CA2085161A1 - Cable machine control - Google Patents

Abstract

IMPROVED CABLE MACHINE CONTROL
ABSTRACT OF DISCLOSURE
A cable operated machine for moving a working element over a span between a machine and a rear sheave, includes a hand controller to generate signals for a controller that controls the brakes and drives of the machine. Thelengths of the cables extending from the machine are measured and the generated signals are biased by the controller in accordance with the position of the working element as defined by the amounts the cables extend from the machine to apply different default tensions to the cables depending on the position of the working element along said span.

Description

~0~3161 IMPROVED C:ABLE MACHINE CONTROL
Field of the Invention The present invention relates to a control system. More particularly the present invention relates to a cable operated machine control system wherein S separate controls are provided to obtain selected operations or movements o~ the working element.

Bacl69roun~ of the Present Invention in cable operated equipment particularly grapple yarclers, the operator 10 must become extremely skilled to properly and rapidly manipulate the grapple or working element to engage and move the logs or the like.
Excluding interlock yarders, there are three main varieties of the basic grapple yarder. Each variation incorporates a main crane structure and a grapplesuspended by cables between the main crane structure and a block or sheave.
IS Each also includes a main line and a haul back line. The main line connects directly to the grapple mechanism and is used to move the grapple towards the crane and to close the grapple. The haul back line passes through the block or sheave and then to the grapple and is used to move the grapple out, i.e. away from the crane. By adjusting the tension in the main line (and in some cases, the 20 opening line) and U~e haul back line the sag in the lines is increased or decreased and the grapple can be raised or lowered. :~
The variations include the use of twin main lines wherein a second main line is used to open the grapple. In this arrangement each of the main lines uses an individually controlled wineh having an on/off clutch connected to the drive 25 and a controlled variable friction water cooled brake. When hauling the grapple in toward the crane, brakes on these winches are released and the clutches engaged while tension and consecutively the grapple height is maintained by application of a haul back brake and the speed is regulated by the engine throttle. To haul the grapple out, these main clutches are disengaged and the 30 main brakes (opening and closing lines) normally applied to adjust line tension and thus the sag of the lines and at the same time the haul back clutch is engaged to activate the haul back winch to draw in the haul back line and move : . ' . ~ :
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2 20~al61 the grapple out, away from the crane. Opening and closing of the grapple is obtained by relative movement beitween the two main lines which are sometimes named as the opening and closing main lines.
In another form of machine, the opening main line is replaced by a smaller 5 diameter tag line whose prime function is to open the grapple. The tag line winch is driven by a variable friction water cooled clutch to haul in the tag line or resist it being pulled out thereby maintaining a tension in tha t,ag line. The grapple is opened by increasing the tension in the tag line to move the tag line relaitive to the main line (i.e., by tag line and main line relative position manipulation).
The third variation incorporates two rnain lines driven at tha same speed, one of which is designated an opening line, passes through a line shortener so that the opening line may be selectively shortened by operating the line shortener to thereby open the grapple.
All machines ar~ provided with locking brakes normally spring applied and air released to lock all the winches for example, for parking.
The cab, boom, winches, drive, etc. of the crane are all mounted on a platform that is rotatable in opposite directions via a swing left or a swing right clutch driven by the main motor to swing the boom, cab, etc to the left or rightrespectively.
The control systems currently available for this equipment require individual . ~
direct manual control oif each of the various drive clutches or brakes and for the operator to selective!y engage and/or disengage clutches and/or brakes to obtain the desired operation or direction of movement of the operating element or grapple. Thus in current machines such as a grapple yarder having a haul 25 back cable drive, a closing main cable drive and an opening main cable drive,each with its own brakes and clutch, the operator is required to select and directly control each of the drives and each of the brakes independently and to adjust the throttle or power source to obtain the desired rate of change. For example to move a grapple in requires that tha operator simultaneously activate 30 both opaning and closing drives (in tag machine only the closing drive is controlled) and disangage the opening and closing brakes, partially releasing the haul back brake to apply the desired dra0 to the haul back cable and adjust the .. . .. ; , . ;

