Patent Publication Number: US-2023160303-A1

Title: Pulser Cycle Sweep Method and Device

Description:
REFERENCE TO RELATED APPLICATIONS 
     This application incorporates U.S. Pat. Nos. 9,133,950 B2, 10,392,931 B2, and 10,689,976 B2, in their entirety. This application claims priority to U.S. Provisional Patent Appl. No. 63/264,347. 
    
    
     FIELD OF THE INVENTION 
     In general, the present invention relates to a device, system or method including a hydraulically assisted pulser system, including a main pulser and a servo pulser that includes a rotary servo valve for actuating the pulser, for generating pressure pulses in a fluid column during the process of drilling a subterranean borehole with the intent of using said pressure pulses to encode information and telemeter such information to the surface in real time. In operation, the assembled apparatus or “Measurement While Drilling (MWD) tool” includes a servo pulser coupled to a main pulser, a controller, a sensor package, and a battery power source, all of which reside inside a short section of drill pipe close to the bit at the bottom of the borehole being drilled. 
     Specifically, in MWD systems, sensor data from many sensors including accelerometers, magnetometers, and gamma ray detectors are encoded. Using a pulser, this encoded information can be telemetered to the surface. The pulser works by directly or indirectly restricting flow from the mud pumps at the surface which causes a small increase in pressure. These pressure pulses are used to encode and transmit the sensor data, and the data is telemetered to the surface using a sequence of pressure pulses. A surface system will read this change in surface pressure caused by these pressure pulses using a pressure transducer at the surface location and decode the encoded data thus telemetered. Battery systems are provided to power all or most of the electronic components. 
     The invention described in this document details a novel and improved invention for the generation of said pressure pulses in a servo pulser that uses a rotary servo valve. 
     BACKGROUND OF THE INVENTION 
     Servo pulser mechanisms are used to open and close small valves which in turn create pressure differences in specific portions of the MWD tool when said MWD tool is exposed to the flow of drilling fluid during the routine course of drilling a borehole. These differences in pressure in portions of the MWD tool are then used to actuate a main valve which in turn causes much bigger pressure changes in the fluid flow during the drilling operation. As servo pulser mechanisms open and close smaller valves which in turn actuate larger valves, the servo pulsers port fluid in such a way as to allow the drilling mud (fluid) flow itself to do most of the work of opening and closing the main pulser valve to generate pulses that are used to transmit data. Such a servo mechanism assisted pulser may also be called a hydraulically assisted pulser. A servo pulser and main pulser may be so configured that the following relationship exists: when the servo valve is closed, the main valve is thus open; the servo valve opens and the main valve thus closes, generating a pressure increase; and the servo valve closes and the main valve thus opens generating a pressure decrease, the combination of the two actions resulting in a complete pressure pulse. 
     A servo pulser may use a pilot valve to restrict or selectively port fluid flow to a larger main valve (main pulser). A servo valve may include a valve seat and a rotating portion driven by a servo shaft. The rotating part includes structures to obstruct flow through the valve seat. The structures may extend axially off the rotating part to contact the valve seat. Those structures may be longitudinally-extending and/or protruding tips formed to slide rotatably over the valve seat. The rotating part may include a rotor having radially-extending arms for the tips. The arms may include one or no digits (or arm-stops) extending axially in a direction away from the tips. More than one fluid path may be provided through the servo pulser, such as by four holes in the valve seat, which may be circular, and may be symmetrical about the axis around which the rotating part rotates 
     The rotation of the rotating part may be limited by one or more stops. The stops are rotationally fixed with respect to the fluid path, or in one embodiment, the valve seat, and are indirectly in contact with that seat. These may be mechanical stops built into the servo pulser. These mechanical stops may thus be located partially inboard of the outer diameter of the servo valve seat and in a fixed rotational orientation to that servo valve seat. Such mechanical stops provide a rotational position that is fixed with respect to the servo valve seat. 
     A servo pulser includes a servo screen housing onto which are mounted a plurality of screens. The screens allow drilling fluid to enter the valve portion of the servo pulser while at the same time restricting the ingress of large particulate matter as are sometimes present in the drilling fluid. The servo screen housing also houses a servo seat (a valve seat). The servo screen housing includes radially-inwardly extended keys, extending from an inner surface of the servo screen housing, to align the servo seat to the servo screen housing and restrict the ability of the servo seat to rotate relative to the servo screen housing or to translate axially toward the rotor. The mechanical stops built into the servo pulser may be formed on an interior surface of the servo screen housing by extending portions of that housing radially-inwardly along portions of the circumferential extent of the housing. 
     The servo valve seat and flow obstructing structures may be hard and/or wear- and abrasion-resistant. The servo shaft, stops, supporting structure, and rotating part may be nonbrittle, and shock and vibration resistant. 
     The rate at which discrete pressure pulses are created affects the data rate of the overall MWD tool. Each servo pulser pulse causes the main pulser to transmit a single pulse which can encode and transmit a finite number of data bits to the surface. Thus, increasing the servo pulser&#39;s pulse rate, and so the main pulser&#39;s pulse rate, can increase the overall data rate. Another factor is the width of the pulse (correlating to its length in time). In many MWD systems, the pulses used have a desired constant width, however varying widths of pulses can be used to encode and transmit additional bits. 
     A rotary servo pulser relies upon electrical power provided by the battery unit in the MWD tool. Electrical power is required for the servo pulser, including electronics and controls in the servo pulser. The primary battery drain caused by the servo pulser is powering the motor that drives the rotation of the pilot valve. That motor must accelerate and decelerate (brake) the mass of the rotating portion of the pilot valve against the drilling fluid in the servo pulser, where braking may be achieved by shorting the windings together to ground. In addition, accelerating the rotor to begin rotation from a stopped state causes a current spike on the battery line, the said current spike consuming a significant portion of the energy required to generate a pulse. 
     As such, designing a servo pulser that can open and close to actuate the main valve efficiently, either by reducing the number of servo pilot movements required per pulse, thereby reducing the number of current spikes and thus the energy required per pulse, or by reducing the time required to open and close the servo valve, or by any other method to reduce energy consumption and relatedly increase hydraulic performance of the servo valve, is advantageous. 
     BRIEF STATEMENT OF THE INVENTION 
     The current invention described below is for a novel rotary servo pilot valve and associated methods for operating said servo valve which provides many improvements over existing prior art. Although many embodiments are possible, specific embodiments are described in described in brief below. 
     In an embodiment, a servo pulser uses a pilot valve/servo valve to restrict flow to a larger main/pulser valve. The pilot valve interacts with/includes external stops for defining two rotational starting/stopping points and at least one sweep zone for a rotor having four laterally-extending arms, the rotor being driven by a servo shaft, and the shaft being driven directly or indirectly by an electric motor. The stops are formed on an interior surface of the servo screen housing and extend inwardly for only some portions of the circumferential extent of the housing and define the one or more sweep zones of around 90 degrees or exactly 90 degrees. The sweep zones define the about or exactly 90-degree sweep arc in which the rotor is permitted to move between the starting/stopping points. Four protruding servo tips extend longitudinally toward the seat, one from each arm of the rotor, for contacting the valve seat and closing the servo holes. Two digits extend longitudinally away the seat, one each from two opposite arms of the rotor, for contacting the stops. Each digit extends into a sweep zone formed in a rotor section of the servo screen housing by the stops, where the interaction between the stops and the digit in the sweep zone limits rotation of the rotor to the swept arc between the stops. The valve seat includes four axial servo holes therein for fluid flow that can be selectively interrupted by the servo tips obstructing flow through the servo holes to create pressure changes. The valve seat also includes four travel zones, through which there is no fluid flow, between the servo holes. The travel zones are locations that the servo tips can be positioned, or could be traveling through, in which the tips do not obstruct the servo holes. In an embodiment, these travel zones are about 20-25 degrees, or about 22 degrees, in extent, and are centered at about midway through the 90-degree sweep arc (thus at about 34 to 56 degrees from a given endpoint). 
