SE538429C2

SE538429C2 - A drive unit for controlling a control valve element, a method for operating a drive unit of a control valve element anda control valve unit

Info

Publication number: SE538429C2
Application number: SE1550334A
Authority: SE
Inventors: Sven-Erik Tegelmark
Original assignee: Ebr Konsult I Rockhammar Ab
Priority date: 2015-03-20
Filing date: 2015-03-20
Publication date: 2016-06-21
Also published as: SE1550334A1; WO2016150644A1

Abstract

14 Abstract A drive unit (3) and a method for controlling a control valve element (5). The drive unit comprisesan electric motor (10) comprising a drive shaft (16) adapted to be connected to a control shaft (7)ofthe control valve element and rotated between a first and a second position. The drive unitcomprises a gear box (12) and a control unit (14) adapted to rotate the drive shaft to positions be-tween the first and the second position. The electric motor, the gear box and the control unit arecombined in a single mechatronic unit (15). The electric motor is of a type configured to allow rota-tion of the drive shaft a number of revolutions. The drive unit comprises a detector (32) adapted,at startup of the drive unit, to detect a position of the drive shaft relating to the first or second po-sition ofthe drive shaft. The control unit is adapted to determine the first and second position ofthe drive shaft based on the detected position. (Fig. 1)

Description

A drive unit for controlling a control valve element, a method for operating a drive unit of a con-trol valve element and a control valve unit Field of the invention The present invention relates to a drive unit for controlling a control valve element. The drive unitcomprises an electric motor comprising a drive shaft adapted to be connected to a control shaft ofthe control valve element and rotated between a first position relating to a closed state of the con-trol valve element and a second position relating to an open state ofthe control valve element.The drive unit further comprises a gear box adapted to control the output momentum ofthe driveshaft and a control unit adapted to receive a control signal and to control the electric motor sothat the drive shaft is rotated to positions between a first position corresponding to a closed stateof the control valve element, and a second position corresponding to an open state of the controlvalve element, in dependency ofthe control signal.

The present invention further relates to a method for operating a drive unit of a control valve ele-ment and a control valve unit comprising the drive unit and the control valve element.

Prior art Various types of control valve elements are used in industrial manufacturing processes for control-ling the flow of a medium to the process. The control valve element is used for regulating the flowof the medium, such as gas, oil, and etcetera, to the industrial process. The medium may be in aliquid phase, a gas phase or mixture of various phases, such as slurry of liquid and solid phase me-dium. The control valve element is for example a ball valve, a butterfly valve, and etcetera. Thecombination ofthe drive unit and the control valve element forms a control valve unit.

Prior art drive units for controlling control valve elements are usually either manually operated or pneumatic driven. Electric driven drive units are not commonly available on the marked due to thechallenging environment which the drive units are subjected to, which can result in problems withmalfunctions ofthe control ofthe control valve elements. A further problem with prior art electricdriven drive units is that they are customized with electric motor, gear box and control unit for theconnected control valve element. Accordingly, the cost of such customized control solution is high and the operation and the control ofthe drive unit are complex.

US2007170385 discloses an electrically driven actuator for controlling a gaseous or liquid volumet-ric flow.

Obiects and summary of the invention The object ofthe present invention is to provide a reliable electric driven drive unit for the controlof a control valve element. A further object ofthe invention is to enable the drive unit to be manu-factured in a cost effective manner compared with prior art electric driven drive unit using massproduced component.

This object is obtained by means of a drive unit according to the preamble of claim 1. The driveunit is characterized in that the electric motor is of a type configured to allow rotation of the driveshaft a number of revolutions, the electric motor, the gear box and the control unit are combinedin a single mechatronic unit, the drive unit further comprises a detector adapted to detect, atstartup of the drive unit, at least one position of the drive shaft corresponding to any of the firstand second position ofthe drive shaft, and the control unit is adapted to determine the first andsecond position of the drive shaft based on the at least one detected position.

The combination ofthe drive unit and the control valve element forms a control valve unit. Thedrive unit is provided with a detector for detecting at least one of the first position and the secondposition relating to the open state respective closed state of the control valve element. The de-tected position is used for determining the first and second position of the drive shaft. The deter-mining positions are used when controlling the control valve element. Accordingly, the drive unit isarranged to be calibrated for the operation ofthe control valve element to which the drive unit isapplied.

