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Publication numberUS3448819 A
Publication typeGrant
Publication dateJun 10, 1969
Filing dateApr 20, 1967
Priority dateApr 20, 1967
Publication numberUS 3448819 A, US 3448819A, US-A-3448819, US3448819 A, US3448819A
InventorsPeterson Robert S, Washburn Darl C Jr
Original AssigneeWestinghouse Electric Corp
Export CitationBiBTeX, EndNote, RefMan
External Links: USPTO, USPTO Assignment, Espacenet
Dragline propulsion apparatus
US 3448819 A
Abstract  available in
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Claims  available in
Description  (OCR text may contain errors)

June 10, 1969 R s, PETERSON ET AL 3,448,819

DRAGLINE PROPULS ION I APPARATUS Filed April 20, 1967 Sheet & of 2 SHOES T B TUB RAISED SHOES LIFTING OFF THE GROUND LOWER'NG FROM THE I TO THE TO THE LOAD TORQUE MOTOR SPEED MOTOR SHUNT FIELD STRONG I c WEAK I WEAK I d I I IOO IOO I |oo% 1 REFERENCE TO THE REGULATOR 50% I FIG. 3.

FIG.5.

United States Patent Office 3,448,819 Patented June 10, 1969 3,448,819 DRAGLINE PROPULSION APPARATUS Robert S. Peterson and Darl C. Washburn, Jr., Williamsville, N.Y., assignors to Westinghouse Electric Corporation, Pittsburgh, Pa., a corporation of Pennsylvania Filed Apr. 20, 1967, Ser. No. 632,344 Int. Cl. B62d 57/02, 51/06 US. Cl. 180-8 12 Claims ABSTRACT OF THE DISCLOSURE A system for electrically controlling and synchronizing the walking movement cycle of a dragline with no rigid Connecting shaft between the walking shoes. A Signal, proportional to the difference in angular displacement of the walking shoes, is used in an additive sense to boost the movement of the lagging shoes and in a subtractive sense to buck the movement of the leading shoe until proper synchronization is achieved.

Field of the invention This invention relates generally to walking draglines, and more particularly, to an improvement in the propel ling of draglines employing walking shoes or pontoons.

Description of the prior art Walking dragl-ines for open-pit mining have increased in size tremendously over the past few years. They move by walking on pontoons similar to the way a human being walks on crutches. The pontoons (feet) are rigidly connected to a leg which is turn is driven through an eccentric by a drive shaft. There are two feet, one on each side of the dragline, which are rotated in synchronism as the dragline walks. In order to improve synchronism, a mechanical shaft has traditionally connected the two feet. This shaft may be as large as 90 feet long and 3 feet in diameter; moreover, the shaft size demands that it be designed in sections with expensive couplings and bearings utilized between the shaft sections.

In operation the shaft is geared to DC drive motors. Generally, an even number of motors is used for the walking motion and the shaft becomes a mere timing device not transmitting any torque from one side to the other. However, on uneven ground, an unbalanced loading on the pontoons can cause transmission of power from one end of the shaft to the other end and, if the shaft is not designed to transmit this torque, it may break. In addition to the expense connected with replacing the shaft, the dragline would ,be inoperable over a significant period of time. Therefore, it would be a significant advantage if this connecting shaft could be removed yet still maintain proper synchronism between the two pontoons. The immediate result would be a substantial savings in space, weight, and dollars.

Summary of the invention It is therefore, a general object of the present invention to provide a new and improved dragline walking system.

A further object of the present invention is to provide a new and improved walking dragline whereby the dragline propel shaft is replaced by an electrical tie.

A still further object of the present invention is to provide a new and improved dragline propel system whereby on uneven ground, the walking shoe (foot) touching the higher ground first will stay in that position until the other walking shoe reaches the ground.

Yet, a further object of'the present invention is to provide an electrically controlled propel system for a drag line whereby the angular position of the walking shoes (feet) are substantially equal regardless of the ground slopc.

A still further object of the present invention is to provide an electrically controlled propel system whereby the torque for any specific angular position -of the crank arms driving the walking shoes may vary, depending on the slope of the ground upon which the dragline is operating.

