AU2008248216A1 - Method and apparatus for establishing a manual governor control setting in an electro-hydraulic system - Google Patents

Abstract

An horizontal directional drilling (HDD) system having dynamically scalable control settings is disclosed. Such a system can include a drill pipe configured to attach to a boring tool, a user control having an input device moveable in position along an input range, the user control configured to output a control signal proportional to the position of the input device along the input range, a pump having an output range, the pump configured to move the drill pipe at various output levels over the output range based on the control signal, and a controller coupled to the user control and the pump, the controller configured to execute program instructions stored in memory to cause the HDD system to: perform drilling operations in a first control setting in which the output range of the pump corresponds to the input range of the user control and changes in output of the pump are proportional to positional changes of the input device along the input range, and perform drilling operations in a second control setting in which the output range of the pump is limited by a output limit and changes in output of the pump are proportionally scaled to positional changes of the input device along the input range.

Description

WO 2008/137042 PCT/US2008/005637 METHOD AND APPARATUS FOR ESTABLISHING A MANUAL GOVERNOR CONTROL SETTING IN AN ELECTRO-HYDRAULIC SYSTEM 5 Field of the Invention The present invention relates generally to underground boring machines and methods for controlling underground boring. More particularly, the present invention relates to underground boring machines for use in horizontal directional drilling and to an improved method of, and apparatus for, establishing a full range of movement of an 10 operator input control device to a reduced output setting and a manual governor control setting. Background of the Invention Utility lines for water, electricity, gas, telephone and cable television are often run 15 underground for safety and aesthetics reasons, among others. Sometimes the underground utilities are buried in a trench that is then back filled. Trenching, however, can be time consuming and can cause substantial damage to existing structures or roadways. Consequently, horizontal directional drilling ("HDD") is often used to avoid these drawbacks. 20 A typical horizontal directional drilling machine includes a frame on which is mounted a rotational drive mechanism. The rotational drive mechanism can be slidably moved along the longitudinal axis of the frame, to rotate a drill string about its longitudinal axis while sliding along the frame to advance the drill sting into, or withdraw it from, the ground. The drill string comprises one or more drill rods attached together in a 25 string. A boring tool is installed onto the advancing end of the drill string (i.e., the end furthest away from the HDD machine). More specifically, a drill bit is used when the drill string is being advanced into the ground. On the other hand, a back reamer is used to enlarge a bored hole and is used when the drill string is being withdrawn after a hole is 30 cut. Boring tools may include a wide variety of soil cutting devices tailored for specific formations. Examples include cutting edges that shear the soil and compression elements WO 2008/137042 PCT/US2008/005637 2 that concentrate longitudinal force from the drill string into a concentrated area to fracture the ground when boring in rock conditions. The boring machines include controls that allow the operator to control both the rotational movement and the longitudinal movement, also referred to as thrust. The 5 optimum setting of rotational movement and thrust movement depends on various factors such as the soil conditions, the formation, and the type of boring tool. The boring process generally requires maintaining consistent thrust pressures and at a low thrust speed control. In some non-homogenous drilling conditions, such as when the formation is 10 primarily glacial till (e.g., a conglomeration of various sized rock, clay and silt) it is difficult for the soil cutting devices to initially engage the formation and drill efficiently. Therefore, when initially engaging these types of formations, often a very low thrust pressure is required to allow the soil cutting device to begin cutting. The thrust pressure is proportional to thrust force, and the rotation pressure is 15 proportional to rotational torque. In many cases the thrust and rotations pressures are directly related to the thrust speed. If the thrust pressure is excessive, the soil cutting device will penetrate into the formation resulting in excessive rotational pressures. Often times rotational stall is associated with high thrust speeds thereby advancing the soil cutting device into the formation too rapidly, or too high of a thrust pressure. Should the 20 soil cutting device become rotationally stalled, high loads can be induced which may damage the boring tool and drill string and reduce the overall drilling performance. If the soil cutting device stalls, the rotation and thrust pressures must be reduced to zero. The soil cutting device needs to be moved a short distance away from the obstacle within the formation. The operator using the input rotation control re-starts the process. 25 Upon restarting the rotation of the drill string, the thrust pressure is increased (thrust speed) to re-position the soil cutting device at the face of the formation to be drilled. This thrust pressure is often less than the thrust pressure causing the initial rotational stall condition. In an ideal control system, the magnitude of the rotational movement and thrust 30 movements are proportional to the position of the input controls. That is, 100% input of a control function, such as thrust or rotation joystick, will result in 100% control output to WO 2008/137042 PCT/US2008/005637 3 the thrust or rotation functions. However, in real control systems, as a result of the inherent characteristics associated with the input control function (joystick), and the output device (hydraulic pump), there may be a cumulative dead band of 5-10% in the input control. That is, no output control will be initiated until the input control is moved enough 5 to exceed the dead-band for the system. In this case -- because of the near proportionality of the input controls to the output control -- it can be difficult for the operator to accurately maintain the necessary low thrust speeds and thrust pressure levels of positions of the input controls. Thus, when drilling in non-homogenous conditions approximately 20-100% of the 10 usable input control thrust function may be non useable. In these conditions, it is desirable to control the thrust speeds at very low values, say at 10% of the maximum input control function. Therefore, there arises a need in the art for a method and system which allows the operator to adjust the controls in order to optimize the working range of the controls to provide a low output control function that is proportional to a large input control. 15 Summary of the Invention The present invention includes a convenient method for allowing the operator to change the proportional relationship between an input control function and an output control device, as the drill string is axially moved, either in a thrust or pullback direction. For example, an input control signal of 100% may be desired while the output signal may 20 be 25%. By doing so, the operator has more control of the function, while not limited to controlling the drilling system at/or near the dead-band level of the control system. The present invention includes a controller for receiving input signals including rotation and thrust setting signals, automatic boring mode signals, and automatic boring mode cancel signals from the controls, for generating rotational motion and thrusting 25 motion control signals in response to the input signals, and for communicating said motion control signals to operatively control said hydraulic system and input-to-input proportional control. Yet another aspect of the invention includes an apparatus for controlling an underground boring tool. The apparatus includes a hydraulic system for imparting 30 rotational motion at a controllable speed of rotation or to generate a controllable level of WO 2008/137042 PCT/US2008/005637 4 torque, in response to the position of a first control, and thrusting motion at a controllable speed or to generate a controllable level of axial thrust, in response to the position of a second control, to a boring tool. The apparatus also includes a third control for generating a rotation setting signal and a thrust setting signal in response to the position of the 5 controls, a fourth operator actuated control that generates a signal for incrementing and decrementing a rotational motion setting, and a fifth operator actuated control that generates a signal for incrementing and decrementing an axial thrust setting. The apparatus also includes a controller for receiving input signals from the first, second, third, fourth, and fifth operator actuated controls, for generating rotational motion and axial 10 thrust control signals in response to the input signals, and for communicating said motion control signals to operatively control said hydraulic system. Generally the linear relationship exists between the output and the input is approximately 1:1. That is, the same percentage of the input control signal will result in the same percentage for the output signal from the controller to the output device. For 15 example, a 50% input control signal will result in a 50% output signal. In the present invention, preferably a linear relationship exists between the input and the output signals through a proportionality constant. The present invention allows the operator, while axially moving the drill string to change the relationship of the output control signal to any value in the range of 1:1 to 1: 0.10 with respect to the input device. Typically, the input 20 control device on an HDD machine is a joystick that provides a signal to the controller to indicate the direction of the axial movement of the drill string. Depending on the program logic, the electronic controller outputs a signal to the output device, which is normally a hydraulic pump, or other device, capable of responding to this signal. For the present control system, the hydraulic pump is equipped with electronic displacement control. That 25 is, the pump's flow output is proportional to the magnitude of output signal. The present invention (in a manual mode of operation) in some embodiments, may require the operator to manually input, via positioning the joystick at the appropriate position, the desired rate of speed and/or pressure for the thrust and rotations functions. A switch positioned proximate the operator is utilized to enable the operator to determine the 30 desired level of proportional constant relationship between the thrust input signal and the output signals. For example, an operator could change the proportional constant, to a WO 2008/137042 PCT/US2008/005637 5 value of 10 with a resulting corresponding maximum value for the output device of 10% when and an input signal of 100% is applied. Continuing with this example, should the present proportional relationship be maintained, and the input set to say 50%, then the corresponding output would now be equivalent to 5%. 5 The present invention allows for normal manual drill operation, but should abnormal drilling conditions be encountered, where slower than normal thrust speeds are required, the proportional relationship can be easily changed by a toggle switch. Another aspect of the present invention is that once a new proportional relationship is set, the manual drilling mode can be changed to an auto drilling mode without stopping the 10 present drilling activity. Auto drill mode allows a set of rotation and thrust speeds and/or pressures parameters to be reached and the control system will then automatically try to maintain these pressure/speed settings within the capability of the control system. Because of the enhanced control provided by the proportional relationship constant to the operator, once actual drilling begins in a non-homogenous, or other formation, and 15 rotation and thrust pressures stabilize, the operator may use the same switch, used to set the proportional constant, to set the auto drill mode. However, other switches may be used for this function. Yet another aspect of the present invention is that the proportional constant can quickly be restored to 100% simply by placing both the thrust and rotation handles in their 20 neutral positions, then press the switch. Another aspect of the present invention is that if the set value for the proportional constant requires changing, its value may be increased or decreased in one percent, or any other suitable, intervals by an increment/decrement switch. While the invention will be described with respect to preferred embodiment 25 configurations and with respect to particular devices used therein, it will be understood that the invention is not to be construed as limited in any manner by either such configuration or components described herein. Also, while the particular types of hydraulic pumps and motors are described herein, it will be understood that such particular mechanisms are not to be construed in a 30 limiting manner. Instead, the principles of this invention extend to any environment in which maintaining and/or resuming drilling is desired. These and other variations of the WO 2008/137042 PCT/US2008/005637 6 invention will become apparent to those skilled in the art upon a more detailed description of the invention. For a better understanding of the invention, reference should be made to the drawings which form a part hereof and to the accompanying descriptive matter, in which there is illustrated and described a preferred embodiment of the invention. 