 and the torque resistance device 46-59 develops resistance to the passing of the grip, the resistance, besides turning sprocket 31, does not urge cable 11 away from the sprocket but tends to bias the cable downwards toward the bottom of annular groove 39 and oscillation of the cable is minimal. As shown in FIG. 5, when grip 12 reaches the position shown therein, the torque friction resistance is released before there is any biasing of the cable 11 out of its groove 39. Thereafter the turning of sprocket 31 is forward by the torque friction device 46-49. The angular relief of the forward edge of flange 41 outward from point 44 (FIG. 4) prevents any oscillation of cable 11 by the turning of sprocket 31 as the grip 12 is released from notch 40.

Referring to FIGS. 3, 9 and 10, means for signalling slippage of each grip 12 by stopping the motor which drives bull wheel 33 includes a cable contacting, speed sensing wheel 57 rotatably carried on one end of an arm 58 substantially parallel to cable 11, the other end of arm 58 being pivotally secured on its support carried on the bull wheel support 32. Wheel 57 is biased downward by gravity or, preferably, is biased against the cable 11 by a spring 59 and preferably has a periphery of rubber-like material to ensure frictional contact with the grip.

Referring to FIGS. 5, 6, 7, 8 and 10, it will be noted that the high points 47 of the rotating teeth of member 46 are aligned with the center portion of the grip track portion 30 and the high points 51 of two of the nonrotating teeth of member 49 are aligned therewith. This results in the maximum torque friction of device 46, 49 being applied to sprocket 31 just as the grip 12 passes the position shown in FIG. 5, when the high points 47 pass the high points 51.

The next succeeding pair of high points 51 are at a 90.degree. angular spacing so that, after the sprocket 31 has been turned one quarter turn another notch will be in position to receive the next grip and be turned to another maximum torque resistance point. It will be apparent that other angular spacings of teeth 51 are possible and a different number of teeth 51 and notches 40 may be provided but it is believed that two teeth 47 and four teeth 51 and notches 40 are preferable since it provides for two teeth 47 being engaged with two teeth 51 and for a 90.degree. turning of sprocket 31 for each passing grip.

As diagrammatically shown in FIG. 9, a tachometer generator 60 is secured on the shaft carrying wheel 57 so as to rotate with the wheel. The generator 60 may be a voltage signaling device, or a frequency or current signaling device. The generator 60 is connected by wires 61 and 62 to a tachometer meter 63, here shown as a voltage sensing relay. The switch arm 64 of the relay is biased by spring 65 toward open position and is normally held in closed position, as shown, by the relay coil when wheel 57 is rotating at the speed with which the cable 11 is traveling. The tension of spring 65 is regulatable, as indicated by the arrows 66, so that the alarm-operating portion of the tester may be set for any predetermined minimum allowable gripping force.

Switch arm 64, when in closed position, completes a circuit, indicated by wires 67 and 68 between an electrical source L.sub.1 -L.sub.2 and the motor M. A manually operated switch 69 is provided for connecting lines 67 and 68 for starting the motor M which drives bull wheel 33.

Other signaling means may be provided as, for example, that shown in FIG. 10.

A voltage signaling tachometer generator 70 is secured on the shaft of wheel 57 and connected by wires 71 and 72 to a volt meter 73. A similar voltage signaling tachometer generator 74 is secured on the shaft of another wheel for sensing the speed of the cable 11. The hold-down pulley 37 may be used for this cable speed sensing wheel. Wires 75 and 76 connect the second generator 74 to a second meter 77 adjacent the meter 73.

The meters 73 and 77 have arms 78 and 79, respectively, mounted in place of the ordinary indicating needles or pointers usually found on such meters. Arm 78 carries a contact element 80 mounted on the arm by means of a spring 81 which is capable of compression. Arm 79 carries another contact element 82 fixed to the arm. The meters 73 and 77 rotate in such a direction and are so spaced that contacts 80 and 82 are in electrical contact when wheels 57 and 37 are running at the same speed. If wheel 57 runs at an increased speed, spring 81 is compressed and contacts 80 and 82 remain in contact but, if wheel 57 decreases in speed to run slower than wheel 37, then contacts 80 and 82 are separated.