     A pulse, or pressure pulse, is experienced in the mud (drilling fluid) in communication with the main pulser. A pulse includes: (i) a low-pressure state in the drilling fluid at the pulser main valve (0-signal), which is a substantially stable low pressure, associated with the servo tips obstructing the servo holes and with being at a stopping point; (ii) a pressure increase state or transition in the drilling fluid flow at the pulser main valve, associated with the servo tips progressively opening up the servo holes as they rotate with the rotor; (iii) a high-pressure state in the drilling fluid at the pulser main valve (1-signal), which is a substantially stable and increased pressure, associated with the servo tips having fully opened up the servo holes; (iv) a pressure drop state or transition in the drilling fluid at the pulser main valve, associated with the servo tips progressively closing off the servo holes as they rotate with the rotor; and (v) a return to the low-pressure state in the drilling fluid at the pulser main valve (0-signal), associated with the servo tips obstructing the servo holes and with being at a stopping point. 
     One embodiment includes a number (“x”) of servo holes, of radially-extending arms on a rotor, and of servo tips, and fewer than x of axially-extending digits and of sweep zones. In an embodiment, the servo holes are even distributed circumferentially about, and on a plane normal to, the rotor&#39;s axis of rotation. An embodiment with x servo holes has a desired sweep arc s of at or about 360/x degrees, to permit the servo tips to be aligned to the servo holes at the end points of the sweep. In an embodiment in which x&gt;2, sweep arc s may be a multiple of 360/x, where the multiple is &lt;x. E.g. if x=3, s could be 120 degrees or 240 degrees; if the latter, then a sweep would cause a given servo tip start at one servo hole, sweep between it and the next, reach and close the next servo hole, sweep off that hole opening it, and sweep between it and the third hole, and then reach and close the third servo hole, thus causing multiple pulses per sweep. 
     One embodiment includes an equal and even number (“n”) of servo holes, or radially-extending arms, and or servo tips, and up to n/2 of axially-extending digits and n/2 of sweep zones. An embodiment with n/2 axially-extending digits and sweep zones permits assembly of the shaft assembly (including the rotor, arms, tips, and digits) with the valve seat, valve seat retainer, and rotor section (with the stops) in up to n/2 radial orientations where each is functional because each digit will hit one of the stops at the end of a desired sweep arc s of at or about 360/n degrees. Additionally, this arrangement permits the digits to be mechanically balanced as they are radially-opposing and further permits distributing stopping forces (i.e. digits impacting the stops) across more than one digit/arm. 
     In an embodiment, each of the stopping points is caused by mechanical interaction of stops on the screen housing and axially-extending digits on arms of the rotor. The axially-extending digits are on a first arm of the rotor and on a second arm of the rotor separated from the first arm by an arm lacking a digit. In an embodiment, a first (or clockwise “CW”) stopping point is caused by mechanical interaction of the axially-extending digits and first, CW, stops on the screen housing at the CW end of the sweep zones. A second (or counterclockwise “CCW”) stopping point is caused by mechanical interaction between the digits and second, CCW, stops on the screen housing at the CCW end of the sweep zones. 
     In an embodiment, there is just one digit, and each of the stopping points is caused by mechanical interaction of a stop on the screen housing and one axially-extending digit on one arm of the rotor. In an embodiment, a first (or clockwise “CW”) stopping point is caused by mechanical interaction of a first, CW, stop on the screen housing and the axially-extending digit on one arm of the rotor, and a second (or counterclockwise “CCW”) stopping point is caused by mechanical interaction of a CCW stop on the screen housing and the digit. In an embodiment, only one sweep zone is provided, to prevent improper orientation/rotation of the rotor. 
     Variants could exist of an odd number of holes and buttons, but it would be necessary during assembly to ensure that the digit(s) were located in the correct sweep zone. 
     In an embodiment, the servo pulser oscillates between the stopping points in alternating clockwise/counterclockwise sweeps. Each sweep in a given direction creates one full pulse. Each sweep starts with the servo pulser in a closed status, with four servo tips at rest and fully obstructing four servo holes, then passes through the servo pulser being in an open state, with the four servo tips at rest or in motion, and not obstructing the four servo holes, and then ends with the servo pulser in a closed status, with the four servo tips at rest and fully obstructing the four servo holes. Each sweep is a 90-degree arc. 
     The period of time from the beginning of rotation of the servo valve to the end of rotation of the servo valve may be referred to as the pulse width. In an embodiment, pulse width may be at or about 1 s, at or about 0.5 s, at or about 0.25 s, or at or about 0.1 s. 
     The number of servo tips, servo holes, travel zones, and servo holes here is four, though the number could vary depending upon needs and the size of the servo pulser in use, and the shape/size of the holes and configuration of the internal fluid flow paths. Embodiments where the holes are not placed in an angularly symmetric pattern are possible, and the resultant shape of the hole pattern and the associated rotor with the servo tips could be envisioned to be in the shape of the letter ‘X’ or the letter ‘Y’. In such embodiments, the angle between pairs of holes and their associated stops on the servo housing can be derived using the relationship between the bolt diameter of the holes and the diameter of the servo seat, and their relationship to the diameter of the servo tips, and subsequently the angle of rotation required to first open the servo holes, the angle required to position the servo tip in the sweep zone and the angle required to further close the servo holes. 
     In an embodiment, the servo pulser oscillates between the stopping points in alternating clockwise/counterclockwise sweeps. Each sweep in a given direction creates one full pulse. Each sweep starts with the rotor at one of the stopping points, with the drilling fluid at a low pressure indicating a 0-signal, then the drilling fluid passing through the pressure increase, then reaching a high pressure indicating a 1-signal, remaining at a pressure indicating a 1-signal for a finite period of time, then the drilling fluid passing through the pressure drop, then the drilling fluid returning to a low pressure indicating a 0-signal. 
     In an embodiment, the servo pulser oscillates between the stopping points in alternating clockwise/counterclockwise sweeps. Each sweep in a given direction creates one full pulse, in a 0-signal-1-signal-0-signal progression (or 0-1-0 progression), rather than each sweep in a given direction creating an initial half-pulse (a 0-signal-1-signal progression or 0-1 progression) followed by a return sweep in the opposite direction to complete the pulse (a 1-signal-0-signal progression or 1-0 progression). 
     In an embodiment, the servo pulser creates a full pulse, beginning at the CCW stop and rotating in a clockwise direction in 0-1-0 progression and ending at the CW stop. Then the servo pulser creates another full pulse, beginning at the CW stop and rotating in a counterclockwise direction in 0-1-0 progression and ending at the CCW stop. 
     In an embodiment, the servo pulser oscillates clockwise and then counterclockwise to create two consecutive pulses, in 0-1-0-1-0 progression, beginning at the CCW stop and rotating in a clockwise direction to the CW stop, then rotating in a counterclockwise direction from the CW stop to the CCW stop. 
     In an embodiment, the servo pulser oscillates between the stopping points in alternating clockwise/counterclockwise sweeps with an intermediate stop between the stopping points in the open state. Each sweep in a given direction creates one full pulse. Each sweep starts with the motor driving the shaft, accelerating the rotor of the servo pulser from a closed state, with the four servo tips at rest and fully obstructing the four servo holes, through the transition, and toward the servo pulser being in an open state. Then, after an optional period of coasting (no applied acceleration or deceleration) the motor then decelerates the rotor so that it stops with the servo pulser in that open state, with the four servo tips not obstructing the four servo holes (and may begin decelerating before or after reaching such state). The period of time for which the servo tips are at rest and not obstructing the servo holes is the dwell time, and the stop (and the dwell time) enlarges the pulse width. Then the motor accelerates the rotor from the open state (in the same direction as the previous acceleration), through the transition, toward the servo pulser being in a closed state. Then, after an optional period of coasting, motor decelerates the rotor so that it stops with the servo pulser in that closed state, with the four servo tips at rest and fully obstructing the four servo holes (and may begin decelerating before reaching such state). Each sweep is a 90-degree arc and each such arc includes two acceleration events and deceleration events. The dwell time lies exists between the first deceleration events and the second acceleration events, and the coasting time(s) exist, optionally, between acceleration and then deceleration events. 