5 Brief Description of the Drawings The accompanying drawings, which are incorporated herein and constitute a part of the specification, illustrate several aspects of the invention and together with the description, serve to explain the principles of the invention. A brief description of the drawings is as follows: 10 Figure 1 illustrates a horizontal directional drilling machine; Figure 2 illustrates the operator control station of a horizontal directional drilling machine according to the principles of the present invention; Figure 3 illustrates a control lever of the operator control station of Figure 2; Figure 4 illustrates a label identifying the function of the controls found on the 15 control lever of Figure 3; Figure 5 illustrates controls found on the right side of the operator control station of Figure 2; Figure 6 illustrates a display according to the principles of the present invention; Figure 7 illustrates the rates of increase of rotational movement and axial thrust 20 when a boring process is resumed; Figure 8 is a flow diagram of a method of resuming automatic control of boring functions; Figure 9 is a flow diagram of the steps which may be used to implement the rescaling of the input control and the governor level of the output pump; 25 and Figure 10 illustrates the timing sequence for setting a manual limit. Detailed Description of the Preferred Embodiment The discussion and illustrations provided herein are presented in an exemplary format, wherein selected embodiments are described and illustrated to present the various WO 2008/137042 PCT/US2008/005637 7 aspects of the present invention. Systems, devices, or methods according to the present invention may include one or more of the features, structures, methods, or combinations thereof described herein. For example, a device or system may be implemented to include one or more of the advantageous features and/or processes described below. A device or 5 system according to the present invention may be implemented to include multiple features and/or aspects illustrated and/or discussed in separate examples and/or illustrations. It is intended that such a device or system need not include all of the features described herein, but may be implemented to include selected features that provide for useful structures, systems, and/or functionality. 10 The present invention generally relates to underground boring machines, such as HDD machines, and more particularly to a method and apparatus for controlling underground boring tools with an electro-hydraulic control system. In one embodiment, an operator can change the thrust pump output relative to the thrust input signal generated by the operator control device. The thrust pump output is thereby scaled proportionally to 15 an input signal, while simultaneously limiting the thrust output value to a predetermined maximum output. This allows for full scale movement of the input control device to equal differing thrust pump outputs. Accordingly, the operator can tailor the output to the appropriate conditions and/or minimize the impact of any dead zone inherent in the control and hydraulic system, among other benefits. 20 In a preferred embodiment, the operator of an underground boring machine can reduce the output thrust signal relative to the input thrust signal, re-set the maximum available output thrust level to the present thrust input signal, and rescale the output thrust signal proportionally to the input thrust signal, while simultaneously propelling the drill string at a rate to perform the drilling operation for the present soil conditions. Further, 25 preferably the reduced thrust pressure output signal may be adjusted up or down to control the drill's speed, and also re-set to any prior 'set' conditions or be canceled. The invention is especially useful for changing the thrust output signal relative to the thrust input signal when the machine is used in drilling conditions in which controllability of the machine's thrust speed is required and/or very low output signals are 30 required. As noted above, inherent dead bands exist in many electro-hydraulic control systems. Such bands limit the ability of the operator to move the drill string at a slow and WO 2008/137042 PCT/US2008/005637 8 controlled rate. However, by increasing the scale of a lower input to a more nearly full scale movement (while re-scaling the output signal to an appropriate maximum amount) the effects of operating in the dead band zone are reduced. In various embodiments of the invention, the input control and pump output 5 relationship can be changed dynamically, such that the output range of a pump is reduced and rescaled relative to an input range of a user control while the pump is rotating or advancing a drill string without stopping or slowing the drill string rotation or advancement. Various embodiments concern an HDD system having dynamically scalable 10 control. Such embodiments can include a drill pipe configured to attach to a boring tool, a user control having an input device moveable in position along an input range, the user control configured to output a control signal proportional to the position of the input device along the input range, a pump having an output range, the pump configured to move the drill pipe at various output levels over the output range based on the control 15 signal, and a controller coupled to the user control and the pump, the controller configured to execute program instructions stored in memory to cause the HDD system to perform drilling operations in a first control setting in which the output range of the pump corresponds to the input range of the user control and changes in output of the pump are proportional to positional changes of the input device along the input range, and perform 20 drilling operations in a second control setting in which the output range of the pump is limited by a output limit and changes in output of the pump are proportionally scaled to positional changes of the input device along the input range. In such embodiments, the output limit in the second control setting may be based on a level of the control signal corresponding to an output level of the pump in the first control setting when a switch was 25 toggled. The level of the control signal may be maintained for a period of time after the switch is toggled in order to set the output limit at that level. The output limit may further be based on an output constant amount, which in some embodiments is added to the output level when the switch is toggled. In some embodiments, the HDD system can dynamically transition operation of 30 the HDD system from the second control setting back to the first control setting without an interruption in drill pipe movement associated with a decrease in output of the pump when WO 2008/137042 PCT/US2008/005637 9 the input device is positioned in a neutral position of the input range when in the second control setting and a switch is toggled. In some embodiments, the HDD system may calibrate the full output range of the pump to the full input range of the user control in the first control setting. In some 5 embodiments the output range of the pump limited by the output limit in the second control setting may proportionally correspond to the full input range of the user control. Some embodiments may calibrate the full output range of the pump to the full input range of the user control in the first control setting, wherein the output range of the pump limited by the output limit in the second control setting proportionally corresponds 10 to the full input range of the user control. Some embodiments may rescale the output range of the pump limited by the output limit to the full input range of the user control when the input device is positioned in a neutral position of the input range when in the second control setting. Some embodiments may change the output limit in response to a user input and 15 then rescale the output range of the pump limited by the adjusted output limit to the full input range of the user control when in the second control setting. In some embodiments, the pump is configured to rotate the drill pipe at various output levels over the output range based on the control signal and the output limit corresponds to one or both of a rotation rate limit and a hydraulic fluid pump pressure 20 limit. In other embodiments, the pump is configured to linearly advance the drill pipe at various output levels over the output range based on the control signal and the output limit corresponds to one or both of an advancement speed limit and a hydraulic fluid pump pressure limit. In some of the above embodiments, as well as others discussed elsewhere herein, 25 program instructions stored in memory may be executed by a processor to cause a HDD system to perform the stated processes. A brief description of the theory of operation and a preferred implementation will be deferred pending a brief overview of an HDD machine and a control system. 30 HDD Machine WO 2008/137042 PCT/US2008/005637 10 A horizontal directional drilling machine 20, illustrated in Figure 1, includes a frame 22 on which is mounted a rotational drive mechanism 30 that is slidably moved along a longitudinal axis of the frame 22. In one embodiment, horizontal directional drilling machine 20 includes a rear stabilizer 26 and front stabilizer 27 for positioning and 5 stabilizing the machine 20 at the drilling site, and a wheel assembly 24 for supporting the machine during transport between job sites. A drill string 18 comprises a boring tool 42 designed to engage the soil and one or more drilling rods 38 that transmit forces from machine 20 to the boring tool 42. The rotational drive mechanism 30 typically includes a gearbox and a drive spindle that rotates the drill string 18 about its longitudinal axis, the 10 rotational power being preferably provided by hydraulic motor 216. The horizontal directional drilling machine 20 also includes a thrust drive mechanism 28 that typically includes gears or sprockets to move the drive mechanism 28 up and down the frame 22 to advance the drill sting 18 into, or withdraw it from, the soil. The thrust power is preferably provided by hydraulic motor 217. In some embodiments, an engine 36 drives 15 hydraulic pumps 16 and 17, which pressurize fluid that is transferred to hydraulic motors 216 and 217. The hydraulic systems can be either open loop where the fluid is transferred from a hydraulic reservoir 14 through the pumps to the motors 216, 217 and back to the reservoir 14, or they can be hydrostatic where the fluid is substantially in a closed loop -- being 20 transferred between the pump and the motor. In either system the pumps 16, 17 and motors 216, 217 are matched, such that by controlling the flow rate of the hydraulic fluid, the speed of rotation of the output shafts of the motors is controlled and can be inferred. The pumps are typically variable displacement pumps capable of producing variable output flow rates, proportional to an electrical current provided by a control system. The 25 output speed of the pumps is proportional to the output flow rates. While the speed can be controlled, the pressure of the hydraulic fluid can be monitored to infer the torque being generated by the motor, which is directly proportional to the longitudinal force or rotational torque being generated. Other embodiments are possible, for instance wherein rotational and thrust drive mechanisms could be actuated by different hydraulic drives 30 (e.g. such as hydraulic cylinders).

