US 3721357 A
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Description (OCR text may contain errors)
March 20, 1973 -372l',357
MULTIFUNCTION INTEGRATED CONTROL MECHANISM Filed Ju 1y 15,. 1970 w. A. WILLIAMSON 5 Sheets-Sheet 1 1' NVENTOR WILLIAM A. WILLlAMSON.
ATTORNEYS March 20, 1.973 w. A. WILLIAMSON 332L357 MULTIFUNCTION INTEGRATED CONTROL MECHANISM.
Filed July 15, 1970 5 Sheets-Sheet 2 FIG. 9
84 f- FIG. 2
INVENTOR WILLIAM A. WlLLlAMSON Al IORNI Y) March 20, 1973 w. A. WILLIAMSON 3 L MULTIFUNCTION INTEGRATED CONTROL MECHANISM Filed July 15, 1970 s Sheets-Sheet a FIG. 3 5
INVENTOR WILLIAM A. WILLIAMSON ATTORNEYS March 20, 1973 w. A. WILLIAMSON 3,
MULTIFUNCTION INTEGRATED CONTROL MECHANISM Filed July 15, 1970 5 Sheets-Sheet 4 N VEN TOR WILLIAM A. WILLIAMSON BY 2 Z 9! E ATTORNEYS w. A. WILLIAMSON 3,721,357
March 20, 1973 MULTIFUNGTION INTEGRATED CONTROL MECHANISM 5 Sheets-Sheet 5 Filed July 15, 1970 FIG. 8
INVENTOR WILLIAM A. WILLIAMSON I Ma M ATTORNEYS United States Patent 3,721,357 MULTIFUNCTION INTEGRATED CONTROL MECHANISM William A. Williamson, Niles, Mich., assignor to Clark Equipment Company Filed July 15, 1970, Ser. No. 54,890 Int. Cl. E02f 3/00 US. Cl. 214-138 R 18 Claims ABSTRACT OF THE DISCLOSURE A control mechanism designed principally for use with a backhoe having a boom, a dipstick connected to the boom, a bucket pivotally mounted on the outer end of the dipstick and an actuating means for raising and lowering and slewing the boom, moving the dipstick forwardly and rearwardly, and curling the bucket, in which a single handle is used to control the multifunctions for simultaneously moving any one or more of the elements in varying degrees. A differential transformer is preferably used as a control producing signal for each of the elements, the transformers having a probe connected to and operated by the single handle or two handles in unison. The control mechanism may be used for other types of equipment and a different combination of functions.
The conventional backhoe consists of a boom, dipstick and bucket mounted on the rear of a tractor and operated through the tractor hydraulic system controlled by the operator at a control station or position on the tractor to perform the four basic backhoe functions of slewing the boom, pivoting the dipstick, curling the bucket, and raising and lowering the boom. In order to obtain optimum operation of the backhoe, two or more of the foregoing functions must be performed simultaneously, and in the conventional backhoe equipment, the operator is required to manipulate several separate controls in overlapping sequence in order to obtain the simultaneous functions. The hydraulic system and control therefor include hydraulic actuators controlled by four individual valve sections normally mounted near the rear of the tractor where, with the tractor seat reversed, the operator will be facing the controls as well as the backhoe. Each valve section has a separate handle which is operated only in the forward and rearward directions to obtain the desired manipulation of the backhoe component. Since the operator has only two hands, normally only .two functions can be conveniently performed simultaneously, and in many instances, these two independent functions are diflicult to accomplish in a smooth, integrated operation. Further, the conventional backhoe hydraulic system is the open center type and, if two functions are controlled simultaneously with different pressure requirements, most of the oil will flow to the actuator requiring the least pressure.
When digging a trench or other hole with the backhoe, the most productive procedure is to operate three functions simultaneously, including curling the bucket, curling the dipstick, and lowering or raising the boom. These three functions are difficult to perform simultaneously with conventional controls, and when the fourth function of slewing the boom to empty the bucket is added to the combination of functions, the functions become virtually impossible to perform smoothly and continuously, even in a partial sequential operation.