The drive unit is based on a single mechatronic unit that comprises the electric motor, the gear boxand the control unit. The single mechatronic unit is an available standard product. The electric mo-tor of the single mechatronic unit is a type configured to allow the drive shaft to rotate a numberof revolutions. The single mechatronic unit is for example used in industrial transportation applica-tions. When the single mechatronic unit is configured for the control ofthe control valve element,rotation of less than a single revolution may be applied, such as a rotation of 70 degrees betweenthe first and the second position ofthe drive shaft. By means of enabling use ofthe single mecha-tronic unit, the cost of manufacturing and installing the drive unit is reduced compared with priorart customized control solution.

According to an embodiment of the invention, the control unit is adapted to receive informationon the angular rotation between the first position and the second position ofthe drive shaft, anddetermine the first and second position ofthe drive shaft based on the at least one detected posi-tion and the angular rotation between the first position and the second position.

The drive unit is adapted to receive information on the connected control valve element, such asdefining the rotational angle between the first position and the second position of the control valve element. The information may for example be the number of pulses of a rotary encoderwhen the drive shaft is rotated between the first position and the second position. The detectedposition and the information on the angular rotation between the first and the second position areused for determining the first and second position of the drive shaft.

According to an embodiment ofthe invention, the drive unit comprises a rotary encoder arrangedto indicate a plurality of angular positions between the first position and the second position ofthedrive shaft, wherein the control unit is adapted, at startup of the of the drive unit, to rotate thedrive shaft until detecting at least one of the first position and the second position, and determineand store the angular position ofthe rotary encoder at the first position and the second position ofthe drive shaft.

The angular positions between the first position and the second position ofthe drive shaft are de-fined for the rotary encoder. At start-up of the drive unit, the angular position ofthe rotary en-coder is determined and stored at the first position and the second position of the drive shaft.

According to an embodiment of the invention, the detector comprises a position sensor that isadapted to indicate when the drive shaft is in at least one of the first position and the second posi-tion. Preferably, the position sensor comprises a marker arranged on the drive shaft and a sensingelement adapted to sense the marker. The marker is arranged on the appropriate position corre-sponding to the at least one ofthe first position and the second position of the drive shaft.

According to an embodiment of the invention, the position sensor is a proximity sensor that indi-cates when the drive shaft is in at least one ofthe first position and the second position withoutphysical contact with the drive shaft. For example, the proximity sensor comprises a passivemarker arranged on the appropriate position on the drive shaft and the sensing element is ar-ranged to be aligned when the drive shaft is in the at least one ofthe first position and the secondposition.

According to an embodiment of the invention, the proximity sensor is one of a capacitive sensor, aDoppler effect, an eddy-current sensor, an inductive sensor, a laser sensor, a magnetic sensor, aninductive sensor, an optical sensor, a thermal infrared sensor, a photocell, an ultrasonic sensor, anHall effect sensor.

According to an embodiment of the invention, the drive shaft comprises a mechanical stop ar-ranged at at least one ofthe first position and the second position of the drive shaft, and the de-tector comprises a sensor adapted to measure the momentum of the drive shaft, wherein the con-trol unit is adapted to determine that the drive shaft is in the at least one of the first position andthe second position in dependency of a significant change in said measured momentum.

The drive shaft is adapted to be rotated towards the mechanical stop in order to detect the signifi-cant change in the momentum of the drive shaft. Thereby, the position ofthe at least one of thefirst position and the second position is defined. The significant change is for example a certainthreshold value of the momentum ofthe drive shaft According to an embodiment of the invention, the significant change in said detected momentum constitutes a threshold ofthe momentum in the interva| of 10 to 30% of the operational momen- tum ofthe drive shaft, preferably a threshold of the momentum in the interva| of 15 to 25% of theoperational momentum ofthe drive shaft.

According to an embodiment ofthe invention, the information on the connected control valve ele-ment, such as defining the rotational angle between the first position and the second position ofthe control valve element is set by means of one or more DlP-switches.

According to an embodiment ofthe invention, the mechatronic unit is encapsulated from the sur-rounding environment. By encapsulating the mechatronic unit comprising the electric motor, thegear box and the control unit, the drive unit is arranged for operation in demanding environments.

According to an embodiment ofthe invention, the drive unit comprises a connection element forconnecting the drive shaft to the control shaft of the control valve element. The connection ele-ment enables the drive shaft to be connected to the control shaft of the control valve element.