WO 2008/137042 PCT/US2008/005637 11 Some embodiments may also include a water flow mechanism that transmits water through the drill string 18 to the vicinity of the boring tool 42, where the water flow entrains cut soil particles and removes them from the hole. The horizontal directional drilling machine 20 may also include a greaser for lubricating various moving components 5 (not shown). Figure 2 illustrates an exemplary operator control station 100 for a horizontal directional drilling machine 20. Operator control station 100 includes rotational control 110 and thrust control 130 that provide inputs to a controller 150. Many embodiments of controls 110 and 130 are usable. For example, in one usable embodiment, each of controls 10 110 and 130 comprise a control lever. In such an embodiment, control levers 110, 130 each produce an electrical signal that is proportional to the position of the control lever relative to a center position. The electrical signal is provided as an input to a controller 150. In one embodiment, when the control lever 110, 130 is moved away from the 15 center position, the electrical signal that is generated corresponds to increased rotational torque (and/or rate of rotational movement) or axial thrust force (and/or rate of axial movement), respectively. As the control lever 110, 130 is moved closer toward the center position, the generated electrical signal corresponds to decreased rotational torque (and/or rate of rotational movement) or axial thrust force (and/or rate of axial movement), 20 respectively. In one embodiment, when the control lever 110 is moved in the forward direction, away from the operator, the generated electrical signal corresponds to counter clockwise rotational movement of the drill string, as viewed looking at the end of the drill string. Alternatively, when the control lever 110 is moved in the backwards direction, toward the operator, the electrical signal that is generated corresponds to the opposite 25 direction, clockwise rotational movement. Likewise, in one embodiment, when control lever 130 is moved forward, away from the operator, the electrical signal that is generated corresponds to forward movement of the drill string into the soil. Alternatively, when control lever 130 is moved in the backwards direction, toward the operator, the electrical signal that is generated corresponds to backwards movement of the drill string back 30 toward the machine.

