CA2848031A1

CA2848031A1 - Method for controlling an artificial lifting system and an artificial lifting system employing same

Info

Publication number: CA2848031A1
Application number: CA2848031A
Authority: CA
Inventors: Kevin Dancek
Original assignee: Tundra Process Solutions Ltd
Current assignee: SSI Lift CDA 2019 Ltd
Priority date: 2014-04-07
Filing date: 2014-04-07
Publication date: 2015-10-07
Anticipated expiration: 2034-04-07
Also published as: CA2848031C

Abstract

An artificial lifting system is disclosed. The artificial lifting system comprises an elongated cylinder fixed to a base or ground. The elongated cylinder receives a piston rod axially movable therein. The piston rod engages a downhole rod pump for driving the rod pump reciprocating uphole and downhole to pump downhole fluid to the surface. A control unit controls the axial movement of the piston rod, and automatically adjust the system operation to adapt to drift of the top and bottom stop positions of the piston rod. In an alternative embodiment, the system further comprises a dump valve controlled by the control unit to prevent over-stroke. In another embodiment, the system further comprises a chemical injection unit for injecting treatment fluid to a wellbore under the control of the control unit.

Description

2 ARTIFICIAL LIFTING SYSTEM EMPLOYING SAME

3

4 FIELD
The present invention relates generally to an artificial lifting system, 6 and in particular to a method for automatically controlling an artificial lifting system 7 to ensure its operation within a defined range of stroke and an artificial lifting system 8 employing the same.

BACKGROUND
11 Artificial lifting systems for pumping downhole fluids such as crude oil 12 or water, from a production well to the surface have been widely used in oil and gas 13 industry. Existing artificial lifting systems include rod pumps, Electric Submersible 14 Pumps (ESPs), Gas lift systems, Progressing Cavity Pumps (PCPs) and Hydraulic pumps.
16 Rod pumps generally comprises a sucker rod connecting to a 17 subsurface pump, and a driver system coupled to the sucker rod for driving the 18 sucker rod in a reciprocating motion for pumping downhole fluids to the surface. For 19 example, traditional pumpjacks or horsehead pumps comprises a prime mover such as an electric motor or gas engine, which drives a set of gears to reduce the speed.
21 The gears drive a pair of cranks, and the cranks in turn raise and lower one end of a 22 beam having a "horse head" on the other end thereof. A steel cable, i.e., a bridle, 23 connects the horse head to a downhole pump via a polished rod and sucker rods.
24 The reciprocating up and down movement of the horse head then drives the 1 downhole pump reciprocating between a fully retracted position and a fully extended 2 position to pump the downhole fluid to the surface. The distance between the fully 3 retracted position and the fully extended position is called a stroke.
Generally, a 4 stroke maybe a down-stroke that resets the rod pump downhole to the fully retracted position, or an up-stroke that moves the rod pump uphole to the fully 6 extended position for pumping fluid to the surface.
7 Generally, long-strokes are preferable because, comparing to a rod 8 pump with shorter pump stroke, a rod pump with longer pump stroke requires 9 slower pumping speed for a given production rate, and therefore results in lower rod string stress and reduced power consumption.
11 The Sure Stroke IntelligentTM Lift System offered by Tundra Process 12 solutions of Calgary, Alberta, Canada, the assignee of the subject patent 13 application, uses a vertical hydraulic cylinder to drive a polished rod moving axially 14 up and down, which in turn drives the downhole pump via sucker rods to pump downhole fluid to the surface with long strokes, e.g., ranging from 168 inches to 360 16 inches based on models.
17 US Patent Number 8,562,308, entitled "Regenerative Hydraulic Lift 18 System", to Krug, et al., discloses a hydraulic cylinder assembly for a fluid pump 19 including a cylinder, a bearing attached to a about a first end of the cylinder, a rod slideably mounted within the bearing, and a piston located about an end of the rod 21 in the cylinder opposite the bearing. A central axis of the rod is offset from, and 22 parallel to, a centerline of the cylinder to impede a rotation of the piston about the 23 rod. The hydraulic cylinder assembly further includes a hydraulic motor fluidly 1 connected to the cylinder, the pump configured to provide a hydraulic pressure to 2 the cylinder during an up-stroke of the piston and rod and the pump further 3 configured to generate electricity on the down-stroke of the piston and rod.
4 US Patent Number 8,267,378, entitled "Triple Cylinder with Auxiliary Gas over Oil Accumulator", to Rosman, discloses a hydraulic lift system for artificial 6 lift pumping or industrial hoisting comprising a three chamber cylinder, a gas-over-7 oil accumulator, a large structural gas accumulator and a large flow pilot operated 8 check valve. A matrix variable frequency drive, a standard variable frequency drive, 9 an electrical squirrel cage motor or a natural gas engines are part of the main prime mover alternatives.
11 In above systems, a movable rod or plunger moves axially in a 12 vertically oriented cylinder to drive the downhole rod pump for pumping fluid to the 13 surface with long strokes. The stroke, however, may drift in operation due to change 14 of environmental factors, such as change of temperature, downhole pump load, and the like. Large safety margins are usually applied to a top and bottom limit to such a 16 stroke to avoid damage the cylinder and wellhead. Safety margins result in reduced 17 stroke and reduced pumping effectiveness. Moreover, operators are thus required 18 to regularly check the travel of the plunger, and reset top and bottom safety 19 margins, causing burden to operators.
It is therefore an object to provide a novel method of automatically 21 controlling an artificial lifting system to ensure its operation within a defined stroke 22 range and an artificial lifting system employing same.

2 According to one aspect of this disclosure, there is provided a lifting 3 system for lifting downhole fluid from a downhole rod pump in a wellbore to surface, 4 comprising: a linear actuator comprising a movable component moveable between a first and a second limit and driveably coupled to the downhole rod pump; a power 6 unit coupled to said linear actuator for driving said movable component to 7 reciprocate; the reciprocating of said movable component driving said downhole rod 8 pump to pump downhole fluid to the surface; a sensor for detecting the position of 9 said movable component; and a control unit coupled to said sensor and said power unit for controlling the power unit for reciprocating said movable component 11 between a first target stop position and a second target stop position, for moving 12 said movable component uphole to stop at about said first target stop position, and 13 for moving said movable component downhole to stop at about said second target 14 stop position; determining, based on the position information received from said sensor, a first actual stop position and a second actual stop position;
determining a 16 first drift being the difference between the first actual stop position and the first 17 target stop position, and a second drift being the difference between the second 18 actual stop position and the second target stop position; and at the control unit, 19 automatically controlling the operation of the power unit to minimize the first and second drifts.
21 According to another aspect of this disclosure, said control unit stores 22 a predefined first deceleration position at which deceleration of the said movable 23 component commences during the movement thereof towards said first target stop 1 position, and stores a predefined second deceleration position at which deceleration 2 of said movable component is commenced during the movement thereof towards 3 said second target stop position; and wherein said automatically adjusting the 4 operation of the power unit comprises: adjusting the position of the first deceleration position based on the first drift; adjusting the position of the second deceleration 6 position based on the second drift; and adjusting the operation of the power unit to 7 decelerate said movable component at the adjusted first deceleration position 8 during the movement thereof towards said first target stop position, and to 9 decelerate said movable component at the adjusted second deceleration position during the movement thereof towards said second target stop position.
11 According to another aspect of this disclosure, the adjusted first 12 deceleration position is the difference between said predefined first deceleration 13 position and said first drift, and said adjusted second deceleration position is the 14 difference between said predefined second deceleration position and said second drift.
16 According to another aspect of this disclosure, the linear actuator 17 comprises: a hollow cylinder receiving a piston rod axially movable therein; and at 18 least a first chamber for receiving a power medium; the intake of the power medium 19 into said first chamber driving said piston rod moving towards the first stop position.
According to another aspect of this disclosure, the power medium is a 21 power fluid; and wherein said power unit is a hydraulic power unit comprising a 22 hydraulic motor and a power fluid reservoir storing said power fluid, said hydraulic

5 1 motor sending said power fluid, via a set of conduits, into and out of said first 2 chamber for driving said piston rod to reciprocate in said cylinder.
3 According to another aspect of this disclosure, said a set of conduits 4 comprises a conduit branch connected to said power fluid reservoir via a normally-closed valve, and said control unit is further controllably coupled to said valve for

6 determining whether the position of said piston rod, during the movement towards

7 said first target stop position, is beyond a first limit, said first limit is further from said

8 first target stop position along the direction of said movement towards said first

9 target stop position; and opening said valve for flowing the power fluid in said a set of conduits into said power fluid reservoir via said conduit branch and said valve.
11 According to another aspect of this disclosure, the control unit of the 12 lifting system further controls said power unit to initialize the operation of the lifting 13 system through a first initialization stage by: determining an initial first stop position 14 and an initial second stop position about the mid-point of the target top and bottom stop positions, the distance between the initial first stop position and the initial 16 second stop position is a predefined percentage of the distance between the first 17 and second target stop positions; and moving the movable component to one of the 18 initial first and second stop positions to reciprocate the movable component for at 19 least one reciprocating cycle, wherein in each of said at least one reciprocating cycle in the first initialization stage, said control unit controls said power unit to 21 expand the first and second stop positions toward the first and second target stop 22 positions, respectively, by a first expansion step value.

According to another aspect of this disclosure, during said first initialization stage, said control unit controls said power unit to reciprocate the movable component until the distance between the first and second stop positions 4 and the first and second target stop positions, respectively, is smaller than said first expansion step value.

