US3625483A

US3625483A - Automatic leveling system for blast hole drills and the like

Info

Publication number: US3625483A
Application number: US13689A
Authority: US
Inventors: Thomas A Stoner
Original assignee: Bucyrus Erie Co
Current assignee: Caterpillar Global Mining LLC
Priority date: 1970-02-24
Filing date: 1970-02-24
Publication date: 1971-12-07
Anticipated expiration: 1988-12-07
Also published as: DE2109549A1; GB1306325A; JPS5334369B1

Abstract

An automatic system for leveling a blast hole drill during raising and lowering includes a front jack on the longitudinal axis of the machine and a pair of rear jacks which straddle the longitudinal axis and define a transverse axis. An operating fluid line for the jacks is connected to a first proportioning valve which is controlled by a first level sensor operative along the longitudinal axis. The proportioning valve apportions flow between the front jack and the two rear jacks and alters the flow ratio as necessary to keep the machine level on the longitudinal axis. A second proportioning valve controlled by a second level sensor operative along the transverse axis is interposed in that output of the first valve which leads toward the two rear jacks. It apportions the flow between the two rear jacks to level the machine along the transverse axis. This sequential apportioning of fluid flow is used to level the machine and keep it level as it is raised and lowered to and from a working position in which it is supported by the jacks.

Description

United States Patent [72] Inventor Thomas A. Stoner Brookiield, Wis. [21] Appl. No. 13,689 [22] Filed Feb. 24, 1970 [45] Patented Dec. 7, 1971 [73] Assignee Bueyrus-Erie Company South Milwaukee, Wis.

[54] AUTOMATIC LEVELING SYSTEM FOR BLAST HOLE DRILLS AND THE LIKE 5 Claims, 6 Drawing Figs.

[52] US. Cl 254/86 ll, 280/6 H [5 1] Int. Cl 1360s 9/02 [50] Field of Search 254/86 R,

[56] References Cited UNITED STATES PATENTS 2,713,402 7/1955 Balogh 254/86 H X 3,265,357 8/1966 Schilling... 254/89 1-1 3,431,727 3/1969 Grumman 254/86 H X 3,516,182 6/1970 Wykert 280/61 X Primary Examiner-Robert C. Riordon Assistant E.raminerDavid R. Melton Attorneys-Allan W. Leiser, Arthur H. Seidel and Ray G.

Olander ABSTRACT: An automatic system for leveling a blast hole drill during raising and lowering includes a front jack on the longitudinal axis of the machine and a pair of rear jacks which straddle the longitudinal axis and define a transverse axis. An operating fluid line for the jacks is connected to a first proportioning valve which is controlled by a first level sensor operative along the longitudinal axis. The proportioning valve apportions flow between the front jack and the two rear jacks and alters the flow ratio as necessary to keep the machine level on the longitudinal axis. A second proportioning valve controlled by a second level sensor operative along the transverse axis is interposed in that output of the first valve which leads toward the two rear jacks. It apportions the flow between the two rear jacks to level the machine along the transverse axis. This sequential apportioning of fluid flow is used to level the machine and keep it level as it is raised and lowered to and from a working position in which it is supported by the jacks.

PATENTEDBEU 7197: 3.625483 SHEET 1 UF 3 INVENTOR THOMAS A. STONER ATTORNEY PATENTEI) DEC 7191:

SHEET 2 [IF 3 ATTORNEY PATENTED 0E0 H971 3625483 SHEET 3 [IF 3 T 5 51/ I l 57 {5 I I I M 1.. g 27 a I I I INVENTOR THOMAS A. STONER ATTORNEY AUTOMATIC LEVELING SYSTEM FOR BLAST HOLE DRILLS AND THE LIKE BACKGROUND OF THE INVENTION Blast hole drills are mobile machines used primarily in sur face mining to drill holes for explosives. They are generally mounted on crawlers which provide mobility over rough terrain, but it is conventional to provide hydraulic jacks to raise and support the machine off the crawler mount during the actual drilling operation. It is imperative that the machine be level for drilling to insure that the drilled hole will be vertical and to prevent unnecessary strain and wear on the machinery. It is also important that the machine be capable of being raised, leveled and lowered quickly to prevent unnecessary delays between drilling operations. It is also highly desirable to have the machine maintained level as it is lowered back to the ground.