WO 2008/137042 PCT/US2008/005637 12 When either of control lever 110, 130 is in the center position, the electrical signal that is generated corresponds to a neutral condition where the rotational or thrust movement respectively is set to zero. A spring or other biasing mechanism is provided to return each of the control levers to the center position, so that if an operator does not hold 5 the lever, it returns to its centered, neutral position such that the rotational or thrust motion settings are set to zero. The controller 150 generates outputs, in response to various inputs, to control the hydraulic system. The system includes the hydraulic pumps 16 and 17 of the drilling machine 20. The hydraulic motors 216, 217 are driven by the hydraulic fluid in a known 10 manner to create rotational and thrust movement of the boring tool 42 and drill string 18. As noted above, this control is typically a variable electrical current, wherein a certain electrical current will cause the pump to create a certain hydraulic flow rate. The output shaft of the motor thereby rotates at a certain speed of rotation. This is typically independent of the pressure in the fluid. The control systems are typically designed to 15 provide speed control that is independent of load. The control systems typically further include pressure transducers 226 and 227 that provide feedback to the control system indicating the pressure in the circuits, and can further include speed sensors 236 and 237 for measuring the output speed of the motors. The circuitry represented in Figure 2 can be used to perform the various 20 methodologies and techniques discussed herein. The circuitry can include memory comprising a computer readable medium encoded with a computer program, software, firmware, computer executable instructions, instructions capable of being executed by a computer, etc. to be executed by circuitry, such as control processor 150. For example, memory can be a computer readable medium storing a computer program, execution of the 25 computer program by control processor 150 causing the moving of a drill string using a pump operating at an output level of an output range, the output level corresponding to a position of an input control along an input range in a first control setting, changing the output level of the pump in the first control setting, wherein changes in the output level of the pump in the first control setting are proportional to positional changes in the input 30 control along the input range, transitioning from the first control setting to a second control setting while maintaining at least some motion of the drill string, determining an WO 2008/137042 PCT/US2008/005637 13 output limit of the output range of the pump, moving the drill string using the pump in the second control setting, the output range of the pump limited by the output limit in the second control setting, and changing the output level of the pump in the second control setting, wherein changes in the output level of the pump within the output range in the 5 second control setting are proportionally scaled to positional changes in the input control along the input range. In similar ways, the other methods and techniques discussed herein can be performed using the circuitry represented in Figure 2. Various embodiments may further include identifying a desired change in output of the pump while in the first control setting, detecting that the desired change in pump 10 output is too small to be effected by a positional change of the input control along the input range in the first control setting, transitioning from the first control setting to the second control setting to increase sensitivity between the input control and pump output, and making the desired change in pump output using the second control setting. In some embodiments, the output limit in the second control setting is based on the level of pump 15 output corresponding to the position of the input control along the input range when a switch is toggled in the first control setting. In some embodiments, the output limit in the second control setting is based on the level of pump output corresponding to the position of the input control along the input range that was maintained for a period of time after a switch was toggled in the first control setting. A output limit may also be based on an 20 output constant amount. Various embodiments may include calibrating the full output range of the pump to the full input range of the input control in the first control setting, wherein the output range of the pump limited by the output limit in the second control setting proportionally corresponds to the full input range of the user control. 25 Various embodiments may include proportionally rescaling the output range of the pump limited by the output limit to the full input range of the user control when the input control is positioned in a neutral position of the input range when in the second control setting. Various embodiments may include changing the output limit in response to a user 30 input and then rescaling the output range of the pump limited by the adjusted output limit to the full input range of the input control when in the second control setting.

WO 2008/137042 PCT/US2008/005637 14 In some embodiments, moving the drill string using the pump in the first and second control settings further comprises rotating the drill using a hydraulic fluid rotation pump corresponding to the pump, wherein changing the output level of the pump in the first and second control settings further comprises changing one or both of a rotation rate 5 and hydraulic fluid pressure of the hydraulic fluid rotation pump, and wherein the output limit is one or both of a maximum rotation rate and a maximum hydraulic fluid pressure of the hydraulic fluid rotation pump. In some embodiments, moving the drill string using the pump in the first and second control settings further comprises linearly advancing the drill string using a 10 hydraulic fluid thrust pump corresponding to the pump, wherein changing the output level of the pump in the first and second control settings further comprises changing one or both of an advancement speed and hydraulic fluid pressure of the hydraulic fluid thrust pump, and wherein the output limit is one or both of a maximum advancement speed and a maximum hydraulic fluid pressure of the hydraulic fluid thrust pump. 15 Figure 3 illustrates the rotational movement control 110 in more detail, showing the various control switches that are mounted on the control. Figure 4 illustrates a sign that indicates the functions of each of these switches to the operator. Control 110 includes switches 112, 118, 120, and 122, each of which generates an electrical signal when actuated, such as by being pressed. Control switch 112 may be called a SET switch. 20 When SET switch 112 is actuated, an electrical signal is sent to controller 150 activating an automatic boring mode (also called auto boring mode). When controller 150 receives a signal from SET switch 112, the rotational movement and thrust movement parameters are set within the controller to the values established by the positions of controls 110, 130 at the time that the SET switch 112 is actuated. The preferred technique includes setting a 25 value for the speed of rotation, while setting a value for the pressure in the axial thrust circuit, as will be explained in more detail later. Thereafter, controller 150 automatically maintains the boring parameters of rotational movement and thrust movement at the set values without further input from the operator. The operator then may release control levers 110, 130 without affecting the boring operation, thereby reducing operator fatigue. 30 It will be appreciated that the auto boring mode may also be turned off by actuating the SET switch 112 when the system is currently activated.