The object of the invention is further obtained by a method for operating a drive unit of a controlvalve element according to claim 11. The method comprises the steps of - receiving information on the angular rotation between the first position and the second positionof the drive shaft, - rotating the drive shaft while using the detector for detecting the position of at least one of thefirst position and the second position of the drive shaft, - bringing the drive shaft to a stand still when detecting the position ofthe at least one of the firstposition and the second position of the drive shaft, and - storing the rotational position ofthe drive shaft in the first position as a first rotational value andthe rotational position ofthe drive shaft in the second position as a second rotational value.

The information on the angular rotation between the first position and the second position is de-pendent on the configuration of the control valve element. The angular rotation may for examplebe 70 degrees or 90 degrees between the first position and the second position. The method fur-ther comprises calibrating the drive unit for the connected control valve element. The drive unit iscalibrated by means of rotating the drive shaft and searching for a detection of at least one of the first position and the second position of the drive shaft. When one of the first position and the sec-ond position has been detected, the drive shaft can be brought to a at a position of the drive shaftthat corresponds to position indicated by the received control signal and the rotational position ofthe drive shaft in the first position is stored as a first rotational value and the rotational position ofthe drive shaft in the second position is stored as a second rotational value. Thereby, the drive unitis calibrated for use with the connected control valve element.

According to an embodiment of the invention, the detector comprises a position sensor that indi-cates when the drive shaft is in at least one of the first position and the second position, whereinthe position of at least one of the first position and the second position of the drive shaft is de-tected when receiving a indication from the position sensor.

According to an embodiment of the invention, the drive shaft comprises a mechanical stop ar-ranged at at least one ofthe first position and the second position of the drive shaft, and the de-tector comprises a sensor adapted to measure the momentum of the drive shaft, wherein the po-sition of at least one of the first position and the second position ofthe drive shaft is detected bydetecting a significant change in said measured momentum.

According to an embodiment ofthe invention, the significant change in the measured momentum of the drive shaft constitutes a threshold ofthe momentum in the interval of 10 to 30% of the op- erational momentum ofthe drive shaft, preferably a threshold ofthe momentum in the interval of15 to 25% of the operational momentum of the drive shaft.

According to an embodiment of the invention, the method further comprises: - receiving a control signal for the control of the control valve element, - determining a position of the drive shaft that corresponds to the control signal, and- rotating to the drive shaft to the determined a position.

The control signal is an external received signal. ln the case of an industrial manufacturing processor an industrial facility, the control signal is received from a control central. The control central isfor example a Distributed Control System (DCS-system), a single loop regulator, a transmitter forlevel or temperature, and etcetera. The control signal is for example an analog or a digital electricsignal. The control signal comprises information on the position in which the control valve elementis to be arranged in. The control signal is for example an analog or digital electric signal. ln the caseof a digital electric signal, the control signal is for example HART, Can, Profibus, etcetera. The con-trol signal may be receive by a wired or wireless connection. ln the case of an analog signal, thesignal may for example be an electric signal in the interval of 4-20 mA, where 4 mA represents theclosed position of the control valve element, 20 mA represents the open position of the controlvalve element, or vice versa. The values in between 4 and 20 mA represent positions between the closed position and the open position of the control valve element. After that the control signalhas been received, the control unit determines a position of the drive shafts that corresponds tothe information of the control signal. Once the position ofthe drive shafts has been determined,the drive shaft is rotated to the determined position.

The object of the invention is further obtained by a control valve unit that comprising the driveunit according to any of claims 1-10 and a control valve element.

Brief description of the drawings The invention will now be explained more closely by the description of different embodiments ofthe invention and with reference to the appended figures.

Fig. 1 shows a control valve element unit comprising a drive unit according to an embodimentof the invention and a thereto connected control valve element.Fig. 2 shows a flow chart of a method for controlling the drive unit in fig. 1 according to an em- bodiment ofthe invention Detailed description of preferred embodiments of the invention Fig. 1 shows a control valve unit 1 comprising a drive unit 3 according to an embodiment of the in-vention and a control valve element 5.

The drive unit 3 is arranged to control the operation of the control valve element 5 between anopen state and a closed state. The control valve element 5 is adapted to regulate a flow of a me-dium through the control valve element 5. The control valve element 5 comprises a control shaft 7for regulating the control valve element 5 to positions between the open state and the closedstate.

The medium may be in various phases, such as in liquid phase, gas phase or a mixture of phases,such as a slurry of liquid and solid phases, or a mixture of liquid and gas. For example, the controlvalve element 5 may be used for regulating the flow of oil, gas, paper pulp, etcetera.