Contact 80 is electrically connected to a line L.sub.2 of a source of electrical current and contact 82 is connected to one terminal of motor M, the other motor terminal being connected to L.sub.1 of the source. When a grip 12 passes under the sensing wheel 57, the wheel is riding on the track portion 30 of the grip and pulley 37 is riding on cable 11.

The spacing between meters 73 and 77 may be adjustable as indicated by the arrows 83.

In either the embodiment shown in FIG. 9 or that shown in FIG. 10, when the grip nears the position shown in FIG. 5, the high points 47 and 51 of teeth on members 46 and 49 of the torque friction device are approaching their maximum resistance to the rotation of sprocket 31. When this maximum resistance is reached, if the grip 12 slips on cable 11, this slippage is sensed by the wheel 57 whether the grip slides on cable 11 or slips for a short distance.

In the embodiment shown in FIG. 9 the signal transmitted by the generator 60 is lessened by any grip slippage resulting in a lessened magnetic force in relay 63 which allows the spring 65 to open the switch 64.

In the embodiment shown in FIG. 10, the signal transmitted by the generator 70 is lessened by any grip slippage resulting in a movement of arm 78 to the right as viewed in the figure. The signal transmitted by generator 74 is not lessened, since wheel 37 is then sensing the speed of cable 11, and as a result the electrical connection between contacts 80 and 82 is broken.

In either case, the electrical supply to motor M is cut off and the bull wheel 33, and therefore cable 11, is stopped.

It will be apparent that, alternatively, any means for giving an audible or visual signal may be operated by sensing wheel 57 and the tow cable 11 may then be manually stopped.

It will also be apparent that there has been provided means for quickly checking fixed or detachable grips secured to a cable at any point therealong with a build-up of resistance at the point of checking without appreciable oscillation of the cable. The speed sensing means is accurate so that even partial slipping is sensed, the grip receiving notches may be of any shape conforming to a portion of the grip, and the resistance and speed sensing means are adjustable so that testing for different loads and cable speeds may be obtained.

Claims

I claim:

1. A cable grip tester for detecting slippage of grips clamped to a linearly driven cable, comprising: a notched sprocket rotatably supported adjacent the cable, the sprocket notches each being adapted to receive a portion of a grip as it passes for turning the sprocket a fraction of a turn and then releasing the grip, the sprocket having at least one tooth projecting from one side thereof, non-rotating teeth secured adjacent the sprocket and adapted to successively engage the sprocket tooth as the sprocket turns, each tooth having a high point and sloping sides and each non-rotating tooth having a low point at the end of each sloping side, the non-rotating teeth being spring biased against the sprocket tooth for providing torque resistance to the rotation of the sprocket for each fractional turn thereof, each grip having an elongated and thin track portion extending along the cable, and speed sensing wheel biased against the cable and adapted to pass over the passing grip track portions while torque resistance is applied to the sprocket, the speed sensing wheel being adapted to drive tachometer means for operating a signal when a slowing of the wheel indicates slippage of a grip.

2. A cable grip tester for detecting slippage of grips clamped to a linearly driven cable, each grip moving a load attached thereto, comprising: a generally circular sprocket rotatably mounted on a fixed support adjacent the passing cable, the sprocket having a plurality of notches adjacent its perimeter, each notch being profiled for receiving therein a portion of a grip passing on the cable for turning the sprocket a fraction of a complete turn and then releasing the grip therefrom, a torque-friction device having a first member coaxially secured to one side of the sprocket and a second member non-rotatably mounted on the fixed support and coaxial with the first member, the first member having at least one tooth extending radially thereof, the second member having a plurality of angularly spaced teeth equal in number to the notches and extending radially thereof, each tooth having a radially extending high point and sides sloping down to low points on either side, the sloping sides of the respective teeth being adapted to be successively interengaged as the sprocket is turned, the second member being adjustably spring biased against the first member, the teeth of the torque-friction device and the sprocket notches being oriented so that as the sprocket turns and the high points on interengaged teeth pass one another the teeth are interengaged for continuing the rotation of the sprocket to a position in which a succeeding notch is adapted to receive a succeeding grip, a speed sensing wheel being rotatably secured adjacent the cable and biased thereagainst, each grip having an elongated track portion lying along one side of the cable and adapted to underlie the sensing wheel during interengagement of the teeth of the torque-friction device, whereby the sensing wheel successively senses the speed of the cable and then the speed of the passing grip, a tachometer generator adapted to be rotated by the rotation of the sensing wheel, the generator being electrically connected to a tachometer meter, the meter being adapted to operate a switch in an alarm device when the sensing wheel slows while sensing the passage of a grip track in contact therewith.