WO 2008/137042 PCT/US2008/005637 15 In one embodiment, rotational movement control 110 also includes control switches 114 and 116 which control the water flow functions for injecting water into a bored hole to remove cuttings from the hole. Rotational movement control 110 also includes control switches 118 and 120 to control the speed of the engine 36, and control 5 switch 122 to control a greaser (not shown). Figure 6 illustrates a display 170 for the control system that includes a light 172 that is energized when an auto boring mode is active. This light 172 is energized after the SET switch 112 is activated and a rotation setting and a thrust setting are defined, so as to enter the auto boring mode. Light 172 is deactivated if the auto boring mode is not active. 10 Figure 5 illustrates additional control switches on the right side of the operator control station 100. In one embodiment, control station 100 includes switches 140, 142 that are in electrical communication with controller 150. Switch 140 has a neutral position, a first operative position, and a second operative position. In one embodiment, switch 140 is spring-loaded to the neutral position, so that when the switch is placed in 15 either the first or second operative positions and then released, switch 140 will return to the neutral position. When switch 140 is in the neutral position, switch 140 has no effect on the boring operation. When switch 140 is placed in the first operative position, such as where switch 140 is rotated clockwise away from the neutral position, and when the auto bore mode is activated, an electrical signal is sent to controller 150 to increase the 20 rotational movement setting by a predefined increment. Similarly, when switch 140 is placed in the second operative position, such as where switch 140 is rotated counterclockwise away from the neutral position, and when the auto bore mode is activated, an electrical signal is sent to controller 150 to decrease the rotational movement setting by a predefined decrement. 25 Operation of switch 142 is similar. Switch 142 has a neutral position, a first operative position, and a second operative position. In one embodiment, switch 142 is spring-loaded to the neutral position, so that when the switch is placed in either the first or second operative positions and then released, switch 142 will return to the neutral position. When switch 142 is in the neutral position, switch 142 has no effect on the boring 30 operation. When switch 142 is placed in the first operative position, such as where switch 142 is rotated clockwise away from the neutral position, and when the auto bore mode is WO 2008/137042 PCT/US2008/005637 16 activated, an electrical signal is sent to controller 150 to increase the axial thrust pressure setting by a predefined increment. Similarly, when switch 142 is placed in the second operative position, such as where switch 142 is rotated counterclockwise away from the neutral position, and when the auto bore mode is activated, an electrical signal is sent to 5 controller 150 to decrease the axial thrust pressure setting by a predefined decrement. During the boring or backreaming processes the system then acts to maintain rotation of the drill string at the selected speed of rotation, independent of the rotational pressure setting and axial pressure setting, and will automatically vary the axial thrust speed as necessary to attempt to maintain the selected pressure in the rotation circuit, or to 10 maintain a set amount of force at the boring tool. In consistent formations maintaining a constant force on the drill bit will result in a constant/consistent torque on the drill bit, and will maximize drilling efficiency. In formations that vary, this same control technique is also effective. It may be necessary to interrupt the auto boring mode, such as when it is required 15 to add or remove a drill rod from the drill string. There are several ways in which the auto boring mode may be interrupted. The machine 20 may be configured so that when the auto boring mode is activated, as indicated by light 172, any further motion of controls 110, 130 sends an electrical signal to controller 150 that causes controller 150 to interrupt the auto boring mode. Alternatively, the machine 20 may be configured so that when the 20 auto boring mode is activated, actuating switch 112 sends an electrical signal to controller 150 that causes controller 150 to interrupt the auto boring mode. Alternatively, other switches or controls may be provided or adapted so as to provide an electrical signal to the controller 150 to interrupt the auto boring mode. One example is a control function related to breaking the connection between the drive chuck of the rotational drive 30 and 25 the drill string. When a drill rod has been completed inserted, and the rotational drive is at the end of the frame 22, then the rotational drive must be unthreaded from the drill string and moved back to the opposite end of the frame so that another drill rod can be added. This action is required when the rotational drive is located at certain positions along the frame, for instance at the extreme opposite ends. Thus, an interrupt signal can be provided 30 automatically by a sensor that measures the position of the rotational drive. When the WO 2008/137042 PCT/US2008/005637 17 interrupt signal is received it may also automatically cancel other functions such as the water flow. The operator control station 100 also includes switch 144 that is in electrical communication with controller 150. Switch 144 may also be called a RESUME switch. 5 When the auto boring mode has been interrupted, the operator may actuate switch 144 to resume the auto boring mode. Switch 144 then sends an electrical signal to controller 150 that causes controller 150 to resume the auto boring mode at the same settings as existed prior to the auto boring mode being interrupted. Many embodiments of the resume process are usable. The resume process of the 10 present invention initiates drilling operation in a manner that minimizes unnecessary vibration and stress in the drill string and drilling tool. Figures 7 and 8 illustrate one usable embodiment of the resume process. The resume process begins (at time equal to 0 seconds) when the switch 144 is depressed to initiate the resume process, sending an electrical signal to the controller 150. The controller 150 will activate the rotational drive 15 mechanism so as to bring the boring tool to the set value of rotational movement, the set rate of rotation. At the same time, not shown on the figures, the water flow is automatically restarted. The resumption of rotational movement occurs rather quickly, usually in about one second. During the time that the rotation is being resumed, controller 150 does not activate the thrust drive mechanism. In this way, the boring tool will resume 20 rotation to the set rate of rotation while there is little or no longitudinal thrust loading or movement. This operation is advantageous because it produces a smooth rotational acceleration without shock loading of the boring tool and drill string. There are additional benefits to reestablish water flow to the cutting tool prior to new cuttings being generated from axial movement of the drill string. 25 After the rotational movement setting is attained, approximately one second after the rotation is started, the controller 150 then beings to apply thrust force to the drill string. However, rather than rapidly increasing the thrust force to the set value, the thrust force is increased from zero to the set value, the set axial thrust, at a predetermined rate. In one usable embodiment, the thrust force is applied at a first constant rate of 25% of the set 30 axial thrust force setting per second for three seconds, from the time of one second after the resume process is initiated to the time of four seconds after the resume process is WO 2008/137042 PCT/US2008/005637 18 initiated. Thus, having increased by 25% of the thrust force setting for three (3) seconds, the amount of thrust force applied at this point will be 75% of the thrust force setting. The thrust force is then applied at a second constant rate of 12.5% per second for two seconds. Under this resumption example, from the time of four (4) seconds after the resume process 5 is initiated to the time of six (6) seconds after the resume process is initiated, the thrust force is increased from 75% of the set value to 100% of the set value. Thus, at six (6) seconds after the resume process is initiated, the boring tool will be operating both at the set rate of rotation and the set axial thrust. An alternative embodiment includes increasing the axial thrust force at a single 10 predetermined rate, such as 25% of the set axial thrust force per second for four (4) seconds. It will be appreciated that other rates may also be used, and that the rates provided herein are presented as preferred embodiments, and not as limitations. Aspects of HDD are further disclosed in U.S. Patent No. 6,766,253, U.S. Patent No. 6,367,564, U.S. Patent No. 6,389,360, U.S. Patent No. 5,556,253, U.S. Patent No. 15 6,554,082, and U.S. Provisional Application No. 60/927,567 filed May 3, 2007, which are incorporated herein by reference in their respective entireties. Theory of Operation of Governor Some electronic control systems receive input signals as a voltage proportional to the displacement of the input devices. The controller converts the voltage to a percentage. 20 For example, an input device, such as a joystick (best seen in Fig. 2 as joystick 130), could be calibrated such that when it is positioned fully forward in the thrust direction, the controller 150 would convert the input signal (voltage) to the percentage value of 100%. Similarly, if the input device was calibrated such that when the control was positioned fully backwards in the pullback direction, the controller 150 would convert the input 25 signal (voltage) to a value of -100%. Any intermediate position of the input control would be converted to a fractional percentage. Normally the maximum thrust pump output signal is set at 100%. Therefore, if the input signal was 100%, then the corresponding output signal would also be 100%. Any intermediate percentage value of the input signal would result in an equivalent 30 intermediate percentage value for the thrust pump output signal. The thrust pump output WO 2008/137042 PCT/US2008/005637 19 preferably keeps a one-to-one percentage relationship (i.e., proportional) with respect to the value of the input signal as shown by Equation 1. Thrust Output Signal (%) = Thrust Input Signal (%) Eq. 1 5 As noted above, the present invention provides a method for changing the relationship between the output and the input signals. The changed limit on the output signal may be considered a manually determined governor setting on the output signal, with such manual governor setting allowing the maximum allowable limit for the output 10 signal to be changed to a value other than 100%. In the preferred embodiment, the SET switch 112 described above in connection with the HDD machine 20 may be used. In addition to the SET switch 112 enabling an auto-drill function (described above), the SET switch 112 may also enable the manual governor function. It will be appreciated, however, that other switches, buttons, keys and 15 other operator activated devices may be utilized to enable the governor function. In the preferred embodiment, when the manual thrust limit SET switch 112 is pressed and held, and if the input signal remains within a predetermined error range for a predetermined length of time the manual governor setting can be changed to a value less than 100%. The new manual governor limit is now equal to the value of the thrust input 20 device plus an arbitrary thrust constant as shown in Equation 2. Manual Governor Limit (%) = Thrust Input Signal (%) + Thrust Constant (%) Eq. 2 For example, the thrust constant can be arbitrarily set to zero. If the input signal 25 was 50%, when the SET switch 112 is depressed and held for a pre-determined length of time, the manual governor limit would be reduced from 100% to 50%. Regardless of the position of the control input handle position, the maximum thrust output would be limited, or "governed" to the 50% value. Setting the thrust constant greater than zero increases the manual governor limit slightly.

