US3759489A

US3759489A - Apparatus for automatically controlling weight-on-bit

Info

Publication number: US3759489A
Application number: US00141157A
Authority: US
Inventors: H Jones
Original assignee: PAT AND CHUCK OIL WELL EQUIPMENT
Current assignee: Varco International Inc; PAT AND CHUCK OIL WELL EQUIPMENT
Priority date: 1971-05-07
Filing date: 1971-05-07
Publication date: 1973-09-18
Anticipated expiration: 1990-09-18

Abstract

Apparatus for automatically controlling the weight on a rotary drilling bit, including cable drum, drum rotation monitor, deadline sensor, brake for the drum, brake actuator, and brake release, and characterized by the improvement of a gate for passing and stopping a brake release signal; a brake release signal generator for generating a brake release signal responsive to excessive tensional force in the cable deadline; and signal length modifier connected with the drum rotation monitor and the gate for stopping passage of the brake release signal responsive to rotation of the cable drum. Two specific embodiments are also described.

Description

United States Patent [191 Jones 1 Sept. 18, 1973 [7 51 Inventor: Barry C. Jones, Dallas, Tex.

[73] Assignee: Pat & Chuck Oil Well Equipment,

Inc., Fort Worth, Tex.

{22] Filed: May 7, 1971 211 App]. No.: 141,157

[56] References Cited UNITED STATES PATENTS 4/1960 Gresham et al. 254/173 B 9/1952 Jaeschke 254/172 3,347,524 10/1967 Melton 254/173 B 3,104,864 9/1963 Melton et a1 254/173 B FOREIGN PATENTS OR APPLICATIONS 456,447

FLUID SUPPLY SOURCE 11/1936 Great Britain l73/6 Primary Examiner-Evon C. Blunk Assistant Examiner-Merle F. Maffei Attorney-Wofi'ord, Felsman & Fails, Wm. T. Wofford, Robert A. Felsman, James C. Fails and Arthur F. Zobal s71 ABSTRACT Apparatus for automatically controlling the weight on a rotary drilling bit, including cable drum, drum rotation monitor, deadline sensor, brake for the drum, brake actuator, and brake release, and characterized by the improvement of a gate for passing and stopping a brake release signal; a brake release signal generator for generating a brake release signal responsive to excessive tensional force in the cable deadline; and signal length modifier connected with the drum rotation monitor and the gate for stopping passage of the brake release signal responsive to rotation of the cable drum. Two specific embodiments are also described.

6 Claims, 4 Drawing Figures LENGTH I H sE DETECTOR I MODIFIER I MEANS l I v LEVEL OETEOTOR Y 1 T A I CONTROLLER ,9 GATE MEANS SIGNAL GENERATOR 1 6 v T A L PATENTED SEN 8l975 3 I T 55) ,489

SHEET 1 [IF 2 FLUID SUPPLY 1 SOURCE ,J/ LII/35 SENSOR I F 'I I I I 75 SOLENOID PHASE DETECTOR j I l 55 I I I LEvEL DETECTOR I I I I CONTROLLER I \LI/ GATE MEANS SIGNAL GENERATOR I I 69 I L .J 6'5 7/) Q I PROPORTIONAL RESPONSE MEANS I TO MuLTIvIBRATOR [51 9.5

INVENTOR 1%?? 6 4 /0748:?

ATTORNEYS PATENTED 3.759.489

SHEET 2 BF 2 I SIGNAL LENGTH MODIFIER MEANS ROTARY CAM 55 87 1 l I I l l g 2 i I SWITCH PASCHALTRlANGLE-TYPE LEVEL MEANS FILTER NETWORK SENSOR 9/ 95 I L I L J 1 15 .2 F i 1 6'5 MULTIVIBRATOR I WE 77 i i 67 "'i V85 1 SIGNAL LENGTH MODIFER MEANS l w L 83 //g DELAY GENERATOR F {/1245 MONOSTABLE l SWITCH TRIGGER I I M EAN s M E A N S I I I MU LTIVIBRATOR l I l l 7 12/ /z9 I /55/ /59 DIFFERENTIATOR 57 l l 1 I FOR TRAILING EDGE L L L .1

' "'1 /3'/ 1\/ 5 MULTIVIBRAT R 77 JR 65 L l //VVE/V7'0R iizmaafle B) wzmw ATTORNEYS BACKGROUND OF THE INVENTION 1. Field of the Invention weight string This invention relates to apparatus for automatically controlling a parameter in drilling a wellbore into subterranean formations. More particularly, the invention relates to apparatus for automatically controlling the weight on the drilling bit, called weight-on-bit, during drilling of a wellbore into subterranean formations by a rotary drilling rig.