A further disadvantage of the existing control systems for backhoes is the nature of the movement of the control levers in performing the various functions mentioned hereinbefore. Since in the conventional control system, the control levers move only in the directions away from and toward the operator, the movement is unnatural to the 3,721,357 Patented Mar. 20, 1973 operator when performing several of the different functions required to fully operate the backhoe. For example, the bucket operates on a rotary motion, the boom on a vertical pivotal motion, the dipstick on a fore and aft motion, and the boom, in its slewing action, operates on a side to side motion. These various movements are in conflict with the forward and backward movement of the conventional control levers, and render the operation of the controls difficult, particularly for the inexperienced operator or with the simultaneous movement of several of the backhoe elements.
One of the primary objects of the present invention is to provide a control mechanism for the hydraulic system of a backhoe, which is so constructed and arranged that the manipulations required to operate the mechanism for performing each of the aforementioned functions are natural movements of the operators hands or arms with respect to the desired movements of the backhoe elements.
Another object of the invention is to provide a control mechanism for backhoes, which can be operated to perform all four functions involved in the operation of the backhoe through the use of a single control handle, the movement of which simulates the desired movement of the various elements of the backhoe, and which permits effective control of any one of the backhoe functions or several or all of the functions simultaneously in a smoothly combined operational movement.
Still another object of the invention is to provide a control for a multifunction mechanism, which utilizes a single control handle capable of controlling all functions simultaneously or any one of the functions individually, and which permits the elements or functions to be precisely controlled regardless of the number of functions being controlled at any given moment.
A further object is to provide a control mechanism of the aforesaid type which can easily be operated to perform several different functions without special training or skill, and which is so constructed and arranged that it can be operated at any convenient location over long periods of time with a minimum amount of fatigue.
Additional objects and advantages of the present invention will become apparent from the following description and accompanying drawings, wherein:
FIG. 1 is a perspective view of a tractor, backhoe, and front end loader assembly, showing the backhoe in operation controlled by an operator on the tractor;
FIG. 2 is a top plan view of one embodiment of the present control mechanism;
FIG. 3 is a partial horizontal cross sectional and elevational view of the mechanism shown in FIG. 2;
FIG. 4 is a partial cross sectional and elevational view of the control mechanism shown in FIGS. 2 and 3, the section being taken on line 4-4 of FIG. 3;
FIG. 5 is a cross sectional view of the control mechanism shown in the preceding figures, the section being taken on line 55 of FIG. 3;
FIG. 6 is a top plan view of another embodiment of the present control mechanism;
FIG. 7 is a side elevational view of the control mechanism illustrated in FIG. 6;
FIG. 8 is a rear elevational view of the control mechanism shown in FIGS. 6 and 7, with the cover removed to permit the elements thereof to be observed; and
FIG. 9 is a schematic diagram of a sub-system, one of the system components illustrating the manner in which the system operates.
Referring more specifically to the drawings, and to FIG. 1 in particular, numeral 10 indicates generally a tractor, having mounted on the rear thereof a backhoe 12 and on the front a loader 14. The control mechanism 20 for the backhoe is mounted on the rear of the tractor and is controlled by an operator 22 seated in a seat 24 facing the control mechanism and backhoe. The seat is reversible so that the operator can operate the front end loader 14 and drive the tractor in the normal manner. As shown in the drawings, a pair of outriggers 26 are mounted on the rear of the tractor to give stability thereto while the backhoe is being operated. For the purpose of the present description, the tractor, backhoe, and loader may be considered as conventional.