     In an embodiment, the servo pulser oscillates between the stopping points in alternating clockwise/counterclockwise sweeps without any intermediate stop between the stopping points in the open state (i.e. dwell time is equal to 0). Each sweep in a given direction creates one full pulse. Each sweep starts with the motor driving the shaft, accelerating the rotor of the servo pulser from a closed state, with the four servo tips at rest and fully obstructing the four servo holes, through the transition, and toward the servo pulser being in an open state. Then, after an optional period of coasting (no applied acceleration or deceleration), the motor then optionally decelerates the rotor to extend the time for which the servo pulser is in that open state, with the four servo tips not obstructing the four servo holes. During this coasting period, the rotor does not cease its rotation at any point in time, resulting in a dwell time of zero (0) seconds. Then the motor optionally accelerates the rotor (in the same direction as the previous acceleration), through the transition, toward the servo pulser being in a closed state. Then, after an optional period of coasting, motor decelerates the rotor so that it stops with the servo pulser in that closed state, with the four servo tips at rest and fully obstructing the four servo holes (and may begin decelerating before reaching such state). Each sweep is a 90-degree arc and each such arc includes at least one acceleration event and at least one deceleration events and may include two of each. The coasting time(s) exist, optionally, between the acceleration and then deceleration events, and between the deceleration and acceleration events. 
     In an embodiment, the servo pulser oscillates between the stopping points in alternating clockwise/counterclockwise sweeps without any intermediate stop or coast between the stopping points in the open state (i.e. dwell time is equal to 0). Each sweep in a given direction creates one full pulse. Each sweep starts with the motor driving the shaft, accelerating the rotor of the servo pulser from a closed state, with the four servo tips at rest and fully obstructing the four servo holes, through the transition, and toward the servo pulser being in an open state. The motor continues to drive the servo tips in the same direction continuously without coasting or decelerating the rotor, and thus rotates continuously. Then, the motor decelerates the rotor so that it stops with the servo pulser in that closed state, with the four servo tips at rest and fully obstructing the four servo holes (and may begin decelerating before reaching such state). Each sweep is a 90-degree arc and each such arc includes at least one acceleration event and at least one deceleration events and may include two of each. In this embodiment, the servo tips make the fastest possible transition from the 0 state, through the 1 state and back to the 0 state, thus resulting in the smallest possible pulse width. 
     It will be obvious to anyone versed in the art that the rotational speed of the motor, and thus the rotor and attached servo tips, could be adjusted by many means, including methods such as changing the voltage applied to the motor thus increasing or decreasing its speed or by pulse width modulating the voltage applied to the motor to achieve a slower rotation speed. Embodiments where such methods are used to achieve desired results are clearly possible, including adjusting the speed of the rotor during the acceleration or deceleration phases to either increase or reduce said acceleration or deceleration times. In addition, in certain embodiments, the motor speed adjusted using one or more of the above methods to entirely eliminate the need for coasting or stopping (dwell) during the generation of single pulse. Conversely, in certain embodiments, the coasting time or the dwell time are increased to achieve wider pulse widths. For example, in an embodiment, the motor speed is set to a high or maximum-achievable value to accelerate the rotor and the attached servo tips to a high rotational speed until the servo tips no longer obstruct the servo holes, and then the speed of the motor (and the attached rotor and servo tips) is reduced so as to rotate at a lower rotational speed through the sweep zone, and then the rotational speed of the motor is increased past the sweep zone to continue rotation in the direction to further close the servo holes (with or without coasting near the end of the 0-1-0 pulse cycle); all done in such a way so as to achieve a desired pulse width without stopping the rotation of the servo valve, or without coasting the servo valve. 
     In other embodiments, there are an equal and odd number (“m”) of servo holes, radially-extending arms, and servo tips, and up to (m−1)/2 axially-extending digits and up to (m−1)/2 sweep zones. An embodiment with (m−1)/2 axially-extending digits permits assembly of the shaft assembly (including the rotor, arms, tips, and digits) with the valve seat, screen housing, and rotor section (with the stops) in up to (m−1)/2 radial orientations where each is functional because each digit will hit one of the stops at the end of a desired sweep arc s of about 360/m degrees. 
     In one embodiment, the pilot valve includes external stops for defining two rotational starting/stopping points for a rotor having three laterally-extending arms and one servo tip on each arm, and three servo holes on the servo seat. The valve seat also includes three travel zones, through which there is no fluid flow, as locations that the servo tips can be positioned, or could be traveling, in which the tips do not obstruct the servo holes. The servo pulser oscillates between the stopping points in alternating clockwise/counterclockwise sweeps. Each sweep in a given direction creates one full pulse. Each sweep starts with the servo pulser in a closed status, with the three servo tips at rest and fully obstructing the three servo holes, passes through the servo pulser being in an open state, with the three servo tips at rest or in motion, and not obstructing the three servo holes, and ends with the servo pulser in a closed status, with the three servo tips at rest and fully obstructing the three servo holes. Each sweep is a 120-degree arc. 
     In an embodiment, the servo pulser&#39;s pulse rate is the same as its sweep rate. That is, the servo pulser creates one full pulse, low-high-low (0-1-0 progression) in one sweep. In this embodiment, the pulser&#39;s sweep time (the time for one sweep) also correlates to the time period required to complete one pulse (not the pulse width). This is in contrast to the situation in which a servo pulser&#39;s pulse rate is half of its sweep rate, such as if it required a first sweep to create the low pressure and a second sweep to return to the high pressure. 
     The time to accomplish any sweep is a function of, among other things, the arc length of the sweep, any stops or coasting during the sweep, and the acceleration (in either direction) applied to the mass of the rotating portion of the pilot valve, including acceleration to an increased rotational velocity (such as from rest) and acceleration (deceleration) to a reduced rotational velocity (such as to rest). The acceleration applied is a function of, among other things, the mass of the rotating portion of the pilot valve, the density of the drilling fluid, and the applied motive power. The first is invariant on a given configuration of the MWD tool, and the second is driven by other factors. Thus, controlling how much power is applied to the motor is used to control acceleration and, indirectly, sweep time. Naturally, shorter sweep times, for a given rotation, require higher (or longer) acceleration and more power, as do starting/stopping during a sweep. And sweep time is also a function of the time required for the rotating portion of the pilot valve to accelerate from rest to a desired rotational speed. 
     In an embodiment, the servo pulser increases the servo pulser&#39;s pulse rate by reducing the time to create one pulse at a particular power requirement (or it could reduce the power required for creating one pulse at a given time). Because one sweep creates one full pulse (in 0-1-0 progression), no change of direction is required for that one pulse. That is rather than the servo pulser having to reverse its direction of rotational travel between a first sweep and a return sweep to create a full pulse. Each change of direction, naturally, requires fully decelerating and the re-accelerating the mass of the rotating portion of the pilot valve. This takes time for the rotating portion to reach a desired speed as its speed comes up from zero. Thus, even though a given sweep arc may be greater, the rotating portion can spend a greater time at a desired speed as it does not return to rest in mid-pulse, meaning the overall sweep speed can be higher, and the sweep time lower. In an embodiment, the servo pulser reduces the servo pulser&#39;s power consumption reducing the amount of acceleration applied to the rotating portion of the pilot valve, and thus the power used by the motors to do so. Because one sweep creates one full pulse (in 0-1-0 progression), no change of direction is required for that one pulse. 
     In an embodiment, when a servo pulser is turned on, an algorithm is used to move the pilot valve to (or confirm its presence at) one of the two stopping points, with CW being the default, thus ensuring that the servo pulser is positioned in the 0 state prior to any operation. Thus, it is set at a fixed location which the servo pulser&#39;s microcontroller can use as an initial condition in commanding further rotation. 