208~
throttle to obtain the desired rate of movement. In such a double main line grapple yarder, the operator, in manipulating the grapple, must coordinate the movement of three levers, two joysticks, three pedals and a knee control.
Obviously this requires a significant amount of physical and mental effort 5 sometimes very rapidly when transferring from one direction to another and to control the movement and operation of the grapple. Obviously excessive mental and physical effort leads to fatigue reducing the effectiveness of the operator.Also, to become a proficient operator takes a significant amount of training time.
Recently issued U.S. Patent 5107977 issued April 28, 1992 to Worsley, 10 discloses a particular machine control wherein movement of the control handlein a given direction results in a particuiar operation of the working elements, i.e.
movement of the control handle up by the operator results in an up movement of the grapple, movement of the handle in towards the body results in movement of the working element toward the machine itself or movement of the control stick 15 or handle away from the body causes a similar movement of the working elementor grapple away from the machine. Also, movements to the left, to the right, causes the machine to turn to the left or to the right so that movement of the grapple is in affect at least partially intuitive.
A problem encountered in the operation of the machine of the Worsley 20 patent involves the different forces applied by the grapple (which weights in the order of a ton and a half3 to the cables, which forces vary depending on the location of the grapple along the span between the machine and the rear sheave.
These changing forces significantly influence the forces or tensions that must be applied to the cables to maintain the ~rappla on a particular course, e.g., a 25 certain height above the ground.

Bri~f Description o7 ~he Pre~0nt Invention It is an object of this invention to improve machine control for cable operated machine over the span of movement of the working element.
Broadly, the present invention relates to a cable operated machine and a method of operating a cable operated machine to move a working element over a span between a machine bas0 and a rear sheave, said machine having a haul , : . :
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2~83161 .

back drive means with a haul back brake means associated therewith, a main drive means with a main brake means associated therewith, and means for opening and closing said working element, a hand controll0r, a control means controlling said haul back brake, haul back drive, main dr;ve and main brake, and said opening and closing means, in aceordance with corresponding signals generated by said hand controller, said control means including a cornputer to control said drive means said brake means and said open and close means in accordance with said signals generated by said hand controller, a first means for measuring the position of a haul back cable, second means for measuring the position of a main cable, said first and second measuring means signalling said computer means the position of its respective said cable and said computer means biasing op0rating signals sant to said drive means and said brake means in accordance with the position of said working element as defined by the amountof said cables extending from said machine to apply a different default tension to said main cable and said haul back cable depending on the position of said working element along said span.
Preferably said computer means biases said operating signals on tha basis of a preset relationship of line tension to location of the working element along said span.
Preferably said computer means will include means for modifying said preset relationship.
Preferably said span of the working element between the rear sheave and the machine will first be mapped by marking a first position adjacent to the machine and a second position locatad at the remotest position from the machine at which the working element may ba operated to define the length of said span and wherein said relationship will be based on said length of said span.
Preferably means will be provided for temporarily selecting a selected position along said working span and wherein said computer means will be programmed to control said drives and brakes to automatically return sai workin0 elament to said salected position on receiving a specific signal.
Preferably, computer means inciudes means for changing the pressure applied by each respective brake means based on the transition of the respective .: . : , . : :~ . ,:
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cabl0 being braked from a stop position into a moving position to provide a smooth transition to sliding friction.

Brie~ Description ot the Drawings Further features, objects and advantages will be evident in the following detailed description of the preferred embodiments of the present invention takenin conjunction with the accompanying drawings in which.
Figure 1 is a schematic illustration of a cable operated machine into which the present invention may be incorporated.
Figure 2 is a schematic illustration of the computer control system of the present invention.
Figure 3 is a graphic representation of the operation of the various drive and brake elements of the cable operated equipment.
Figure 4 is a typical graph of applied brake pressure or cable tension over the working span of the machine, i.e. illustrating a default curve of tension vsdistance.
Figure 5 illustrates graphs similar to Figure 4 showing modified default curves.