The drive unit 3 comprises an electric motor 10, a gear box 12 and a control unit 14 for controllingthe electric motor 10 and the gear box 12. The electric motor 10, the gear box 12 and the controlunit 14 are combined in a single mechatronic unit 15 arranged for industrial transportation applica-tions. The single mechatronic unit 15 is encapsulated from the surrounding environment. Thereby,the drive unit 3 is suitable to operate in challenging environment of the control valve element 5 and may be rinsed with water. The single mechatronic unit 15 is for example encapsulated with an|P65 class encapsulation.

The electric motor 10 comprises a drive shaft 16 that is connected to the control shaft 7 by meansof a connection element 18. The drive shaft 16 is adapted to be rotated between a first positionrelating to the closed state of the control valve element 5 and a second position relating to theopen state ofthe control valve element 5.

The control unit 14 is adapted to receive a control signal 20 relating to the control of the controlvalve element 5. The control signal 20 is for example transmitted from a control center of an indus-trial manufacturing plant in which the control valve element unit 1 is arranged. The control signal20 comprises information on the desired position ofthe control valve element 5, such as theclosed or open position, or certain positions in between the closed and the open position.

The control signal 20 is for example an analog electric signal, such as 4-20mA, where 4 mA repre-sents the closed position ofthe control valve element 5, 20 mA represents the open position ofthecontrol valve element 5, or vice versa, and values in between 4 and 20 mA represents positions be-tween the closed position and the open position of the control valve element 5.

The control unit 14 is adapted to determine the position of the drive shaft 16 on basis of the re-ceived control signal 20, and rotate the drive shaft 16 to the determined position between the firstposition and the second position. The control signal 20 may be received continuously or at certaintime interval.

The control unit 14 comprises a logic unit 22, such as a CPU, a motor controller, etcetera, andmemory storage 24. The logic unit 22 is adapted to handle the calibration of the drive unit 3 for thespecific configuration of the connected control valve element 5 and the operation ofthe drive unit3.

The drive unit 3 further comprises a rotary encoder 30 arranged at the drive shaft 16 and a detec-tor 32. The rotary encoder 30 arranged to indicate a plurality of angular positions between the firstposition and the second position of the drive shaft 16. The detector 32 is arranged to detect a posi-tion of the drive shaft 16 relating to the first position and/or the second position ofthe drive shaft16. The control unit 14 is adapted to receive information from the rotary encoder 30, the detector32 and the electric motor 10. The information from the electric motor 10 is for example relating tothe current and voltage to the motor.

The detection ofthe first position and/or the second position ofthe drive shaft 16 is done at astartup phase ofthe drive unit 3 in order to calibrate the drive unit 3 for the configuration of theconnected control valve element 5.

The control unit 14 is adapted, at startup of the of the drive unit 3, to rotate the drive shaft 16 un-til detecting the first position and/or the second position, and determine and store the angular po-sition of the rotary encoder 30 at the respective first position and/or second position of the driveshaft 16 on basis of the detected position of the first position and/or the second position and infor-mation of the angular rotation between the first and the second position. The angular positionmay also be stored for both the first position and the second position of the drive shaft during cali-bration ofthe drive unit 3. Thereby, information on the rotational angular rotation between thefirst position and the second position of the drive shaft 16 is not necessary for the determinationof the first position and the second position. The stored angular position of the rotary encoder 30is used during operation to assured that the drive shaft 16 is rotated to the correct position in de-pendency of the received control signal 20. The calibration and the control of the drive unit 3 willbe discussed further in details in connection to fig. 2.

According to an embodiment of the invention, the detector 32 is a proximity sensor that indicateswhen the drive shaft 16 is in at least one of the first position and the second position without phys-ical contact with the drive shaft 16. The proximity sensor comprises a marker 35 arranged on thedrive shaft 16 and a sensor element 37 is arranged to detect when the marker 34 and the sensorelement 37 are aligned The proximity sensor is for example one of a capacitive sensor, a Doppler effect, an eddy-currentsensor, an inductive sensor, a laser sensor, a magnetic sensor, an inductive sensor, an optical sen-sor, a thermal infrared sensor, a photocell, an ultrasonic sensor, an Hall effect sensor.