A still further object of the present invention is to provide an improved dragline walking system whereby the mechanical stresses on the cab and frame structure are substantially reduced from the stresses normally present with a rigid propel shaft. 1

In general the present invention relates to a system for cyclically controlling, in synchronism, the running speeds of the DC drive motors that independently drive the separate shoe (foot) operating cranks of a self-propelled dragline shovel. Use is made of a variable speed reference to control thejgaverage rotational speed of the shoe cranks. The mechanically separate motor driven propel cranks for the shoes are tied to the common reference through a Synchrotie system which compares the positions of the respective cranks and generates separate error signals for correcting the deviation of each shoe crank from their average position. The speed of the cranks is controlled during different parts of the 360 cycle to effect slow movement on the power portion of the cycle and speed-up during the recovery portion of the" cycle, with a cushioning transition from the speed of the recovery cycle at a point just before the power impact. Speed and torque are regulated through feedback loops.

The objects of our invention hereinbefore recited are merely illustrative. Other objects and advantages will become more readily apparent from a study of the following specification when made in conjunction with the accompanying drawings.

Description of the drawings propel system synchronization control using Laplace transforms.

Descriptioln 0f the preferred embodiment Referring to FIG. 1, numeral 1 denotes the cab and frame structure of the dragline. The cab is mounted on a supporting frame structure 2 which is rotatable on a A circular rail 3. The rail is carried by a tub 4 of cylindrical shape. 1

In order to move the shovel along the ground, a walking arrangement is provided which includes two walking pontoons (feet) 10 arranged at opposite sides ofth'e cab and frame structure 1. Each pontoon 10 is attached to a walking structure member 12 which is in turn connected to a crank 14. A beam 15 is attached from a freely' rotating point on the cab 16 to a freely rotating point on the walking structure member 12. There is no mechanical linkage or tie between the rotating cranks 14 on each side of the tub 1.

During a walking cycle, propel motors rotate the crank in the clockwise direction. As a result, the walking structure member 12 and the pontoons 10 are moved toward the righthand side of the illustration until the pontoons reach ground as indicated by the Diagram A. Thereafter, while the cranks continue to rotate in a clockwise direction, the pontoons exert pressure against the ground and cause the tub 4 and hence the entire machine to be lifted vertically with the lifting motion beginning at the rear of the machine as shown in Diagram B. As the cranks 14 continue to rotate in a clockwise direction, as shown in Diagram C, the pontoons impart a horizontal motion to the machine towards the rear as indicated by arrow 20. As a result, the front end of the tub 4 is dragged over the ground a distance d. At the end of a walking cycle, the pontoons 10 are lifted olf the ground as the respective cranks 14 continue to move in a clockwise rotation. The pontoons come to rest as shown in Diagram D where they are idly suspended from their respective crank arms; further motion can be achieved by performing additional walking cycles. The cranks 14 are considered to be in'phase with each other when the pontoons 10 are in step (i.e., in phase) with each other.

In the movement of the dragline over the ground, it is imperative that the walking shoes or pontoons by synchronized to a significant extent. With no connecting shaft between the two cranks driving the walking shoes, the design of the control equipment in achieving a predetermined mode of operation becomes significant. In this regard, the principles of the present invention are designed to meet minimum specific requirements for pontoon synchronization as given below:

(1) The crank arm position error should not exceed :5 during any walking cycle.

(2) Shoes and tub should accelerate together with a position error not exceeding i5% (3) If one side of the dragline is stalled due to external loading, the other side should remain within 15 without creating any abnormal effects or damage to the mechanical equipment.

(4) All motors should have proper current limit protection.

(5) On uneven ground, the shoe touching the higher ground first should remain in that position until the other shoe touches the ground. Thus, a necessary error in shoe positions should exist to compensate for unevenness of the ground. This error generally should not exceed FIGURE 2 presents a diagrammatic representation of the propel system with pontoon synchronization control. A master switch 20 is provided to give a reference or command signal for setting the proper speed with which the walking cycle should occur. This input reference signal is fed to a propel regulator 22 which acts as a voltage controller until current reaches certain predetermined limits at which time the regulator operates as a current controller. In effect then, the regulator 22 operates as a parallel control for both voltage and current. A further and. more complete description as such a parallel controller is given in copending patent application Ser. No. 597,010 entitled Limit of Rate of Rise of Current in a Parallel Control Scheme and filed Nov. 25, 1966 by Hermann Eisele and assigned to the same assignee as the present invention. Output from the propel regulator 22 is fed to a power amplifier having a high gain and providing a signal to the summing junctions 2 and E The summations of signals at summing junctions 2 and E are passed on respectively to coils C and C to energize respectively the generators G and G Generator voltage is then directed to respective propel motors PM and PM which operate respective synchro devices SY and SY through associated gear mechanisms such that each synchro will only complete a single turn for each walking cycle. For purposes of the illustration only one motorgenerator set is shown for each pontoon; however, in practice, it would probably be necessary to energize a plurality of motor-generator sets for each pontoon. The angular displacements of the synchros 0 and O are fed to a synchro-tie error detector E which generates a position error signal a which is fed to a synchronizing controller 30. The synchro-tie error detector E compares vectorially the voltages 0 and 0 from the synchros SY and SY to produce the output signal 0 which is proportional to error position. For a more detailed description, reference should be made to Patent No. 3,086,153, entitled Synchronized Conveyor Control by G. E. Mathias et al. and assigned to the same assignee as the present invention. An output signal from the synchronizing controller 30 is then fed to a power amplifier 32 which has considerably less gain than power amplifier 24. Output from amplifier 32 is less than added to the regulator module output on one side and subtracted from the regulator module on the other side.