Descrip~ion of the Preferred Embodim~nts Figure 1 schematically illustrates a two rnain line cable operated system 10 such as that used for grapple yarding of logs. The two rnain line (cable) rnachine is the most complicated (has the most number of controls) of the three variations of tho ~rappl0 yarder as described above and thus the control will be described for this type of machine which incorporates separate opening and closing drives each of which is provided with its own cable and brake.
The system 10 includes a prime mover such as a diesel engine 12 adapted to provide power via a common drive which for sirnplicity has been illustrated as a sha~t 14. Clutches 16, 18, 20 and 22 couple the haul back drive 2~, closing drive 26, opening drive 28, or cab and bovm plafform swing drive 30 respectivelyto the prime mover 12. (Only a single boom swing drive clutch 22 has been shown but in many machines two such clutches are provided; one to initiate , ........ .......... . . .
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2~8~161 clockwise rotation of the plafform and the other to obtain counterclockwise rotation of the plafform.) The prime mover 12 is provided with a torque or throttle control 32 that governs the amount of energy available and thus ~he power or speed of the shaft 14.
The various drives, namely the haul back drive 24, closing drive 26 and opening drive 28 are each coupled to the prime mover shaft 14 through their respective selectively actua~ed haul back, closing and oF7ening clutches 16, 18 and 20. Each drive 24, 26 and 28 is also provided with a brake, namely a haul back brake 34, a closing brake 36 and an opening brake '38 respectively. A haul back cable 40 passes from the haul back drive 24 around a return pulley 42 and connects with a working element 44 which in the illustrated system is a grapple 44 so the tension in ~he line 40 draws the grapple 44 in the haul back directionas indicated by the arrow 46. The closing drive 26 has a main cable 48 connected to the grapple element 50 via an extension cable 52 and the opening drive 28 has a cable 54 that is connected to cable 48 as indicated at 55. The grapple element 50 may be opened and closed by shifting the cables 48 and 54 and thus the position of the joint 55 toward and away from grapple 44.
Movement of joint 55 toward ths grapple extends the available length of cable 52and opens the grapple element 50.
The grapple 44 is slung from the outgoing section 40A of the cable 40 via a pulley 56 that rides on the section 40A of the cable 40 and a suspension cable58.
A suitable hand controller for controlling the operation of the various drives and brakes is illustrated in Figure 2. Controller 100 is mounted on the base 102and is composed of a control arm rest 104 supported on a support post 106.
Projecting axially from the arm rest 104 is shaft 120 on which is mounted a hand grip 122. The shaft 120 may be moved in and out as indicated by the arrow 124. The degree of displacement is measured via the sensor 126 which senses the hori~ontal displacement of the shaf~ 120. Displacement of the shaft 120 in a forward direction away from rest 104 as indica~ed by the arrow 124 results in the haul back drive 24 moving the grapple 44 in the direction of the arrow 46, i.e. towards the pulley 42. The opening and closing brakes are applied 2~161 to resist such movement and apply the required tension to the cables.
Mov~ment of the shaft 120 in the opposite direction deactivates th~ haul back drive 24 and activates the opening 26 and closing 28 drives through the clutches18 and 20 respectively as required to move the grapple 44 away from the pulley 5 42, i.e. in the opposite direction to the arrow 46 and the haul back brakc is activated to apply the required tension to the cables (as weil be described below).
The grapple 44 is moved up or down by pivoting the shaft 120 as indicated by the arrow 132. Such pivotal movement is sensed b~ the sensor 134 which generates an up signal for movement up when the shaft 120 is moved up or a 10 down signal when moved down. Up and down rnovement is obtained presumably by varying the tension in the cables.