     In an embodiment, the servo pulser&#39;s microcontroller receives and/or calculates the time required to move the rotating portion of the valve, and retains that time for use in further computations or actuations. This includes retaining the time for previous sweeps. Likewise, the microcontroller retains such information as the intended velocity/acceleration profile, the time required to accelerate or decelerate, the time spent in the sweep zone under various conditions such as coasting, etc, and receives and retains information about the applied current or applied power from previous sweeps. 
     Frequently, each pulse has the same desired constant width and the microcontroller can assume that the previous pulse&#39;s width (which was retained) is the same as the next one. In an embodiment, the microcontroller applies feedback to calculate the intended velocity/acceleration, coasting or dwell profile and current and/or power usage for the next sweep, by using the previous sweep&#39;s (or sweeps&#39;) data for those items to adjust the current sweep&#39;s applied current/power (or velocity/acceleration, coasting or dwell profile) to attempt to cause the current sweep&#39;s pulse width, power, current, energy consumed, sweep time, dwell time, stop time or any other parameter to conform to the desired value. 
     In an embodiment, the system calculates the amount of dwell time or braking without dwell time is needed to achieve the desired pulse width. A calculated solution might be if the desired pulse width is smaller than can be achieved by applying maximum acceleration (and deceleration) to the rotor; or in other words, the rotor cannot open and close fast enough to generate the desired pulse width. Other situations could be when the pulse width desired is longer than the minimum calculated time to open and close the servo valve. Solutions to meet this situation could include: a no-dwell, no-brake, no coast (direct) solution in which the desired pulse width is achieved by using chosen acceleration and deceleration values to a rotate the servo valve to a stop at the end of the single pulse 0-1-0 cycle in such a manner as to achieve the required pulse width; a no-dwell, no-brake (coasting) solution in which the desired pulse width is achieved by using chosen acceleration and deceleration values to first rotate the servo valve to a stop, with an intervening period of coasting where the rotor is allowed to continue rotation but without any energy being delivered to the motor; a no-dwell (braked coasting) solution in which the desired pulse width is achieved by using acceleration and one or more deceleration values to rotate the servo valve to a stop and the end of the 0-1-0 cycle in such a manner as to generate the required pulse width, with an intervening period of coasting (optionally following a first braking/deceleration), with such coasting achieved by intermittently braking the motor so as to reduce the speed of the rotor, but not to stop its rotation; a dwell-time (paused) solution in which the desired pulse width is achieved by using a first acceleration and deceleration phase with first acceleration and deceleration values to rotate the servo valve to a stop in the travel zone, followed by a chosen dwell time, and then further followed a second acceleration and deceleration phase with second acceleration and deceleration values to rotate the servo valve to a second stop at the end of 0-1-0 cycle, this generating the desired pulse width; and a coasting dwell-time (coasting paused) solution in which the desired pulse width is achieved by using a first acceleration and deceleration phase with first acceleration and deceleration values to rotate the servo valve a stop in the travel zone, with an intervening chosen period of coasting where no energy is delivered to the motor, thus allowing it to decelerate naturally to a full stop in the travel zone, subsequently followed by a dwell time, and then a second acceleration and deceleration phase with second acceleration and deceleration values to further rotate the servo valve to a second stop at the end of the 0-1-0 cyele, with a intervening chosen period of coasting so as to allow the servo valve to close the servo holes at the end of the pulse cycle in such a manner as to coast to the stop and simaltaneously achive the desired pulse width. 
     In an embodiment, the rotor can coast or stop/pause within its sweep arc in a travel zone where the servo tips do not obstruct the servo holes. 
     In an embodiment, the rotor can coast or stop/pause within its sweep arc in the sweep zone in suach a manner as to partially onstruct the servo holes in either opening phase of the pulse cycle or the closing phase of the pulse cycle. 
     In an embodiment in which four servo holes are provided, and there are four servo tips for obstructing them, the rotor can coast or stop/pause within its sweep arc in a travel zone of about 20-25 degrees, or about 22 degrees, in extent. The travel zone may centered at about midway through the 90-degree sweep arc and thus be positioned at about 34 to 56 degrees from a starting point. 
     In many MWD systems, the pulse command is sent as a digital voltage signal on a single wire so as to command the opening of the servo valve with a rising edge of the digital voltage signal and the closing of the servo valve with a falling edge of the digital voltage signal. In this instance, the rising edges/falling edges operate as a command to the motor to activate and thus to rotate the shaft and rotor and associated structures in the desired direction. In most system such pulse signals and the required pulse widths do not change and a single width of pulse is required, albeit at varying times. In this situation, the first time a pulse command is sent on the digital voltage signal, the microcontroller in the servo pulser has no a-priori knowledge of the required pulse width as it is required to begin rotation when the digital signal transitions from a low state to a high state, and may not be able to initiate the closure of the servo valve until a high to low transition is seen on the digital voltage signal. In this situation, the microcontroller in the pulser may be forced to generate an imperfect pulse as best it as it can using algorithmic defaults. However, in this situation, the microcontroller in the servo pulser may store the results of the first pulse, including information regarding the required pulse width (as measured by the time between the rising and falling edge of the digital voltage signal), times related to acceleration, deceleration, coasting, dwelling or stopping as may be required, and use this information to generate the next pulse at the required pulse width (which is assumed to be the same as the first pulse width) using the data thus measured and saved. 
     In some MWD systems, digital communication (bus) commands may be sent to initiate the servo pulser to generate a pulse of the required pulse width. If such a bus command is sent with the width of the desired pulse, and possibly other parameters as may be specified by the MWD system sending the bus command, the servo pulser can use data gathered and saved from previously generated pulses to accommodate different pulse widths as requested by the MWD system. 
    
    
     
       BRIEF DESCRIPTION OF THE FIGURES 
         FIG.  1 A  is a representative view of parts of the surface and downhole portions of a drilling rig. 
         FIG.  1 B  is a partial cutaway of the upper portion of the MWD tool as shown in  FIG.  1 A . 
         FIG.  1 C  shows a front view of portion of a servo pulser showing several sections separated from one another. 
         FIG.  2    is a representative view of the various components that together may comprise the downhole portion of an MWD tool. 
         FIG.  3 A  shows a right, front, top, oblique exploded view of a portion of an embodiment of the invention. 
         FIG.  3 B  shows a left, rear, top, oblique exploded view of portion of the embodiment of the invention shown  FIG.  3 A . 
         FIG.  4 A  shows a right, front, top, oblique view of a servo screen housing of an embodiment of the invention. 
         FIG.  4 B  shows a left elevation of the screen housing in  FIG.  4 A . 
         FIG.  4 C  shows a section view along line A-A from  FIG.  4 B . 
         FIG.  4 D  shows a section view along line B-B from  FIG.  4 C . 
         FIG.  5 A  shows right elevation of a servo seat of an embodiment of the invention. 
         FIG.  5 B  shows a section view along line C-C from  FIG.  5 A . 
         FIG.  6 A  shows left elevation of a nozzle insert of an embodiment of the invention. 
         FIG.  6 B  shows a section view along line D-D from  FIG.  6 A . 
         FIGS.  7 A-E  show a series of opening/closing states of the servo pulser as viewed along internal sightline E in  FIG.  3 A . 
         FIGS.  7 F-J  show a second series of opening/closing states of the servo pulser in the reverse order as in  FIGS.  7 A-E . 
         FIG.  8    shows interrelationships between certain operational statuses and actions of an embodiment of the invention in a first process. 
         FIG.  9    shows interrelationships between certain operational statuses and actions of an embodiment of the invention in a second process. 
         FIG.  10    shows interrelationships between certain operational statuses and actions of an embodiment of the invention in a third process. 