WO 2008/137042 PCT/US2008/005637 20 Another aspect of the invention is after the governor is set, and should the input device returned to the neutral position (i.e., 0%), the thrust pump output signal is then re scaled proportionally to the manual governor limit as shown in Equation 3. Thrust Ouptut = Input Device (%) X Manual Governor Limit (%) 5 100% Eq. 3 Therefore, for example, if the thrust constant was 10%, the input device signal was originally 30% at the time the manual governor was set, then after re-scaling, a 20% input device signal would result in an actual thrust output signal of 8% as calculated in Equation 4. 10 Thrust Ouptut = 20% X (30% + 10%) = 8% 100% Eq. 4 In the present invention when the manual governor is set, a high thrust output resolution is available to the operator to operate in conditions when low thrust speed, or a precise thrust or rotation pressure is required. 15 Embodiment and In Operation A preferred environment in which the present invention may be employed is in an 20 electro-hydraulic control system of an HDD, trenching or other ground boring machine. In this type of system an electronic controller receives input signals from input devices such as pressure transducers and operator controlled joysticks. A controller uses the input devices to provide electronic signals to output devices such as thrust and rotation hydraulic pumps or valves. 25 In a preferred embodiment constructed in accordance with the principles of the present invention, the rotation joystick 110 and thrust joystick 130 are used to set the desired drilling parameters. The set button 112 may be used to enable the setting of the manual governor limit. More specifically, the SET button 112 is depressed and held for WO 2008/137042 PCT/US2008/005637 21 two seconds while maintaining at least one joystick 110 and 130 within a predetermined error range. In one embodiment, the predetermined error range (approximately 5%) requires the thrust input device 130 to be held reasonably constant over the two second period. 5 If the two conditions have been satisfied (i.e., the SET button 112 has been depressed for two seconds and the thrust input device has not exceeded the predetermined error range), then upon release of the SET button 112 the maximum output for the thrust pump (normally 100%) is re-set to be equal to the input thrust signal value plus a thrust constant. This new maximum thrust output pump signal acts as a governor. 10 If after setting the manual governor, and should the handle not be returned to neutral, then any additional increase in thrust input signal will only allow for an increase in thrust pump output signal equal to the governor setting. When the thrust handle is returned to neutral, the controller 150 rescales the thrust output signal to be equal to: [(future instantaneous thrust input signal (%)) X (times the newly set manual governor 15 limit (%))]/100%. With the manual governor set, a 100% input signal will result in a maximum output signal equal to the manual governor setting. All intermediate thrust output signals will be proportional to the thrust input signal. After the manual governor has been set, a separate increment/decrement switch can be used to increase/decrease the manual 20 governor setting. To re-set the manual govern setting back to 100%, both input handles are returned to the neutral position and the SET button 112 is pressed. The output thrust signal will be equal to the input signal, with an effective governor of 100%. Turning now to Figure 9 one embodiment of the logical flow that may be utilized to implement the principles of the present invention is shown. The logical flow may be 25 implemented with controller 150 or some other on-board computer, cpu or special programmed device. The logical flow is shown generally at 900. The process starts at 901 where the thrust/pull back handle or joystick 130 is in the neutral position. Moving to block 902, the operator may move the thrust/pull back handle 130 to obtain the desired thrust/pull back output percent. In this type of use, the thrust output signal is proportional 30 to the thrust input signal. This use may correspond to a normal or default use of the equipment.

