Abstract:
Apparatus for controlling a diamond drill feed cylinder which includes a linear position sensor coupled to the feed cylinder for generating a position signal, a positioning module for generating a feed control signal in dependence upon the position signal, a proportional flow control valve having two hydraulic ports for connecting to the feed cylinder and responsive to the feed control signal for controlling flow rate of the two hydraulic ports, a plurality of operation sensors coupled to the diamond drill for generating operation status signals, a plurality of input modules for receiving the operation status signals and converting them to digital operation status signals and a programmable logic controller connected to the plurality of input modules for modifying the feed control signal in dependence upon the digital operation status signals. The rate of penetration of the diamond drill is controlled by controlling the flow rate applied to the feed cylinder. In an alternative embodiment the positioning module, programmable logic controller and input/output modules are integrated into an integrated programmable logic controller.

Description:
The present invention relates to a method of and apparatus for controlling diamond drill feed and is particularly concerned with computer controlled system. 
     BACKGROUND OF THE INVENTION 
     Core drilling with a diamond drill consists of rotating a tubular rod string and diamond bit at high speed (normally up to approx. 1800 rpm) and feeding a drill string into a rock formation. Diamonds impregnated in the matrix of the bit cut the rock resulting in a core entering the hollow drill rods as the bit advances. This core is retrieved by methods such as wirelining or reverse circulation, and retained for analysis. Water is pumped down the inside of the drill string (outside the drill string if using reverse circulation) in order to clear the cuttings from the bit, and keep the bit cool. The exposed diamonds on the bit wear and become dull, and thus require sharpening. Sharpening the bit is done in the hole and involves stripping a part of the matrix off the bit in order to expose new diamonds. This drilling and sharpening is a continual process until the bit is worn out and must be replaced. All the rods must be pulled out of the hole to replace the bit, and reinserted with a new bit. 
     Conventionally, diamond drilling has been done with manually operated hydraulic machines using a pressure controlled feed system. More recently, some attempts have been made to control the drilling process using microprocessors and electrically controlled actuators. To our knowledge, all of these attempts have involved using electric actuators to replace the handle on otherwise manually controlled pressure control valves. This approach may not allow a microprocessor to be used to its full potential in the control of the drilling process. Some of the most important inherent difficulties in these systems include poor positioning accuracy and poor response time to changing load conditions in the hole, as would occur when penetrating through rock formation transitions or faults, and sharpening the bit, particularly in deep hole conditions. 
     U.S. Pat. No. 4,157,231 discloses a hydraulic drilling unit for precision machine drilling, which uses a modulating servo valve to adjust a feed rate under computer control, but in the positive direction only. Because this patent does not provide a holdback force to compensate for the length and weight of a diamond drill string, it can not be applied to a diamond drill. 
     U.S. Pat. No. 5,449,047 discloses a computer control system for blast hole drilling, which also uses unidirectional modulation. Again, because it does not provide a holdback force to compensate for the length and weight of drill string, it is not appropriate for a diamond drill. Further, this patent teaches that the drill rate of penetration should be reduced when passing through less dense material or voids. 
     Germany Patent No. 94 02 360 discloses a computer control system for auger drilling, which also uses unidirectional modulation. Again, because it does not provide a holdback force to compensate for the length and weight of drill string, it is not appropriate for a diamond drill. 
     SUMMARY OF THE INVENTION 
     An object of the present invention is to provide an improved method and apparatus for controlling the drilling process on a diamond drill. 
     In accordance with an aspect of the present invention there is provided an apparatus for controlling a diamond drill, wherein, during operation, a bi-directional hydraulic drive, having a head end and a rod end, is coupled to the drill string of the diamond drill allowing either holdback or pulldown forces to be applied thereto, the apparatus comprising: (a) position sensor means adapted to be coupled to said diamond drill for generating a position signal; (b) computing means, including means for setting a desired rate of drill penetration, for determining a feed rate control signal in response to said position signal and said desired rate of drill penetration; and (c) valve means for controlling hydraulic flows to said bi-directional hydraulic drive which, in use, is coupled to said diamond drill, to apply either holdback or pulldown forces to the latter, in response to said feed rate control signal to approximate the desired rate of drill penetration, thus accommodating for a varying length and weight of drill string. 