The generator voltages from G; and G are detected respectively by voltage sensors VS and VS which provide signals to a summing amplifier 34. The summing amplifier 34 then averages the two signals and thereby provides a feedback signal V to the propel regulator 22. Armature currents from the propel motors PM and PM which drive the pontoons are monitored through shunt circuits S and S respectively and measured by current sensors CS and CS The sensors feed the current from each side into a switching circuit 40 whose output I corresponds to the higher of the two current inputs. The output l is then used as current feedback to the regulator 22.

Generally, the circuit of FIG. 2 operates such that a reference voltage provides an energizing signal for operation of the walking pontoons which under normal circumstances will be synchronized, i.e. be in step with each other. At such times when the pontoons may be out of synchronization an error signal indicating the position error is fed back to the energizing circuits which correct for this position. Meanwhile, the approximate speed of operation of both pontoons is sensed and compared to a reference; lack of correspondence with this reference voltage will then set up a compensating signal which will tend to draw the actual operating characteristics close to the reference signal.

Referring now to FIG. 3 and by way of example, typical operating characteristics of the crank arm position in degrees is shown with respect to various operating parameters. For each walking cycle the crank arm moves 360. During the first 113 the walking shoes or pontoons are being lowered to the ground. From 113 to 208 the pontoons are pushing against the ground to lift the tub off the ground; from 208 to 267 the tub is lowering back to the ground level. The final portion of the cycle, from 267 to 360 merely lifts the pontoons from the ground back to their original starting position where they are hanging idly at the sides of the tub.

The motor speed which is used to control the rate of change of the crank arm position is shown in curve B of FIG. 3. During the first 113 while the pontoons are lowering to the ground it as advantageous that the crank arm move relatively quickly; however, as the shoes near the ground it is advisable that the speed at which the come into contact with the ground be considerably slowed to elminiate any sudden jolting. During this portion of the' walk cycle there is essentially no load on the motor since there is no resistance to the movement of the shoes from the idle position to the ground position as seen load torque curve in curve A. During this period the motor shunt field remains weak until a decrease in speed is necessary as the shoes near the ground whereupon the field increases as shown by curve C. Curve D indicates that the reference to the regulator remains 100% until just before the shoes touch the ground whereupon the reference drops to since the motor speed is decreased.

During the second portion of the walking cycle where the tub is lifting off the ground the load torque suddenly increases as shown by curve A. Load torque continues to increase slightly until a maximum is reached when the tub is furthest from the ground. Fromthen on, as the cycle shifts away from maximum lift, load torque rapidly falls off as the weight of the machine itself contributes heavily to lowering. Meanwhile, the motor speed initially causes a return to 100% reference to the regulator.

During the third portion of the walking cycle where the tub is lowering, the load torque moves from 0 to negative as the gravitational force of the tub and cab and frame structure generates most of the loading force, as

shown by curve A. In the meantime the motor speed remains constant to a position near where the tub will touch the ground at which time the motor speed is gradually decreased to a minimum Speed such that the tub may be gently set upon the ground again. The motor shunt field remains strong throughout the tub lowering to provide braking and the reference to the regulator generally follows the motor speed curve reaching a minimum at a point just before the tub actually touches the ground. Should there be different ground levels for the pontoons, the load torque curve for each during the raising and lowering of the tub would not be coincident; the pontoon reaching the ground last would then follow the dashed portion of curve A.

The last portion of this cycle where the shoes are lifted from the ground to their idle position requires only a minimum of load torque. And once the shoes have left the ground they can rapidly return to their idle position as shown by the quick increase of motor speed in curve B. With no load the motor shunt field again becomes quite weak and the increased speed means that a 100% reference to the regulator can again be used.

It should be noted that curve D, reference to the regulator, may be achieved either by an operator manually changing reference during the respective portions of the cycle as indicated by a curve or preferably, it may be done automatically by a system of contacts and relays.