To rotate the boom (not shown) via the boom swing drive 30, the shaft 120 is rotated as indicated by the arrow 136. This rotation of the shaft at 120 relative to the arm 104 is sensed by the sensor 138 that sends a signal to activate the 15 clutch 22 to drive the boom swivel 30 in the appropriate direction. The machine, i.e. boom, drives, clutches, powar generator and operator are all on a common plafform that rotates when the boom is rotated.
Displacement of the shaft in any direction adjusts the throttle or torque control 32 to increase the amount of torque available in drive 14. In all cases the 20 major demand for power, i.e. maximurn displacement will govern the setting ofthrottle 32, however this setting will be further influenced if two controls (e.g. up and out or up and in? are actuated simultaneously. For example, if the grapple is to be lifted and moved in the direction opposite to the direction of the arrow 46 the control handle 122 will be moved toward the arm 104 to move the grapple in 25 and at the same time pulled upwardly as indicateci by the arrow 132 which will result in shortening the length of the cables to the working element. As above indicated displacement of the shaft 120 in any direction normally result in a particular adjustment of the throttle 32. Whichever of the above movements (in the directions of the arrow 124, 132 or 136 frorn a rest position or normal position 30 to which the shaft 120 automatically returns when free~ would result in the higher torqua setting for the throttle 32 is the predominant factor by which the throttle 32 will be adjusted. However, if desired the computer 144 (to be described ~08~161 below) may be programmed to add to this higher setting a further throttle increment based on an increment in proportion to the displacemen~ of the control100 in the directions demanding the lower throttle settin~s.
Operl or close command si~nals are provided by rotating the handle 122 S around the axis of sha~t 120 as indicated by the arrow 140. Preferably, clockwise rotation provides an open signal, counterclockwise, a close signal and the rest or normal position no signal. A suitable sensor such as that schematically indicated in 142 may be used to generate the open and close signals.
The above described device is very similar to that described in U.S. Patent 5,107,997 referred to herein above. The modifications of the present convention include the application of the cable extension sensors 300, 302 and 304 for the haul back cable 40, for the closing cable (main cable) 48 and the opening cable 54 respectively. Each of these sensors 300, 302 and 304 measures the drum rotation for the particular cable to determine the amount of cable 40, 48 or 5 respectively extending from the machine so that the approximate position o~ the working element 44 can be determined based on signals generated by these sensors 300, 302 and 304. These signals are sent to the computer 144 which determines the approximate location of th0 element 44 as indicated at 306. This information may then be used in conjunction with a prese~ relationship of line tension to span length as will be described below to provide modified signals tocontrol pressures applied to the brakes 34, 36 and 38 to maintain the required tension in the cables 40, 48 and 54 in accordance with a preselected relationship of the location of the working element along the working span between the machine and the return of sleeve 42. '~
Figure 4 shows a typical preset tension curve 303 illustrating the changes in the basic tension required for the working element 44 to travel along the working span for each of the cables 40, 48 and 54. The precise stresses or tension on these cables obviously may be different, however curves wiil generally conform with the curve 308 in Fi~ure 4. The basic or preselected amount of brake pressure or drive tension applied to the cable is obtain this preset relationship be~ween cable tension and distance along the span length, e.g.
distance of the working element 40 from the machine is illustra~ed by the curve .. , ~ , , ", . . . . ............ . . .