2. Description of the Prior Art A wide variety of methods and apparatus have been employed for automatically controlling weight-on-bit,

but such prior art methods and apparatus have disadvantages that are overcome by this invention. For example, the prior art apparatus has been complex, frequently requiring major modifications for installation on certain drilling rigs, and has not been readily installable on any rig with only minor modifications. The prior art apparatus and methods have employed attempts to control weight-on-bit by automatically controlling the usual brake lever of the draw works; but, because of the inherent lag of the control system and the action of the brake system and lever, over controlled and produced erratic drilling and wellbore deviations. Specifically, the prior art systemshave not had a sufficient degree of flexibility and adjustability. to effect the desired successful and economically feasible automation of the conventional rotary drilling rigs. A couple of the prior art systems have attempted to provide a partial'brake release signal so as to only release.

the brake part of the way to the full release position. The latter systems have not been totally successful, primarily because of the tendency of a cable drum to wear unevenly such that varyinglengths of cable are released from different parts of the drum when a partial brake release signal is employed, effecting nonuniform payout even with a constant signal level.

BRIEF DESCRIPTION OF THE DRAWINGS ing one embodiment of the signal length modifier means ofF-IG.1. I y,

FIG. 3 is ,a' partial electrical schematic diagram de picting the proportional response means in the embodi-j ment of FIG. 2. I r

FIG.4is a partial schematic block diagram illustratinganother embodiment means of FIG. 1

DESCRIPTION OF PREFERRED EMBODIMENTS of the signal length'modifier 3. in a specific embodiment, provide manual adjustment at both the front end and trailing edge of a brake The cable drum 29 is rotated in the opposite direction release signal to better compensate for inertia of the brake system and the control system on a rotary drilling rig; and

4. in another specific embodiment provide a manual adjustment at the front end and an inverse proportioning response at the trailing edge of a brake release signal to compensate for inertia of the brake and control systems.

Referring to FIG. 1, the numeral 11 designates the conventional crown block comprising a plurality of sheaves mounted at the top of a rotary drilling rig (not shown). A travelling block 13 is suspended from the crown block 11 by means of a cable system, 15 providing the requisite mechanical advantage for raising and lowering the large weights of the drill string 17. As is well known, the drill string 17 is connected with the travelling block 13 by a kelly 19 traversing a rotary table 21 for rotating the bit. Suitable drilling mud circulation means typified by hose 23 may be employed for circulating drilling mud into and from the wellbore, carrying cuttings and the like.

v The cable system comprises a-tensioned cable having a first end, or deadline, 25 that is, non-moving, or dead, in normal operation. The second, or fast, end 27 of the cable moves most rapidly in normal operation, as by being spooled onto or from cable drum 29. Specifically, the deadline 25 is wound around an eccen-' trically mounted spool .31 and connected with an anchored cable storage drum 33 to facilitate spooling off worn cable and replacing it-with new cable. As is well known, the cable drum 29. is rotated in one direction by suitable power equipment (not shown for raising the travelling block 13 and the drill string 17.

by the weight of the drill string to pay out cable and lower the weight of the drill string onto a drilling bit 35 carried at the lower end-of the drill string 17. Pay out of the cable from the cable drum 29 is controlled by a brake 37. Conventionally, rotary drilling rigs .will have a brake'lev er 39 foricontrollingthe brake. Inattention by a driller or different drillers effected a wide variance in the straightness, as well as the rate of drilling for well recognized reasons; To facilitate installation of the automatic control apparatus on existing rigs, therefor, the brake lever 39 isincorporated into the control apparatus. Specifically, a brake applying means is connected with the brake 37 viajthe brake lever 39 for automatically restoring and maintaining the brake applied when the brake is not being released by a brake'release It is an object of this invention to-provide improved means; the brake applying means being illustrated in the form of a spring 41 connected with support 43 such as the floor of a drilling rig. Thus, the brake is normally applied and prevents rotation of the cable drum 29 to pay out cable. A brake release means-incorporating a fluid-powered ram 45 connected witha suitable support 47 is connected with the brake 37 via brake lever 39 for releasing the brake and allowing a pay out of the cable in response to abrake release signal. Specifically, the ram 45 is connected with a suitable motive fluid supply source; such as, a rigs pneumatic air supply; via conduit 49 and solenoid-operated, three-way valve 51. The three-way valve 51 supplies motive fluid under pressure to release the brake, or releases the presure to the atmosphere to allow the spring 41 to apply the brake. The three-way valve 51 is connected with sole- 3 noid 53, as indicated by dashed lines 55. Suitable auxiliary valves such as quick release valves may be employed to reduce the lag in the brake release system, if desired.

During the actual drilling operation it is necessary to apply at least part of the weight of the drill string 17 to the bit 35 to secure proper rate of penetration of the formation and proper inclination of the wellbore, or hole. Moreover, different formations require differentweights-on-bit. Improper weight on the bit can result in damage to the drill bit with the expense of having to prematurely pull the bit from the hole, crooked holes, damage to drill pipe, cave-ins and other difficulties effecting sticking of the drill pipe, and the like. Thus, efficiently controlling the weight on the bit is one of the most important factors in improving the proper drilling of wellbores into the subterranean formation. The apparatus of this invention for automatically controlling weight on a bit includes, in addition to the elements described hereinbefore, sensor means 59, signal generator, or generating, means 61, gate means 63, drum rotation monitor means 65, and signal length modifier means 67. i v