According to an alternative embodiment of the invention, the drive shaft 16 is provided with a me-chanical stop. The mechanical stop is arranged at the first position and/or the second position ofthe drive shaft 16. The detector 32 comprises a sensor element adapted to measure the momen-tum ofthe drive shaft 16 and the control unit 14 is adapted to determine when the drive shaft 16is in the first position and/or the second position in dependency of a significant change in saidmeasured momentum. The significant change is for example, the detection of a threshold value ofthe momentum of the drive shaft 16 in the interval of 10 to 30% ofthe operational momentum ofthe drive shaft 16, preferably a threshold value of the momentum in the interval of 15 to 25% ofthe operational momentum of the drive shaft 16.

Fig. 2 shows a flow chart of a method for controlling the drive unit 3 in fig. 1 according to an em-bodiment ofthe invention. The method comprises a calibration of the drive unit 3 in the method steps 110-140, and operation of drive unit 3 for the control ofthe control valve element 5 in themethod step 150-170.

The method is initiated in a step 110 by receiving information on the angular rotation between thefirst position and the second position ofthe drive shaft 16. The information is for example receivedfrom a setting arrangement comprising one or more DlP-switches. ln the case when the controlunit is connected to single loop controller with 4-20 mA interval control, the configuration of thedrive unit can be performed by means of DCS-bus communication protocol, such as the setting ofrotational angel between the first and the second position of the drive shaft and information onmanner of detecting the first and/or the second position of the drive shaft. The first and/or thesecond position of the drive shaft is/are for example detected by means of a proximity sensor or athreshold in the momentum of the drive shaft when the drive shaft is rotated towards a mechani-cal stop. ln a step 120, the method comprises rotating the drive shaft 16 while using the detector 32 for de-tecting the position of the first position and/or the second position of the drive shaft 16, The drive shaft 16 is preferably during detection ofthe first position and/or the second position rotated at a lower speed of rotation than the speed of rotation used during the control of the control valve ele-ment 5. ln a step 130, the method comprises bringing the drive shaft 16 to a stand still position when thefirst position and/or the second position is/are detected. ln a step 140, the method comprises stor-ing the rotational position of the drive shaft 16 in the first position as a first rotational value andthe rotational position ofthe drive shaft 16 in the second position as a second rotational value.The drive shaft 16 is brought to a stand still in order to accurately determine the rotational posi-tion of the drive shaft 16 in the detected position. Thereafter, the rotational position in the firstposition and the second position is stored in the memory unit 24. ln a step 150, the method comprises receiving a control signal 20 for the control ofthe controlvalve element 5. The control signal 20 is an external signal originating from a control center oftheindustrial facility in which the control valve element is arranged. The control signal 20 is for exam-ple an analog electric signal, such as 4-20 mA. ln a step 160, the method comprises determining a position ofthe drive shaft 16 that correspondsto the received control signal 20. For example, a 4 mA control signal 20 represents a closed posi-tion, wherein the drive shaft 16 is to be arranged on the first position. Correspondingly, a 20 mAcontrol signal 20 represents an open position, wherein the drive shaft 16 is to be arranged on thesecond position. A control signal 20 with a value between 4 and 20 mA represents a position ofthe drive shaft 16 between the first and the second position. The position of the drive shaft 16 is deter-mined and scaled to the value of the rotary encoder 30 that corresponds to the desired position. ln a step 170, the method comprises rotating the drive shaft 16 to the determined a position hav-ing the value of the rotary encoder 30 that corresponds to the desired position.

The method steps of 150-170 are iterated at certain time interva| during the control of the controlvalve element 5 in order to assure that the control valve element 5 is controlled at a suitable rate.

The present invention is not limited to the disclosed embodiments but may be modified within the framework of the claims.

Claims

i

1. A drive unit (3) for controlling a control valve element (5), the drive unit (3) comprises: - an electric motor (10) comprising a drive shaft (16) adapted to be connected to a control shaft (7)of the control valve element (5), - a gear box (12) adapted to control the output momentum of the drive shaft (16), and - a control unit (14) adapted to receive a control signal (20) and to control the electric motor (10)so that the drive shaft (16) is rotated to positions between a first position corresponding to aclosed state of the control valve element (5), and a second position corresponding to an open stateof the control valve element (5), in dependency of the control signal (20), characterized in that theelectric motor is of a type configured to allow rotation of the drive shaft a number of revolutions,the electric motor (10), the gear box (12) and the control unit (14) are combined in a single mecha-tronic unit (15), the drive unit (3) further comprises a detector (32) adapted to detect, at startup ofthe drive unit (3), at least one position of the drive shaft (16) corresponding to any ofthe first andsecond position of the drive shaft (16), and the control unit is adapted to determine the first andsecond position of the drive shaft based on the at least one detected position.