         FIG.  11    shows steps of a process for carrying out an embodiment of the invention. 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     In one embodiment of the invention, as described in detail below, information of use to the driller is measured at the bottom of a borehole relatively close to the drilling bit and this information is transmitted to the surface using pressure pulses in the fluid circulation loop that manifest as pulses in the surface pressure. The command to initiate the transmission of data may be sent by stopping fluid circulation and allowing the drill string to remain still for a minimum period of time. Upon detection of this command, the downhole tool measures at least one downhole condition, usually an analog signal, and this signal is processed by the downhole tool and readied for transmission to the surface. When the fluid circulation is restarted, the downhole tool waits a predetermined amount of time to allow the fluid flow to stabilize and then begins transmission of the information by repeatedly closing and then opening the pulser valve to generate pressure pulses in the fluid circulation loop. The sequence of pulses sent is encoded into a format that allows the information to be decoded at the surface and the embedded information extracted and displayed. 
     Referring now to the drawings and specifically to  FIG.  1 A , there is generally shown therein a simplified sketch of the apparatus used in the rotary drilling of boreholes  12 . A borehole  12  is drilled into the earth using a rotary drilling rig which consists of a derrick  14 , drill floor  16 , draw works  18 , traveling block  20 , hook  22 , swivel joint  24 , kelly joint  26  and rotary table  28 . A drill string  30  used to drill the bore well is made up of multiple sections of drill pipe that are secured to the bottom of the kelly joint  26  at the surface and the rotary table  28  is used to rotate the entire drill string  30  while the draw works  18  is used to lower the drill string  30  into the borehole and apply controlled axial compressive loads. The bottom of the drill string  30  is attached to multiple drilling collars  32 , which are used to stiffen the bottom of the drill string  30  and add localized weight to aid in the drilling process. A measurement while drilling (MWD) tool  10  is generally depicted attached to the bottom of the drill collars  32  and a drilling bit  34  is attached to the bottom of the MWD tool  10 . 
     The drilling fluid or “mud” is usually stored in mud pits or mud tanks  36 , and is sucked up by a mud pump  38 , which then forces the drilling fluid to flow through a surge suppressor  40 , then through a kelly hose  42 , and through the swivel joint  24  and into the top of the drill string  30 . The fluid flows through the drill string  30 , through the drill collars  32 , through the MWD tool  10 , through the drilling bit  34  and its drilling nozzles (not shown). The drilling fluid then returns to the surface by traveling through the annular space  44  between the outer diameter of the drill string  30  and the well bore  12 . When the drilling fluid reaches the surface, it is diverted through a mud return line  46  back to the mud tanks  36 . 
     The pressure required to keep the drilling fluid in circulation is measured by a pressure sensitive transducer  48  on the kelly hose  42 . The measured pressure is transmitted as electrical signals through transducer cable  50  to a surface computer  52  which decodes and displays the transmitted information to the driller. 
       FIG.  1 B  shows a partial cutaway of the upper portion of the MWD tool  10  to reveal pulser  62  (main pulser, main valve) connected to servo pulser  64 . Both are located within the inner diameter of MWD tool  10 . The one end of pulser  62  is connected to servo pulser  64  to create a path for drilling fluid between those components. The other end of pulser  62  is in contact with the internal drilling fluid column  13  within the inner diameter of MWD tool  10 . 
       FIG.  1 C  shows servo pulser  64  with the several sections separated from one another for clarity. Servo nozzle housing  102  is hydraulically and mechanically attached to pulser  62  at its first end via female connector  109 , and mechanically to a first end of compensator housing  306  at its second end, so that servo shaft  126  and be driven therefrom through keyed end  127  which is permanently attached to servo shaft  126 . Second end of compensator housing  306  is mechanically attached via male connector  108  and female connector  109  to a first end of electronics housing  310 , and second end of electronics housing  310  is mechanically and electrically attached as part of MWD tool  10 .  FIG.  2    generally shows a schematic representation of the various components that together make up the downhole portion of an MWD tool. The downhole MWD tool  10  consists of an electrical power source  54  coupled to controller  56 . Controller  56  is coupled to sensor package  58  and servo pulser  64 . The servo pulser  64  is coupled to a vibration and rotation sensitive switch  60  and a pulser  62 . 
       FIG.  2    shows one embodiment of the method of the MWD tool. Another embodiment (not depicted) is one in which the vibration and rotation sensitive switch  60  is integrated into the servo pulser  64 . Another embodiment (not depicted) is one in which controller  56  is integrated into the servo pulser  64  which is directly connected to sensor package  58 . 
     Controller  56  in  FIG.  2    has the ability to be alerted or informed of the status of the vibration and rotation present in the drill string either by directly communicating to the vibration and rotation sensitive switch  60  or by having this information transmitted through the servo pulser  64 . The vibration and rotation sensitive switch  60  can be integrated into the controller  56  and can thereby acquire this information directly. 
     Returning to  FIG.  1 C , and with reference to  FIGS.  3 A- 3 B , in an embodiment of the invention, servo nozzle housing  102  includes screen housing  103  and nozzle bulkhead  104 , with servo valve  101  within screen housing  103 . Screen housing  103  includes fluid inlets  146  in this embodiment, two thereof, spaced about the circumference of screen housing  103 , and which are screened by servo screens  147  as a filtering/screen mechanism to restrict large particulate matter as are sometimes present in the drilling fluid  66  from entering into fluid inlets  146 . Fluid inlets  146  allow drilling fluid to enter screen housing  103  and be hydraulically connected to/from servo valve  101  via central channel  142 , and through valve  101 , and via valve  101  to nozzle bulkhead  104  and then on to pulser  62 . 
     Compensator housing  306  encloses a dual shaft gearbox (not shown) for coupling to and driving servo shaft  126  by drive shaft  326  via keyed end  127 , drive shaft  326  being located at a first end of compensator housing  306 . The gearbox is attached at its second end to magnetic bulkhead  308  via a shaft through a piston compensator (not shown). Oil fill plugs  304  are provided in compensator housing  306  to permit filling the interior thereof with hydraulic oil for lubrication and pressure compensation, that is, to balance internal oil pressure on gaskets and seals with the exterior fluid pressure. Compensator housing  306  includes a piston compensator exposed to the pressure of the drilling fluid on one upstream side and transmitting that pressure to compress the oil-filled interior of compensator housing  306 . Magnetic bulkhead  308  also includes a coupling device (not shown) to transmit torque between to drive shaft  326  (via a dual-shaft gearbox) from electronics housing  310  through the use of a plurality of magnets on compensator housing  306  matched to a plurality of magnets on magnetic coupling  312  of electronics housing  310 . That magnetic coupling device drives one end of the dual-shaft gearbox resident inside compensator housing  306 , the other end of the dual-shaft gearbox being connected to drive shaft  326 . 
     Electronics housing  310  includes magnetic coupling  312  at its first end, connected to electric motor  328 . Electronics housing  310  includes motor driver  316 , and at its second end includes mechanical connections and electrical connection  318 . Connection  318  allows servo pulser  64  to be mechanically and electrically connected to controller  56  or electrical power source  54  or in general, to other components that may make up part of MWD tool  10 . 
     Turning to  FIGS.  3 A,  3 B, and  4 A- 4 D , in an embodiment of the invention, screen housing  103  includes female connectors  109  on each end of body  140 , valve section  150  at the end adjacent to nozzle bulkhead  104 , and with fluid inlets  146  between valve section  150  and female connector  109  that connects to electronics housing  310 . Central channel  142  creates a connecting space down the center of body  140  fluidically connecting fluid inlets  146  to valve section  150 . That fluidic connection allows drilling fluid  66  to reach servo valve  101 . Central channel  142  also is a space for servo shaft  126  to pass axially toward female connector  109  connected to electronics housing  310  to permit keyed end  127  to be connected to and driven by drive shaft  326 . 
     Valve section  150  of screen housing  103  contains servo valve  101  positioned within valve section  150 , which includes servo seat retainer  153  and dl, with rotor section  151  being more proximal to fluid inlets  146  and between valve seat retainer  153  and fluid inlets  146 . Servo valve  101  includes servo rotor  120  and servo seat  170 . 