WO 2008/137042 PCT/US2008/005637 22 Moving to block 903, if the operator presses the set switch 112 and holds it for a specified period of time, then the process moves to block 904 where it is determined whether the operator moved the thrust/pull back handle 130 more than a predetermined amount during the hold time. If the answer is yes at block 905, then the process returns to 5 block 901. However, if it was not moved more than a predetermined amount, the process moves to block 906. Proceeding to block 907 a new manual governor limit is set to the value of the thrust pull back handle percent plus a second constant percent value. This corresponds to equation 2 above. Proceeding to block 908 and then 909, the thrust/pull back output percent is now scaled to be from 0 up to the manual governor percentage. 10 This is the amount that was set at step 907. The percentage is also proportional to the thrust/pull back handle input from 0 to 100%. This corresponds to equation 3 described above. Proceeding to block 910, an embodiment of the present invention also provides for optionally providing the ability to increase/decrease the manual governor setting by 15 selecting increase or decrease switches, buttons or other operator selected devices. If these are requested at block 911, then the process moves to block 912 where the manual governor percentage is incremented or decremented as appropriate. If there is no request to increase or decrease the manual governor setting, then the process moves to block 913. Moving on to block 914, if the operator presses the set switch again while the 20 thrust/pull back handle is in neutral position then the process moves to block 916 and 917 where the manual governor limit is reset to 100% of the output and the process returns to block 901 in its neutral condition. However, if the operator does not press the set switch at block 914, then the process proceeds to block 915 and the process returns to block 909. Figure 10 illustrates a timing sequence for setting manual limits. The thrust output 25 (identified as 184) begins at zero and the operator establishes a relatively steady state by time to (it will be appreciated that human operators generally cannot maintain a perfect steady state in view of the boring conditions experienced by the HDD machine 20 and other factors). At point 183 (corresponding to to designated at 180), the SET button 112 is depressed starting a two second period. The point 183 establishes a level about which the 30 processor 150 determines whether the joystick 130 has been moved more than a certain maximum amount. Here, the maximum amounts are designated 185. In some WO 2008/137042 PCT/US2008/005637 23 embodiments, a certain predetermined amount of time exceeding the maximum amount may be allowed. This area is noted by the shaded areas, with one such area identified as 190. ti identified by the designation 181 and t 2 identified by the designation 182 correspond to one and two seconds, respectively. At the end of two seconds, the 5 maximum output thrust is changed from 100% identified by the designation 186 to a new maximum level identified by the designation 186M. The thrust output continues but is limited by the new maximum setting (shown by the dotted line). At point 189, the limit is returned to the original maximum. The above description refers to systems and components normally found in a 10 control system and the thrust speed, thrust pressure and thrust input signals. Additionally, rotation pressure, rotation speed, rotation feedback signals, thrust feedback signals could also be monitored and controlled in a similar manner. Among other things, the above discussion and the associated drawings disclose a HDD system with dynamic scalable controls, comprising: means for moving a drill string 15 using a pump operating at an output level of an output range, the output level corresponding to a position of an input control along an input range in a first control setting; means for changing the output level of the pump in the first control setting, wherein changes in the output level of the pump in the first control setting are proportional to positional changes in the input control along the input range; means for transitioning 20 from the first control setting to a second control setting while maintaining at least some motion of the drill string; means for determining an output limit of the output range of the pump; means for moving the drill string using the pump in the second control setting, the output range of the pump limited by the output limit in the second control setting; and means for changing the output level of the pump in the second control setting, wherein 25 changes in the output level of the pump within the output range in the second control setting are proportionally scaled to positional changes in the input control along the input range. While particular embodiments of the invention have been described with respect to its application, it will be understood by those skilled in the art that the invention is not 30 limited by such application or embodiment or the particular components disclosed and described herein. It will be appreciated by those skilled in the art that other components WO 2008/137042 PCT/US2008/005637 24 that embody the principles of this invention and other applications therefore other than as described herein can be configured within the spirit and intent of this invention. The arrangement described herein is provided as only one example of an embodiment that incorporates and practices the principles of this invention. Other modifications and 5 alterations are well within the knowledge of those skilled in the art.

Claims (25)

1. An horizontal directional drilling (HDD) system having dynamically scalable control, comprising: a drill pipe configured to attach to a boring tool; a user control having an input device moveable in position along an input range, 10 the user control configured to output a control signal proportional to the position of the input device along the input range; a pump having an output range, the pump configured to move the drill pipe at various output levels over the output range based on the control signal; and a controller coupled to the user control and the pump, the controller configured to 15 execute program instructions stored in memory to cause the HDD system to: perform drilling operations in a first'control setting in which the output range of the pump corresponds to the input range of the user control and changes in output of the pump are proportional to positional changes of the input device along the input range; and 20 perform drilling operations in a second control setting in which the output range of the pump is limited by a output limit and changes in output of the pump are proportionally scaled to positional changes of the input device along the input range.

2. The HDD system of claim 1, wherein the controller is further configured to 25 dynamically transition operation of the HDD system from the first control setting to the second control setting without an interruption in drill pipe movement associated with a decrease in output of the pump.

3. The HDD system of claim 1, wherein the controller is further configured to 30 execute stored program instructions to cause the HDD system to dynamically transition operation of the HDD system from the second control setting to the first control setting WO 2008/137042 PCT/US2008/005637 26 without an interruption in drill pipe movement associated with a decrease in output of the pump when the input device is positioned in a neutral position of the input range when in the second control setting and a switch is toggled. 5

4. The HDD system of claim 1, wherein the output limit in the second control setting is based on a level of the control signal corresponding to an output level of the pump in the first control setting when a switch was toggled.