The backhoe shown in the drawings basically consists of a boom 30 pivotally connected to the tractor, dipstick 32 pivotally connected to the outer end of the boom, and a bucket 34 pivotally mounted on the outer end of dipstick 32. Hydraulic cylinders or actuators 36, 38, and 40 raise and lower the boom, swing the dipstick forwardly and rearwardly, and curl the bucket inwardly and outwardly, respectively. The hydraulic actuators are connected to the tractors hydraulic system and the control mechanism 20 by hydraulic lines, part of which are shown at numeral 42. The control mechanism to which the present invention relates may be used not only with different types of backhoes, but may also be used to control different types of equipment and apparatus requiring a plurality of functions performed simultaneously.
FIG. 9 illustrates schematically the basic operating component or subsystem of the present control system, as used in connection with a hydraulic actuator such as those used in the operation of the aforementioned backhoe, involving both embodiments of the control mechanism illustrated herein. In the system component shown in the diagram, a pressure compensated variable displacement pump 50 delivers pressurized oil to the closed center electro-hydraulic proportional valve 52 which distributes the oil to hydraulic actuator 54 for performing one of the functions of the backhoe. Valve 52 is actuated by solenoids 56 and '58 arranged to change a variable electrical current into a variable valve opening; i.e., the higher the value of electrical current, the farther open the valve will be, and consequently the more oil delivered to the actuator. The variable electrical signal is established by the electronic unit '60, and a l2-volt DC electrical signal is delivered through wires 62 and 64 to electronic module 66, where the signal is converted to an AC signal and sent to a linear variable differential transformer.
The differential transformer is cylindrically shaped and has a hollow core in which is disposed a probe 70, the probe being free to move longitudinally inside the transformer. The AC electrical signal, as determined by the position of the probe, is sent from the differential transformer back to electronic module 66, the strength of this AC signal being dependent on the position of the probe in the core of the transformer. When the probe is in the center of the transformer, there is no output electrical signal. As the probe moves to the right, there is a positive signal which increases with the increasing movement of the probe, and as it moves to the left there is a comparable negative signal. This AC signal in the electronic module is boosted to a sufiicient level and converted to a DC signal which is sent through wires 72 and 74 to the solenoid valves 56 and 58. Movement of the probe 70 within the transformer will actuate the valve 52 and cause hydraulic actuator 54 to move, the speed of movement of the hydraulic actuator being dependent on the position of the probe within the transformer. FIG. 9 shows the arrangement for only one system component and actuator, these being duplicated for each system component or subsystem, with the exception that only one pump and one electronic module are required for all of the functions. While the differential transformer is an effective means and the preferred means of producing the desired control signal for the various elements actuated by the system, other types of signal producing means, such as pneumatic and hydraulic means, may be used satisfactorily in some installations and on some equipment.
In the embodiment of the present control mechanism illustrated in FIGS. 2 through 5, the control mechanism is mounted on a horizontal support which in turn is mounted rigidly on the tractor. A frame 82 is secured to support 80 and supports the control mechanism indicated generally by numeral 84. The operator sits facing the left, as viewed in FIG. 2, and grasps handle 86 to perform the various functions previously referred to herein, the handle normally being approximately in line with the operators right shoulder.
The frame generally indicated by numeral 82 consists of end plate 88 and end plate 90 held in longitudinally displaced relationship by spacer rods 92, In the center of end plate 88 is welded a boss 94 which contains a ball joint 96. A handle or operating rod extends approximately the full length of the frame and has hand grip 86 mounted on the outer end, and is supported at its inner end by ball joint 96, the joint permitting angular movement of rod 100 in any direction as pressure is applied by the operator to handle 86, this arrangement permitting limited universal movement of the rod and handle.