Various raising and leveling systems for blast hole drills have been provided in the past, but none of these has proven entirely satisfactory. In many cases, the entire leveling operation must be controlled manually. These systems require that the operator constantly observe and control the attitude of the machine on at least two axes, which is both a difficult and a time consuming task. Automatic leveling systems have been provided on machines, but these generally involve actuating or controlling one jack or axis at a time resulting in substantial delay and in an undesirable stepping type of operation. Furthermore, previously devised systems, both manual and automatic, are undesirably complicated and expensive for application to blast hole drills.

SUMMARY OF THE INVENTION The present invention contemplates an automatic leveling system based on the use of proportioning valves which sequentially apportion fluid flow between jacks located along at least two axes so that the machine is automatically leveled as it is raised. The invention also contemplates reverse use of the proportioning valves to provide that the machine is leveled as it is lowered back to the ground. Further, the invention contemplates a controlled operating sequence in which pressure-actuated switches are used to determine when a desired percentage of the weight of the machine is being supported by the jacks and which then initiate a timed final phase of raising, there are cutoff networks to allow lowering while the machine is on uneven terrain, and there is a pressure device to shut off the lowering cycle automatically. The circuitry also includes check valve systems to prevent fluid flow from the jacks during drilling. The system disclosed by the invention is highly versatile and readily adaptable to machines of various sizes, while remaining relatively simple, inexpensive and easy to operate.

The invention is particularly intended and suitable for blast hole drills. It will be apparent from the description, however, that it is readily adaptable to various other machines and applications in which it is desired to raise and level a platform or the like.

Other features, objects and advantages of the invention will become apparent from the description to follow.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. I is a schematic partial side view of a blast hole drill incorporating the automatic leveling system of this invention,

FIG. 2 is a schematic view in perspective illustrating the frame or base plane of the machine of FIG. 1, the supporting jacks, and the reference axes to be referred to in the specification,

FIG. 3 is a schematic electrical and hydraulic circuit dia gram illustrating the leveling system in the machine of FIG. 1,

FIG. 4 is a schematic electrical circuit diagram illustrating one cutout circuit for the leveling system of FIG. 3,

FIG. 5 is a schematic electrical circuit diagram illustrating another cutout circuit for the leveling system of FIG. 3, and

FIG. 6 is a schematic hydraulic circuit diagram illustrating a check valve system for the jacks of the leveling system of FIG. 3.

DESCRIPTION OF THE PREFERRED EMBODIMENT The blast hole drill shown in FIG. I is designated generally by the reference numeral 1, and because it is of a generally conventional construction well known to those skilled in the art it is not shown and will not be described in detail. The machine proper is supported on a crawler vehicle 1' by means of which it may be moved from location to location. It is supported in working position and raised and lowered to this position by means of three conventional double acting hydraulic jacks, comprising a front jack 2, a left rear jack 3, and a right rear jack 4 which is not visible in FIG. I. The

jacks

2, 3 and 4 are mounted on a main frame 5 which is supported on the crawler 1 and which serves as a platform for the drill mast 6 and operating machinery 7. The frame 5 also serves to define a base plane for the machine I which must be leveled in order for the machine as a whole to be level.

As can be seen most clearly in FIG. 2, the front jack 2 is at the forward end of a central, longitudinal axis 8. The

rear jacks

3 and 4 are at the rear end of the axis 8 and straddle it to define a transverse axis 9. Both axes are in the frame 5 and define the base plane. The arrow 10 represents a vertical gravitational force vector. The plane 5 defined by

axes

8 and 9 is shown in FIGS. 1 and 2 ma level working position, perpendicular to the gravitational force vector 10. The

jacks

2, 3 and 4 together form a tripod support for the frame 5, and when they are suitably extended they serve to lift the frame 5, crawler 1, mast 6 and machinery 7 off of the ground to working position.