According to another aspect of this disclosure, said control unit further controls said power unit to initialize the operation of the lifting system through a second initialization stage by: reciprocating the movable component for at least one reciprocating cycle, wherein in each of said at least one reciprocating cycle in the second initialization stage, said control unit controls said power unit to expand the first and second stop positions toward the first and second target stop positions, 12 respectively, by a second expansion step value.

According to another aspect of this disclosure, said first and second 14 expansion step values are second predefined values.
According to another aspect of this disclosure, during said second initialization stage, said control unit controls said power unit to reciprocate the movable component until the distance between the first and second stop positions 18 and the first and second target stop positions, respectively, is smaller than said 19 second expansion step value.
According to another aspect of this disclosure, said control unit controls said power unit to move the movable component towards the first target stop position at a first speed and to move the movable component towards the second target stop position at a second speed; and wherein said control unit 1 receives a command from an operator indicating the change of at least one of the 2 first and the second speeds, and in response to said command, re-initializes the 3 operation of the lifting system by: determining an initial first stop position if the first 4 speed is changed, said initial first stop position being intermediate to the first and second target stop positions with a distance to the first target stop position of 6 (1 - Ci) SN / 2, wherein SN is the distance between the first and second target stop 7 positions and Ci is a predefined percentage; determining an initial second stop 8 position if the second speed is changed, said initial second stop position being 9 intermediate to the first and second target stop positions with a distance to the second target stop position of (1 - Ci) SN / 2; determining at least a first expansion 11 step value; determining at least a first number p of reciprocating cycles 12 corresponding to said first expansion step value; and reciprocating the movable 13 component for p reciprocating cycles, wherein in the first cycle of the p 14 reciprocating cycles, said control unit controls said power unit to move the movable component to the initial first stop position if the first speed is changed;
move the 16 movable component to the initial second stop position if the second speed is 17 changed; and in the next (p - 1) reciprocating cycles, said control unit controls said 18 power unit to expand the first stop position toward the first target stop position by 19 the first expansion step value if the first speed is changed; and expand the second stop position toward the second target stop position by the first expansion step 21 value if the second speed is changed.
22 According to another aspect of this disclosure, said control unit re-23 initializes the operation of the lifting system by further: determining a second 1 expansion step value; determining a second number q of reciprocating cycles 2 corresponding to said second expansion step value; and after said p reciprocating 3 cycles are completed, reciprocating the movable component for q reciprocating 4 cycles, wherein in each of the q reciprocating cycles, said control unit controls said power unit to expand the first stop position toward the first target stop position by 6 the first expansion step value if the first speed is changed; and expand the second 7 stop position toward the second target stop position by the first expansion step 8 value if the second speed is changed.
9 According to another aspect of this disclosure, the lifting system further comprises a chemical injection assembly coupled to said control unit and the 11 wellbore; wherein said control unit enables said chemical injection assembly when 12 said lifting system is in operation, and disables said chemical injection assembly 13 when the operation of said lifting system is stopped.
14 According to another aspect of this disclosure, there is provided a method for lifting downhole fluid from a reciprocating downhole fluid lifting device to 16 surface, comprising: setting up a first and a second target stop position;
17 reciprocating a movable component of a linear actuator between said first and 18 second target stop positions for driving the downhole fluid lifting device; determining 19 a first actual stop position corresponding to said first target stop position and a second actual stop position corresponding to said second target stop position;
21 determining a first drift being the difference between the first actual stop position 22 and the first target stop position, and a second drift being the difference between 23 the second actual stop position and the second target stop position; and 1 automatically adjusting the reciprocating of the movable component to minimize for 2 the first and second drifts.
3 According to another aspect of this disclosure, said automatically 4 adjusting the reciprocating of the movable component comprises:
determining a first deceleration position based on the first drift; determining a second deceleration 6 position based on the second drift; and decelerating said movable component at the 7 first deceleration position during the movement thereof towards said first target stop 8 position, and decelerating said movable component at the second deceleration 9 position during the movement thereof towards said second target stop position.
According to another aspect of this disclosure, said determining a first 11 deceleration position comprises: calculating the first deceleration position as the 12 difference between a predefined first deceleration position and said first drift; and 13 calculating the second deceleration position as the difference between a predefined 14 second deceleration position and said second drift.
According to another aspect of this disclosure, said reciprocating a 16 movable component of a linear actuator comprises: sending a power fluid into a 17 chamber coupled to said movable component to move the movable component 18 towards the first target stop position.
19 According to another aspect of this disclosure, said reciprocating a movable component of a linear actuator further comprises: determining whether the 21 position of said movable component, during the movement towards said first target 22 stop position, is beyond a first limit, said first limit being further from said first target 1 stop position along the direction of said movement towards said first target stop 2 position; and preventing the power fluid from entering into said chamber.
3 According to another aspect of this disclosure, the method further 4 comprising an initialization process, comprising: determining an initial first stop position and an initial second stop position about the mid-point of the target top and 6 bottom stop positions, the distance between the initial first stop position and the 7 initial second stop position is a predefined percentage of the distance between the 8 first and second target stop positions; moving the movable component to one of the 9 initial first and second stop positions to reciprocate the movable component for n reciprocating cycle(s), wherein n ? 1, and in each of the n reciprocating cycle(s), 11 said control unit controls said power unit to expand the first and second stop 12 positions toward the first and second target stop positions, respectively, by the first 13 expansion step value; and when the distance between the first and second stop 14 positions and the first and second target stop positions, respectively, is smaller than said first expansion step value, reciprocating the movable component for m 16 reciprocating cycle(s), wherein m ?. 1, and in each of the m reciprocating cycle(s), 17 said control unit controls said power unit to expand the first and second stop 18 positions toward the first and second target stop positions, respectively, by a 19 second expansion step value.

Figure 1A is a schematic, partial cross-sectional, side view of a 3 hydraulically-actuated rod pump system according to an embodiment of this 4 disclosure;
Figure 1B is a schematic, partial cross-sectional, side view of the 6 hydraulically-actuated rod pump system of Fig. 1A in a fully extended position;

Figure 1C is a schematic diagram of the hydraulically-actuated rod 8 pump system of Fig. 1A showing the interconnection of components therebetween;

Figure 2A is schematic cross-sectional view of the hydraulically-actuated rod pump system of Fig. 1A during an up-stroke;

Figure 2B is schematic cross-sectional view of the hydraulically-12 actuated rod pump system of Fig. 1A during a down-stroke;

Figures 3A and 3B illustrates the piston rod position parameters used 14 by the hydraulically-actuated rod pump system of Fig. 1A;
Figure 4A is a flowchart showing a process of operating the hydraulically-actuated rod pump system of Fig. 1A, performed by the control unit in 17 the automatic adjusting mode;

Figures 4B and 4C illustrate the hydraulically-actuated rod pump system of Fig. 1A during the determination of the top and bottom operation limits HOT and HOB;
21 Figure 5 shows an example of the initialization process;

Figure 6 shows the detailed steps for adjusting the top and bottom 23 deceleration positions PDT and PDB;

1 Figures 7A and 7B illustrate the adjustment of the top deceleration 2 position PDT following the steps of Fig. 6;
3 Figures 8A and 8B illustrate the adjustment of the bottom deceleration 4 position PDT following the steps of Fig. 6;
Figure 9 shows an example of the re-initialization process when, after 6 k stroke cycles, the up-stroke speed VU is changed by a user but the down-stroke 7 speed VD is unchanged;
8 Figure 10 shows an example of the re-initialization process when, 9 after k stroke cycles, the down-stroke speed VD is changed by a user but the up-stroke speed VU is unchanged;
11 Figure 11 shows an example of the re-initialization process when, 12 after k stroke cycles, both the up-stroke speed VU and the down-stroke speed VD
13 are changed by a user;
14 Figure 12 shows an example of a GUI displayed on the touch-sensitive screen for users to select between the automatic adjusting mode and the 16 manual adjusting mode, and to input system parameters;
17 Figure 13 shows an example of a GUI displayed on the touch-18 sensitive screen for entering a value;
19 Figure 14 is a simplified schematic diagram of the hydraulically-actuated rod pump system, according to an alternative embodiment;
21 Figure 15 is a flowchart showing a process of operating the 22 hydraulically-actuated rod pump system of Fig. 14, performed by the control unit;

1 Figure 16 shows an example of a GUI display on the touch-sensitive 2 screen for an administrator to enter a top-dump-valve-activation height Hy; and 3 Figure 17 shows a simplified schematic diagram of a chemical 4 injection unit used in the hydraulically-actuated rod pump system, according to another embodiment.