A block 102 is mounted on rod 100 near the inner end thereof and is held securely in place by a setscrew, and thus moves with rod 100. A transformer held in place by a plurality of bolts 112 and spacer sleeves 114 controls the raising and lowering of the boom of the backhoe. This transformer is operated by a probe 116 connected to block 102 by a spherical rod 118. Movement of the hand grip upwardly or downwardly as viewed in FIG. 3 causes a pivotal movement at ball joint 96, and a to and fro movement of the spherical rod, which in turn causes the probe to move inwardly or outwardly in the transformer. A second transformer is mounted in frame 82 in the same manner as transformer 110 and is placed forwardly, i.e. toward the backhoe with respect to rod 100 and handle 86, this transformer being operated by a probe 122 which is connected to block 102 by a spherical rod 124. The probes 116 and 122 are loosely mounted in their respective transformers so that they have the freedom of some lateral movement. For example, vertical movement of handle 86 and rod 100 causes longitudinal movement of probe 116 within transformer 110. This movement of probe 116 causes, by means of the circuitry shown in FIG. 9, the hydraulic actuator similar to that illustrated at numeral 54 to operate, which in turn causes the boom of the backhoe to swing upwardly; i.e. raising the handle and rod 100 causes the boom to rise, and lowering the handle causes the boom to lower. Since rods 118 and 124 are mounted on the center of ball joint 96, movement of rod 100 in the vertical direction will not cause longitudinal movement of rod end 124, only a slight lateral displacement occurring. Consequently, the longitudinal relationship of probe 122 with respect to transformer 120 will remain unchanged and will be inoperative during the raising and lowering movement of handle 86 and rod 100. Likewise, if handle 86 is moved fore and aft, probe 122 will move in transformer 120 which in turn causes actuation of the hydraulic cylinder controlling the dipstick. Thus, when the operator pushes the control handle forward, the dipstick moves away from the operator, and when he pulls the handle rearwardly, the dipstick moves toward him. It is therefore seen that the two movements of the handle, i.e. upwardly or downwardly causing the boom to move upwardly or downwardly and fore and aft causing the dipstick to move forwardly and rearwardly, constitute natural movements corresponding to the movement of the boom and dipstick elements controlled by the handle. If the handle 86 and rod 100 are moved in any other plane than the two right angle planes previously referred to hereinabove, both transformers will operate, and the amount of operation of these transformers with respect to each other will depend upon the angle at which the handle is moved. For example, if the handle is moved upward and forward at an approximate 45 angle, both the boom cylinder and the dipstick cylinder will operate at the same time and in approximately the same amount, i.e. the boom will rise and the dipstick will extend. If it is desired to change the rate of speed of these two functions with respect to each other, it is only necessary for the operator to change the angle of the handle and rod.
The third function controlled by mechanism 20 is the motion of the bucket. Since the bucket rotates on an axis at the end of the dipstick, the natural operation for the operator is to rotate the handle to operate the bucket. This is accomplished in the embodiment of FIGS. 1 through 5 by a transformer 130 mounted on end plate 88 by a bracket 132. The axis of the transformer is in a general tangential position with respect to rod 100, and a probe 134 is connected by a spherical rod 136 to block 102 and rod 100. Consequently, rotational movement of rod 100 causes probe 134 to move to and fro on the axis of transformer 130, in either the positive or negative direction, thus resulting in a rotational movement of the bucket in either direction, the solenoid being connected to the actuating cylinder 40 by a hydraulic system such as illustrated in FIG. 9. The rotational movement of rod 100 is readily integrated with the angular movement of the rod for controlling transformers 110 and 120 so that a smooth operation for raising and lowering the boom, pivoting the dipstick, and rotating the bucket can be performed using only natural movements of the operator.
The slewing of the boom, which is the fourth function of the present control mechanism, is controlled by a thumb operated control, generally indicated by numeral 137 incorporated in handle 86 and having a thumb contact member 138 connected to a transformer 140 by a rod 141, lever 1-42 and probe 144. Movement of thumb contact 138 to either the right or the left as viewed in FIG. 3 results in longitudinal movement of rod 141 and probe 144, thus operating the boom either to the right or left. If the boom is to be moved to the left, the thumb contact member 138 is moved to the left and if the boom is to be moved to the right, the thumb contact member is moved to the right. This movement of the thumb contact member, while the hand is controlling the handle 86-, can be readily integrated into the movement of the three previously described functions involving transformers 110, 120 and 138. Transformer 140 is supported by a frame 148 connected to a support member 150, which in turn is connected to plate 88, thus holding the transformer rigidly in place in the mechanism. Movement of the handle Without simultaneous movement of the control button 138 has no actuating effect on the transformer.