FIG. 3 shows the basic electrical and hydraulic circuitry used to operate the jacks 2-4 to raise and lower the machine 1 to and from its working position. The reference numeral 11 designates a reservoir of hydraulic fluid, and the reference numeral 12 indicates a conventional closed center directional control valve which serves as a main operating valve. A pump 13 serves to move fluid under pressure from the reservoir 11 to the valve 12 through a line 13'. An exhaust line 14 allows fluid to move from the valve 12 back to the reservoir 11. A branched return line 15 leads from the rod ends of the jacks 2-4 to one port of the valve 12. A main operating line 16 leads from the other port of the valve I2 and conducts fluid under pressure from the valve 12 during a raising operation.

The operating line 16 leads to a first proportioning valve 17 having first and second output lines 18 and 19. A proportioning valve is one which apportions fluid flow between two or more outlets and which can be operated to vary the flow ratio, and various types of proportioning valves are known to those skilled in the art. In the preferred embodiment of this invention the proportioning valves comprise generally conventional open center, self-centering directional control valves with two motor ports, but one of the two exhaust ports is capped and the other exhaust port is connected to an operating line, the linel6 in the case of the valve 17. The valve is set so that there is a selected normal position with a normal flow ratio, and movement of the spool in either direction will reapportion the flow or in other words vary the flow ratio in favor of one outlet or the other. This action is continuous in nature, and is also reversible in that the flow ratio in either direction through the valve can be controlled. It should be appreciated that the normal position of the proportioning valve 17 may not be exactly its center position since it may be necessary to accept a slight constant error, as is common in servosystems. Normal" positions as used herein is intended to mean the position the valve is in when its control axis is level. An electrical operating coil 20 is provided to effect such operation of the valve 17.

The first outlet line 18 leads directly to the cylinder end of the front jack 2, and fluid passing therethrough causes the jack 2 to be extended to raise the machine 1. The second outlet line 19 leads toward the

rear jacks

3 and 4, but is connected to a second proportioning valve 24. The valve 24 is substantially identical to the proportioning valve 17, and it has a right outlet line 25 and a left outlet line 26 which lead to the cylinder ends of the right rear jack 4 and the left rear jack 3, respectively. Fluid under pressure passing through these outlet lines serves to extend the

jacks

3 and 4 thus raising the machine 1. The valve 24 is controlled in its operation by a coil 29 which imparts reciprocal movement to the valve spool.

A first level sensor unit designated generally by the reference numeral 30 and a second level sensor unit designated generally by the reference numeral 31 are provided to control, respectively, the first proportioning valve 17 and the second proportioning valve 24. This control is exercised by passing current through the

coils

20 and 29. Except for their orientation on the frame the two level sensor units are substantially identical so that like reference numerals have been used to refer to like parts. Each unit includes a pendulum 32 which is mounted to swing in a single vertical plane and move a contact 33 along a resistance element 34 as it swings. The resistance element 34 is part of a signal circuit which generates an error signal indicating the direction and amount of movement of the contact 33 away from the center of the resistance element 34. This output is fed to a conventional amplifier 35, and the outputs of the two amplifiers 35 are connected by operating circuitry to the

coils

20, 29 as will be described. This type of sensor is quite satisfactory but other sensors, such as resolvers, could be substituted.

Both level sensors are mounted on the base plane 5. The pendulum 32 of the first level sensor unit 30 is arranged to swing in the vertical plane defined by the longitudinal axis 8, so that its position indicates the attitude of the base plane 5 along this axis. The unit 30 is connected to the coil through normally closed switches 40 and 41 to control the first proportioning valve 17. The pendulum 32 of the second sensor unit 31 is arranged to swing in the vertical plane defined by the transverse axis 9 to indicate the attitude of the plane 5 along this axis. The output of the unit 31 is connected to the coil 29 through normally closed switches 43 and 44 to operate and control the second proportioning valve 24.

The two

units

30, 31 continuously sense the attitude of the frame or base plane 5 and therefore the attitude of the entire machine 1. The outputs of the amplifiers 35 indicate the amount and direction that the base plane 5 is tilted from a level attitude. By actuating the

coils

20 and 29, these outputs continuously control the first and

second proportioning valves

17, 24 which in turn control the flow ratio of fluid to the jacks 2-4 in a manner that will be described below.

