Abstract:
The invention relates to an actuating device ( 1 ) for displacing a control device ( 3 ), which is subjected to the action of force counter to the direction of displacement ( 2 ). Said actuating device comprises an actuating element, which, inside a device housing ( 4 ), can be axially displaced in a direction of displacement by a turning spindle ( 5 ) of an advancing device ( 6 ). The turning spindle is connected in a rotationally fixed manner to a turning sleeve ( 8 ), which is rotatably mounted in the device housing ( 4 ) and which surrounds the turning spindle. Said turning sleeve is fixed, in relation to an annular flange ( 9 ) that is connected to the device housing in a rotationally fixed manner, counter to an advance turning direction ( 11 ) of the turning spindle by means of a spiral spring ( 10 ). An emergency disengagement device for resetting the actuating element counter to the direction of displacement is assigned to the spiral spring. The aim of the invention is to improve the actuating device by providing it with a compact and simple design and, at the same time, by enabling the winding of the spiral spring to be easily and precisely adjusted with regard to the torsional strength of the connection of the turning sleeve and the annular flange. To this end, the emergency disengagement device comprises a tension sleeve ( 13 ) for the spiral spring that is detachably held in a tensioning position. Said tension sleeve can be torsioned between a tensioning position and a final tensioning position and is subjected to the action of force toward its final tensioning position.

Description:
DESCRIPTION  
         [0001]    This invention relates to an actuator system for shifting a control device that is pressure-loaded in the direction opposite the shift direction, said actuator system incorporating an actuator element capable of being axially moved in the shift direction within a system enclosure by a rotating spindle of an advance mechanism, which rotating spindle is rigidly connected to a rotating sleeve that is pivot-mounted in the system enclosure and surrounds the rotating spindle which latter, relative to a circular flange rigidly connected to the system enclosure, is locked in position in the direction opposite the direction of advance rotation of the rotating spindle by means of a volute spring which volute spring is associated with an emergency release unit for resetting the actuator element against the shift direction.  
           [0002]    An actuator system of this type has been known in prior art, serving to actuate control devices such as valves, pressure regulators and other control mechanisms but employed most particularly in submarine oil and gas exploration and production equipment. Evidently, the actuator system can be employed equally well in comparable land-based, difficult-to-access or remote locales.  
           [0003]    When the switching device is shifted against the direction of the pressure load, the actuator element is moved axially so that in its extended position it serves to shift the control device into the operational ready-state. When the actuator element is retracted away from the shift direction, the control device is deactivated. An actuator system of this type is provided with a suitable system enclosure protecting it from the elements in a marine or land-based environment. The actuator element is shifted by the rotation of a rotating spindle which is rigidly connected to a rotating sleeve surrounding it. In the direction opposite the direction of advance rotation, a volute spring locks this rotating sleeve in position relative to a circular flange rigidly attached to the system enclosure. This ensures that, while a rotation of the rotary spindle in the advance direction for extending the actuator element is possible without being impeded by the volute spring, any automatic insertion of the actuator element into the system enclosure by the pressure load in the control device against the shift direction is prevented by the volute spring. Thus, for example, any pressure on the advance mechanism is neutralized and absorbed by the system enclosure.  
           [0004]    However, in order to permit an automatic resetting of the actuator element for closing the control device in the event of a power failure or other problem, the volute spring connects to an emergency release unit which releases the volute spring to a point where the rotating sleeve can be turned relative to the circular flange, allowing the rotating spindle that is rigidly connected to the rotating sleeve to turn against the direction of advance rotation and thus moving the actuator element against the shift direction.  
           [0005]    In the prior-art actuator system, the emergency-release unit is mounted on the outside of the system enclosure and is constituted of an electromagnet with a plunger protruding into the system enclosure. The plunger is located away from the end of the volute spring which thus rigidly connects the rotating sleeve and the circular flange. In the event of a power failure a spring strikes the plunger, moving it against the end of the volute spring which allows the latter to be released. The overall design of that actuator system is relatively complex while at the same time it is difficult if not impossible to adjust the tension of the volute spring seated on the rotating sleeve and circular flange.  