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9 20~5~63 308.
The default curve 308 of tension in cables 40, 48 and 55 vs span (distance of the working element from the machine) is defined empirically for each of the cables based on moving the working element back and forth between a first 5 position adjacent to the machine and a second position remote from the machineunder selected load conditions, e.g. average load, no loacl, etc. to provide default curves 308 for each of the different cables and their respective drives and brakes to maintain the desired required tension. ,, Once the default curves 308 have been establishet:l for any given piece of 10equipment they may be used for most operations. Howlsver, if a particular siterequires a dfflerent set of operating curves 308, thess default curves may be modified as will be described below.
Also, it will be apparent that the default curves are based on a span which normally will be the maximum span that the equipment is likely to be used. If in15any operation the span is dfflerent, i.e. the length of the span is say shorter the curve will be modified accordingly by shortening the distance between the back sheave and the machine. Generally in such modified default curves the tension at the back sheave and adjacent the machine and the maximum tension (at mid-span~ will be the same as the basic for original default curve so that the curve20~308) takes on a different shape for the shorter span. For example, as indicated by the curve 308A in Figure 4 between the points A and B in Figure 4, i.e. the total span length between points A & B is less than i~he normal or complete spanlength between A & C however the tensions in the cable at B or C would be essentially the same as indicated by the horizontal line 110. Similarly the tension 25adjacent the yarder will be essentially the same and the maxirnum tension which - - -will ba about mid-point of ~he span will be the same for curve 308 as for curve 308A.
Generally these curves are defined by a set of points along the length. It has been found that 6 uniformly spaced points as indicated at 1, 2, 3, 4, 5 and 306 along the curve 308 in Figure 5 is sufficient. In some cases it is desired to change the shape of the default cume 308 at least temporarily, for exarnple by changing the tension along the curve, i.e. by an amount equal to X for example, 20~161 adjacent the back sheave, Y in the mid-span and Z at or adjacent the yarder to produce a curve shown by the dash lines 312 in Figure S. This adjustment of the shape of the default curve 308 can be done at all six of the points 1, 2, 3, 4, 5, 6, or only at selected points as desired with the points in between being made S to conform to the normal curvature of curve 308.
Referring back to Figure 4 it will be apparent that if one simply attempts to move the working element in either direction, the tensions will be maintainedin each of the cables in accordance with its particular curve 308 by appropriatecontrol of drive and brakes. Assuming one now further wishes to either raise or 10 lower the working element which requires an adjustment of the tension in the cables, then the hand controller puts a + or - signal as indicated by the dimensions + and - for position a on curve 308 to thereby change the tension significantly from the default tension which will cause the working element to either rise or to lower.
As indicated in Fi~ure 2, the signal from the sensor 126 is fed via line 142 to the main computer 144 to provide an in or a haul back signal as indicated at 146 and 148 respectively.
The sensor 134 provides the computer 144, via line 150, an up signal 152 or a down signal schematically indicated at 154. The line 156 delivers an open 20 signal schematically represented at 158 or a close signal 160 from the sensor 142 and the si~nals from the sensor 138 are delivered by line 162 to provide a swingri~ht signal (clockwise) signal as schernatically indicated 164 or a swing le~t (counterclockwise) signal 166 to the computer 144.
The comput0r 144 analyzes the signals and controls the main drive power 25 control or throttle 32, the haul back drive via the clutch 16, the haul back brake 34, the main or closing drive 26 via clutch 18, the opening brake 36, the secondmain or opening drive 28 via clutch 20 and the opening brake 38 and modifies the signals from the controller 100 based on the location of the working elementalong the span between the machine and the sheave 42. The computer 144 also 30 controlled the boom swing 30 via the clutch 22 (if desired the boom swing mayalso be provided with a boom brake that would likewise be controlled by the maincomput~r control 144). The operation of the main computer control to control the ' !
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various operations is summarized in Table 1 and will be described now in respectto the schematic illustration of Figure 3.
TA~LE 1 Preferred Sy~lem An AltQrnativaSystem (Further Alternative) GrappleDrive~ or Drive BrakeDrive Brako MovementBrakes CondiUon Condmon Condition Condilion In anti o~n (Haul B~ck) Control In Haul Back Off Drag 10Opening On Off Closing On Off Control displacement adjusts speed of operative drives (opening and closing) through throttle control and adJust drag by varyiny pressure ~o the haul back brake. The dra~ Is also determlned by the deslred helght of the working element.
15 Haul Haul Back On Off Back Opening Off Drag Closlng Off Drag Control dlsplacement adJusts speed of operative drive and drag applled vla closlng and opening brakes. The drag also governs the height of the worklng element.
20 Up and Down Control per se Up Haul Back On ff OH(on) Locked(off) Per Se Openlng Off Locked On(on) (~ff(o~ :
Closlng Ofl Locked On(on) Off(of Control dlsplacement adjusts speed of operative devlce through throttle control.
25 Down Hau! Back Off Drag OH(of~ Drag~locked) Per Se Opening Off . Drag Off~ff) Locked(drag) ~ ~ :
Gloslng Off Drag Off(offl Locked(drag) Control displacement adjusts drag applied by activated brakes.
Open and Close Control per se ~ :
30 Open Haul Back Off On Off On ~ -Opening On Off Off On Closlng Off On Off Off Control displacement adjusts speed of operative drive through throttle control when the ~ -closing drive is on.