Turning now to Figs. 1A and 1B, a hydraulically-actuated rod pump system is shown and is generally identified by the numeral 100. The hydraulically-actuated rod pump system 100 comprises a vertically oriented jacking actuator mounted or otherwise installed on a base 104. The jacking actuator 102 comprises 6 a vertically oriented, elongated hydraulic cylinder 106, which receives a piston rod axially movable therewithin. A pulley assembly 112 having one or more 8 rotatable wheels is rotatably mounted to the top end 110 of the piston rod 108.

set of cable 114 engages the wheels of the pulley assembly 112 about the upper radial section thereof. One end 116 of the cable 114 is connected 11 to the base 104, and the other end 118 thereof is connected to a carrier bar 120, hanging under the pulley assembly 112. A sucker rod 122 is connected to the carrier bar 120 at one end, and connected at the other end a downhole pump 124 14 via a wellhead 126.
A hydraulic power unit 128 is connected to the hydraulic cylinder 106 16 via a set of conduits (not shown). The hydraulic power unit 128 comprises a power fluid reservoir (not shown) and a hydraulic motor (not shown) for pumping the power fluid from the power fluid reservoir into the hydraulic cylinder 106 to drive the piston 19 rod 108 to reciprocate up and down. A position sensor (not shown), such as a position sensor manufactured by Celesco of Chatsworth, CA, U.S.A., is mounted in 21 the hydraulic cylinder 106 adjacent the piston rod 108 for measuring the position of 22 the piston rod 108. Those skilled in the art appreciate that, in some alternative embodiments, other position sensors may be used. For example, in an alternative 1 embodiment, a linear encoder may be used to monitor the cable 114 for determining 2 the position of the piston rod 108. In another embodiment, a rotary encoder may be 3 used for monitoring the rotation of the wheels of the pulley assembly 112 for 4 determining the position of the piston rod 108.
An electrical unit 130 comprising an electrical power supply 132 and a 6 control unit 134 provides electrical power to all necessary components, and controls 7 the operation of the hydraulically-actuated rod pump system 100. A gas vessel 136 8 containing a suitable type of pressurized gas, such as pressurized nitrogen, is 9 coupled to the hydraulic cylinder 106 via a set of conduits (not shown) for providing counterbalance to downhole components during operation.
11 Fig. 2A shows a schematic cross-sectional view of the hydraulically-12 actuated rod pump system 100 in operation during an up-stroke. For ease of 13 illustration, only the hydraulic cylinder 106, piston rod 108, hydraulic power unit 128 14 and gas vessel 136 are shown.
As shown, the piston rod 108 has a top wall 202, a hollow cylinder 16 body 204 with a diameter smaller than that of the hydraulic cylinder 106, and an 17 radially extended piston 206 as the bottom wall thereof and sealably engaging the 18 inner wall of the hydraulic cylinder 106. The top wall 202, hollow cylinder body 204 19 and the piston 206 thus forms an up chamber 208 for lifting the piston rod 108. The piston 206 also divides the hydraulic cylinder 106 into an upper portion forming a 21 down chamber 210, and a lower portion forming a counterbalance gas chamber 22 212.

1 The piston 206 of the piston rod 108 comprise an opening receiving 2 an up chamber inlet 220, which connects the up chamber 208 to the hydraulic 3 power unit 128 via up-flow conduits 222.
4 The down chamber 210 of the hydraulic cylinder 106 comprises a down chamber inlet 224, connecting the down chamber 210 to the hydraulic power 6 unit 128 via down-flow conduits 226.
7 The counterbalance gas chamber 212 comprises a gas inlet 228, connecting the counterbalance gas chamber 212 to the gas reservoir 136 via gas 9 conduits 230.
More detail of the hydraulically-actuated rod pump system 100 can be seen from Fig. 1C, which shows the interconnection of various components thereof.

detailed description of the working mechanism of the hydraulically-actuated rod pump may be found in U.S. Patent Number 4,801,126, entitled "Hydraulically Operated Lift Mechanism" to Rosman, issued on Jan. 31, 1989. Generally, in operation, the hydraulic motor alternatively pumps power fluid into the up chamber and the down chamber 210. In particular, during an up-stroke, the hydraulic motor pumps power fluid from the power fluid reservoir into the up chamber 208 via 18 the up-flow conduits 222, as indicated by the arrow 252, to lift the piston rod 108 as indicated by the arrow 254. The power fluid in the down chamber 210 flows back to the power fluid reservoir via the down-flow conduits 226, as indicated by the arrow 21 256.
22 As shown in Fig. 2B, during a down-stroke, the hydraulic motor pumps power fluid from the power fluid reservoir into the down chamber 210 via the down-1 flow conduits 226, as indicated by the arrow 262, to lower the piston rod 108 as 2 indicted by the arrow 264. The power fluid in the up chamber 208 flows back to the 3 power fluid reservoir via the up-flow conduits 222, as indicated by the arrow 266.
4 During the down-stroke, the gas in the counterbalance gas chamber 212 is compressed, which provides weight counterbalance to the piston rod 108 to prevent 6 it from abruptly falling down.
7 Referring back to Figs. 1A and 1B, the hydraulic power unit 128 drives 8 the piston rod 108 to reciprocate up and down. As shown in Figs. 1A and 2A, during 9 an up-stroke, the piston rod 108 is moving up as indicated by the arrow 138, raising the pulley assembly 112 mounted thereon. As the end 116 of the cable 114 is fixed 11 to the base 104, the wheels of the raising pulley assembly 112 also rotates counter-12 clockwise as indicated by the arrow 140, pulling up the cable 114 and the carrier bar 13 120, and lifting the sucker rod 122 and the downhole pump 124 to pump fluid to the 14 surface, as indicated by the arrow 142.
As shown in Figs. 1B and 2B, during a down-stroke, the piston rod 16 108 is moving down as indicated by the arrow 144, lowering the pulley assembly 17 112 mounted thereon. As the end 116 of the cable 114 is fixed to the base 104, the 18 weight of the sucker rod 122, downhole pump 124 and liquid therein causes the 19 wheels of the pulley assembly 112 to rotate clockwise as indicated by the arrow 146, pulls down the cable 114, the carrier bar 120, and moves the sucker rod 21 and the downhole pump 124 to a downhole position ready for lifting fluid to surface 22 in the subsequent up-stroke, as indicated by the arrow 148.

1 In this embodiment, the control unit 134 in the electrical unit 130, implemented as a Programmable Logic Controller (PLC) having a microprocessor, a memory, input/output interface and necessary circuitry, controls the operation of the hydraulically-actuated rod pump system 100 to reciprocate the piston rod 108 up and down for pumping fluid to the surface.
6 The control unit 134 stores a predefined top safety limit Hsi representing a top limit that the piston rod 108 may be safely extended thereto, and 8 a predefined bottom safety limit HSB representing a bottom limit that the piston rod may be safely lowered thereto, both determined during manufacturing of system 100 and are not user-adjustable. Generally, for safety reasons, the top safety limit HST is lower than the physical top limit that the piston rod 108 can be extended thereto, and the bottom safety limit HSB is higher than the physical bottom 13 limit that the piston rod 108 can be lowered thereto.
14 The control unit 134 also stores a set of predefined piston rod up-stroke speeds and down-stroke speeds determined during manufacturing of system 100, at which the piston rod 108 may move during an up-stroke and a down-stroke, respectively. For example, in this embodiment, seven (7) up-stroke speeds and seven (7) down-stroke speeds are predefined and stored in the memory of the control unit 134. As will be described in more detail later, the up-stroke speed and the desired down-stroke speed may be independently set up by a user as required.

Figs. 3A and 3B illustrates the piston rod position parameters used by 22 the hydraulically-actuated rod pump system 100. For the ease of illustration, Figs.

and 3B only shows the base 104, hydraulic cylinder 106 and the piston rod 108, 1 all drawn in solid lines. The dashed lines illustrate a previous position of the piston 2 rod 108.
3 As shown, during operation, the control unit 134 generally operates 4 the piston rod 108 at a user-selected up-stroke speed VU and a user-selected down-stroke VD, between a user-selected top operation limit HOT lower than the top safety 6 limit HST, i.e., HOT < HST, and a user-selected bottom operation limit HOB higher than 7 the bottom safety limit HSB, i.e., HOB > HSB. The stroke length S of an up- or down-8 stroke is then 9 S = HOT ¨ HOB.
However, as will be described later, the actual top and bottom stop positions PSI
11 and PSB of the piston rod 108 may be different than HOT and HOB, respectively, 12 causing the actual stroke length S to vary normally within a relatively small range.
13 The control unit 134 calculates a top deceleration position PDT
based 14 on the up-stroke speed VU, the top operation limit HOT and a predefined up-stroke deceleration rate, and calculates a bottom deceleration position PDB based on the 16 down-stroke speed VD, the bottom operation limit HOB and a predefined down-stroke 17 deceleration rate.
18 During an up-stroke, the control unit 134 controls the hydraulic power 19 unit 128 to move the piston rod 108 upward at the up-stroke speed VU.
When the piston rod 108 reaches the top deceleration position PDT, the control unit 134 21 controls the hydraulic power unit 128 to decelerate the piston rod 108 to stop the 22 piston rod 108 about the top operation limit HOT.

1 Similarly, during a down-stroke, the control unit 134 controls the 2 hydraulic power unit 128 to move the piston rod 108 downward at the down-stroke 3 speed VD. When the piston rod 108 reaches the bottom deceleration position PDB, 4 the control unit 134 controls the hydraulic power unit 128 to decelerate the piston rod 108 to stop the piston rod 108 about the bottom operation limit HOB.
6 Although it is generally desirable to consistently and repeatedly stop 7 the piston rod 108 at the top operation limit HOT during an up-stroke, and to stop the 8 piston rod 108 at the bottom operation limit HOB during a down-stroke, the actual top 9 and bottom stop positions PST and PSB of the piston rod 108, respectively, may drift from the top and bottom operation limits HOT and HOB due to the change of 11 operational factors including the environmental temperature and the load of the 12 downhole pump.
13 In this embodiment, the control unit 134 provides a manual adjusting 14 mode for users to manually adapt to top and bottom stop position drift, and an automatic adjusting mode for automatically adapting to top and bottom stop position 16 drift. In the manual operation mode, a user has to observe any top or bottom 17 position drift and manually adjust top and bottom deceleration positions PDT and 18 PDB. For example, if the actual top stop position PST is higher than the top operation 19 limit HOT, then one can lower the top deceleration position PDT. When the user need to change the up-stroke and/or down-stroke speed VU and VD, the user has to first 21 manually set up new top and/or bottom deceleration positions PDT and PDB
based 22 on the new up-stroke and/or down-stroke speed VU and VD, and then change Vu 23 and/or VD.