To prevent the starting or continuation of a raising cycle when the machine is at too great an angle, excess error relays (not shown) can be connected across the amplifiers 35 or, preferably, across additional amplifiers (not shown) which are designed for excess error operation. These can be used to break the main operating circuit and initiate a lowering cycle, as will be apparent to those skilled in the art.

A main operating coil 45 is provided for the main operating valve 12, and is connected to a source of power 46 through a manually operable switch 47. A second or reverse operating coil 48 is also provided for the valve 12, and is connected to power source 46 through a second manually operable switch 49. Both switches 47 and 49 are preferably held "on" by a suitable locking circuit (not shown) after being closed. The reverse operating coil 48 is connected in series with a reversing relay coil 50. When reversing relay coil 50 is actuated, it opens the

switches

40, 41, 43 and 44, and simultaneously closes normally

open switches

52, 53, 54 and 55. This effectively reverses the connections of the

level sensor units

30 and 31 with the

respective coils

20 and 29 on the

proportioning valves

17 and 24.

Pressure-sensing

devices

56, 57 and 58 are connected, respectively, to the first output 18 of the valve 17 and the first and second outputs 2S and 26 of the valve 24. These are conventional types of devices in which there is a diaphragm exposed to pressure in the line with a microswitch which is closed when a given pressure is reached. The pressure sensors 56-58 are connected with their switches in series between a DC voltage source and a time delay relay 60, this arrangement providing a shutoff means for terminating a raising cycle. When all three switches close the time delay relay coil 59 is energized which, in turn, actuates a normally closed switch 61 in series with the manual switch 47. The sensors 56-58 are preset to close their switches when their respective jacks are supporting approximately percent of the weight they are intended to support in the fully raised position. When all three sensors read this pressure the time delay shutoff coil 59 actuates the switch 61 after a designated time delay and thus terminates the raising operation by deactivating the main operating coil 45. Another pressure operated switch 62 is connected in series with the reverse coil 48 and serves to stop the lowering action upon a predetermined pressure in the line 15 which indicates that all of the jacks have been fully raised.

Cutout circuits

63 and 64, the locations of which are shown in broken lines in FIG. 3 and which are themselves shown in FIGS. 4 and 5, are interposed in the operating circuitry for the

valves

17, 24. These serve in effect to disconnect the

level sensors

30, 31 from the

valves

17, 24 during lowering when certain conditions occur, allowing the

valves

17, 24 to return to centered position, which they will do automatically when they are deenergized. The purpose of the

cutout circuits

63, 64 is to terminate leveling action when the machine is on uneven terrain and one portion touches down before the rest. Absent any such control, if, for example, the front of the machine were to touch down first, further lowering would cause the machine to tip down toward the rear, and this would cause an error signal which would cause the valve 17 to shift so as to restrict flow from the

rear jacks

3 and 4, which are the jacks from which there must be flow to lower the machine.

To avoid this problem, the

cutout circuits

63 and 64 terminate leveling action along either axis when one end of that axis in on the ground. This means that the associated

valve

17 or 24 will center, which will allow flow through both sides so that lowering can continue in satisfactory fashion. In the preferred embodiment, this is accomplished through normally closed switches in the operating circuitry which are opened in response to low pressure detected by the pressure devices 56-58; it is known to those skilled in the art that these devices can be made to read both high and low pressure and that they can activate a number of switches. In FIG. 4, the reference numerals 56-58 have been used for the pressure devices proper, and corresponding prime and double prime numbers are used to indicate respective additional switches operated by each.

In cutout circuit 63, seen in FIG. 4, switches 57' and 58, openable by

devices

57 and 58, respectively, are connected in series with each other and the coil 29, which controls the valve 24. The

switches

57 and 58 are both shunted by a switch 47 which closes automatically upon closing of the switch 47, as the result of which the cutout circuit 63 is deactivated during a raising action. The switches 57' and 58' are set to open when the associated device reads a predetermined low or zero pressure, which indicates that the associated

jack

3 or 4 is no longer supporting any weight, or in other words that the left or right side of the machine has touched down. Opening of either switch 57' or 58' breaks the circuit for the coil 29, whereupon the valve 24 will center and allow continued normal flow.