     In accordance with a further aspect of the present invention there is provided a method of controlling a diamond drill, wherein a bi-directional hydraulic drive is coupled to the diamond drill to apply pulldown or holdback forces thereto, the method comprising the steps of: (a) pre-setting a desired rate of drill penetration; (b) sensing a position of said drill and generating a position signal in response thereto; (c) computing a feed rate control signal in response to said position signal and said pre-set desired rate of penetration; and (d) applying the pulldown or holdback forces to said drill during a drilling operation in response to said feed rate control signal to approximate the desired rate of drill penetration. 
     A further embodiment of the invention includes a hydraulic drive head, a hydraulic feed cylinder coupled to the drive head for changing the position of the drive head, a feed control apparatus including a linear position sensor coupled to the feed cylinder for generating a position signal, a positioning module for generating a feed control signal in dependence upon the position signal, a flow control valve having two hydraulic ports for connecting to the feed cylinder and responsive to the feed control signal for controlling flow rate of the two hydraulic ports, a plurality of operation sensors coupled to the diamond drill for generating operation status signals, a plurality of input modules for receiving the operation status signals and converting them to digital operation status signals and a programmable logic controller connected to the plurality of input modules for modifying the feed control signal in dependence upon the digital operation status signals. 
     A still further embodiment of the invention includes a hydraulic drive head, a hydraulic feed cylinder coupled to the drive head for changing the position of the drive head, a feed control apparatus including a linear position sensor coupled to the feed cylinder for generating a position signal, an integrated programmable logic controller including positioning means, input means and logic means, said positioning means for generating a feed control signal in dependence upon the position signal, a flow control valve having two hydraulic ports for connecting to the feed cylinder and responsive to the feed control signal for controlling flow rate of the two hydraulic ports, a plurality of operation sensors coupled to the diamond drill for generating operation status signals, said input means for receiving the operation status signals and converting them to digital operation status signals and said logic means connected to said input means for modifying the feed control signal in dependence upon the digital status signals. 
     A feed system controlling flow rate to the feed cylinder offers many advantages over the conventional drill as well as over those using microprocessors to control pressure control valves. 
     The foregoing and other objects of the invention are accomplished by utilizing a microprocessor controlled closed loop positioning system-to control the rate of penetration (ROP) at the desired level. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     The present invention will be further understood from the following description with reference to the drawings in which: 
     FIG. 1 illustrates, a stylized block drawing, a diamond drill including the feed control apparatus in accordance with an embodiment of the present invention; 
     FIG. 2 illustrates, in a flow diagram, the steps performed by the programmable logic controller of FIG. 1, during the drilling control method, in accordance with an embodiment of the present invention; and 
     FIG. 3 illustrates, a stylized block drawing, a diamond drill including the feed control apparatus in accordance with a second embodiment of the present invention. 
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     Referring to FIG. 1, there is illustrated, in a stylized block diagram, a diamond drill including a feed control apparatus in accordance with an embodiment of the present invention. The feed control apparatus includes a primary closed loop control having a positioning module  10 , a proportional valve  12 , a feed cylinder  14 , and a linear displacement transducer (S 1 ). Output from the positioning module  10  is applied as input to the proportional valve  12  via a line  16 . Hydraulic output from the proportional valve  12  is applied to a head end  18  of feed cylinder  14  via a first hydraulic line  20  and to a rod end  22  of feed cylinder  14  via a second hydraulic line  24 . 
     A secondary or supervisory control system includes a programmable logic controller (PLC)  26 , PLC input/output (I/O) modules  28 , an operator interface  30 , a feed cylinder head end pressure transducer S 2 , a feed cylinder rod end pressure transducer S 3 , a drive head chuck RPM sensor S 4 , a water pressure sensor S 5 , a rotation pressure sensor S 6 , and a current sensor S 7 . 
     The programmable logic controller  26  is connected to the positioning module  10  via a first line  32  for sending commands thereto and via a second line  34  for receiving status therefrom. The operator interface  30  is connected to the programmable logic controller  26  via a line  36 . The linear displacement transducer S 1  is connected directly to the positioning module  10  via a line  38 . The feed cylinder head end pressure transducer S 2 , the feed cylinder rod end pressure transducer S 3 , the drive head chuck RPM sensor S 4 , a water pressure sensor S 5 , the rotation pressure sensor S 6 , and the current sensor S 7  are connected to the PLC I/O modules  28  via lines  40 ,  42 ,  44 ,  46 ,  48 , and  50 , respectively. 