In order to retain the various probes in neutral position when they are not being manipulated by the operator, a series of springs are used. Springs 160, 162, 164 and 166 each are connected respectively at their outer ends to spacer rods 92, 168, 170, and 172 and to handle 180 at their inner ends. Since the springs have an equal rate and tension, the rod 100 is yieldably retained in its centered position, thus holding the probes in their neutral position. The rotation of the handle is held in its neutral position by springs 174 and 176 connected at their outer ends to spacer rods 168 and 170 and at their inner ends to a pin 178 connected to block 180, which in turn is rigidly connected to rod 100. Whenever the handle is released after a rotational movement is performed, it will be returned to its neutral position by the two springs 174' and 176-. The slewing control, generally indicated by numeral 137, is returned to its neutral position by diametrically acting springs 18-2 and 184 reacting on inwardly extending flanges 186 and 188 at their outer ends and on a collar 190 rigidly mounted on rod 141.
The operator sitting on the tractor in the manner illustrated in FIG. 1 and holding handle 86 in his right hand, controls the boom, dipstick, and bucket solely by the movement of the handle and the thumb engaging member, so that all of the functions are performed by the one hand manipulated in a manner natural to the type of operation being performed. Raising and lowering the handle raises and lowers the boom, moving the handle forwardly or rearwardly pivots the dipstick forwardly or rearwardly, rotating the handle pivots the bucket, and movement of the thumb engaging member either to the right or left slews the boom to the right or left. These four functions can be easily integrated into one single operation so that all four or any combination thereof can be performed simultaneously in varying degrees as desired. While this mechanism has been designed primarily for use in controlling a backhoe, it can be adapted to various other types of apparatus requiring control by the multiple, integrated operation of several functions.
The embodiment disclosed in FIGS. 6, 7, and 8 is essentially the same as the embodiment previously described herein, involving a system such as that shown in FIG. 9 controlled by the various differential transformers. The primary basic difference between the two devices is a dual hand control arrangement which permits the operator to control the backhoe with either hand, rather than by a single hand as in the previously described embodiment. In the second embodiment, the mechanism is mounted in or on a column 200 secured to the tractor as illustrated in FIG. 1 and having two laterally projecting arm rests 202 and 204 supported by arms 206 and 208, respectively. With the operators arms resting on arm supports 202 and 204, the hands grasp the control handles 218 and 212 on the respective sides of column 200. The two handles are pivotally mounted on a horizontally extended shaft 214 extending through column 200, and on bell cranks 216 and 218 for the two handles, respectively.
The two handles 210' and 212 operate in unison, and movement of the handle to rotate shaft 214 operates a linkage 220 which operates a probe 222 in transformer 224, which, using a system such as that shown in FIG. 9, operates the hydraulic cylinder to raise and lower the boom. A centering spring assembly 226 maintains the probe 222 in its neutral position when the operator is not rotating the handles in either direction to raise or lower the boom.
The dipstick is controlled by a forward and rearward movement of the handles transmitted through shaft 214 to a bar 230 pivoted on a pin 232, which in turn is supported by brackets 234 and 236 secured to column 200. Movement of the handles in the forward or rearward direction pivots bar 230, thereby actuating transformer 240 through a probe 242 connected to bar 230 by a spherical stem 244. As the handles are pushed forward, movement is transmitted through shaft 214 to bar 230, which likewise pivots forwardly, thereby moving the probe in the direction to cause the dipstick to move forwardly. When the handles are moved in the opposite direction, the dipstick is moved rearwardly. The bar is maintained in its centered position, and hence the probe in its neutral position, by a spring assembly 248 mounted on the column and connected to the bar.