1 In the automatic adjusting mode, the control unit 134 detects the actual top and bottom stop positions PST and PSB, and automatically adjusts the system operation to minimize detected drift to ensure that the piston rod stops about 4 the top and bottom operation limits HOT and HOB within an allowable range.
Fig. 4A is a flowchart showing a process 300 of operating the hydraulically-actuated rod pump system 100 performed by the control unit 134 in 7 the automatic adjusting mode.
8 The process 300 starts (step 302) when the system 100 is first installed at a jobsite. After start, the control unit 134 first sets up required system parameters (step 304). In this embodiment, the control unit 134 comprises a touch-sensitive screen (not shown) and provides a graphic user interface (GUI) thereon 12 for users to input required system parameters, including the up-stroke and down-stroke speeds VU and VD and the top and bottom operation limits HOT and HOB.
The control unit 134 also provides a job mode to facilitate users to determine the top and bottom operation limits HOT and HOB.

Figs. 4B and 4C illustrate the system 100 during the determination of the top and bottom operation limits HOT and HOB. For ease of illustration, some 18 components of system 100 are omitted.

As shown in Fig. 4B, in the jog mode, the control unit 134 gradually lowers the piston rod 108 under the control of a special user such as a system administrator, to a lowest position suitable for normal operation. Such a lowest position is the piston rod position at which the downhole pump is moved to the furthest downhole position and at which the carrier bar 120 is adjacent to the wellhead 126 spaced by a suitable safe distance. Other conditions may also be applied in determining the lowest position. Generally, it is required that the lowest 3 position would not be lower than the bottom safety limit HsB.
4 The administrator then obtains a position reading from the position sensor (not shown) regarding the position of the piston rod 108 with respect to a predefined reference point, e.g., the top end of the hydraulic cylinder 106, the base 104, the ground or the like. The obtained position reading is used as the bottom 8 operation limit HOB.
9 As shown in Fig. 4C, the control unit 134 then gradually lifts the piston rod 108 under the control of the administrator, to a highest position suitable for normal operation. Such a highest position is the piston rod position at which the carrier bar 120 is adjacent to the pulley assembly 112 at a suitable safe distance 13 and the downhole pump is lifted to a highest position within its operation range.

Other conditions may also be applied in determining the highest position.
Generally, it is required that the highest position would not be higher than the top safety limit 16 HST.

The administrator then obtains a position reading from the position sensor (not shown) regarding the position of the piston rod 108 with respect to the predefined reference point. The obtained position reading is used as the top operation limit HOT.

Referring back to Fig. 4A, after setting up system parameters, the control unit 134 starts system operation (step 306). At this step, the control unit 134 first performs an initialization process to automatically control the system 100 to 1 initialize the up-stroke and down-stroke operation, and then enters normal operation 2 after the initialization is finished.
3 The purpose of initializing the up- and down-stroke operation is to 4 smoothly and safely adapt the system to the top and bottom operation limit HOT and HOB of the piston rod 108.
6 In one embodiment, the initialization process starts by operating the 7 piston rod 108 between an initial top stop position HT1 and initial bottom stop 8 position HB1 about the mid-point of the top and bottom operation limit HOT and HOB.
9 The stroke length is incrementally increased until reaching the operation limit HOT
and HOB. In an embodiment, the available differential stroke between the initial stop 11 positions HT1, HB1 and limit HOT and HOB can be divided into a known number of 12 incremental step values.
13 In this embodiment, the piston rod 108 is be operated with an 14 adequately small initial stroke length Si, i.e., Si = C1 SN, 16 where Si = HT1 ¨ HB1 is the initial stroke length, Ci is a predefined ratio, which in 17 this embodiment is Ci = 60%, and SN = HOT - HOB is the desired normal stroke 18 length. Therefore, the initial top stop position Firi is below the top operation limit HOT
19 with a distance of (1 - C1) SN / 2, and the initial bottom stop position HB1 is above the bottom operation limit HOB with a distance of (1 - C1) SN /2.
21 The control unit 134 then controls the piston rod 108 to reciprocate up 22 and down and, by adjusting the up- and down-stroke deceleration positions, 23 gradually expanding the stroke length. In this embodiment, the expansion of stroke 1 length may comprise a coarse expansion stage, at which the control unit 2 extends the top/bottom stop position towards Hor/HoB, respectively, in an up-/down-3 stroke by a relatively large extension step value AC, until no longer practical.
4 Thereafter, expansion of the stroke length occurs by a fine expansion stage, at which the control unit 134 extends the top/bottom stop position more carefully 6 towards HOT/HOB, in an up-/down-stroke by a relatively small extension step value 7 AF. In this embodiment, the step values are appropriate for dimensions typical of 8 rod pump operation, AC = 5 inches and AF = 1 inch. Of course, Ac, and AF
may take 9 other suitable values in alternative embodiments.
Figs. 5A and 5B show an example of the start or initialization process 11 306 of Fig. 4A. The control unit 134 first sets up the initial top and bottom stop 12 positions HT1 and HB1 (step 342), and calculates the number n of stroke cycles 13 required in a coarse-expansion stage, and the number m of stroke cycles required 14 in the fine expansion stage (step 344) based on a stage-transition stroke length ST
predefined as:
16 ST = SN - 2SF, 17 where SF is a predefined distance that the top/bottom stop position will be expanded 18 in the fine expansion stage, which in this embodiment is SF = 10 inches.
Therefore, 19 n and m are calculated as, respectively, n = (I-10T ¨ SF ¨ HT1) / AC;
21 m = SF / AF.
22 Those skilled in the art appreciate that the control unit 134 may adjust SF and HT1 to 23 ensure that n and m are integers.

1 At step 344, the control unit 134 also initialize a stroke cycling loop by setting an internal variable i to 1. Then the control unit 134 starts the first stroke cycle of the piston rod 108 between the initial top and bottom stop positions H-ri and 4 Hi (step 346).
As illustrated in Fig. 5B, in the first down-stroke Di, the control unit moves the piston rod 108 to the initial bottom stop position HB1, and then moves the piston rod 108 to the initial top stop position HT1 in the first up-stroke Ui 8 to complete the first stroke cycle.

Referring back to Fig. 5A, the control unit 134 then checks if i is greater than n (step 348). If not, the control unit increases i by 1 (step 350), and then raises the top stop position as HTi = HT(i-1) Ao, and lowers the bottom stop position as HBI = HB(i-i) - Ac (step 352). The control unit 134 then controls the piston 13 rod 108 to perform a stroke cycle (step 354).
14 As illustrated in Fig. 5B, in the down-stroke D2, the control unit moves the piston rod 108 to an expanded bottom stop position HB2 = HB1 - Ac.
Similarly, in the successive up-stroke U2, the control unit 134 moves the piston rod 108 to an 17 expanded top stop position HT2 = HT1 Referring back to Fig. 5A, the process goes back to step 348 to check if i is greater than n. In this manner, the top and bottom stop positions of the piston rod 108 are expanded for n stroke cycles, wherein the control unit 134 lowers the bottom stop position HB by a relatively large stroke expansion step value Ac in each 22 down-stroke, and raises the top stop position HT by AC in each up-stroke.

1 When at step 348 the control unit 134 determines that i is greater than 2 n, the process enters the fine stroke expansion stage.
3 At step 356, the control unit 134 check if i is greater than (n+m). If not, 4 the control unit increases i by 1 (step 358), and then raises the top stop position as HTi = HT(i-1) /IF, and lowers the bottom stop position as HBi = HB(i-1) ¨ AF
(step 360).
6 The control unit 134 then controls the piston rod 108 to perform a stroke cycle 7 (step 362).
8 As illustrated in Fig. 5B, in the first down stroke Dn+1 of the fine stroke 9 expansion stage, i.e., in the overall (n+1)-th down-stroke, the control unit 134 moves the piston rod 108 to an expanded bottom position HB(n+i) = HBn ¨AF, where 11 HBn is the stop position of the last down-stroke Dn in the coarse stroke expansion 12 stage (i.e., overall n-th down-stroke). In the successive up-stroke Un+1, the control 13 unit 134 moves the piston rod 108 to an expanded top position H-r(n+i) =
H-rn + AF, 14 where H-rn is the stop position of the last up-stroke Un in the coarse stroke expansion stage (i.e., overall n-th up-stroke).
16 Referring back to Fig. 5A, the process goes back to step 356 to check 17 if i is greater than (n+m). In this manner, the top and bottom stop positions of the 18 piston rod 108 are expanded for m stroke cycles, wherein the control unit 134 19 lowers the bottom stop position HB by a relatively small stroke expansion step value AF in each down-stroke, and raises the top stop position HT by AF in each up-stroke, 21 to expand the top and bottom stop positions of the piston rod 108, respectively, to 22 the top and bottom operation limits HOT and HOB.

When the control unit 134 determines at step 356 than i is greater than (n+m), the initialization process is then completed, and the control unit controls the piston rod 108 in normal operation mode, reciprocating up and down between the top and bottom operation limits HOT and HOB. The process then goes to step 308 of Fig. 4A.