     Servo rotor  120  is placed inside rotor section  151  and includes servo shaft  126 , with keyed end  127 , and rotor arms  122 , each having a common axis of rotation  121 . Rotor arms  122  are lateral extensions reaching radially off axis of rotation  121  of servo shaft  126 . Rotor arms  122  include servo tips  124  attached thereto, e.g. by means of an interference press fit, into tip holes  123  formed on valve seat side  130  of rotor arms  122 . Servo tips  124  thus extend axially seat-wise from rotor arms  122  toward servo seat  170  and away from stops  156  and fluid inlets  146  and servo shaft  126 . Rotor arms  122  also include digits  125  either formed thereon, or attached thereto, onto opposing stop side  131  thereof. Digits  125  thus extend axially stop-wise from rotor arms  122  away from servo seat  170  and toward stops  156  and fluid inlets  146  and servo shaft  126 , and in the opposing direction of servo tips  124 . Digits  125  include opposing faces substantially tangent to the directions of rotation, clockwise CW face  133  and counter-clockwise CCW face  134 . In this embodiment, there are four rotor arms  122 , each with one servo tip  124 , but only two digits  125 , rotor arms  122  with a digit  125  are separated from one another by another one rotor arm  122  without a digit  125 . In addition, dowel pin  129  is also attached to servo shaft  126  on axis of rotation  121 , e.g., by means of an interference press fit for fitting into rotor pin hole  179  of servo seat  170 . 
     Turning to  FIGS.  3 A,  3 B,  4 A- 4 D, and  5 A- 5 B , in an embodiment of the invention, servo seat  170  is set within cylindrical servo seat retainer  153  and includes rotor face  175 , facing servo rotor  120 , and opposing nozzle face  176 . Servo holes  171  pass through servo seat  170  from rotor face  175  to nozzle face  176 . Servo seat  170  also includes rotor pin hole  179  at the center thereof on rotor face  175 , and keyholes  178  depressed into the outer edge of rotor face  175  for locking into anti-rotation keys  154  of servo seat retainer  153  on the interior of servo screen housing  103 . Nozzle face  176  of servo seat  170  includes axially-extending peripheral ring  173 . Ring  173  extends axially toward nozzle bulkhead  104 . Ring  173  extends from at or about the outer periphery of servo seat  170  to at or about 30% of the radius of ring  173 , and is broad enough to occlude a fraction, at or about 50% of the axially-oriented flow area  174  of servo holes  171 . Servo holes  171  are circular on rotor face  175 , and spaced about symmetrically radially outward of rotor pin hole  179  and inward of the outer edge of servo seat  170 . Rotor face  175  includes travel zones  177 , being the portions of rotor face  175  not pierced by servo holes  171  and over which servo tips  124  can pass in rotational fashion without occluding servo holes  171 . Servo holes  171  extend axially through nozzle face  176  but are roughly semi-circular as viewed axially, being partially occluded by the inner edge of ring  173 . Servo holes extend axially past nozzle face  176  and terminate in angled flow redirect  172 , which acts to turn the flow of drilling fluid  66  from essentially axial at rotor face  175  to partially radially inwardly beyond nozzle face  176  to direct flow into nozzle insert  112 . 
     In operation, servo tips  124  are pressed onto rotor face  175  of servo seat  170  and are located radially by guiding dowel pin  129  into rotor pin hole  179 . In this manner, servo shaft  126 , rotor arms  122 , and servo tips  124  are located to the servo seat  170  to allow servo shaft  126  to be rotated relative to servo seat  170  and servo holes  171 . 
     Servo seat  170  and servo tips  124  are preferably made out of a hard material to provide significant resistance to erosion and wear caused by the repeated opening and closing of said servo valve  101 . Some such materials can be made from cemented ceramics or carbides such as aluminum oxide, silicon carbides, tungsten carbides. Although such hard materials are generally better in applications, it can be seen that in some embodiments, standard metal or plastic components may be used as a means to reducing manufacturing costs. Having the edge of the servo tip  124  be sharp where it is in contact with servo seat  170  significantly adds to the cutting and sweeping ability of the servo valve  101 . The action of rotating the servo shaft  126  in effect causes the sharp knife-like edge of the servo tips  124  to sweep across rotor face  175  of servo seat  170  and thereby cut any contaminants that may be obstructing servo holes  171 . This shearing action is highly desirable in MWD applications where additives and contaminants in the drilling mud may frequently cause jams in some equipment. 
     Rotor section  151  includes stops  156  to limit rotation of servo rotor  120 . Stops  156  are mechanical and rotationally fixed with respect to valve seat  170  and rotor section  151  of screen housing  103  and extend partially radially inward of the outer diameter of the servo seat. Stops  156  are formed on interior surface  152  of rotor section  151  of screen housing  103  and extend radially-inwardly along only some portions of the circumferential extent of screen housing  103  and extend axially toward servo seat  170  only around halfway of the axial extent of rotor section  151 . Stops  156  have both a clockwise CW surface  163  and a counter-clockwise CCW surface  164 . Each of CW surface  163  and CCW surface  164  may contact digits  125 . 
     By extending inwardly for only some portions of that circumferential extent, stops define two arcuate sweep zones  158  of around 90 degrees or exactly 90 degrees, and which are rotationally fixed with respect to valve seat  170  and rotor section  151 . Sweep zones  158  define an about or exactly 90-degree sweep arc  159  in which servo rotor  120  is permitted to move between starting points  161  and stopping points  162  (see  FIG.  4 B ). The two digits  125 , extending axially away from servo seat  170 , and stops  156  extend axially toward servo seat  170  sufficiently for digits  125  to contact stops  156  and for stops  156  to create limited rotation of servo rotor  120 . Thus, each digit  125  extends into one of the two sweep zone  158  formed in rotor section  151  by stops  156 , and the interaction between stops  156  and digit  125  in sweep zone  158  limits rotation of servo rotor  120  to sweep arc  159 . 
     As stops  156  extend axially toward servo seat  170  only around halfway of the axial extent of rotor section  151 , rotor section  151  also defines cylindrical open area  157 , in which rotor arms  122  and servo tips  124  can rotate unobstructed (though their rotation is limited by interaction of stops  156  and digits  125 ).\ 
     Starting points  161  and stopping points  162  may be created by mechanical interaction of matching faces on the stop and axially-extending digits on the arms of the rotor. In particular, a first (or clockwise “CW”) stopping point  162  is caused by mechanical interaction of CW faces  133  of digits  125  with a CW surface  163  on stop  156  on rotor section  151  at the CW end of a sweep zone  158 . A second (or counterclockwise “CCW”) stopping point  162  is caused by mechanical interaction of CCW faces  134  of digits  125  with a CCW surface  164  on stop  156  on rotor section  151  at the CCW end of a sweep zone  158 . These stopping points  162  thus define the permitted sweep arc  159  and are then starting points  161  when the direction of rotation or rotor section  151  is reversed. 
     Turning to  FIGS.  3 A,  3 B,  6 A- 6 B , in an embodiment of the invention, nozzle bulkhead  104  includes male connector  108  for connection to screen housing  103  and female connector  109  for connection to pulser  62 . Cylindrical insert receiver  117  is formed adjacent or within female connector  109  to receive cylindrical nozzle insert  112  which seats on insert seat  113 . Nozzle insert  112  includes reducer section  115  in which the cross-sectional flow area reduces to transition section  116 , which is at or about the same size as throat  114  formed through insert seat  113 . Flow of drilling fluid  66  can thus flow through nozzle insert  112 , throat  113  and into female connector  109  to continue to pulser  62 . 