The sensor means 59 isresponsively connected with the tensioned deadline 25 of the cable so as to sense the tension therein. As indicated hereinbefore, the tension in the deadline is a function of the weight on the travelling block 13 and is inversely related to the wweight on the bit. Expressed otherwise, the greater the portion of the weight of the drill string that is being sustained by the travelling block 13, the lesser the portion of the weight of the drill stirng-17 that is bearing on the drill bit 35. Accordingly, as the length of the drill string is increased, as by adding joints of tubing, the control tension in the deadline, about which the sensor means controls, is altered, or zeroed, to maintain the desired weight on the bit. An example of establishing the desired control tension is describedin the operation of the apparatus hereinafter. Any of the coenventional sensor means may be employed. As illustrated, however, the sensor means 59 includes a conventional load indicator 68 with its sensor incorporating a movable iron core employed in a conventional linear differential transformer arrangement for great sensitivity in detecting small changes in deformation of the deadline 25 under tension.

The signal generator means 61 is connected with the sensor means 59 and the gate means 63. Responsive to the sensing of a tension greater than a predetermined control tension by the sensor means 59, the signal generator means 61 generates a brake release signal and actuates the gate means to pass the brake release signal to the brake release means, comprising the solenoid 53, three-way valve 51 and ram 45. The signal generator means includes a controller 69 and a signal generator 7 l The controller 69 may comprise any of the conventional elements that are compatible with the output from the sensor means 59 and will effect an on-off signal. As illustrated, the controller 69 comprises a phase detector 73 and a level detector 75. The phase detector 73 is the most sensitive known means of comparing, via a bridge circuit arrangement, the sensor-connected linear differential transformer with a standard'matched linear differential transformer. This combination of sensor means 59 and phase detector 73 has great sensitivity and detects the small changes in tension in the deadline 25. Any on-off switch means that is compatible with the phase detector 73 may be employed as the level detector 75. As illustrated, the level detector 75 comprises a Schmitt trigger circuit that is connected with the phase detector 73 and with the signal generator to turn on the signal generator 71 upon receipt of a voltage output above a predetermined control voltage from phase detector 73.

The signal generator 71 may produce a continuous signal for useas a brake release signal, or it may produce a plurality of pulses for use as the brake release signal. Any of the conventional signal generators that produce the desired pulse and that are compatible with the output from the level detector 75 may be employed. As illustrated, the signal generator 71 is an oscillator. In a preferred embodiment, it comprises a unijunction oscillator. The oscillator produces pulses of a time duration in the range of about one-fourth to onehalf second and repeats at a frequency in the range of one pulse each 1-3 seconds.

The gate means 63 may comprise any compatible element that can be turned on or off for passage, or conduction, of the brake release signal from the signal generating means 61 to the brake release means- An economical and unsatisfactory gate means has been found to comprise a multivibrator such as a bistable multivibrator that can be turned on by the signal generator means 61 and turned off by the signal length modifier means 67; A preferred multivibrator is a monostable multivibrator which effects a pulse length of a predetermined time duration such that it will automatically terminate the pulse serving as the brake release signal after the predetermined time duration even if the signal length modifier means should fail to operate. Thus, the monostable multivibrator provides an inherent safety factor, or fail-safe device. As employed in a preferred embodiment of this invention, the multivibrator is interconnected with a potentiometer, such as Helipot, illustrated as calibrated dial 77, FIGS. 2 and 4. The Helipot allows adjusting the time interval, or the duration, of the pulse from the monostable multivibrator by manual adjustment of the calibrated dial 77. The Helipot provides for an adjustment at the front end of the brake release signal to compensate for the inherent dynamics and lag characteristics of the brake, the brake lever, and the control system on the particularrotary drilling rig on which it is installed. Thus, by a brief period of trial and error operation, the most nearly optimum control can be effected for a given drilling rig operating under a given drilling condition. 1

The drum rotation monitor means 65 may comprise any control unit which feeds back intelligence responsive to movement of the cable as effected by rotation of the drum. conventionally, such units employ a movement detection wheel 79 which is mounted on the extended end of a main shaft 81. The wheel 79 is adapted to engage a surface disposed near the periphery of the cable drum and, when engaged, rotate at a much greater rotational speed in revolutions per minute than the cable drum, because of the wide variance in their respective radii. The wheel 79 is in fixed engagement with the shaft 81 so that rotation of the wheel effects rotation of the shaft 81. The shaft 81 extends through a suitable housing and is joumalled on bearings therein (not shown).'Additionally, the main shaft 81 is pivotally mounted by a conventional structure so it can be pivoted so as to disengage from the cable drum for operations other than normal drilling operation; for example, when a trip is being made to run a bit into or out of the wellbore. Since such drum rotation monitor means are conventional and do not, per se, comprise a part of this invention, no further detailed explanation need be given herein. It is sufticient to note that the main shaft is connected with a suitable means; such as, a rotary cam 83, FIGS. 3 and 4; in the signal length modifier means 67; as denoted by dashed line 85.