Referring back to Fig. 4A, during normal operation, the control unit automatically adapts the system 100 to any drift of the top and bottom stop 8 positions (step 308).
9 In this embodiment, the control unit 134 detects drift of the top and bottom stop positions, and calculates automatically adjusts the top and bottom deceleration positions PDT and PDB, respectively. The control unit 134 then adjusts 12 the hydraulic power unit 128 in accordance to the adjusted top and bottom deceleration positions PDT and PDB to minimize detected drift of the top and bottom 14 stop positions, respectively.
Fig. 6 shows the detailed steps for adjusting PDT and PDB. In each up-stroke, the control unit 134 receives position information from the position sensor to detect the actual top stop position PST of the piston rod 108, and checks whether 18 the actual top stop position PST is about the top operation limit HOT, which is the target top stop position, within a predefined accuracy range, i.e., PST HOT
(step 402). If yes, the process branches to step 406; otherwise, top stop position drift occurs, and the control unit 134 adjusts the top deceleration position PDT to minimize the drift (step 404). At this step, the control unit 134 calculates the 1 difference LT between the actual top stop position PST and the top operation limit 2 HOT:
3 LT = PST - HOT.
4 Obviously, LT > 0 if PST > HOT, and LT < 0 if PST < HOT. Then, the control unit 134 adjusts the top deceleration position PDT as:
6 PDT' = PDT - LT.
7 That is, the adjusted top deceleration position PDT' is lowered by a distance of 8 (Psi- - HOT) if PST > HOT, as shown in Fig. 7A; and the adjusted top deceleration 9 position PDT' is raised by a distance of (HOT - PST) if PST < HOT, as shown in Fig. 7B.
The process then goes to step 406.
11 In each down-stroke, the control unit 134 receives position information 12 from the position sensor to detect the bottom stop position PSB of the piston rod 108, 13 and checks whether the bottom stop position PSB is about the bottom operation limit 14 HOB, which is the target bottom stop position, within a predefined accuracy range, i.e., PSB = HOB (step 406). If yes, the process branches to step 310 of Fig.
4A;
16 otherwise, bottom stop position drift occurs, and the control unit 134 adjusts the 17 bottom deceleration position PDB to minimize the drift (step 408). At this step, the 18 control unit 134 calculates the difference LB between the actual bottom stop position 19 PST and the bottom operation limit HOB:
LB = PSB - HOB.
21 Obviously, LB > 0 if PSB > HOB, and LB < 0 if PSB < HOB. Then, the 22 control unit 134 adjusts the bottom deceleration position PDB as:
23 PDB' = PDB - LB.

1 That is, the adjusted bottom deceleration position PDB' is lowered by a distance of 2 (PsB - HOB) if PSB > HOB, as shown in Fig. 8A; and the adjusted bottom deceleration 3 position PDB' is raised by a distance of (HOB - PsB) if PSB < HOB, as shown in Fig. 8B.
4 The process then goes to step 310 of Fig. 4A.
Referring back to Fig. 4A, the control unit 134 also monitors user input 6 during system operation to determine if a user has selected a different up-stroke or 7 down-stroke speed, and adjusts system operation accordingly (step 310).
8 As described above, in this embodiment, the control unit 134 9 comprises a touch-sensitive screen (not shown). The control unit 134 provides a graphic user interface (GUI) on the touch-sensitive screen for users to adjust the 11 up- and/or down-stroke speed by selecting one of seven (7) predefined speeds. In 12 response to an up- and/or down-stroke speed change, the control unit 134 re-13 initializes the system operation to adapt to the adjusted up- and/or down-stroke 14 speed (step 320).
The control unit 134 first calculates the number p of stroke cycles 16 required in coarse-expansion stage, and the number q of stroke cycles required in 17 the fine expansion stage, in a manner similar to the calculation of n and m in Figs.
18 5A and 5B. Then, the control unit 134 re-initializes the top stop position if the up-19 stroke speed is changed, and re-initializes the bottom stop position if the down-stroke speed is changed. The control unit 134 re-initializes both the top and bottom 21 stop position if the up- and down-stroke speeds are changed.
22 Fig. 9 shows an example of the re-initialization process, when, after k 23 stroke cycles, the up-stroke speed VU is changed by a user but the down-stroke speed VD is unchanged. In this example, the control unit 134 continues to lower the piston rod 108 to the bottom operation limit HOB in a series of down-strokes and gradually raises the top stop position HT of the piston rod 108 in steps from an initial 4 top stop position HT1, which is below the top operation limit HOT with a distance of (1 - C1) SN I 2, to the top operation limit Hor via a coarse stroke expansion stage and, as the stroke closely approaches top operation limit HOT, in a fine stroke 7 expansion stage.
8 At the first re-initialization down-stroke Dk+1, i.e., the overall (k+1)-th down stroke, the control unit 134 lowers the piston rod 108 to the bottom operation limit HOB. In the successive up-stroke Uk+1, the control unit 134 lifts the piston rod 11 108 to the predefined initial top stop position Hi-i.
12 In the next down-stroke Dk+2, the control unit 134 lowers the piston rod to the bottom operation limit HOB, and lifts the piston rod 108 to an expanded 14 top stop position HT2 = HT1 + Ac in the next up-stroke Uk+2.
In this manner, the top stop position of the piston rod 108 is expanded 16 for p stroke cycles, wherein the control unit 134 continues to lower the piston rod to 17 the bottom operation limit HOB in each down-stroke, and raises the top stop position by a relatively large stroke expansion step value Ac in each up-stroke. When the spacing between the top operation limit HOT and the last upstroke is less than or equal to the coarse step Ac, then the process then enters the fine stroke expansion 21 stage.
22 At the first down-stroke Dki-p+i of the fine stroke expansion stage, i.e., 23 the overall (k+p+1)-th down-stroke, the control unit 134 lowers the piston rod 108 to the bottom operation limit HOB, and lifts the piston rod 108 to an expanded top stop 2 position HT(p+1) = HTp AF in the successive up-stroke Uk+p+i, where HTp represents 3 the stop position of the last up-stroke Uk+p in the coarse stroke expansion stage 4 (i.e., overall (k+p)-th up-stroke).
In this manner, the top stop position of the piston rod 108 is expanded 6 for q stroke cycles, wherein the control unit 134 lowers the piston rod to the bottom 7 operation limit HOB in each down-stroke, and raises the top stop position HT by a 8 relatively small stroke expansion step value AF in each up-stroke, to expand the top 9 stop position of the piston rod 108 to the top operation limit HOT. The re-initialization process is then completed, and the control unit 134 controls the piston rod 108 into 11 the normal operation, reciprocating up and down between the top and bottom 12 operation limits HOT and HOB.
13 Fig. 10 shows an example of the re-initialization process when, after k 14 stroke cycles, the down-stroke speed VD is changed by a user but the up-stroke speed VU is unchanged. In this example, the control unit 134 always lifts the piston 16 rod 108 to the top operation limit HOT in up-strokes and gradually lowers the bottom 17 stop position HB of the piston rod 108 from an initial bottom stop position HB1, which 18 is above the bottom operation limit HOB with a distance of (1 - C1) SN /
2, to the 19 bottom operation limit HOB via a coarse stroke expansion stage and a fine stroke expansion stage.
21 At the first re-initialization down-stroke Dk+1, i.e., the overall (k+1)-th 22 down stroke, the control unit 134 lowers the piston rod 108 to the predefined initial bottom stop position HB1. In the successive up-stroke Uk+1, the control unit 134 lifts 2 the piston rod 108 to the top operation limit HOT.
3 In the next down-stroke Dk+2, the control unit 134 lowers the piston rod to an expanded bottom stop position HB2 = HB1 - Ac. In the successive up-stroke Uk+2, the control unit 134 lifts the piston rod 108 to the top operation limit HOT.
6 In this manner, the bottom stop position of the piston rod 108 is expanded for p stroke cycles, wherein the control unit 134 lowers the bottom stop position HB by a relatively large stroke expansion step value Ac in each down-stroke, and lifts the piston rod to the top operation limit HOT in each up-stroke. The process then enters the fine stroke expansion stage.
11 At the first down-stroke Dk+p+1 of the fine stroke expansion stage, i.e., 12 the overall (k+p+1)-th down-stroke, the control unit 134 lowers the bottom stop position to an expanded bottom stop position HB(p+1) = HBp + AF, where HBp represents the bottom position of the last down-stroke Dk+p in the coarse stroke expansion stage (i.e., overall (k+p)-th down-stroke). The control unit 134 lifts the 16 piston rod 108 to the top operation limit HOT in the successive up-stroke Uk+p+1.