     The hydraulic circuit is completed by a hydraulic power pack  52  and a hydraulic drive head  54 . The hydraulic power pack  52  is connected to the proportional valve via hydraulic lines  56  and  58 . The hydraulic power pack is also connected to the hydraulic drive head  54 , but for the sake of simplicity these connections are not shown in FIG. 1. A diamond drill bit  60  attached to a drill string  62 , a water pump  64  and a water supply line  66  are the remaining components of the diamond drill of FIG.  1 . 
     In operation, the feed control apparatus provides the precise control required to maintain a constant rate of penetration (ROP) even under varying load conditions. The proportional valve  12  directs the flow of hydraulic fluid into or out of the feed cylinder  14 . Adding fluid to the rod end  22  of the cylinder  14  advances the drive head  54  and thus the drill string  62  into the material being cored, while adding fluid to the head end  18  of the feed cylinder  14  retracts the drill string  62  from the hole. The linear displacement transducer S 1  monitors the movement of the feed cylinder  14  and inputs this information back to the positioning module  10 . The positioning module  10  calculates a positioning correction and sends a signal, modified accordingly, to the proportional valve, via the line  16 , to maintain the desired ROP setpoint. The positioning module  10  of the closed loop control functions independently of the programmable logic control, updating its analog outputs every two milliseconds. The positioning module  10  receives a parameter block, from the programmable logic controller  26 , containing various tuning parameters that are required to match the positioning module  10  to the hydraulic and mechanical system being controlled. Once configured with the parameter block, the positioning module  10  is ready to receive commands that define the movement profile desired (i.e. velocity, acceleration, deceleration, and final position). 
     In order to accommodate varying conditions in the hole, both from a geological perspective (i.e. different rock types, faults, shears etc.) and from a tooling perspective (i.e. as the bit wears and resharpens), the supervisory PLC  26  monitors various other operational parameters on the drill and makes adjustments accordingly. Integral to this system is the hydraulic high performance proportional directional valve (or servo valve), proportional valve  12  that directs hydraulic fluid to each side of the feed cylinder  14  at a high response frequency in such a manner as to allow the ROP to be accurately controlled. The proportional valve  12  receives its command signals from the positioning module  10 , which in turn is controlled by the program within the supervisory processor (PLC)  26 . Position indication is given by the linear displacement transducer (S 1 ) that communicates directly with the positioning module  10 . When a velocity command is issued from the PLC  26  to the positioning module, the positioning module  10  controls the proportional valve  12 , independently of the PLC processor and its inherently slower scan time, to maintain the setpoint velocity. The velocity setpoint is adjusted by the PLC  26  in response to various conditions. If the bit weight becomes excessive, or current consumption becomes excessive, or the RPM falls below a preset minimum, or the water pressure goes above or below preset values, or the rate of penetration falls below a preset minimum, the feed rate is reduced and sometimes reversed for a short period of time (called pullback) before either continuing drilling, or initiating a controlled shutdown. This ability to compensate for drill hole variations, and to shut down when a fault occurs, provides superior drilling control, and allows for unattended drilling whereby the operator can attend to other duties while the PLC  26  monitors and controls the drill during the drilling cycle. The method used by the PLC  26  is describe hereinbelow with reference to FIG.  2 . 
     Referring to FIG. 2 there is illustrated, in a flow diagram, the steps performed by the programmable logic controller of FIG. 1, during the drilling control method, in accordance with an embodiment of the present invention. The flow diagram of FIG. 2 provides the method by which the programmable logic controller  26  modifies the commands sent to the positioning module  10 . An operator, using the operator interface  30  adjusts the operational setpoints as required for the drilling conditions at hand, as represented by a process block  100 . The operational setpoints include maximum allowable rate of penetration (ROP SP), maximum allowable bit weight (BW SP), rotation hydraulic fluid flow and therefor a resultant chuck RPM (RPM Actual), minimum allowable RPM (RPM Min SP), water flow and therefor a resultant water pressure (WP Actual), and high and low water pressure setpoints (High WP SP and Low WP SP respectively). 