The signal length modifier means 67 is connected with the drum rotation monitor means 65 and with the gate means 63. Responsive to rotation of the cable drum 29, as monitored by cable drum rotation monitor means 65, the signal length modifier means 67 renders the gate means 63 nonconductive to stop passage of a brake release signal.

In the embodiment of FIG. 2, the signal length modifier means 67 comprises proportional response means 87 for stopping passage of the brake release signal after a time interval having a magnitude that is inversely proportional to the rate at which the drum starts to rotate. Any proportional response controller which is compatible with the output from the drum rotation monitor means 65; for example, by way of rotary cam 83; and which will yield an on-off output signal for control of gate means 63 may be employed to effect the proportional response means. As illustrated, the proportional response means 87 comprises a switch means 89 that is serially connected with a Paschal triangle-type filter network 911, and a level sensor 93. The drum rotation monitor means 65 is drivingly connected with the switch means 89 via rotary cam 83 and mechanically juxtaposed interconnection, indicated by dashed line Y 95. The rotary cam 83 may comprise any of the conventional cams having one or more eccentric lobes for converting the rotational movement of the shaft 81 of g the drum rotation monitor means 65 into a reciprocal motion for effecting switching of the switch means 89.

FIG. 3 illustratesan electrical schematic diagram incorporating elements of the proportional response means 87. Therein,'the level sensor 93 is illustrated as an-electronic switch means, specifically transistor 97. The switch means 89- is shown incorporated into the Paschal triangle-type, or Paschal-type, filter network 91. The transistorhas a means such as base'99 for rendering it electrically"conductive. The transistor 97 is serially connected with the gate means 63, such as the multivibrator, and a power source, illustrated as B+, for rendering the gate means nonconductive when the transistor 97 is rendered electrically conductive; Serially connected with the base 99 are biasing capacitor 101 and biasing resistor 103. The biasing resistor 103, as illustrated, is connected directly with the base 99. The biasing capacitor 110i is connected at its other side with the center pole 105 of the switch means 89. A discharging resistor 107 is connected with the juncture of the biasing resistor 103 and the biasing capacitor i011 and with a first contact 109 of the switch means 89 so as to discharge the biasing capacitor 101 when the switch means 89 connects the biasing capacitor 101 with the first contact 109. The second contact Ill of the switch means 89 is connected with electrical common, or ground, for charging the biasing capacitor 101 when the switch means connects the biasing capacitor 101 withthe second contact 111. A second capacitor 113 and third resistorllS are connected in parallel. The parallel-connected resistor 115 andcapacitor 113 are serially connected with the power source 8+ and with the juncture of the base 99 and the biasing resistor 103. The values of the capacitors and resistors are chosen such that the biasing capacitor 101 is charged more rapidly with more rapid switching of the switch means 89, as by a rapidly turning rotary cam 83, cffected by rapid acceleration of the cable drum 29 as it begins to rotate. Thus, the speed with which the gate means 63 is turned off, or rendered electrically nonconductive, is proportional to the rate of rotation of the movement detecting wheel 79 monitoring rotation of the cable drum 29. Expressed in more conventional language, the time duration of a brake release signal from signal generator 71 has a magnitude that is inversely related to the rate of rotation of the wheel 79, or the rate at which switching by the switch means 89 is effected; the time duration being lessened, or shortened, by a greater switching rate; that is, by more rapidly opening and closing the switch means 89.

- In operation, the apparatus is installed on a conventional rotary drilling rig as illustrated and drilling started. During drilling, the sensor means 59 detects a tension greater than the control tension and produces an output to controller 69. The controller69 turns on the signal generator 71 which generates a brake release signal and turns on gate means 63. The brake release signal then actuates solenoid 53, opening three-way valve 51 to vent motive fluid through conduit 49 into ram 45.. The ram 45'1ifts the brake lever 39 to allow pay out of the fast end 27 of thecable. As the cable drum 29 starts to rotate, the cable drum monitor means rotates much more rapidly and effects a signal via signal length modifiermeans 67 to render gate means 63 nonconductive, closing three-way valve 51 and venting the motive fluid to the atmosphere; allowing the spring 411 to return to brake lever downwardly to apply the brake to the drum and stop pay out of thecable. This cycle is repeateda plurality of times during the drilling operation, of course, to maintain a uniform weight-on- .bit. In fact, it has been found preferable to employ a pulse generator as the signal generator 71. Thus, the brake release signal will comprisea plurality of discrete pulses of short time duration, as described hereinbefore. Each pulse, however, effects a full on brake release signal to avoid the disadvantages of the prior art and approach a perfect driller using manual operation.