2 0 ~

Close Haul Back Off On Off On Opening Off On Off Off Closin~ On C)ff Off On Control dlsplaceme~ aclJusts speed of op~rativ~ drive through throttle control 5 In and Up Simultaneous Haul Back Off Drag increased Open On Off Close On Off Dlsplacement of control increases throttle and the speéd of open and clos0 drives primarily 10 dependent on the control displacement that is the greater and Increases the drag above that normally applied to haul back brake 34 at a rate in proportlon to the displacement of control 100 in the Up direction I.e. in the direction of the arrow 132 until the desired height is reachecl and the Up direction control moved to ne~ral pos~ion. -~
As indicated in Figure 3, the throttle control as indicated by the line 200 has a neutral position 202 and increases after a preset displacement of the handcontroller in any direction, i.e. for a signal to move the working element in the direction is shown to the left of the neutral or centre line 204, and in tha haul back direction whieh obtains movement of the working element 44 in the out 20 direction (arrow 46 in Figure 1) is shown to the right of line 204. The sloping parts 206 which are mirror images on the curve 2û0 indicate the increase in throttle as directly dependent on displacement of haul back or in controls.
Movement in the in direction causes en~agement of the closing clutch (assuming that the grapple is now moving inwardly with the log the grapple must 25 be closed as indicated by the engaged line 210. Similarly the opening clutch is also cngaged as indicated by line 208 so ~hat the line or cables 48 and 54 ar0 drawn in toward the closing and opening drives 26 or 28 respectively so that both cables 48 and 54 share the load to drive the working elernent 44 in. The relative positions of these cables 48 and 54 determine whether the grappls 50 is open or 30 closed. Obviously under these conditions the haul back clutch 16 must be disan~aged as indicated by the line 212. The opening and closing brakes 36 and 38 are disengaged as indicated by the line 214 and 216 respectively.
The pressure on ~he haul back brake 34 has been indicated by two sets of substantially horizontal curves 218 and 220 indicating that the pressure or back ..

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13 ~083161 pressure (tension) applied via the haul back brake to the cable 40 is difFerent depending on the height of the grapple (higher pressure greater dray the higher the grapple under stable conditions). These curves will be further modified to take into account the position o~ the grapple or workin~3 element 44 along the 5 working span as shown in Figure 4.
The control of the opening and closing clutches is in part regulated by rotation of the handle 122 as indicated by the arrow 144. If the handle 122 is in the open position when the grapple approaches the boom, the closing clutch is disengaged before the opening clutch thereby to open the grapple. To close the 10 grapple and pick up a log the handle 122 will be rotated to the close position activating the closing clutch before the opening clutch to close the grapple before the grapple is moved in the direction opposite to the arrow 46.
With the preset default curve 308 or the modified preselected curves 308A
or 312 of $ension vs distance (i.e. Iocation of the working element along the span) 15 defined as above described, the computer may be further programmed to return the working element to a selected location along the span and if desired to openthe working element and further if desired to drop or lower it to pick up a log or the like. This is obtained by activating the switch 125 as indicated by the arrow 127 (see Figure 2) to first set the location by movement in one direction and then 20 sent to the set or selected location or when the selected locatisn is reached, cause the machine to stop or open the grapple or both or perform other desired functions substantially automatically on command depanding on the programming of the computer by movement of switch 125 in the opposite direction. When the haul back drive 24 is activatad throttle control 3~ acts as above described and 25 follows the curve 206. Both the opening and closing clutches 18 and 29 are disengaged as indicated by the curves or lines 208A or 210A respectively and thehaul back clutch 16 is engaged as indicated by the line 212A. The opening and closing brakes 36 and 38 are each designated by two curves 214A and 214B and 216A and 216B respectively whieh indica~e that both brakes are applied and the 30 degree of applied pressure to the brakes is dependent on the desired height of the grapple and the desirecl state (e.g. open or close). The curves 214A and 216A simply indicat~ a different brak0 se$ting than $he curves 214B and 216B

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208al~1 whereby the tension in the cable system is changed ancl thus the height of the grapple changed for a given position along the working span.
Superimposed on the setting illustrated in Figure 3 are the conditions implicit in the selected tension curve examples of which are shown in Figures 4 5 and 5 which further adjust the brake settings based on location of the working element 44 along the working span.
The haul back brake obviously must be disengaged as indicated by the line 222 when the working element 4~ is moved in the direction of arrow 46. - -It will be apparent from Table 1 and from a review of Figure 3 that displacement of the control to opposite sides o7 the neutral position as indicated by centre line 204 and the hori~ontal section of the curve 202 automatically results in operation of the various brakes and clutches and adjustment of the throttle setting to obtain the desired movement of the working element 44.
It will be apparent that the forces applied to the brakes when its respective cable is stopped is different from the forces required to maintain the same tension in its respective cable under moving friction conditions. The computer is programmed to correspondingly vary the pressure applied by the brakes during the transition periods, e.g. by pulsing the brakes at a selected Frequency during the transition period.
The above description has dealt with systems wherein two main lines, i.e.
both the opening and closing lines act as driving lines to pull the grapple in towards the unit. In a tag line system wherein a tag line position is used primarily to open and close the grapple, the tag line t~nsion is maintained at a substantially constant relationship relative to that of the main line except when it is desired to open and close the grapple. Thus the ta0 line is reelsd in at essentially the same rate as the main line or fed off at essentially the same speed as the main line with the rate of feeds being changed by adjusting the drive to the tag line drum to relatively displace the two cables and cause selectad opening and closing of thegrapple or working element 44. The control system controls the clutch to the opening cable and there need be no brake on the opening cable drive. If such a brake is provided the control need only active the brake when the grapple is in a stop position.