The boom is slowed to either the right or left by movement of the handles to the right or left. This movement is transmitted to shaft 214 and to a linkage 250, which moves a probe 252 in transformer 254, the probe moving to the right or left as the handles are moved to the right or left, thus moving the boom to the right or left. A centering spring assembly 256 retains the handles and shaft 214 in their centered position and the probe in its neutral position when the operator is not shifting the handles in either direction to slew the boom.
The curling of the bucket is controlled by the two handles through upper and lower switches 26!) and 262 in each of the handles and operated by push buttons 264 and 266, respectively. The push buttons are connected to a lever 268 which is seated on the inner surface of a support 270 by coil spring 272. The two handles are essentially identical in construction and operation and are interconnected so that each will perform the same opera:
tion, either independently or in unison with the other handle.
The operation of the control mechanism disclosed in FIGS. 6, 7, and 8 is basically the same as the operation of the control mechanism shown in FIGS. 2 through 5, in that the plurality of functions can be easily integrated with one another so that all four functions can be performed simultaneously. To slew the boom, the handles are moved laterally in either direction; to raise and lower the boom the handles are rotated to rotate shaft 214; to move the dipstick forwardly or rearwardly, the handles are moved forwardly or rearwardly, thus pivoting bar 230 forwardly and rearwardly; and to curl the bucket, the push buttons on either handle are manipulated to close the switch required to perform the desired function. Any one or any combination of the foregoing functions can be readily integrated into a smooth operational performance by the operator, using either of the two handles alone or both together while his arms are supported on arm rests 202 and 204. The mechanism of the second embodiment can be adapted to apparatus other than backhoes; however, it is primarily designed for control of the backhoe operation.
While only two embodiments of the present multi-function control mechanism have been described in detail herein, various changes and modifications may be made without departing from the scope of the invention.
1. A control mechanism for a backhoe having a boom, a dipstick connected to said boom, a bucket pivotally mounted on the outer end of said dipstick, and an actuating means for raising and lowering and slewing the boom, moving the dipstick forwardly and rearwardly, curling and uncurling the bucket: said mechanism comprising a handle having a center position, means for self-centering said handle, means movable axially and rotatively in either direction and to an infinite number of angular positions, from said center position, and being in a substantially horizontal position, a signal producing means operated when said handle is angularly raised and lowered to raise and lower the boom, a signal producing means operated when said handle is moved angularly fore and aft to move the dipstick forwardly and rearwardly, a signal producing means operated in response to a rotary movement in said handle to curl and uncurl said bucket, and a signal producing means operated from said handle for slewing the boom, each of said signal producing means consisting of a linear variable differential transformer and a probe for each of said transformers connected to said handle and movable selectively in one of two directions as said handle is moved from said center position.
2. A control mechanism as defined in claim 1 in which a resilient means returns said handle to neutral position, at which said signal producing means are inoperative.
3. A control mechanism as defined in claim 1 in which means is provided in conjunction with each of said signal producing means for returning said probes to an inoperative position.
4. A control mechanism as defined in claim 3 in which said means for returning said probes to the neutral posi tion consists of opposed springs connected to said handle.
5. A control mechanism as defined in claim 1 in which the probe of each of said transformers when moved in one direction causes the respective element of the backhoe to move in one direction and movement of the probe in the opposite direction causes the respective element thereby to move in the opposite direction.