3. A cable grip tester for detecting slippage of grips clamped to a linearly driven cable, each grip being connected to a load for moving the attached load, comprising: a notched sprocket removably and rotatably mounted on a fixed support adjacent the passing cable, the sprocket having an annular groove therein for containing the cable and four angularly spaced notches across the perimeter thereof, each notch being profiled for receiving and later releasing a portion of a passing grip therein for turning the sprocket a quarter of a turn by each grip, a torque-friction device having a first member coaxially secured to one side of the sprocket and a second member non-rotatably mounted on the fixed support and coaxial with the first member, the first member having two diametrically opposite teeth extending radially thereof, the second member having four teeth extending radially thereof and spaced at 90 degress from one another, each tooth having a radially extending high point and sides sloping down to low points on either side of the tooth, the sloping sides of the respective teeth being adapted to be successively interengaged as the sprocket is turned, the second member being adjustably spring biased against the first member, the teeth of the torque-friction device and the sprocket notches being oriented so that as the sprocket turns and the teeth high points on interengaged teeth pass one another the teeth are interengaged for continuing the rotation of the sprocket to a postion in which a succeeding notch is adapted to receive a succeeding grip, at least one speed sensing wheel being rotatably mounted on a shaft journalled at one end of an arm, the other end of the arm being pivotally secured to the fixed support and the arm being spring-biased for engaging the wheel against the cable, each grip having an elongated track portion clamped against one side of the cable and adapted to underlie the one sensing wheel during interengagement of the teeth of the torque-friction device, the track portion having a ramp portion sloping along the cable away therefrom followed by another ramp portion sloping along the cable back toward the cable, whereby the one sensing wheel successively senses the speed of the cable and the speed of the passing grip, a tachometer generator having a part connected to the sensing wheel shaft and adapted to rotate in unison with the one sensing wheel, the generator being electrically connected to a tachometer meter, the meter being adapted to operate a switch in an alarm device when the sensing wheel slows while sensing the passage of a grip track in contact therewith.

4. The cable grip tester defined in claim 3 wherein the motor for driving the cable is electrically operated and electrically connected to a source of electrical power, and the alarm device switch is in the circuit between the driving motor and the power source, whereby the cable is stopped for repairs to the grip when a slipping grip is detected.

5. The cable grip tester defined in claim 4 wherein the tachometer meter is a relay, the relay operating coil being operable to close the alarm device switch in the circuit between the driving motor and the power source, the alarm device switch being adjustably spring-biased toward open position, whereby the alarm device is operated by a slowing of the one speed sensing wheel to a speed less than a predetermined speed.

6. The cable grip tester defined in claim 4 wherein the tachometer meter responsive to the speed of rotation of the one sensing wheel has an arm pivotally secured thereto and adapted to move arcuately in response to changes in the electrical signal received from its connected tachometer generator due to changes in speed of rotation of its connected sensing wheel, a second rotatably mounted speed sensing wheel spaced from and adjacent the one sensing wheel and biased toward contact with the cable for sensing the cable speed, the second sensing wheel being operatively connected to a second tachometer generator electrically connected to a second tachometer meter, the second meter having an arm pivotally secured thereto and adapted to move arcuately in response to changes in cable speed sensed by the second speed sensing wheel, the respective arms of each tachometer meter each carrying one contact of the alarm device switch, one contact being connected to its associated arm by spring means, the two meters being adjustably spaced and so oriented and regulated that the slowing of the one speed sensing wheel breaks the electrical contact between the contacts of the alarm device switch and an increase of the speed of rotation of the one sensing wheel relative to the speed of rotation of the second sensing wheel is absorbed by the spring connecting the one contact to its associated arm.