In this manner, the bottom stop position of the piston rod 108 is expanded for q stroke cycles, wherein the control unit 134 lifts the piston rod to the top operation limit HOT in each up-stroke, and lowers the bottom stop position HB by a relatively small stroke expansion step value AF in each down-stroke, to expand 21 the bottom stop position of the piston rod 108 to the bottom operation limit HOB.
The re-initialization process is then completed, and the control unit 134 controls the 1 piston rod 108 into the normal operation, reciprocating up and down between the 2 top and bottom operation limits HOT and HOB.
3 Fig. 11 shows an example of the re-initialization process when, after k 4 stroke cycles, both the up-stroke speed Vt.) and the down-stroke speed VD
are changed by a user.
6 In this example, the control unit 134 starts the re-initialization process 7 by operating the piston rod 108 between an initial top stop position HT1, which is 8 below the top operation limit HOT with a distance of (1 - C1) SN / 2, and initial bottom 9 stop position HB1, which is above the bottom operation limit HOB with a distance of (1 - C1) SN / 2. The control unit 134 then gradually expands the top and bottom stop 11 positions HT and HB, respectively, to the top and bottom operation limits HOT and 12 HOB, via a coarse stroke expansion stage and a fine stroke expansion stage.
13 At the first re-initialization down-stroke Dk+1, i.e., the overall (k+1)-th 14 down stroke, the control unit 134 lowers the piston rod 108 to the predefined initial bottom stop position HB1. In the successive up-stroke Uk+1, the control unit 134 lifts 16 the piston rod 108 to the predefined initial top stop position HT1.
17 In the next down-stroke Dk+2, the control unit 134 lowers the piston rod 18 108 to an expanded bottom stop position HB2 = HB1 - Ac. In the successive up-19 stroke Uk+2, the control unit 134 lifts the piston rod 108 to an expanded top stop position HT2 = HT1 + Ac.
21 In this manner, the top and bottom stop positions of the piston rod 108 22 are expanded for p stroke cycles, wherein the control unit 134 lowers the bottom 23 stop position HB by a relatively large stroke expansion step value Ac in each down-stroke, and raises the top stop position HT by Ac in each up-stroke. The process 2 then enters the fine stroke expansion stage.
3 At the first down-stroke Dk+p+1 of the fine stroke expansion stage, i.e., 4 the overall (k+p-F1)-th down-stroke, the control unit 134 lowers the bottom stop position to an expanded bottom stop position HB(p+1) = HBp + AF, where HBp represents the bottom position of the last down-stroke Dk+p in the coarse stroke expansion stage (i.e., overall (k+p)-th down-stroke). The control unit 134 lifts the piston rod 108 to an expanded top stop position H-Rp+i) = HTp + AF in the successive 9 up-stroke Uk+p+1, where HTp represents the stop position of the last up-stroke Uk+p in the coarse stroke expansion stage (i.e., overall (k+p)-th up-stroke).
11 In this manner, the top and bottom stop positions of the piston rod 108 12 are expanded for q stroke cycles, wherein the control unit 134 lowers the bottom stop position HB by a relatively small stroke expansion step value AF in each down-stroke, and raises the top stop position HT by AF in each up-stroke, to expand the top and bottom stop positions of the piston rod 108, respectively, to the top and bottom operation limits HOT and HOB. The re-initialization process is then completed, and the control unit 134 controls the piston rod 108 into the normal operation, reciprocating up and down between the top and bottom operation limits HOT and 19 HOB.
Fig. 12 shows an example of a GUI 502 displayed on the touch-sensitive screen 500 for users to select between the automatic adjusting mode and 22 the manual adjusting mode, and to input system parameters. The GUI 502 comprises five (5) input zones, including a stroke control mode selection zone 1 for selecting the automatic adjusting mode or the manual adjusting mode, an auto height input zone 506 for inputting the top and bottom operation limits, a speed 3 input zone 508 for inputting the up-stroke and down-stroke speeds, a directory selection zone 510 for displaying a list of functions provided by the control unit 134, and a manual adjustment zone 512 for manually adjusting the top and bottom 6 deceleration positions PDT and PDB. The stroke control mode selection zone 7 and the auto height input zone 506 are only accessible by special users such as an 8 administrator.
9 To enter the automatic adjusting mode, an administrator first touches the AUTO CMD button 522 in the stroke control mode selection zone 504. Text "AUTO ACTIVE" is then displayed in the mode display field 526 indicating that the automatic adjusting mode is activated. The system 100 then enters the jog mode to facilitate the administrator to determine the top and bottom operation limits HOT and HOB. The administrator then touches the button 532 to enter the top operation limit HOT.

When the administrator touches the button 532, a GUI pops up on the touch-sensitive screen for the administrator to input a value. Fig. 13 shows an example of a value-input GUI 600. As shown, the GUI 600 comprises a numerical zone 602 having buttons for inputting digits 0 ¨ 9 and the digital point ".".
The entered value is displayed in the display field 604. The GUI 600 also comprises a backspace button 606 for deleting an entered digit, and a CLR button 608 for clearing the entered value. The administrator may touch the ESC button 610 to cancel the value input, or touch the ENTER button 612 to accept the entered value.

Referring back to Fig. 12, the administrator may also touch the button 534, each time increasing the top operation limit HOT by one (1) inch, or touch the 3 button 536, each time decreasing the top operation limit HOT by one (1) inch.

Similarly, the administrator may touch the button 538 to enter the bottom operation limit HOB. GUI 600 of Fig. 13 is then popped up for user to enter a value as the bottom operation limit HOB. The administrator may also touch the button 540, each time increasing the bottom operation limit HOB by one (1) inch, or touch the button 542, each time decreasing the bottom operation limit HOB by one 9 (1) inch.
The control unit 134 checks the user-entered values of HOT and HOB, 11 and rejects invalid value(s), such as a value entered for the top operation limit HOT

that is larger than the top safety limit HST or smaller than the value entered for the 13 bottom operation limit HOB, and remind the user to correct the error.
14 The user may also touch the button 552 in the speed input zone 508 to enter an up-stroke speed. As in this embodiment, the system 100 provides seven 16 (7) speed levels each corresponding to a predefined up-stroke speed, the user may enter an integer number between 1 and 7 to select an up-stroke speed Vu. The 18 entered speed level is displayed in the up-stroke speed level display field 554.

Similarly, the user may touch the button 556 in the speed input zone 508 to enter a down-stroke speed. As in this embodiment, the system 100 provides seven (7) speed levels each corresponding to a predefined down-stroke speed, the user may enter an integer number between 1 and 7 to select a down-stroke speed 1 VD. The entered speed level is displayed in the down-stroke speed level display =
2 field 558.
3 After the system parameters have been input via the GUI 500, and the 4 system 100 has started, the GUI 500 displays some measured data in real-time, such as the top stop position HT in field 572, the bottom stop position HB in field 6 574, the stroke length S in field 576 and the strokes per minute measurement in 7 field 578.
8 During system operation, a regular user, e.g., an operator, may use 9 the buttons 552 and 556 in the GUI 500 to adjust the up- and down-stroke speeds Vu and VD. The control unit 134 automatically adjust the system operation as 11 described above, in response to the up- and/or down-stroke speed change.
12 The manual adjustment zone 512 is disabled when the automatic 13 adjusting mode is activated. However, an administrator may touch the MAN
CMD
14 button 524 in the stroke control mode input zone 504 to activate the manual adjusting mode. The mode display field then displays "MANUAL ACTIVE" to 16 indicate that the manual adjusting mode is activated. The manual adjustment zone 17 512 is enabled, and the auto height input zone 506 is disable.
18 In the manual adjusting mode, a user, e.g., an administrator or an 19 operator, has to constantly monitor the up- and down-strokes, and use the buttons 582 and 588 to enter a top and a bottom deceleration position PDT and PDB. The 21 user may also use the buttons 584 and 590 each time increasing the top and 22 bottom deceleration position PDT and PDB, respectively, by one (1) inch, or use the 1 buttons 586 and 592 each time decreasing the top and bottom deceleration position 2 PDT and PDB, respectively, by 1 inch.
3 As described above, for safety reasons, the top safety limit HST
is 4 lower than the physical top limit that the piston rod 108 can be extended thereto, and the bottom safety limit HSB is higher than the physical bottom limit that the 6 piston rod 108 can be lowered thereto. During operation, the control unit 7 operates the piston rod 108 at a user-selected up-stroke speed VU and a user-8 selected down-stroke VD, between a user-selected top operation limit HOT
lower 9 than the top safety limit HST, i.e., HOT < HST, and a user-selected bottom operation limit HOB higher than the bottom safety limit HSB, i.e., HOB > HSB.
11 Although the control unit 134 automatically adjusts the up- and down-12 strokes if the top and/or bottom stop positions HT and HB of the piston rod 108 are 13 drifted from HOT and HOB, respectively, such automatic adjustment may fail if the 14 drift is too large. For example, if, during an up-stroke, the load applied to the piston rod is lost because, for example, the cable 114 snaps, or the rod string 122 fails, the 16 upward hydraulic force applied to the piston rod 108 may drive the piston rod 108 to 17 quickly move upward beyond the top safety limit HST, which is commonly denoted 18 as "over-stroke". Serious hazard would occur if the piston rod 108 hit and break 19 through the top wall of the hydraulic cylinder 106. In an alternative embodiment, the system 100 further comprises a safety dump valve that is opened when over-stroke 21 occurs, to prevent the piston rod 108 from hitting the top wall of the hydraulic 22 cylinder 106.

Fig. 14 shows a simplified schematic diagram of the hydraulically-actuated rod pump system 100 in this embodiment, indicating the flow of the power fluid. For the ease of illustration, Fig. 14 only shows the hydraulic power unit 128, 4 the hydraulic cylinder 106, and conduits connected therebetween, as well as the control unit 134 and control switches.
6 As shown, the hydraulic power unit 128 is connected to the down chamber 210 of the hydraulic cylinder 106 via a set of conduits 226, and connected 8 to the up chamber 208 of the hydraulic cylinder 106 via a set of conduits 222. In this embodiment, a conduit 642 branches from the conduit 222, and connects back to the power fluid reservoir of the hydraulic power unit 128 via a normally-closed dump valve 644 such as a normally-closed solenoid valve. The control unit 134 controls 12 the operation of the hydraulic power unit 128, and controls the open and close of 13 the dump valve 644.

Fig. 15 is a flowchart showing a process 700 of operating the hydraulically-actuated rod pump system 100 performed by the control unit 134 in this embodiment. The process 700 is similar to process 300 of Fig. 4A with additional steps 702 to 708. The steps same in both processes 300 and 700 are 18 identified using the same numerals, and are not described.
19 As shown in Fig. 15, after setting up system parameters (step 304) as described above, the control unit 134 further provides a GUI for an administrator to 21 set up a top-dump-valve-activation height Hy, the default value of which is the top safety limit HST (step 702). Fig. 16 shows an example of a GUI 702 display on the touch-sensitive screen 500. An administrator may touch the field 704 of the 1 to enter a top-dump-valve-activation height Hy. The control unit checks if the entered Hy value is valid, e.g., being smaller than the predefined top safety limit 3 HST, and rejects any invalid Hy value.