     Turning to  FIGS.  4 ,  7 A- 7 J , and  FIGS.  8 - 10   , pulse (or pressure pulse)  200  is experienced in surface pressure  220  of drilling fluid  66  in communication with the pulser  62 . Pulse  200  includes: (i) low-pressure state  221  (0-signal  226 ), as a substantially stable lower pressure associated with servo tips  124  obstructing servo holes  171  and with being at one of starting point  161 ; (ii) pressure increase transition  222 , associated with servo tips  124  progressively opening up servo holes  171  as they rotate with rotor  120 ; (iii) high-pressure state  223  (1-signal  227 ), as a substantially stable and increased pressure, associated with servo tips  124  having fully opened up servo holes  171 ; (iv) pressure drop transition  224 , associated with servo tips  124  progressively closing off servo holes  171  as they rotate with rotor  120 ; and (v) a return to low-pressure state  221  (0-signal  226 ), associated with servo tips  124  obstructing servo holes  171  and with being at one of stopping points  164 . The period of time during which digital voltage signal  205  is at its high voltage state  227  is digital pulse width  201 . The period of time between when pulser  62  starts to open and when pulser  62  starts to close is hydraulic pulse width  202 , which corresponds closely to the period of time surface pressure  220  shows an increasing value before dropping off, thus pressure increase transition  222  and high-pressure state  223 . 
     In an embodiment, digital pulse width  201  may be at or about 1 s, at or about 0.5 s, at or about 0.25 s, or at or about 0.1 s. In an embodiment, hydraulic pulse width  202  may be narrower, equal or wider than the associated digital pulse width  201  that causes the pulse  200  to be generated, with the difference in time explained by the lag between the onset of the digital voltage signal&#39;s transition to a high state or subsequently to a low state and the associated delay to the opening or subsequent closing of the servo tips  124  over servo holes  171 . 
       FIG.  8    details the behavior of an embodiment of the current invention as it pertains to the operation of servo valve  101  in situations where servo rotor  120  of servo valve  101  moves continuously between starting and stopping points  161  and  162  without any coasting, braking or stops. Servo rotor  120  accelerates and travels continuously in one direction from servo tips  124  fully closing servo holes  171 , to first rotate servo tips  124  to fully open servo holes  171 , then continues to rotate to servo tips  124  then subsequently close and fully obstruct servo holes  171 , changing rotary valve position from 0-degrees to 90-degrees. This action begins in closed state  231  and is followed by acceleration event  241  upon the reception of rising edge  206  of digital voltage signal  205 . Current spike  331  in motor current  330  reflects power being applied to motor  238 , followed by falling current  332 . This acceleration causes servo rotor  120  to rotate to its open position  232  where servo tips  124  are in travel zone  160  in which servo holes  171  are not obstructed, initiating pulse  200 . Servo rotor  120  continues to further rotate away from starting point  161  and causes servo tips  124  to sweep over servo holes  171 , first partially obstructing them and then onto fully obstructing them to fully close servo valve  101 , thus ending pulse  200 . As shown in  FIG.  8   , servo rotor  120  then moves continuously between starting and stopping points  161  and  162  in the reverse direction, as shown by it changing rotary valve position back from 90-degrees to 0-degrees. During this rotation in the reverse direction, a second pulse  200  is created. 
       FIG.  9    details the behavior of an embodiment of the current invention as it pertains to the operation of the servo valve in situations where servo rotor  120  of servo valve  101  moves in one direction to open servo holes  171  by rotating servo tips  124  from fully closing servo holes  171  to fully open servo holes  171 . This action begins in closed state  231  and is followed by acceleration event  241  upon the reception of rising edge  206  of digital voltage signal  205 . Current spike  331  in motor current  330  reflects power being applied to motor  238 , followed by falling current  332 . This acceleration causes servo rotor  120  to rotate to its open position  232  where servo tips  124  are in travel zone  160  in which servo holes  171  are not obstructed, beginning pulse  200 . Servo rotor  120  then enters coasting phase  242  where motor  238  is not energized (current  330  flowing through the motor is zero), but the rotational inertia of the rotating portions of servo valve  101  (including servo rotor  120 , servo tips  124 , servo shaft  126 ) causes servo rotor  120  to continue to rotate, to coast, servo rotor  120  towards the edge of travel zone  160 . Here, the rotary valve position of servo valve  101  changes, albeit at a slower rate than the opening portion of the pulse event. When falling edge  207  is detected on digital voltage signal  205 , servo pulser  64  initiates second acceleration event  241 , causing another current spike  331  in motor current  330 , and causing servo rotor  120  to further rotate away from starting point  161  at a higher speed towards the end of sweep zone  158 , and causes servo tips  124  to sweep over servo holes  171 , first partially obstructing them and then onto fully obstructing them to fully close servo valve  101 , thus ending pulse  200 . Prior to the end of pulse  200 , and slightly before the end of the required rotation, servo pulser  64  may enter into deceleration event  243 , to cause servo rotor  120  to decelerate as it approaches stop  156 , with the aim being to cause digits  125  to contact stop  156  at the end of pulse  200  with a minimum amount of force, this creating a reasonably optimal pulse event where energy consumption is minimized and unnecessary impacts to the servo valve and stop surfaces are minimized or avoided. As shown in  FIG.  9   , servo rotor  120  then moves between starting and stopping points  161  and  162  in the reverse direction, as shown by it changing rotary valve position back from 90-degrees to 0-degrees. During this rotation in the reverse direction, a second pulse  200  is created. 
       FIG.  10    details the behavior of an embodiment of the current invention as it pertains to the operation of servo valve  101  in situations in which servo rotor  120  of servo valve  101  moves in one direction to open servo holes  171  by rotating servo tips  124  from fully closing servo holes  171  to fully open servo holes  171 . This action begins in closed state  231  and is followed by acceleration event  241  upon the reception of rising edge  206  of digital voltage signal  205 . Current spike  331  in motor current  330  reflects power being applied to motor  238 , followed by falling current  332 . This acceleration causes servo rotor  120  to rotate to its open position  232  where servo tips  124  are in travel zone  160  in which servo holes  171  are not obstructed, starting pulse  200 . Servo pulser  64  may enter into deceleration event  243  prior to the full entry of servo tips  124  into travel zone  160  so as to cause the servo rotor  120  to stop rotation inside travel zone  160 . Servo rotor  120  then enters intermediate stop phase  244  where motor  238  is not energized (current  330  flowing through the motor is zero), and motor  238  may be held in a brake state so as to stop its further rotation, this action being shows by the rotary valve position being steady and unchanging. Dwell time  203  is the period of time for which servo tips  124  are at rest and not obstructing servo holes  171 ; dwell time  203  thus enlarges pulse width  201 . When falling edge  207  is detected on digital voltage signal  205 , servo pulser  64  initiates a second acceleration event  241 , causing current spike  331  in motor current  330 , followed by falling current  332 , and causing servo rotor  120  to further rotate away from starting point  161  at a higher speed towards the end of sweep zone  158 , and causes servo tips  124  to sweep over servo holes  171 , first partially obstructing them and then onto fully obstructing them to fully close servo valve  101 , thus ending pulse  200 . Prior to the end of pulse  200 , and slightly before the end of the required rotation to fully close servo valve  101 , servo pulser  64  may enter into deceleration event  243 , to cause servo rotor  120  to decelerate as it approaches stop  156 , with the aim being to cause digits  125  to contact stop  156  at the end of pulse  200  with a minimum amount of force, this creating a reasonably optimal pulse event where energy consumption is minimized and unnecessary impacts to the servo valve and stop surfaces are minimized or avoided. As shown in  FIG.  10   , servo rotor  120  then moves between starting and stopping points  161  and  162  in the reverse direction, with the same or other dwell time  203  as shown by it changing rotary valve position back from 90-degrees to 0-degrees. During this rotation in the reverse direction, a second pulse  200  is created. In this embodiment, the act of stopping the rotation of the servo in the middle of a single sweep or pulse event may require up to two acceleration and two deceleration events, and may result in higher power consumption when compared to modes that utilize no coasting or stopping, but may enable proper pulse generation and required valve motion control in geometries where the travel zones inside the swept zones are narrow or just sufficient to retain the servo tips in the travel zone, thereby allowing servo pulser diameters while allowing the use of larger servo tips and servo holes. 