5. The HDD system of claim 4, wherein the output limit in the second control setting 10 is further based on the level of the control signal corresponding to an output level of the pump in the first control setting that was maintained over a period of time beginning when a switch was toggled.

6. The HDD system of claim 1, wherein the output limit in the second control setting 15 is based on an output constant amount and a level of the control signal corresponding to an output level of the pump in the first control setting when a switch was toggled.

7. The HDD system of claim 1, wherein the controller is further configured to execute stored program instructions to cause the HDD system to calibrate the full output 20 range of the pump to the full input range of the user control in the first control setting.

8. The HDD system of claim 1, wherein the controller is further configured to execute stored program instructions to cause the HDD system to calibrate the full output range of the pump to the full input range of the user control in the first control setting, and 25 wherein the output range of the pump limited by the output limit in the second control setting proportionally corresponds to the full input range of the user control.

9. The HDD system of claim 1, wherein the controller is further configured to execute stored program instructions to cause the HDD system to rescale the output range 30 of the pump limited by the output limit to the full input range of the user control when the WO 2008/137042 PCT/US2008/005637 27 input device is positioned in a neutral position of the input range when in the second control setting.

10. The HDD system of claim 1, wherein the controller is further configured to 5 execute stored program instructions to cause the HDD system to change the output limit in response to a user input and then rescale the output range of the pump limited by the adjusted output limit to the full input range of the user control when in the second control setting. 10

11. The HDD system of claim 1, wherein the pump is configured to rotate the drill pipe at various output levels over the output range based on the control signal and the output limit corresponds to one or both of a rotation rate limit and a hydraulic fluid pump pressure limit. 15

12. The HDD system of claim 1, wherein the pump is configured to linearly advance the drill pipe at various output levels over the output range based on the control signal and the output limit corresponds to one or both of an advancement speed limit and a hydraulic fluid pump pressure limit. 20

13. A method of horizontal directional drilling (HDD) with dynamic scalable controls, comprising: moving a drill string using a pump operating at an output level of an output range, the output level corresponding to a position of an input control along an input range in a first control setting; 25 changing the output level of the pump in the first control setting, wherein changes in the output level of the pump in the first control setting are proportional to positional changes in the input control along the input range; transitioning from the first control setting to a second control setting while maintaining at least some motion of the drill string; 30 determining an output limit of the output range of the pump; WO 2008/137042 PCT/US2008/005637 28 moving the drill string using the pump in the second control setting, the output range of the pump limited by the output limit in the second control setting; and changing the output level of the pump in the second control setting, wherein changes in the output level of the pump within the output range in the second control 5 setting are proportionally scaled to positional changes in the input control along the input range.

14. The method of claim 13, further comprising identifying a desired change in output of the pump while in the first control setting; 10 detecting that the desired change in pump output is too small to be effected by a positional change of the input control along the input range in the first control setting; transitioning from the first control setting to the second control setting to increase sensitivity between the input control and pump output; and 15 making the desired change in pump output using the second control setting.

15. The method of claim 13, wherein the output of the pump and associated drill string movement is not changed during the transition from the first control setting to the second control setting. 20

16. The method of claim 13, wherein the output limit in the second control setting is based on the level of pump output corresponding to the position of the input control along the input range when a switch is toggled in the first control setting. 25

17. The method of claim 13, wherein the output limit in the second control setting is based on the level of pump output corresponding to the position of the input control along the input range that was maintained for a period of time after a switch was toggled in the first control setting. 30

18. The method of claim 13, wherein the output limit in the second control setting is based on an output constant amount and the level of pump output corresponding to the WO 2008/137042 PCT/US2008/005637 29 position of the input control along the input range when a switch is toggled in the first control setting.

19. The method of claim 13, further comprising calibrating the full output range of the 5 pump to the full input range of the input control in the first control setting, wherein the output range of the pump limited by the output limit in the second control setting proportionally corresponds to the full input range of the user control.

20. The method of claim 13, further comprising proportionally rescaling the output 10 range of the pump limited by the output limit to the full input range of the user control when the input control is positioned in a neutral position of the input range when in the second control setting.

21. The method of claim 13, further comprising changing the output limit in response 15 to a user input and then rescaling the output range of the pump limited by the adjusted output limit to the full input range of the input control when in the second control setting.

22. The method of claim 13, wherein moving the drill string using the pump in the first and second control settings further comprises rotating the drill using a hydraulic fluid 20 rotation pump corresponding to the pump, wherein changing the output level of the pump in the first and second control settings further comprises changing one or both of a rotation rate and hydraulic fluid pressure of the hydraulic fluid rotation pump, and wherein the output limit is one or both of a maximum rotation rate and a maximum hydraulic fluid pressure of the hydraulic fluid rotation pump. 25

23. The method of claim 13, wherein moving the drill string using the pump in the first and second control settings further comprises linearly advancing the drill string using a hydraulic fluid thrust pump corresponding to the pump, wherein changing the output level of the pump in the first and second control settings further comprises changing one or both 30 of an advancement speed and hydraulic fluid pressure of the hydraulic fluid thrust pump, WO 2008/137042 PCT/US2008/005637 30 and wherein the output limit is one or both of a maximum advancement speed and a maximum hydraulic fluid pressure of the hydraulic fluid thrust pump.

24. A horizontal directional drilling (HDD) system with dynamic scalable controls, 5 comprising: means for moving a drill string using a pump operating at an output level of an output range, the output level corresponding to a position of an input control along an input range in a first control setting; means for changing the output level of the pump in the first control setting, 10 wherein changes in the output level of the pump in the first control setting are proportional to positional changes in the input control along the input range; means for transitioning from the first control setting to a second control setting while maintaining at least some motion of the drill string; means for determining an output limit of the output range of the pump; 15 means for moving the drill string using the pump in the second control setting, the output range of the pump limited by the output limit in the second control setting; and means for changing the output level of the pump in the second control setting, wherein changes in the output level of the pump within the output range in the second control setting are proportionally scaled to positional changes in the input control along 20 the input range.

25. The HDD system of claim 24, wherein the output of the pump and associated drill string movement is not changed during the transition from the first control setting to the second control setting. 25