The circuit 64, seen in HQ 5, controls the valve 17, and includes a parallel combination of normally closed switches 57" and 58" (operated by the

devices

57 and 58, respectively) in series with the coil 20 and a normally closed switch 56" (operated by the device 56). A switch 47", also closed automatically when the switch 47 closes, shunts all of the switches and deactivates the circuit 64 during raising. All of the switches 56-58" will be opened when the associated device 56-58 reads low or zero pressure. If the rear end of the machine touches down first, switches 57" and 58" will open, and if the front touches down switch 56" will open; in either event the coil 20 will be deactivated and the valve 17 will center. The reason for putting switches 57" and 58" in parallel is of course that leveling should not be stopped if only one rear comer has touched down.

During drilling it is desirable to close off the lines leading to the rod and cylinder ends of the

jacks

2, 3 and 4 to prevent fluid flow. FIG. 5 illustrates how this is accomplished for the cylinder 4, and similar systems are used for the other cylinders. As shown in FIG. 5, normally closed pilot operated check valves 65 and 66 are connected in the fluid lines leading to the cylinder and rod ends of jack 4, with the pilot line of each check valve 65 and 66 connected to the others fluid line. With this arrangement, the check valves 65 and 66 do not interrupt fluid flow when fluid flows toward the jack 4 during raising or lowering, but they prevent fluid from leaving jack 4 when the pump 13 is shut off.

OPERATION When it is desired to raise the machine to the position of FIG. ll, the switch 47 is closed, activating the coil 45 and causing the spool in the main operating valve 12 to shift to a position in which fluid under pressure moves through the output line 16 to the first proportioning valve 17 and returns from line through valve 17 and exhaust line 14 to the reservoir 11. Assuming that the valve 17 is in its normal position the fluid flow will be distributed between the output lines 18 and 19 in a ratio which will cause the

jacks

2, 3 and 4 to be extended at the same rate.

The actual flow rate will depend upon the relative piston areas of the several jacks. Assuming jacks of equal size this means that in the normal position one-third of the flow would be sent through the outlet line 18 and two-thirds would be sent through the outlet line 19 because the latter supplies fluid to two

jacks

3 and 4. If, however, the machine is not level along the longitudinal axis 8 the pendulum 32 in the. level sensor 30 will shift, generating a signal to the coil 20 which will proportionally shift the spool in the valve 17 to alter the flow rate to compensate for the nonlevel attitude of the machine. The sensing action of the unit 30, its control of the coil 20, and the actuation of the valve 17 is a continuing operation so that the machine is promptly brought to and maintained in a level attitude along the axis 8 throughout the raising operation.

The fluid flow through the outlet line 19 is fed into the second proportioning valve 24 and, assuming the

jacks

3 and 4 are of the same size, it is fed equally through the

output lines

25 and 26 when the valve 24 is in its nonnal position. Deviation from level about the transverse axis 9 will cause movement of the pendulum 32 in the level sensor 31 which results in a signal to the coil 29 proportionally shifting the spool in the valve 24 to alter the flow rate. This alteration compensates for the deviation and brings the machine back to level along the transverse axis 9. Again, the sensing, control and actuation is a continuous operation so that the machine is brought to and maintained in the level attitude along the transverse axis 9 throughout the raising operation.

When the jacks are supporting 80 percent of the machine weight, the pressure sensors 56-58 close their switches and energize the coil 59 which will, after a preset time delay, open the switch 61 to terminate the raising action. The time delay is preset to allow the jacks to extend to the point where they support 100 percent of the machine weight.