In setting the control tension, a portion of the drill string weight is suspended from the travelling block 13. For example, if 32,000 pounds of weight is desired on the bit and the drillstring weighs 160,000 pounds, then the drill bit will be placed on the bottom and slacked off until there is 128,000 pounds being supported by the travelling block 13, as determined by an appropriate conventional instrument; such as, a deadline monitor or a load cell in the hook support mechanism. With the 128,000 pounds being supported, the sensor means 59 is zeroed to establish the control tension in the cable. As the bit drills into the formation, there is a tendency for additional weight to be picked up by the cable, eflecting increased tension on the deadline 25. Accordingly, the sensor means 59 will effect an output to indicate that additional cable should be payed out from cable drum 29. As indicated'hereinlbefore, the controller 69 employs the phase detector 73 to afford sensitive monitoring of the output from the sensor means 59. Similarly, the level detector responds to output from phase detector 73 to start the pulse signal generator switch of the switch means 89 charges biasing capacitor 101 to the voltage that renders the transistor 97 conductive. The rate at which the capacitor is charged is proportional to the rate at which the switch means 89 is switched between first contact 109 effecting discharging and contact 111 effecting charging of the biasing capacitor 101. In any event, when the transistor is rendered conductive, it effects a resettingof the monostable multivibrator back to its stable state by appropriate conventional means. If the cable drum is in a worn region such that it begins to rotate more rapidly and pay the cable out more rapidly upon the release of the brake, the capacitor 101 is charged more rapidly and renders the transistor 97 conductive after a shorter time period, cutting short the brake release signal and reapplying thebrake. Conversely, if the cable drum starts to rotate more slowly, as caused by an out-ofround condition, the switch means 89 is switched more slowly and the biasing capacitor 101 is charged more slowly. Consequently, there is a longer time interval before the transistor 97 is rendered conductive to stop the brake releasesignal. Thus, a proportional response is effected on the trailingedge of the brake release signal to compensate for any imperfections in the initial adjustment of the multivibrator, as effected by the setting of the calibrated dial 77. At the same time, all of the advantages of a full on brake or a full oifbrake are effected. v

Another embodiment of this invention is illustrated in FIGS. 1 and 4 wherein the signal length modifier means 67 comprises serially connected variable time delay generator means 119 and switch means 121. As described hereinbefore, the switch means 121 comprises a switch that is responsively connected with the drum rotation monitor means 65 via rotary cam 83 and mechanical connections described hereinbefore, illustrated by dashed

lines

85 and 123. Thus, after a brake releasesignal haseffected release of the brake 37 and the cable drum 29 has started to rotate to pay out cable 27, closure of the swith means '121 is effected and the resulting signal is transmitted via the delay of the variable time delay generator 119 to the gate means 63 to stop the brake release signal. As illustrated, the switch means 121 is serially electrically connected with a power source (not shown) via conductor 127, a trigger means 129, the variable time delay generator H19 and the gate means 63 such as multivibrator 131. The switch means 121 may comprise any acceptable onoff" switching device. Similarly, any conventional trigger means may be employed as trigger means 129. As illustrated, the trigger means 129 comprises a Schmitt trigger circuit for shaping the pulse effected by the switch means 121.

Any of the conventional delay generators that may be adjusted for time duration are acceptable as delay generator 119. As illustrated, the delay generator comprises a monostable multivibrator and a differentiator for trailing edge 137. Specifically, the monostable multivibrator 135 has a Helipot arrangement, as described hereinbefore with respect to the monostable multivibrator employed as the gate means 63 and as illustrated by the calibrated dial 139. Thus, the calibrated dial 139 may be turned to a predetermined setting to effect, via suitable Helipot, a pulse output that has a predetermined time duration which will ultimately serve as the time delay. The differentiator for trailing edge 137 is a conventional circuit which converts the turning off of thepulse from the monostable multivibrator 135 into a positive going pulse suitable to turn 0E the multivibrator 131 serving as the gate means 63. As indicated hereinbefore, the multivibrator 131 is also preferably a monostable multivibrator that effects a pulse of a predetermined time duration for ensuring the stopping of the brake release signal even if the signal length modifier means 67 fails to stop the brake release signal. The monostable multivibrator 131 has, as indicated hereinbefore, a Helipot arrangement, indicated by calibrated dial 77 for varying the time interval of the pulses comprising the brake release signal. Thus, with this embodiment, the brake release signal may be manually adjusted at its frontend to effect the desired time interval for the pulses'comprising the brake. release signal, and a manuallyadjustable feedback from the cable drum rotation monitor means employed to provide additional compensation for the inherent lag and operating characteristics of the brake and control systems. a

In operation, a brake release signal is effected as de-' scribed hereinbefore with respect to FIGS. 1-3. The brake is released, similarly as described hereinbefore, and the cable drum 29 starts to rotate to pay out cable.

As it has rotated a short distance; for example, from a lineal distance of from one-half inch up to several inches, effected by proper sizing of the movement detecting wheel 79'ultimately driving the switch means 121; the switch means 121 is closed. Closure of the switch means 121 effects, via the Schmitt trigger circuit in trigger means 129, a pulse to turn on the monostable multivibrator 135. The monostable multivibrator 135 effects a pulse of a predetermined width, or time interval. Then the pulse is terminated. Upon the termination of the pulse, the differentiator for trailing edge 137 effects a signal which is passed to the multivibrator 131 to turn it off and stop passage of any brake release signal being sent to the brake release means.