2. The drive unit (3) according to claim 1, wherein the control unit (14) is adapted to receive infor-mation on the angular rotation between the first position and the second position of the drive shaft (16), and determine the first and second position of the drive shaft (16) based on the at leastone detected position and the angular rotation between the first position and the second position.

3. The drive unit (3) according to any of claim 1 and 2, wherein the drive unit (3) comprises a rotaryencoder (30) arranged to indicate a plurality of angular positions between the first position and thesecond position of the drive shaft (16), wherein the control unit (14) is adapted, at startup e-R-šefes-ofthe drive unit (3), to rotate the drive shaft (16) until detecting at least one of the first position andthe second position, and determine and store the angular position of the rotary encoder (30) atthe first position and the second position of the drive shaft (16).

4. The drive unit (3) according to any of the previous claims, wherein the detector (32) comprises aposition sensor that is adapted to indicate when the drive shaft (16) is in at least one of the firstposition and the second position.

5. The drive unit (3) according to claim 4, wherein the position sensor is a proximity sensor that in-dicates when the drive shaft (16) is in at least one of the first position and the second positionwithout physical contact with the drive shaft (16).

6. The drive unit (3) according to claim 5, wherein the proximity sensor is one of a capacitive sen-sor, a Doppler effect sensor, an eddy-current sensor, an inductive sensor, a laser sensor, a mag-netic sensor, 1 ' ' , ' _' * . , an optical sensor, a thermal infrared sensor, a photocell sensor, an ultrasonic sensor, an Hall effect sensor.

7. The drive unit (3) according to any of the previous claims, wherein the drive shaft (16) comprisesa mechanical stop arranged at at least one of the first position and the second position of the driveshaft (16), and the detector (32) comprises a sensor adapted to measure the momentum of thedrive shaft (16), wherein the control unit (14) is adapted to determine that the drive shaft (16) is inthe at least one of the first position and the second position in dependency of a significant changein said measured momentum.

8. The drive unit (3) according to claim 7, wherein the significant change in said detected momen-tum constitutes a threshold of the momentum in the interval of 10 to 30% of the operational mo-mentum of the drive shaft (16), preferably a threshold of the momentum in the interval of 15 to25% of the operational momentum of the drive shaft (16).

9. The drive unit (3) according to any of the previous claims, wherein the mechatronic unit (15) isencapsulated from the surrounding environment.

10. The drive unit (3) according to any of the previous claims, wherein the drive unit (3) comprisesa connection element for connecting the drive shaft (16) to the control shaft (7) of the controlvalve element (5).

11. A method for operating a drive unit (3) for a control valve element (5), wherein the drive unit(3) comprises an electric motor (10) comprising a drive shaft (16) connected to a control shaft (7)of the control valve element (5) and adapted to be rotated between a first position relating to aclosed state of the control valve element (5) and a second position relating to ag open state of thecontrol valve element (5), wherein the drive unit (3) further comprises a control unit (14) for con-trolling the rotation of the drive shaft (16) and a detector (32) for detecting a position of the driveshaft (16) relating to at least one of the first position and the second position of the drive shaft(16), the method comprises the steps of - rotating the drive shaft (16) while using the detector (32) for detecting the position of at leastone of the first position and the second position of the drive shaft (16), - bringing the drive shaft (16) to a stand still when detecting the position of the at least one of thefirst position and the second position of the drive shaft (16), and - determining and storing the rotational position of the drive shaft (16) in the first position and therotational position of the drive shaft (16) in the second position based on the at least one detectedposition.

12. A method according to claim 11, wherein the method comprises: - receiving information on the angular rotation between the first position and the second positionof the drive shaft (16), - determining and storing the rotationa| position of the drive shaft (16) in the first position and therotationa| position of the drive shaft (16) in the second position based on the at least one detectedposition and the angular rotation between the first position and the second position.

13. A method according to any of claim 11 and 12, wherein the method further comprises: - receiving a control signal (20) for the control of the control valve element (5), - determining a position of the drive shaft (16) that corresponds to the control signal (20), and- rotating to the drive shaft (16) to the determined aposition.

14. A control valve unit (1) comprising a drive unit (3) according to any of claims 1-10 and a control valve element (5).