6. A control mechanism for a backhoe having a boom, a dipstick connected to said boom, a bucket pivotally mounted on the outer end of said dipstick, and an actuating means for raising and lowering and slewing the boom, moving the dipstick forwardly and rearwardly, curling and uncurling the bucket: said mechanism comprising a handle having a center position, means for self centering said handle, means movable axially and rotatively in either direction and to an infinite number of angular positions, from said center position, and being in a substantially horizontal position, a signal producing means operated when said handle is angularly raised and lowered to raise and lower the boom, a signal producing means operated when said handle is moved angularly fore and aft to move the dipstick forwardly and rearwardly, a signal producing means operated when said handle is rotated in one direction to curl the bucket and in the other direction to uncurl the bucket, a signal producing means for slewing said boom, and a means connected to said handle for actuating said last mentioned signal means, each of said signal producing means consisting of a linear variable differential transformer and a probe for each of said transformers connected to said handle and movable selectively in one of two directions as said handle is moved from said center position.
7. A control mechanism as defined in claim 6 in which a plurality of opposed spring means returns said handle to neutral position, at which said signal producing means are inoperative.
8. A control mechanism as defined in claim 6 in which means is provided in conjunction with each of said signal producing means for returning said probes to an inoperative position.
9. A control mechanism as defined in claim 7 in which said spring means for returning said handle to the neutral position are connected to said handle.
10. A control mechanism as defined in claim 8 in which the probe of each of said transformers when moved in one direction causes the respective element of the backhoe to move in one direction, and movement of the probe in the opposite direction causes the respective element thereby to move in the opposite direction.
11. A control mechanism as defined in claim 6 in which said means connected to the handle for actuating the signal producing means for slewing the boom consists of a thumb engaging member on the underside of said handle movable longitudinally with respect to said handle.
12. A control mechanism for a backhoe having a boom, a dipstick connected to said boom, a bucket pivotally mounted on the outer end of said dipstick, and an actuating means for raising and lowering and slewing the boom, moving the dipstick forwardly and rearwardly, curling and uncurling the bucket: said mechanism comprising a support means pivoted near its lower end movable forwardly and rearwardly, an axial movable rotatable shaft mounted on said support means near the upper end thereof and having a center position, a handle connected to one end of said shaft and extending radially outwardly therefrom on an axis transverse to the axis of said shaft, means for self centering said handle, a signal producing means connected to said shaft and being responsive to rotational movement of said shaft for raising and lowering said boom, a signal producing means connected to said pivoted support means and being responsive to the fore and aft movement thereof for moving the dipstick fore and aft, a signal producing means connected to said shaft and being responsive to axial movement of said shaft for slewing the boom, and a dual switch means in said handle for curling and uncurling the bucket, each of said signal producing means consisting of a linear variable differential transformer and a probe for each of said transformers connected to said handle and movable selectively in one of two directions as said handle is moved from said center position.
13. A control mechanism as defined in claim 12 in which yieldable means return said handle to neutral position at which said signal producing means are inoperative.
14. A control mechanism as defined in claim 12 in which means is provided in conjunction with each of said signal producing means for returning said probes to an inoperative position.
15. A control mechanism as defined in claim 14 in which said means for returning said probes to the neutral position consists of opposed springs.
16. A control mechanism as defined in claim 14 in which the probe of each of said transformers when moved in one direction causes the respective element of the backhoe to move in one direction and movement of the probe in the opposite direction causes the respective element thereby to move in the opposite direction.
17. A control mechanism as defined in claim 12 in which a second handle spaced laterally from said first handle and interconnected therewith controls equally and simultaneously said signal producing means.
18. A control mechanism as defined in claim '12 in which said handle is in a generally vertical position and one of the switch means of said dual switch means is at the upper part of said handle and the other of said 10 dual switch means is at the lower part of said switch means.
References Cited UNITED STATES PATENTS 3,214,040 10/1965 Willinger 214138 3,166,143 l/1-965 Gonter, Jr. et a1. 318587 X 3,550,466 12/1970 Ham 74471 X Y FOREIGN PATENTS 847,656 9/1960 England 214-132 GERALD M. FORLENZA, Primary Examiner I. M. FORSBERG, Assistant Examiner US. Cl. X.R.
74471 XY; 2141 CM