The block diagram of FIG. 4 presents a mathematical model using Laplace tarnsforms for the synchronizing control loops in the system shown in FIG. 2. A reference voltage V is fed to the regulator 22. A signal output from the regulator is separated at terminal 6 to be fed to each of the summing junctions 2 and E Output from the respective summing junctions are then fed to the generators which have a transfer function of where T is the generator time constant. The respective m and ax are in radians per second. Feedback from the respective motors is returned respectively to summing junction 2 and E The speed of the respective motors a 40 and aw is then fed through transfer functions i as and

to summing junction 2 at which point the relative angular generator voltages V and V are fed back by a factor of one-half to the regulator 22. The generator voltages as applied to summing junctions 2 and 2 drive the propel motors which have a transfer function of where T is the armature time constant. The motors are connected respectively through gear mechanisms having a transfer function,

where T is the mechanical time constant. Input voltages at junctions Z and E consist of two components, motor torque i R and load torque z' R i R where R is is armature resistance, 1',, is armature current, and i and i are armature load currents. Output from the gear mechanism transfer function then provides signals representative of speeds a and aw where a is the voltage constant of the motor in volts per radian per second and positions 0 and 0 of the crank arms are determined. The angular difference between 0 and G is then transferred to the synchronizing controlled 30 which has a transfer function of where T and T are respective lead and lag time constants of the synchronizing controller. The synchronizing controller 30 is a lag-lead controller designed so as to cancel the generator time constant T with the lead time constant T and to make the lag time constant be as small as practical depending on the selection of components to meet other requirements such as controlled gain and lead time constant T Output from the synchronizing controller is then fed to junction 6 whereupon it is sent to either summing junction E or is changed in polarity and fed to summing junction 2 This signal acts along with the reference input to provide an energizing signal for the respective generators.

If the leadtime constant of the synchronizing controller T i sset equal to the time constant of the generator T then the following expression for the crank arm error position (6 0 can be obtained from the diagram of FIG. 4.

where:

a=voltage constant of the motors I I =armature load current c th gs K =controller 3-0 gain in volts/radian K =amplifier 32 gain in volts/radian K =generator gain and I =generator field amps for stall current 1 R =generator field resistance in ohms I =stall current tar nR.

Normalizing the above equation gives the following:

where M is the maximum allowable error in radians. The worst condition occurs when one side crank arm is stalled and the other side is free to rotate. Under this condition we have the following:

While our invention as described in the foregoing refers to walker drives of draglines, it will be understood that the principle and means are also adaptable to walking equipment if used in connection with other than draglines and that the invention can be used to advantage wherever a hoisting machine or shovel operates in accordance with the speed and torque cycle which involves load variations similar to those discussed in the foregoing.

We claim as follows:

1. A synchronizing system for operating a pair of walker-type mechanisms each including a foot operable through a predetermined walking cycle and rotatable propulsion means coupled to the foot, each foot having a correlative pos tion within said walking cycle for any given angular position of its associated rotatable propulsion means, said respective rotatable propulsion means being mechanically independent of each other, said synchronizing system comprising:

variable reference means providing a reference signal for setting desired operation for said walker-type mechanisms, first and second drive means, each for driving a difierent one of said rotatable propulsion means,

regulat ng means responsive to said reference signal and PI'OVldll'lg a corresponding drive signal for each of said drive means for the control thereof,

controller means responsive to the positions of said walker-type mechanisms for providing compensating signals to each of said drive means proportional to the relative difference in angular displacement of said walker-type mechanisms, and

feedback means responsive to at least one electrical operating characteristic of each of said drive means to provide correction signals to said regulating means.

2. The synchronizing system as set forth in claim 1 wherein said controller means includes error signal providing means for developing an error displacement signal proportional to the difference in angular displacement of said walker-type mechanisms, and a synchronizing controller responsive to said error displacement signal to provide a subtractive compensating signal to the leading drive means and an additive compensating signal to the lagging drive means.

3. The synchronizing system as set forth in claim 1 wherein said feedback means includes:

first condition sensing means to detect the level of a first electrical condition relative to each said drive means to provide a first condition correction signal to said regulating means, and

second condition sensing means to detect the level of a second electrical condition relative to each said drive means to provide a second condition correction signal to said regulating means.

4. The synchronizing system as set forth in claim 3 wherein said first condition is drive speed and said second condition is drive torque.

5. The feedback means as set forth in claim 3 wherein said first condition is generator voltage and said second condition is armature current.