     In an embodiment, rotor  120  oscillates between stopping points  162  in alternating clockwise and counterclockwise sweeps  210 . Each sweep  210  in a given direction creates one full pulse  200 . Thus, each sweep  210  starts with servo pulser  64  in closed state  231 , with servo tips  124  at rest and fully obstructing servo holes  171 . Sweep  210  then passes through servo pulser  64  being in open state  232 , with servo tips  124  at rest or in motion, and not obstructing servo holes  171 . Sweep  210  then ends with servo pulser  64  back in closed state  231 , with servo tips  124  at rest and fully obstructing servo holes  171 . Sweep  201  may have a characteristic sweep rate  212 , being the number of sweeps  210  in a unit time, ordinarily per second, as well as sweep time  213  being the time to complete one sweep  210 . 
     In an embodiment, pulse rate  204  of servo pulser  64  is the same or substantially the same as sweep rate  212 . That is, servo pulser  64  creates one full pulse  200  in one sweep  210  of rotor  120 . In this embodiment, sweep time  213  also correlates to the time period required to complete one pulse (not pulse width  201 ). 
     In an embodiment, each sweep  210  in a given direction creates one full pulse  200 . Each sweep  210  starts with rotor  120  at one of stopping points  162 , with drilling fluid  66  at in low pressure state  221  indicating 0-signal  226 , then drilling fluid  66  passing through pressure rise transition  222 , then reaching high pressure state  223  indicating 1-signal  227 , remaining at that pressure for pulse width  201 , then drilling fluid  66  passing through pressure drop transition  224 , then drilling fluid  66  returning to high pressure state  221  indicating 0-signal  226 . 
     In an embodiment, rotor  120  oscillates between stopping points  162  in alternating clockwise/counterclockwise sweeps  210 . Each sweep  210  in a given direction creates one full pulse, in a 0-signal-1-signal-0-signal progression ( 226 - 227 - 226 ) (or 0-1-0 progression  228 ). In an embodiment, servo pulser  64  creates a full pulse  200 , rotor  120  beginning at a CCW stop  156  and rotating in a clockwise direction in 0-1-0 progression  228  and ending at CW stop  156 . Then servo pulser  64  creates another full pulse  200 , rotor  120  beginning at the CW stop  156  and rotating in a counterclockwise direction in 0-1-0 progression  228  and ending at the CCW stop  156 . 
     In an embodiment, rotor  120  oscillates clockwise and then counterclockwise to create two consecutive pulses  200 , in a 0-1-0-1-0 progression  229 , beginning at the CCW stop  156  and rotating in a clockwise direction to the CW stop  156 , then rotating in a counterclockwise direction from the CW stop  156  to the CCW stop  156 . 
     In an embodiment with an intermediate stop, rotor  120  of servo pulser  64  oscillates between stopping points  162  in alternating clockwise/counterclockwise sweeps  210  with intermediate stop  244  (between stopping points  156 ) with servo pulser  64  in open state  232 . Each sweep  210  in a given direction creates one full pulse  200 . Each sweep  210  starts with electric motor  328  driving servo shaft  126 , accelerating rotor  120  (acceleration  241 ) from closed state  231  of servo pulser  64  (servo tips  124  at rest and fully obstructing servo holes  171 ) towards servo pulser  64  being in open state  232 . Then, after an optional coasting event  242 , electric motor  328  then decelerates rotor  120  (deceleration  243 ) so that it stops for dwell time  203  with servo pulser  64  in open state  232  (servo tips  124  not obstructing servo holes  171 ), creating pulse width  201  of pulse  200 . Then electric motor  328  accelerates  241  rotor  120  from open state  232  (in the same direction as the previous acceleration  241 ) towards servo pulser being in closed state  231 . Then, after an optional coasting  242 , electric motor  238  decelerates  243  rotor  120  so that it stops with servo pulser  64  in closed state  231  (servo tips  124  at rest and fully obstructing servo holes  171 ). Each sweep  210  is through sweep arc  159  of at or about 90 degrees and each such arc may include two acceleration events  241  and deceleration events  243 . Dwell time  203  exists between first deceleration event  243  and second acceleration event  241 , and coasting event  242  is, optionally, between acceleration events  241  and then deceleration events  243 . 
     In an embodiment with no intermediate stop, rotor  120  of servo pulser  64  oscillates between stopping points  156  in alternating clockwise/counterclockwise sweeps  210  with no intermediate stop between stopping points  156 . Each sweep  210  in a given direction creates one full pulse  200 . Each sweep  210  starts with electric motor  238  driving servo shaft  126 , accelerating  241  rotor  120  from closed state  231  toward servo pulser being in open state  232 . Then, after an optional coasting event  242 , electric motor  328  then optionally decelerates  243  rotor  120  to extend the time for which servo pulser  64  is in open state  232 , creating pulse width  201  of pulse  200 . Then electric motor  328  optionally accelerates  241  rotor  120  (in the same direction as the previous acceleration  241 ) toward servo pulser  64  being in a closed state  231 . Then, after an optional coasting event  242 , electric motor  328  decelerates  243  rotor  120  so that it stops with servo pulser  64  in closed state  231 . Each sweep  210  is through sweep arc  159  of at or about 90 degrees and each such arc includes at least one acceleration event  241  and at least one deceleration event  243  and may include two of each. Any coasting event  242  exists, optionally, between acceleration event  241  and then deceleration event  243 , and between deceleration event  243  and acceleration event  241 . 
     Turning to  FIG.  11   , in an embodiment, a microcontroller in servo pulser  64  carries out feedback/decision loop  400  between hyraulic pulses (and sweeps) to determine how fast or slow it should drive servo rotor  120 , including if it should carry out an intermediate stop or carry out a coasting operation. Feedback/decision loop  400  computes and executes the desired velocity/acceleration, coasting or dwell profile, having received and/or calculated the time required to move the rotating portion of the valve, and other information on one or more previous pulses, such as sweep time  213 , digital pulse width  201 , applied current. 
     Loop  400  includes initiating pulse command  402 , followed by slow/fast evaluation step  406  in which saved sweep time  213  (from the last pulse) is compared to digital pulse width  201  (from the last pulse). If sweep time  213  is not greater, then the valve closed faster than commanded, leading to coast mode check  410 . If coast mode is off, then commands are issued to motor  328  to carry out an acceleration event  241  to drive servo rotor  120  to intermediate stop  244  in travel zone  160 . Following that stop, pulse end check  416  checks if it is time to complete the pulse, e.g. if sufficient dwell time  203  has now elapsed that servo rotor  120  should be moved to the final position at stopping point  162 . If the answer is no, it loops back to pulse end check  416  until it answers yes; if the answer is yes, final position order  420  causes the commands to be issued to carry out an acceleration event  241  to drive motor  328  to drive servo rotor  120  to stopping point  162 , including an optional deceleration  243 . If coast mode is on, then coasting process step  426  causes coasting event  242  to be carried out across servo holes  171  in place of intermediate stop  244  described above. If sweep time  213  is greater, then the valve closed more slowly than commanded, leading to the close fast command  430 . In this case servo rotor  120  is commanded to move continuously between starting and stopping points  161  and  162  without any coasting, braking or stops. Thus, commands are issued to carry out an acceleration event  241  to drive motor  328  to drive servo rotor  120  to directly to stopping point  162  using a high or max current to motor  328 . Following each of steps  420 ,  426 , and  430 , sweep time  213  and digital pulse width  201  are saved for use in the next pulse in save data step  436 . Then, in reversal step  438 , the direction of the next pulse is set to the opposite direction of the current pulse. Then, in waiting step  440 , the system delays until the next pulse is initiated, leading back to step  402 . Thus, the system uses an algorithmic feedback loop to control the speed and timings of the servo valve.