     Upon initiating the drilling sequence, the PLC  26  sends the ROP SP to the positioning module  10 , as represented by a process block  102 , which in turn begins to feed the bit toward the rock face. The PLC  26  continues to scan its input modules  28  for information that may require a modification to the feed control. 
     As represented by decision blocks  104 ,  106 ,  108 ,  110 ,  112 , and  114 , the PLC  26  compares drill operation to the set points. For example, at the decision block  104 , the PLC  26  compares the actual water pressure to the high water pressure set point (High WP SP). If the water pressure goes above the High WP SP then the feed cylinder will quickly pullback and partially advance twice in succession, as represented by a process block  116 , in order to attempt to clear any blockage that may have caused the high water pressure alarm. If the water pressure returns to normal, as represented by a process block  118 , the drill feed returns to the ROP SP, as represented by a process block  102 . If not, the drill rod string will pullback, as represented by a process block  124 , and the unit will go through a controlled shutdown, as represented by a process block  126 . An alarm message is displayed which informs the operator of the shutdown situation, to which he would respond accordingly, as represented by a process block  128 . A low water pressure, as represented by a yes to the decision block  106 , also initiates a pullback and controlled shutdown accompanied with an alarm message. 
     If the RPM Actual falls below a minimum allowable RPM, as represented by a yes to decision block  108 , the drill string is pulled back, as represented by a process block  130  in order to assist in regaining RPM before advancing back to the face, as represented by a process block  132 . If this occurs three times within a given period, as represented by a yes to decision block  134 , a pullback, as represented by the process block  124  and controlled shutdown, as represented by the process block  126  will occur. Otherwise, after checking the ROP SP as represented by the decision block  120 , the method returns to the ROP SP process block  102 . 
     Bit weight (BW), the actual force of the bit on the rock face, is calculated using sensors  2  and  3 , and accounting for drill string and drive head weight. The operator has the ability to limit the force of the bit on the face by adjusting the BW SP to the desired maximum. If BW goes above this setpoint, as represented by a decision block  110 , the ROP SP is decreased, as represented by a process block  136 . In order to prevent polishing the bit, a minimum ROP, as represented by a process block  138 , is set which will initiate a pullback, as represented by the process block  124 , and a controlled shutdown, as represented by the process block  126 , if it falls below. As the BW falls below the BW SP, the ROP SP will be increased ,as represented by the process block  122 , but not beyond the Max ROP SP, as represented by the decision block  120 . 
     If the current draw by the electric motor on the hydraulic power pack exceeds the maximum allowable, as represented by a yes to the decision block  112 , the rotation hydraulic oil flow will be reduced, as represented by a process block  140  to prevent nuisance trips of the motor starter. As current consumption decreases, rotation volume will be increased to the rotation setpoint (ROT SP). 
     If the end of stroke position (End SP) is reached, as represented by a yes to the decision block  114 , and the desired stroke count (SC) is less than the SC SP, as represented by a yes to a decision block  146 , the unit will go through a rechuck routine, as represented by a process block  148 , and begin drilling from the rechucked position at the top of the stroke. If the SC SP is achieved, the unit will go through a controlled shutdown, as represented by a process block  126 . 
     An alternative embodiment, shown in FIG. 3 integrates the positioning module, programmable logic controller and I/O modules into an integrated programmable logic contoller. 
     The feed control system described herein has been used on the JKS Boyles B-Series diamond drills. However, it will be evident from the following that this system is capable of controlling the drilling portion of any hydraulically fed diamond drill. 
     In an exemplary embodiment, the linear displacement transducer is a series BTL-2 by Balluff, the proportional valve is a proportional directional control valve series D1FH by Parker, and the positioning module and programmable logic controller are by Allen-Bradley LPM (Cat. No. 1771-QB) and PLC-5/11 (Cat. No. 1785-LT11), respectively. 
     While a specific preferred embodiment of the invention has been described, it will be understood that various substitutions and modifications may be made in the described embodiment without departing from the spirit and scope of the invention as defined by the appended claims.