Referring back to Fig. 15, after setting up the top-dump-valve-activation height Hy, the control unit 134 starts the system operation (step 306) as described above. As the dump valve 644 is normally closed, the hydraulic power unit 128, under the command of the control unit 134, alternately pumps power fluid into the up and down chambers 208 and 210 of the hydraulic cylinder 106 to pump 9 downhole fluid to the surface.
The control unit 134 monitors the position of the piston rod 108, and checks whether the position Pc of the piston rod 108 has move upward beyond the 12 top-dump-valve-activation height Hy (step 704). If not, the process goes to step 13 to detect the drift of stop positions and adapt thereto, as described above.

If, however, the control unit 134 detects that the position Pc of the piston rod 108 is above the top-dump-valve-activation height Hy, the control unit 134 commands the dump valve 644 to open (step 706). As a result, the power fluid pumped into the conduits 222 flows back into the power fluid reservoir of the hydraulic power unit 128 without entering the up chamber 208 of the hydraulic cylinder 106 to drive the piston rod 108. The hydraulic force driving the piston rod 108 upward is then removed, and the piston rod 108 decelerates and stops by the 21 gravity.

1 At step 706, the control unit 134 triggers an alarm to warn operators that an emergency event has occurred, and shuts down the system 100 (step 708).
3 The process then terminates (step 314).
4 In an optional embodiment, the hydraulically-actuated rod pump system further comprises a chemical injection unit for injecting suitable treatment fluid into a borehole for treating the downhole production fluid. Fig. 17 shows a simplified schematic diagram of the chemical injection unit 740. As shown, the chemical injection unit 740 comprises a treatment fluid reservoir 742 and a chemical injection assembly 744 interconnected by a set of conduits 746. The chemical injection assembly 744 is connected to the wellhead 126 via a set of conduits 750.
11 Any suitable chemical injection assembly may be used in this embodiment for injecting treatment fluid into a wellbore, possibly with modification 13 and addition of electrical control such that the operation of the chemical injection assembly may be controlled by the control unit 134. For example, the chemical injection assembly may be a chemical injection assembly as disclosed in U.S.

Patent Number 5117913, entitled "Chemical injection system for downhole treating"
17 to Themig, issued on June 2, 1992. Such a chemical injection assembly comprises 18 a fixed packer having an opening passing therethrough for receiving a production tubing string, a closable orifice in the packer that is actuated by the tubing string and appropriate seals for preventing fluid transfer within the packer. When the tubing string is inserted into the packer, a collar on the tubing string engages a shiftable sleeve that places an orifice in the shifting sleeve in alignment with the orifice in the injection sleeve so that chemical treatment fluid from the surface can be forced 1 down the bore-hole casing through the closable orifice in the packer and into the 2 production fluid at the perforations near the producing formations.
3 The operation of the chemical injection assembly 744 is controlled by 4 the control unit 134 in accordance with the system operation. In particular, in one embodiment, the control unit 134 automatically turns on the chemical injection 6 assembly 744 to injection treatment fluid to the wellbore via the wellhead 126 when 7 the system is in operation such as pumping downhole fluid to the surface, and turns 8 off the chemical injection assembly 744 to stop chemical injection when the system 9 is not in operation.
In an alternative embodiment, the chemical injection unit 740 11 comprises an injection control component (not shown) controlling chemical injection.
12 The injection control component is connected to the control unit 134, and may be 13 enabled or disabled by the control unit 134. In this embodiment, the control unit 134 14 disables the injection control component to stop chemical injection when the system is not in operation. When the system is in operation, the control unit 134 enables the 16 injection control component, and the injection control component controls the 17 chemical injection. For example, when enabled, the injection control component 18 may automatically start or stop chemical injection based on a set of predefined 19 criteria. An operator may manually turn off the injection control component to stop chemical injection.
21 In an alternative embodiment, the chemical injection assembly 744 22 further comprises a normally-off manual control switch (not shown), which turned on by an operator, turns on the chemical injection regardless whether or not the system 2 is in operation.

In another embodiment, the system 100 comprises two or more 4 pressurized gas vessels 136 for weight counterbalancing.
In above embodiments, the coarse and fine extension step values Ac and AF are predefined, and the control unit 134 calculates the numbers n and m of the stroke cycles required in the coarse and fine initialization/re-initialization stages, respectively, based on Ac and AF. In an alternative embodiment, the stroke cycle numbers n and m may be predefined, and the control unit 134 calculates a suitable AC and AF based on n and m, respectively.

In above embodiments, the jacking actuator 102 comprises a three-chamber hydraulic cylinder 106. However, those skilled in the art appreciate that, other types of jacking actuator may be alternatively used. For example, in one embodiment, the jacking actuator 102 comprises a double-acting hydraulic cylinder receiving a piston rod. A first hydraulic chamber is formed in the hydraulic cylinder under the piston rod, and a second hydraulic chamber is formed about the piston rod. The first and second hydraulic chambers are connected to the power fluid reservoir of the hydraulic power unit via a first and a second set of conduits, respectively. A hydraulic motor of the hydraulic power unit pumps power fluid into the first hydraulic chamber to lift the piston rod, and pumps power fluid into the 21 second hydraulic chamber to lower the piston rod.

Those skilled in the art also appreciate that, in some alternatively 2 embodiments, the piston rod may be driven by other power means, e.g., 3 combusting fluid or compressed gas, to reciprocate.

Although in above embodiments, the jacking actuator 102 is vertically oriented, in an alternative embodiment, the jacking actuator is in a tilted orientation.

In yet another embodiment, the jacking actuator is horizontally oriented with the 7 cable 114 being aligned with the rod string 122.

Although in above embodiments, the jacking actuator 102 comprises a cylinder 106 and a piston rod 108 received therein for reciprocating the pulley assembly 112, in some other embodiments, the jacking actuator 102 is a linear actuator reciprocating between a first and a second stop positions to drive the pulley assembly 112 and in turn the sucker rod 122 to pump downhole fluid to the surface.
13 A control unit detects the drift of the first and second stop positions and 14 automatically minimize detected drift as described above.
In these embodiment, the power unit may be any suitable drive, such as a variable frequency drive (VFD), a linear motor or the like, that drives the linear actuator reciprocating between the first and second stop positions.
Accordingly, the power unit may engage the linear actuator via any suitable mechanical traction 19 means such as cable, chain or the like.
In above initialization and re-initialization processes of Figs. 5A, 5B, 9 and 10, a stroke cycle starts from a down-stroke followed by an up-stroke, and the first stroke cycle is between the initial top stop position HT1 and the initial bottom stop position HB1 before the top and/or bottom stop positions are expanded.
Those skilled in the art appreciate that, a stroke cycle may alternatively start from an up-stroke followed by a down-stroke. Moreover, in some alternative embodiments, the control unit 134 starts to expand the stop position after the first down- or up-stroke 4 is completed.
Those skilled in the art also appreciate that, in some embodiments, 6 the initialization and/or re-initialization processes may comprise a single stop position expansion stage. In some other embodiments, the initialization and/or re-initialization processes may comprise three or more stop position expansion stages.

However, the last stop position expansion stage is preferably a fine expansion stage.
11 In above embodiments, the control unit 134 adjusts the actual top and bottom stop positions PST and PSB by adjusting the top and bottom deceleration positions, respectively. In an alternative embodiment, the control unit 134 does not adjust the top and bottom deceleration positions. Rather, the control unit 134 maintains a predefined top and a predefined bottom deceleration position, and adjusts the up- and down-stroke deceleration rate to adapt to the drift of the top and bottom stop positions. In particular, if the actual top stop position is higher than the 18 top operation limit HOT, the deceleration rate of the next up-stroke is then increased 19 to decelerate the piston rod faster. If the actual top stop position is lower than the top operation limit HOT, the deceleration rate of the next up-stroke is then decreased 21 to decelerate the piston rod slower. Similarly, if the actual bottom stop position is higher than the top operation limit HOT, the deceleration rate of the next down-stroke 23 is then decreased to decelerate the piston rod slower. If the actual top stop position 1 is lower than the top operation limit HOT, the deceleration rate of the next down-2 stroke is then increased to decelerate the piston rod faster.
3 In the embodiment of Fig. 1A, the deceleration rate is adjusted by 4 adjusting the pressure of the power fluid in the up and down chambers, as those skilled in the art have known. In embodiments where other types of linear actuators 6 are used, mechanisms for changing the deceleration rate suitable for the respective 7 linear actuators may be used, which is also known to those skilled in the art, and is 8 omitted herein.
9 In the initialization and re-initialization processes of above embodiments, the control unit 134 calculates n and m based on Ac and AF, 11 respectively. In an alternative embodiment, the control unit 134 does not calculate n 12 and m. Rather, the control unit 134 measures the distance between the top/bottom 13 stop positions and the top/bottom operation limits during the coarse expansion 14 stage, and enters the fine expansion stage when the distance between the top/bottom stop positions and the top/bottom operation limits is smaller than or 16 equal to Ac. During the fine expansion stage, the control unit 134 also measures the 17 distance between the top/bottom stop positions and the top/bottom operation limits, 18 and completes the initialization process when the distance between the top/bottom 19 stop positions and the top/bottom operation limits is smaller than AF.
The control unit 134 sets the top and bottom stop positions to the top and bottom operation 21 limits, respectively, if AF 0 0.
22 In another embodiment, the initialization/re-initialization process only 23 comprise one stage. During the initialization/re-initialization, the control unit 134 1 expands each stroke by a stroke expansion value A, and measures the distance 2 between the top/bottom stop positions and the top/bottom operation limits.
When 3 the distance between the top/bottom stop positions and the top/bottom operation 4 limits is smaller than A, the control unit 134 sets the top and bottom stop positions to the top and bottom operation limits, respectively.
6 Although embodiments have been described above with reference to 7 the accompanying drawings, those of skill in the art will appreciate that variations 8 and modifications may be made without departing from the scope thereof as defined 9 by the appended claims.