The operation during lowering is essentially the same, except the flow of fluid is reversed. To begin lowering, the switch 49 is closed causing the valve 12 to be actuated in the opposite direction. Fluid under pressure is then sent through the line 15 to the rod ends of the jacks 2-4 and fluid from the cylinder ends of said jacks will return ultimately through the line 16. Fluid flows from the

jacks

3 and 4 through the

lines

25 and 26 and through the second proportioning valve 24 at an equal rate when the valve 24 is in its normal position. If, however, the machine deviates from a level position along the axis 9 the level sensor unit 31 will generate a signal causing the valve 24 to alter the equal flow rate. The connections for the unit 31 to the coil 29 have been reversed by the reversing relay 51 so that the signal generated by the level sensors will result in a shifting of the spools in the proportioning valves in the opposite direction from that when tilting occurs during the raising operation. Return flow through the lines 18 and 19 and through the valve 17 will also be in the normal ratio when the valve 17 is in its normal position. If there is a deviation along the longitudinal axis 8 the valve 17 will be actuated to alter the flow rate and maintain the machine level.

As discussed above, the

circuits

63 and 64 cut off the leveling action when one portion of the machine is completely lowered to the ground before the others. Once the crawler 1 is resting entirely on the ground there is a pressure flow through the line 15 for a short period of time so that the jacks 2-4 will reach the upper limit of their travel, and this is shut off by pressure-operated switch 62.

The system of the invention is easy to operate and relatively inexpensive. It also provides highly accurate, continuous and extremely quick-acting control of machine attitude. A preferred embodiment of the invention has been shown and described herein, but it will be obvious that various modifications might be made without departure from the spirit of the invention. Various types of level sensors and pressure sensors, all of which are well known to those skilled in the art, might be substituted for the particular forms shown. Modifications might also be made in the electrical circuitry, elements may be added or combined, and different types of proportioning valves might be used. Further, the invention is not necessarily restricted to the use of three jacks on two axes. It is possible, for example, to have four jacks on three axes. To accomplish this, it would be necessary only to replace the front jack 2 with a pair of jacks situated like the

jacks

3 and 4 and to interpose a third proportioning valve like the valve 24. The result would be that the structure at the end of the output line 18 would be essentially a mirror image of that now shown in FIG. 3 at the end of the line 19. The third proportioning valve could be controlled by the same transverse level sensor unit 31, or by its own sensor. As a further alternative, two slightly transversely spaced jacks both fed ofi the same output line could be substituted for the single front jack 2, although these would operate essentially as a single jack. Still further, it is not necessary that the actual central longitudinal axis of the machine be used as a reference or that a perpendicular transverse axis be selected as a reference for leveling. In essence, it is necessary only that there be two jack means each aligned to define one axis in the base plane of the machine. One of the two jack means should be comprised of at least two jacks aligned to define a second axis in the base plane which intersects and is at least generally transverse to the first axis. In view of the several possible modifications, it is not intended that the invention be limited by the showing herein or in any other manner except as may specifically be required.

I claim:

1. In a leveling system for a blast hole drill or the like having a base plane, the combination comprising:

a first and a second jack means which are spaced from one another and together define a first axis in the base plane, the second jack means comprising a pair of spaced jacks defining a second axis in the base plane that is generally transverse to the first axis;

a fluid supply line;

a first proportioning valve in the supply line which has a first output leading to the first jack means and a second output leading toward the second jack means, said first proportioning valve being operable to continuously apportion the flow of fluid to the first and second jack means to maintain the base plane level along said first axis;

a first level sensor means adapted to continuously detect the attitude of the base plane along the first axis and operate the first proportioning valve in proportional response thereto;

a second proportioning valve connected to the second output of the first proportioning valve, said second proportioning valve having two outputs leading to respective members of the second jack means and being operable to continuously apportion the flow of fluid to the two jacks to maintain the base plane level along the second axis; and

a second level sensor means adapted to continuously detect the attitude of the base plane along the second axis and operate the second proportioning valve in proportional response thereto.

2. The combination of claim 1 wherein both proportioning valves have normal positions which are assumed when the base plane is level and said proportioning valves can be actuated in either direction from said normal position; and the ratio of flow through the first and second outputs of the first proportioning valve when it is in normal position is approximately equal to the ratio of the piston area of the first jack means to the total piston area of the jacks of the second jack means; and the ratio of flow through said outputs of the second proportioning valve when it is in normal position is approximately equal to the ratio of the respective piston areas of the jacks of the second jack means.