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., ~ . , 2~8~161 It is preferred to provide a ~dead man' control in the system that will stop the working element in its current location should the operator release the control handle.
Having described the invention, modifications will be evident to those S skilled in the art without departing ~rom the spirit of ~he invention as defined in the appended claims.

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Claims (10)

1. A cable operated machine for moving a working element over a span between a machine base and a rear sheave, said machine having a haul back drive means with a haul back brake means associated therewith, a main drive means with a main brake means associated therewith, and means for opening and closing said working element, a hand controller, a control means controllingsaid haul back brake, haul back drive, main drive and main brake, and said opening and closing means, in accordance with corresponding signals generated by said hand controller, said control means including a computer to control saiddrive means, said brake means and said opening and closing means in accordance with said signals generated by said hand controller, a first means for measuring the position of a haul back cable, a second means for measuring the position of a main cable, said first and second measuring means signaling said computer means the position of its respective said cable and said computer means biasing operating signals sent to said drive means and said brake means in accordance with the position of said working element as defined by the amountof said cables extending from said machine to apply a default tension to said main cable and said haul back cable depending on the position of said working element along said span.

2. A machine as defined in claim 1 wherein said computer means biases said signals to apply said different default tensions based on a preset relationship of cable tension to location of said working element along said span.

3. A machine as defined in claim 2 further comprising means for temporarily selecting a selected position along said span and wherein said computer means is programmed to control said drives and brakes to return said working element to said selected position.

4. A machine as defined in claim 2 wherein said computer means includes means for changing the pressure applied by each respective brake means based on the transition of the respective cable being braked from a stop position intoa moving position to provide a smooth transition to sliding friction.

5. A method of operating a cable operated machine to move a working element over a span between a machine base and a rear sheave said machine having a haul back drive means with a haul back brake means associated therewith to apply tension to a haul back cable, a main drive means with a main brake means associated therewith to apply tension to a main cable, and means for opening and closing said working element, a hand controller, a control meanscontrolling said haul back brake, haul back drive, main drive and main brake, and said opening and closing means, in accordance with corresponding signals generated by said hand controller, said control means including a computer to control said drive means said brake means and said open and close means in accordance with said signals generated by said hand controller, the improvement comprising measuring the position of a haul back cable wound on said haul back drive and sending a first signal to said computer means, measuring the position of a main cable, wound on said main drive and sending a second signal to said computer means, said computer biasing operating signals sent to said drive means and said brake means in accordance with the position of said working element as defined by the amount of said cables extending from said machine as defined by said first and second signals to apply a different tension to saidmain cable and said haul back cable that changes depending on the position of said working element along said span.

6. A method as defined in claim 5 further comprising varying said default tension in accordance with a default curve of tension vs position of said work element along said span between said rear sheave and said machine.

7. A method as defined in claim 6 further comprising temporarily marking a selected position along said span and controlling said drives and brakes to return said working element to said selected position.

8. A method as defined in claim 5 further comprising changing the pressure applied by each said brake means based on the transition of the respective cablebeing braked from a stop position into a moving position to provide a smooth transition to sliding friction.

9. A method as defined in claim 6 further comprising changing the pressure applied by each said brake means based on the transition of the respective cablebeing braked from a stop position into a moving position to provide a smooth transition to sliding friction.

10. A method as defined in claim 7 further comprising changing the pressure applied by each said brake means based on the transition of the respective cablebeing braked from a stop position into a moving position to provide a smooth transition to sliding friction.