           [0006]    It is therefore the objective of this invention to improve the design of an actuator system of the aforementioned type so as to offer a more compact and simpler configuration while at the same time permitting simple and precise adjustment of the volute spring in terms of a torsionally stable connection of the rotating sleeve and the circular flange.  
           [0007]    This is accomplished, in the context of the characteristic conceptual features per claim 1, by providing the emergency release unit with a tensioning sleeve for the volute spring, rotatable between a tensioned position and a relaxed position, pressure-loaded in the direction of the relaxed position and releasably held in the tensioned position.  
           [0008]    In its relaxed position the volute spring is released to a point where it permits a rotation of the rotating sleeve relative to the circular flange and thus a rotation of the rotating spindle in the direction opposite the direction of advance rotation. When the tensioning sleeve is turned out of its relaxed position, the coiling strength of the volute spring can prevent any turning of the rotating sleeve relative to the circular flange. Besides, the tensioning sleeve is usually contained inside the system enclosure so that no part of the emergency release unit protrudes from the system enclosure. The emergency release unit is thus far less susceptible to damage or similar problems.  
           [0009]    For moving the rotating spindle in the direction of advance rotation, the advance mechanism can be equipped with an electric motor, for instance a direct-current servomotor.  
           [0010]    It is possible to connect the motor and the rotating spindle in a direct-drive configuration. For an advance mechanism with a high torque transfer the rotating spindle may be a revolving ball screw and the connection of the electric drive motor may be by way of a ball nut holding the revolving ball screw.  
           [0011]    A drive assembly may be installed between the electric motor and the ball nut for converting the rotational speed of the electric motor into a corresponding number of revolutions of the rotating spindle. Such a drive unit may be in the form of a standard clutch-and-brake combination or alternatively a so-called flex-spline drive without the traditional gears.  
           [0012]    For a better suspension of the rotating spindle and/or the ball nut the annular disk can be provided with a ring extension on the side facing the ball nut, with a connecting sleeve pivot-mounted on the ring extension. One end of the connecting sleeve is attached, particularly in removable fashion, to the motor-drive unit, the other end to the ball nut. The rotating spindle revolves in the connecting sleeve either as a rotatably supported insert or independently pivot-mounted. The motor-drive unit turns the connecting sleeve and the rotation is transferred to the ball nut, causing the rotating spindle to turn in the direction of advance rotation as related to the ball nut, or in the opposite direction.  
           [0013]    To permit a rotation of the connecting sleeve only in the advance direction of the rotating spindle while at the same time causing the overall system enclosure to absorb any corresponding counterpressure exerted on the rotating spindle, an additional volute spring can be positioned between the connecting sleeve and the ring extension.  
           [0014]    As a simple way to determine the position of the actuator element and the corresponding position of the rotating spindle, the advance mechanism and more specifically the electric motor can be equipped with a positional sensor. The sensor would detect for instance the respective longitudinal position of the rotating spindle from which it determines the position of the actuator element. It is also possible to track the advance path of the actuator element directly by means of an appropriate positional sensor in the motor. This applies in analogous fashion to the reverse rotation of the rotating spindle and thus to the resetting of the actuator element.  
           [0015]    For protecting the additional volute spring against external factors and/or for positioning the connecting sleeve and ball nut especially in a radially and axially suspended direction, a casing may be provided to enclose the ring extension and the connecting sleeve, the casing to be removably attached to the annular disk. By virtue of being attached to the annular disk the casing is rigidly connected to the system enclosure.  