Thus, it can be seen that the invention accomplishes the objects delineatedhereinbefore and provides one or more of the desirable features not heretofore provided. Specifically, this invention employs the proven on-off approach to controlling the pay outof cable to maintain the proper weight-on-bit, while providing means at the front end and at trailing edge of the brake release signal to compensate for the inertia, lag, and dynamics of the braking system and the control system to eliminate over controlling.

Although the invention has been described with a certain degree of particularity, it is understood that the present disclosure has been made only by way of example and that numerous changes in the details of construction and the combination and arrangement of parts may be resorted to without departing from the spirit and the scope of the invention. What is claimed is:

1. ln apparatus for automatically controlling weight on the bit in a rotary drilling rig including:

a. cable drum for spooling the fast end of a tensioned cable bearing a portion of the weight of a drill string;

b. drum rotation monitor means responsively connectable with said drum for monitoring rotation thereof; r

c. sensor means connected responsively with the tensioned dead end of said cable;

d. brake for said drum;

e. brake applying means connected with said brake for automatically restoring and maintaining said brake applied when said brake is not being released by a brake release means;

f. brake release means connected with said brake releasing said brake;

the improvement comprising:

g. gate means connected with said brake release means for passing a brake release signal to said brake release means to fully release said brake and for terminating said brake release signal to fully apply said brake;

h. signal generating means comprising controller means and a signal generator connected'with said sensor means and said gate means for generating a brake release signal and actuating said gate means to pass said brake release signal to said brake release means responsive to sensing of a cable tension greater than a predetermined control tension; 'said brake release signal being sufiicient to efiect a full release of said brake; and

i. signal length modifier means comprising a proportional response means connected with said drum rotation monitor means and said gate means for supplying to said gate means a signal responsiveto both rate and degree of rotation of said drum causing said gate means to terminate passage of said brake release signal after a time interval the magnitude'of which is inversely proportional to the rate at which said drum starts to rotate such that said brake is fully applied and fully released to avoid the diadvantages of partially releasing said brake; said propor-tional response means including a switch vmeansga Paschal-type filter network and a level sensor; said drum rotation monitormeans being drivingly connected with said switch means that is connnected into said Paschal-type filter network; said Paschal-type filter network being connected with said level sensor that isc'onnected with said gate means. i i

2. The apparatus of claim iwherein said level sensor comprises an electronic switch means having means rendering'it conductive; said electronic switchmeans being serially connected with said gate means and a power source for rendering said gate means nonconductive; and said switch means isa single-pole, double throw type, and is connected into said Paschal-type filter network comprising: p

a. a biasing resistor and capacitor serially connected between said means rendering said electronic switch means conductive and the center pole of said switch means;

b. first resistor connected with the juncture of said biasing resistor and said biasing capacitor and with a first contact of said switch means so as to discharge said biasing capacitor at a first rate when g. gate means connected with said ill) said switch means connnects said capacitor with said first contact;

c. electrical common connected with the second contact of said switch means for charging said biasing capacitor at a second rate when said switch means connects said capacitor with said second contact; and

d. parallel-connected resistor and capacitor serially connected with said power source and the juncture of said means rendering said electronic swith means conductive and said biasing resistor; said capacitors and said resistors being chosen such that said second rate is greater then said first rate and said biasing capacitor is charged more rapidly with more rapid switching by said switch means, said biasing capacitor being charged to a voltage such that said electronic switch means is rendered conductive;

whereby said brake release signal is terminated after a time interval that is shortened by more rapidly opening and closing said switch means as by rapid acceleration of said cable drum as it starts to rotate.

3. In apparatus for automatically controlling weight on the bit in a rotary drilling rigincluding:

a. cable ,drum for spooling the fast. end of a tensioned cable bearing a portion of the weight of a.

drill string;

b. drum rotation monitor means responsively connectable with said drum from monitoring'rotation thereof; a t y a y 0. sensor means connected responsively with the tensioned "dead end of said cable;

d. brake for said drum; 1 y

e. brake applying means connected with said brake for automatically restoring and maintaining said brake applid when said brake is not being released by a brake release means; 1 a r f. brake release means connected with said brake for releasing said brake;

the improvement comprising:

brake release a means for passing a brake release signal to said I brake release means to fully release said brake and for terminating said brake release signal to fully apply said brake; said gate meansbeing a multivibrator that is turned on by a signal generator and tumed' off by a proportional response fmeans; I h. signal generating means comprising controller means and signal generator connected, with said sensor means and said gate means for generating a brake release signal and actuating said gate means to'pass said brake release signal to said brake release means responsive to sensing of cable tension greater than a predetermined control tension; said brake release signal being sufficient to effect a full release of said brake; and

. signal length modifier means comprising a proportional response means connected with said drum rotation monitor means and said gate means for supplying to said gate means a signal responsive to both rate and degree of rotation of said drum causing said gate means to-terminate passage of said brake release signal after a time interval the magnitude of which is inversely proportional to the rate at which said drum starts to rotate such that said brake is fully applied and fully released to avoid the disadvantages of partially releasing said brake.