Claims

WHAT IS CLAIMED IS:

1. A
lifting system for lifting downhole fluid from a downhole rod pump in a wellbore to surface, comprising:
a linear actuator comprising a movable component moveable between a first and a second limit and driveably coupled to the downhole rod pump;
a power unit coupled to said linear actuator for driving said movable component to reciprocate; the reciprocating of said movable component driving said downhole rod pump to pump downhole fluid to the surface;
a sensor for detecting the position of said movable component; and a control unit coupled to said sensor and said power unit for controlling the power unit for reciprocating said movable component between a first target stop position and a second target stop position, for moving said movable component uphole to stop at about said first target stop position, and for moving said movable component downhole to stop at about said second target stop position;
determining, based on the position information received from said sensor, a first actual stop position and a second actual stop position;
determining a first drift being the difference between the first actual stop position and the first target stop position, and a second drift being the difference between the second actual stop position and the second target stop position; and at the control unit, automatically controlling the operation of the power unit to minimize the first and second drifts.

2. The lifting system of claim 1 wherein said control unit stores a predefined first deceleration position at which deceleration of the said movable component commences during the movement thereof towards said first target stop position, and stores a predefined second deceleration position at which deceleration of said movable component is commenced during the movement thereof towards said second target stop position; and wherein said automatically adjusting the operation of the power unit comprises:
adjusting the position of the first deceleration position based on the first drift;
adjusting the position of the second deceleration position based on the second drift; and adjusting the operation of the power unit to decelerate said movable component at the adjusted first deceleration position during the movement thereof towards said first target stop position, and to decelerate said movable component at the adjusted second deceleration position during the movement thereof towards said second target stop position.

3. The lifting system of claim 2 wherein said adjusted first deceleration position is the difference between said predefined first deceleration position and said first drift, and said adjusted second deceleration position is the difference between said predefined second deceleration position and said second drift.

4. The lifting system of any one of claims 1 to 3 wherein said linear actuator comprises:
a hollow cylinder receiving a piston rod axially movable therein; and at least a first chamber for receiving a power medium; the intake of the power medium into said first chamber driving said piston rod moving towards the first stop position.

5. The lifting system of claim 4 wherein said power medium is a power fluid; and wherein said power unit is a hydraulic power unit comprising a hydraulic motor and a power fluid reservoir storing said power fluid, said hydraulic motor sending said power fluid, via a set of conduits, into and out of said first chamber for driving said piston rod to reciprocate in said cylinder.

6. The lifting system of claim 5 wherein said a set of conduits comprises a conduit branch connected to said power fluid reservoir via a normally-closed valve, and said control unit is further controllably coupled to said valve for determining whether the position of said piston rod, during the movement towards said first target stop position, is beyond a first limit, said first limit is further from said first target stop position along the direction of said movement towards said first target stop position; and opening said valve for flowing the power fluid in said a set of conduits into said power fluid reservoir via said conduit branch and said valve.

7. The lifting system of any one of claims 1 to 6 said control unit further controls said power unit to initialize the operation of the lifting system through a first initialization stage by:
determining an initial first stop position and an initial second stop position about the mid-point of the target top and bottom stop positions, the distance between the initial first stop position and the initial second stop position is a predefined percentage of the distance between the first and second target stop positions; and moving the movable component to one of the initial first and second stop positions to reciprocate the movable component for at least one reciprocating cycle, wherein in each of the at least one reciprocating cycle, said control unit controls said power unit to expand the first and second stop positions toward the first and second target stop positions, respectively, by a first expansion step value.

8. The lifting system of claim 7 wherein during said first initialization stage, said control unit controls said power unit to reciprocate the movable component until the distance between the first and second stop positions and the first and second target stop positions, respectively, is smaller than said first expansion step value.

9. The lifting system of claim 7 or 8 wherein said first expansion step value is a predefined value.

10. The lifting system of any one of claims 7 to 9 wherein said control unit further controls said power unit to initialize the operation of the lifting system through a second initialization stage by:
reciprocating the movable component for at least one reciprocating cycle, wherein in each of said at least one reciprocating cycle in the second initialization stage, said control unit controls said power unit to expand the first and second stop positions toward the first and second target stop positions, respectively, by a second expansion step value.

11. The lifting system of claim 10 wherein during said second initialization stage, said control unit controls said power unit to reciprocate the movable component until the distance between the first and second stop positions and the first and second target stop positions, respectively, is smaller than said second expansion step value.

12. The lifting system of claim 10 or 11 wherein said second expansion step value is a predefined value.

13. The lifting system of any one of claims 1 to 12 wherein said control unit controls said power unit to move the movable component towards the first target stop position at a first speed and to move the movable component towards the second target stop position at a second speed; and wherein said control unit receives a command from an operator indicating the change of at least one of the first and the second speeds, and in response to said command, re-initializes the operation of the lifting system by:
determining an initial first stop position if the first speed is changed, said initial first stop position being intermediate to the first and second target stop positions with a distance to the first target stop position of (1 - SN
/ 2, wherein SN
is the distance between the first and second target stop positions and C1 is a predefined percentage;
determining an initial second stop position if the second speed is changed, said initial second stop position being intermediate to the first and second target stop positions with a distance to the second target stop position of (1 - C1) SN / 2;
determining at least a first expansion step value;
determining at least a first number p of reciprocating cycles corresponding to said first expansion step value; and reciprocating the movable component for p reciprocating cycles, wherein in the first cycle of the p reciprocating cycles, said control unit controls said power unit to move the movable component to the initial first stop position if the first speed is changed;
move the movable component to the initial second stop position if the second speed is changed; and in the next (p - 1) reciprocating cycles, said control unit controls said power unit to expand the first stop position toward the first target stop position by the first expansion step value if the first speed is changed;
and expand the second stop position toward the second target stop position by the first expansion step value if the second speed is changed.

14. The lifting system of claim 13 wherein said control unit re-initializes the operation of the lifting system by further:
determining a second expansion step value;
determining a second number q of reciprocating cycles corresponding to said second expansion step value; and after said p reciprocating cycles are completed, reciprocating the movable component for q reciprocating cycles, wherein in each of the q reciprocating cycles, said control unit controls said power unit to expand the first stop position toward the first target stop position by the first expansion step value if the first speed is changed;
and expand the second stop position toward the second target stop position by the first expansion step value if the second speed is changed.

15. The lifting system of any one of claims 1 to 14 further comprising:
a chemical injection assembly coupled to said control unit and the wellbore; wherein said control unit enables said chemical injection assembly when said lifting system is in operation, and disables said chemical injection assembly when the operation of said lifting system is stopped.

16. A method for lifting downhole fluid from a reciprocating downhole fluid lifting device to surface, comprising:
setting up a first and a second target stop position;
reciprocating a movable component of a linear actuator between said first and second target stop positions for driving the downhole fluid lifting device;
determining a first actual stop position corresponding to said first target stop position and a second actual stop position corresponding to said second target stop position;
determining a first drift being the difference between the first actual stop position and the first target stop position, and a second drift being the difference between the second actual stop position and the second target stop position; and automatically adjusting the reciprocating of the movable component to minimize for the first and second drifts.

17. The method of claim 16 wherein said automatically adjusting the reciprocating of the movable component comprises:
determining a first deceleration position based on the first drift;
determining a second deceleration position based on the second drift;
and decelerating said movable component at the first deceleration position during the movement thereof towards said first target stop position, and decelerating said movable component at the second deceleration position during the movement thereof towards said second target stop position.

18. The method of claim 17 wherein said determining a first deceleration position comprises:
calculating the first deceleration position as the difference between a predefined first deceleration position and said first drift; and calculating the second deceleration position as the difference between a predefined second deceleration position and said second drift.

19. The method of any one of claims 16 to 18 wherein said reciprocating a movable component of a linear actuator comprises:
sending a power fluid into a chamber coupled to said movable component to move the movable component towards the first target stop position.

20. The method of claim 19 wherein said reciprocating a movable component of a linear actuator further comprises:
determining whether the position of said movable component, during the movement towards said first target stop position, is beyond a first limit, said first limit being further from said first target stop position along the direction of said movement towards said first target stop position; and preventing the power fluid from entering into said chamber.

21. The method of any one of claims 16 to 20 further comprising an initialization process, comprising:
determining an initial first stop position and an initial second stop position about the mid-point of the target top and bottom stop positions, the distance between the initial first stop position and the initial second stop position is a predefined percentage of the distance between the first and second target stop positions;
moving the movable component to one of the initial first and second stop positions to reciprocate the movable component for n reciprocating cycle(s), wherein n >= 1, and in each of the n reciprocating cycle(s), said control unit controls said power unit to expand the first and second stop positions toward the first and second target stop positions, respectively, by the first expansion step value; and when the distance between the first and second stop positions and the first and second target stop positions, respectively, is smaller than said first expansion step value, reciprocating the movable component for m reciprocating cycle(s), wherein m >= 1, and in each of the m reciprocating cycle(s), said control unit controls said power unit to expand the first and second stop positions toward the first and second target stop positions, respectively, by a second expansion step value.