6. The synchronizing system as set forth in claim 3 wherein said second condition sensing means provides a feedback signal equivalent to the higher one of the levels of said second condition of the respective first and second drive means.

7. In a vehicle provided with at least a pair of walking pontoons and mechanically separate rotatable propulsion members for operating said respective pontoons, the combination of drive means including a motor coupled to each of said rotatable propulsion members, synchronizing means operative with said drive means and responsive to the difference between the angular positions of said rotatabel propulsion members for synchronizing the angular displacement of said rotatable propulsion members within predetermined limits, and feedback means responsive to an electrical characteristic of said drive means for affecting the operation of the drive means.

8. The combination as set forth in claim 7 wherein said synchronizing means includes: detector means for detecting the relative difference in angular displacement of said rotatable propulsion members to provide an error signal proportional to said angular displacement, and controller means responsive to said error signal for providing an additive signal to the drive means of the lagging rotatable propulsion member and a subtractive signal to the drive means of the leading rotatable propulsion member until said rotatable propulsion members are synchronized in a predetermined manner.

9. The synchronozing system as set forth in claim 2 wherein said feedback means includes:

first condition sensing means to detect the level of a first electrical condition relative to each said drive means to provide a first condition correction signal to said regulating means, and

second condition sensing means to detect the level of a second electrical condition relative to each said drive means to provide a second condition correction signal to said regulating means.

10. The synchronizing system as in claim 3 wherein:

each of said drive means includes a motor having an armature coupled to said rotatable propulsion means associated with that drive means and a power supply source responsive to said regulating means for energizing the motor,

said first condition is power supply source output voltage, and

said second condition is armature current.

11. In a vehicle provided with first and second walking pontoons and first and second mechanically separate rotatable propulsion member for operatng the first and second pontoons respectively, the combination of first and second drive means for respectively driving said first and second propulsion members, each said drive means including a motor coupled to the propulsion member associated with that drive means, regulating means responsive to a control force for supplying similar drive signals to the first and second drive means for the control thereof, synchronizing means operative with the first and second drive means and responsive to phase difference between said propulsion members for forcing said pontoons toward synchronism, and means for supplying feedback from both said drive means to said regulating means for modifying the output of the regulating means, said feedback relating to at least one kind of electrical characteristic.

12. The combination as in claim 1'1 wherein said synchronizing means includes means for detecting the phase difference between said rotatable propulsion members to provide anerror signal proportional to said phase difference, and means responsive to said error signal for providing an additive signal to the drive means of the lagging rotatable propulsion member and a subtractive signal to the drive means of the leading rotatable propulsion mem- 9 10 her until said rotatable propulsion members are synchro- 2,469,140 5/ 1949 Wahlberg 318-85 nized in a predetermined manner. 3,267,345 8/1966 Boening 318-52 3,366,192 1/1968 Le Tourneau 180-8 References Cited UNITED STATES PATENTS 5 LEO FRIAGLIA, Prz'mary Exammer. 2,380,431 7/1945 'I-Iardin-g et a1. 1808 U.S. C1.X.R.

2,399,417 4/1946 Wilson et a1. 1808 31885

Patent Citations
Cited PatentFiling datePublication dateApplicantTitle
US2380431 *May 8, 1943Jul 31, 1945Westinghouse Electric CorpDragline control
US2399417 *Oct 18, 1943Apr 30, 1946Marion Steam Shovel CoWalking tractor
US2469140 *Jul 2, 1945May 3, 1949Electrolux CorpSynchronizing system for geared motors
US3267345 *Jul 2, 1963Aug 16, 1966Allis Chalmers Mfg CoPlural motor control for a locomotive with anti-slip and load distribution
US3366192 *Jun 20, 1966Jan 30, 1968Robert G. LetourneauPerambulatory vehicle
Referenced by
Citing PatentFiling datePublication dateApplicantTitle
US3671828 *Apr 21, 1970Jun 20, 1972Westinghouse Electric CorpMethod and control system for d.c. electric motor drive means
US3789280 *Oct 19, 1971Jan 29, 1974Westinghouse Canada LtdMulticable drum hoisting system
US3853196 *May 29, 1974Dec 10, 1974Sprague & Henwood IncSelf-propelling mechanism
US4462476 *Sep 7, 1982Jul 31, 1984Nikolay ShkolnikWalking apparatus
EP0074286A2 *Jul 8, 1982Mar 16, 1983International Robotic Engineering Inc.Robot system with legs or arms
Classifications
U.S. Classification180/8.5, 318/85
International ClassificationB62D57/00
Cooperative ClassificationB62D57/00
European ClassificationB62D57/00