4. The apparatus of claim 3 wherein said multivibrator is a monostable multivibrator for ensuring termination of said brake release signal and thereby providing a fail-safe, feature.

5. In apparatus for automatically controlling weight on the bit in a rotary drilling rig including:

b. drum rotation monitor means responsively connected to said drum for monitoring rotation thereof;

c. sensor means responsively with the tensioned dead end of said cable;

d. brake for said drum;

f. brake release means connected with said brake for releasing said brake;

the improvement comprising:

g. gate means connected with said brake release means for passing a brake release signal to said brake release means to fully release said brake and for terminating said brake release signal to fully applysaid brake; said gate means being a bistable multivibrator;

h. signal generating means comprising controller means and a signal generator connected with said sensor means and said gate means for generating a brake release signal and actuating said gate means to pass said brake release signal to said brake release means responsive to sensing of cable tension greater than a predetermined control tension; said brake release signal being sufficient to effect a full release of said brake; said signal generator when energizedproducing a continuous signal that turns on said bistable multivibrator to effect said brake release signal; and

. signal length modifier'means connected with said drum rotation monitor means and said bistable multivibrator serving as said gate means for turning off said bistable multivibrator responsive to both rate and degree of rotation of said drum causing said bistable multivibrator to terminate passage of said brake release signal; whereby said brake is fully applied and fully released to avoid the disadvantage of partially releasing said brake.

6. In apparatus for automatically controlling weight on the bit in a rotary drilling rig including:

b. drum rotation monitor means responsively connectable with said drum for monitoring rotation thereof;

d. brake for said drum;

f. brake release means connected with said brake for releasing said brake;

the improvement comprising:

g. gate means connected with said brake release means for passing a brake release signal to said brake release means to fully release said brake and for terminating said brake release signal to fully apply said brake; said gate means being a monostable multivibrator that produces a plurality of discrete pulses of a first time duration, each said pulse effecting passage of said brake release signal and termination thereof when not otherwise terminated;

h. signal generating means comprising controller means and signal generator connected with said sensor means and said gate means for generating a brake release signal and actuating said gate means to pass said brake release signal to said brake release means responsive to sensing of cable tension greater than a predetermined control tension; said brake release signal being sufficient to effect a full release of said brake; and

i. signal length modifier means connected with said drum rotation monitor means and said gate means for supplying said gate means a signal responsive to both rate and degree of rotation of said drum causing said gate means to terminate passage of said brake release signal; whereby said brake is fully applied and fully released to'avoid the disadvantages of partially releasing said brake; said signal length modifier means being operable to render said.

monostable multivibrator nonconductive responsive to rate and degree of rotation of said drum to shorten saidfirst time duration as needed to effect optimum control of the weight-on-bit and alleviate difiiculties with over controlling.

Claims

1. In apparatus for automatically controlling weight on the bit in a rotary drilling rig including: a. cable drum for spooling the ''''fast'''' end of a tensioned cable bearing a portion of the weight of a drill string; b. drum rotation monitor means responsively connectable with said drum for monitoring rotation thereof; c. sensor means connected responsively with the tensioned ''''dead'''' end of said cable; d. brake for said drum; e. brake applying means connected with said brake for automatically restoring and maintaining said brake applied when said brake is not being released by a brake release means; f. brake release means connected with said brake releasing said brake; the improvement comprising: g. gate means connected with said brake release means for passing a brake release signal to said brake release means to fully release said brake and for terminating said brake release signal to fully apply said brake; h. signal generating means comprising controller means and a signal generator connected with said sensor means and said gate means for generating a brake release signal and actuating said gate means to pass said brake release signal to said brake release means responsive to sensing of a cable tension greater than a predetermined control tension; said brake release signal being sufficient to effect a full release of said brake; and i. signal length modifier means comprising a proportional response means connected with said drum rotation monitor means and said gate means for supplying to said gate means a signal responsive to both rate and degree of rotation of said drum causing said gate means to terminate passage of said brake release signal after a time interval the magnitude of which is inversely proportional to the rate at which said drum starts to rotate such that said brake is fully applied and fully released to avoid the diadvantages of partially releasing said brake; said proportional response means including a switch means, a Paschal-type filter network and a level sensor; said drum rotation monitor means being drivingly connected with said switch means that is connnected into said Paschal-type filter network; said Paschal-type filter network being connected with said level sensor that is connected with said gate means.

2. The apparatus of claim 1 wherein said level sensor comprises an electronic switch means having means rendering it conductive; said electronic switch means being serially connected with said gate means and a power source for rendering said gate means nonconductive; and said switch means is a single-pole, double throw type, and is connected into said Paschal-type filter network comprising: a. a biasing resistor and capacitor serially connected between said means rendering said electronic switch means conductive and the center pole of said switch means; b. first resistor connected with the juncture of said biasing resistor and said biasing capacitor and with a first contact of said switch means so as to discharge said biasing capacitor at a first rate when said switch means connnects said capacitor with said first contact; c. electrical common connected with the second contact of said switch means for charging said biasing capacitor at a second rate when said switch means connects said capacitor with said second contact; and d. parallel-connected resistor and capacitor serially connected with said power source and the juncture of said means rendering said electronic swith means conductive and said biasing resistor; said capacitors and said resistors being chosen such that said second rate is greater then said first rate and said biasing capacitor is charged more rapidly with more rapid switching by said switch means, said biasing capacitor being charged to a voltage such that said electronic switch means is rendered conductive; whereby said brake release signal is terminated after a time interval that is shortened by more rapidly opening and closing said switch means as by rapid acceleration of said cable drum as it starts to rotate.