3. The combination of claim 2 wherein the proportioning valves are adapted to control the flow ratio of fluid moving through them in either direction; and the sensors are adapted to generate signals corresponding in polarity and magnitude to the attitude of the base plane along their respective axes; and there is a first set of connections between each sensor and the associated proportioning valve which is used during a raising action; and there is a second set of connections between each sensor and the associated proportioning valve which is used during a lowering action and in which the polarity of the signal to the valve is reversed; and there is switch means to select which set of connections is to be used.

4. The combination of claim 3 wherein there are three pressure-sensing devices, one associated with the first output of the first proportioning valve and the other two associated, respectively, with the first and second outputs of the second proportioning valve, each device being adapted to be actuated upon the occurrence of a predetermined low pressure in its associated output which indicates that the associated jack or jack means is no longer supporting a substantial load during a lowering cycle; and there is an operating circuit between each level sensor unit and its associated proportioning valve; and each proportioning valve has a self-centering action so that upon an interruption in its operating circuit it will return to centered position; and there is a first cutoff circuit in the operating circuit for the first proportioning valve which comprises a parallel combination of two normally closed switches, one adapted to be opened upon actuation of one of said other two devices and the other adapted to be opened upon actuation of the other of said other two devices, said combination being connected in series with a third normally closed switch adapted to be opened upon actuation of said one device; and there is a second cutofl circuit in the operating circuit for the second proportioning valve which comprises a normally closed switch adapted to be opened upon actuation of one of said other two devices and connected in series with another normally closed switch which is adapted to be opened upon actuation of the other of said other two devices; and each cutoff circuit includes means to deactivate the same during a raising cycle.

5. The combination of claim 4 wherein each of the three pressure-sensing devices is also adapted to be actuated when a preselected percentage of the total weight of the drill is supported by its associated jack or jack means; and there is a shutoff circuit which is adapted to terminate fluid flow through said fluid supply line, the shutoff circuit including three normally open switches connected in series, each switch being adapted to be closed upon actuation of a respective device, and a time delay means which, upon closing of all three switches causes flow to be terminated after a predetermined time interval.

Claims

1. In a leveling system for a blast hole drill or the like having a base plane, the combination comprising: a first and a second jack means which are spaced from one another and together define a first axis in the base plane, the second jack means comprising a pair of spaced jacks defining a second axis in the base plane that is generally transverse to the first axis; a fluid supply line; a first proportioning valve in the supply line which has a first output leading to the first jack means and a second output leading toward the second jack means, said first proportioning valve being operable to continuously apportion the flow of fluid to the first and second jack means to maintain the base plane level along said first axis; a first level sensor means adapted to continuously detect the attitude of the base plane along the first axis and operate the first proportioning valve in proportional response thereto; a second proportioning valve connected to the second output of the first proportioning valve, said second proportioning valve having two outputs leading to respective members of the second jack means and being operable to continuously apportion the flow of fluid to the two jacks to maintain the base plane level along the second axis; and a second level sensor means adapted to continuously detect the attitude of the base plane along the second axis and operate the second proportioning valve in proportional response thereto.

4. The combination of claim 3 wherein there are three pressure-sensing devices, one associated with the first output of the first proportioning valve and the other two associated, respectively, with the first and second outputs of the second proportioning valve, each device being adapted to be actuated upon the occurrence of a predetermined low pressure in its associated output which indicates that the associated jack or jack means is no longer supporting a substantial load during a lowering cycle; and there is an operating circuit between each level sensor unit and its associated proportioning valve; and each proportioning valve has a self-centering action so that upon an interruption in its operating circuit it will return to centered position; and there is a first cutoff circuit in the operating circuit for the first proportioning valve which comprises a parallel combination of two normally closed switches, one adapted to be opened upon actuation of one of said other two devices and the other adapted to be opened upon actuation of the other of said other two devices, said combination being connected in series with a third normally closed switch adapted to be opened upon actuation of said one device; and there is a second cutoff circuit in the operating circuit for the second proportioning valve which comprises a normally closed switch adapted to be opened upon actuation of one of said other two devices and connected in series with another normally closed switch which is adapted to be opened upon actuation of the other of said other two devices; and each cutoff circuit includes means to deactivate the same during a raising cycle.