3. In apparatus for automatically controlling weight on the bit in a rotary drilling rig including: a. cable drum for spooling the ''''fast'''' end of a tensioned cable bearing a portion of the weight of a drill string; b. drum rotation monitor means responsively connectable with said drum from monitoring rotation thereof; c. sensor means connected responsively with the tensioned ''''dead'''' end of said cable; d. brake for said drum; e. brake applying means connected with said brake for automatically restoring and maintaining said brake applid when said brake is not being released by a brake release means; f. brake release means connected with said brake for releasing said brake; the improvement comprising: g. gate means connected with said brake release means for passing a brake release signal to said brake release means to fully release said brake and for terminating said brake release signal to fully apply said brake; said gate means being a multivibrator that is turned on by a signal generator and turned off by a proportional response means; h. signal generating means comprising controller means and signal generator connected with said sensor means and said gate means for generating a brake release signal and actuating said gate means to pass said brake release signal to said brake release means responsive to sensing of cable tension greater than a predetermined control tension; said brake release signal being sufficient to effect a full release of said brake; and i. signal length modifier means comprising a proportional response means connected with said drum rotation monitor means and said gate means for supplying to said gate means a signal responsive to both rate and degree of rotation of said drum causing said gate means to terminate passage of said brake release signal after a time interval the magnitude of which is inversely proportional to the rate at which said drum starts to rotate such that said brake is fully applied and fully released to avoid the disadvantages of partially releasing said brake.

5. In apparatus for automatically controlling weight on the bit in a rotary drilling rig including: a. cable drum for spooling the ''''fast'''' end of a tensioned cable bearing a poRtion of the weight of a drill string; b. drum rotation monitor means responsively connected to said drum for monitoring rotation thereof; c. sensor means responsively with the tensioned ''''dead'''' end of said cable; d. brake for said drum; e. brake applying means connected with said brake for automatically restoring and maintaining said brake applied when said brake is not being released by a brake release means; f. brake release means connected with said brake for releasing said brake; the improvement comprising: g. gate means connected with said brake release means for passing a brake release signal to said brake release means to fully release said brake and for terminating said brake release signal to fully apply said brake; said gate means being a bistable multivibrator; h. signal generating means comprising controller means and a signal generator connected with said sensor means and said gate means for generating a brake release signal and actuating said gate means to pass said brake release signal to said brake release means responsive to sensing of cable tension greater than a predetermined control tension; said brake release signal being sufficient to effect a full release of said brake; said signal generator when energized producing a continuous signal that turns on said bistable multivibrator to effect said brake release signal; and i. signal length modifier means connected with said drum rotation monitor means and said bistable multivibrator serving as said gate means for turning off said bistable multivibrator responsive to both rate and degree of rotation of said drum causing said bistable multivibrator to terminate passage of said brake release signal; whereby said brake is fully applied and fully released to avoid the disadvantage of partially releasing said brake.

6. In apparatus for automatically controlling weight on the bit in a rotary drilling rig including: a. cable drum for spooling the ''''fast'''' end of a tensioned cable bearing a portion of the weight of a drill string; b. drum rotation monitor means responsively connectable with said drum for monitoring rotation thereof; c. sensor means connected responsively with the tensioned ''''dead'''' end of said cable; d. brake for said drum; e. brake applying means connected with said brake for automatically restoring and maintaining said brake applied when said brake is not being released by a brake release means; f. brake release means connected with said brake for releasing said brake; the improvement comprising: g. gate means connected with said brake release means for passing a brake release signal to said brake release means to fully release said brake and for terminating said brake release signal to fully apply said brake; said gate means being a monostable multivibrator that produces a plurality of discrete pulses of a first time duration, each said pulse effecting passage of said brake release signal and termination thereof when not otherwise terminated; h. signal generating means comprising controller means and signal generator connected with said sensor means and said gate means for generating a brake release signal and actuating said gate means to pass said brake release signal to said brake release means responsive to sensing of cable tension greater than a predetermined control tension; said brake release signal being sufficient to effect a full release of said brake; and i. signal length modifier means connected with said drum rotation monitor means and said gate means for supplying said gate means a signal responsive to both rate and degree of rotation of said drum causing said gate means to terminate passage of said brake release signal; whereby said brake is fully applied and fully released to avoid the disadvantages of partially releasing said brake; said signal length modifier means being operable to render said monostable multivibrator nonconductive responsive to rate and deGree of rotation of said drum to shorten said first time duration as needed to effect optimum control of the weight-on-bit and alleviate difficulties with over controlling.