           [0016]    To ensure proper guidance of the rotating spindle in the area between the ball nut and the actuator element, the rotating sleeve may extend essentially from the ball nut all the way to the exit end of the system enclosure opposite the electric motor, while the guide sleeve is provided with at least two guide slots in which appropriate guide lugs, protruding radially in relation to the rotating spindle, can be moved in an axial direction. Since the guide lugs engage in the corresponding guide slots, the rotating sleeve and the rotating spindle are rigidly connected to each other. This means that when the rotating spindle turns for instance in the advance direction, the rotating sleeve remains stationary and the volute spring holds the guide sleeve in place, preventing it from turning. Relative to the system enclosure the rotating sleeve is pivot-mounted in appropriate bearings.  
           [0017]    To allow the use of standard rotary spindles or ball screws, the guide lugs can be positioned on a spindle head that is removably attached to one end of the rotating spindle. For example, the spindle head may be screwed onto the end of the rotating spindle and thus rigidly connected to it.  
           [0018]    To permit in simple fashion a conversion of a rotation of the rotating spindle and of the spindle head into an axial movement of the actuator element, the spindle head can be equipped on the far side from the rotating spindle with a rotary mount accepting the end of the actuator element. By means of this rotary mount the actuator element and the rotating spindle can turn in relation to each other, except that in general the actuator element does not turn but is moved strictly in the axial forward or reverse direction.  
           [0019]    In a simple design example the guide sleeve and the casing may feature mutually facing end sections of an essentially identical outer diameter, onto which the volute spring is wound.  
           [0020]    The volute spring itself is surrounded by the tensioning sleeve whose respective rotational position causes the volute spring to open or close.  
           [0021]    As a simple way to seal off the system enclosure at least at the end from which the actuator element can be extended, the exit end of the enclosure can be equipped with an enclosure lid which is provided with a guide bore for the actuator element. The enclosure lid may be designed to screw either into or onto the system enclosure. In addition, the enclosure lid may be detachably fastened to the system enclosure by other suitable means such as screws or bolts.  
           [0022]    To permit simplified suspension of the guide-sleeve end on the enclosure lid, the system enclosure may be provided with at least one sleeve insert which protrudes into the enclosure and surrounds the guide sleeve and in which the guide sleeve is pivot-mounted.  
           [0023]    A particularly compact design of the emergency release unit can be obtained by pivot-mounting the tensioning sleeve for instance on the outside of the casing and the sleeve insert.  
           [0024]    By way of a suitable drive unit, possibly with a clutch mechanism, the tensioning sleeve can be connected to the electric motor for the rotating spindle or ball nut. For relatively independent and precise rotation of the tensioning sleeve it is possible to rotate the tensioning sleeve by means of an electric tensioning motor and in particular a step motor.  
           [0025]    As a simple way to more or less tighten the volution of the guide sleeve and casing in the corresponding areas as the tensioning sleeve turns, a cam may be provided especially on the inside of the rotating sleeve in a way as to make contact with with one coil end of the volute spring. The cam will open the coil end as a function of the rotation of the tensioning sleeve. By virtue of its intrinsic elastic force the volute spring will cause friction blockage against the opening direction.  
           [0026]    For a particularly compact design of the actuator system the tensioning motor may be positioned within the enclosure next to the casing.  
           [0027]    For as long as electric power is fed to the tensioning motor, it applies a holding force to the tensioning sleeve, counteracted by the pressure load of the tensioning sleeve in the relaxed position. If and when the electric power fails or drops off, the elastic force will turn the tensioning motor and especially the tensioning sleeve in the direction of the relaxed position. In a simple design example, the pressure load on the tensioning sleeve in the direction of the relaxed position can be provided by a return spring mounted between the tensioning sleeve and the enclosure or a component rigidly attached relative to the enclosure. As the tensioning sleeve turns, the relaxed return spring is tensioned, whereby the elastic energy in the return spring can be used to reset the tensioning sleeve in its relaxed position. It should be noted that the return spring is employed both for an emergency closure and for normal closing i.e. resetting of the tensioning sleeve as the volute spring is released.  
           [0028]    In the simplest case the rigidly mounted component in question may be the enclosure lid and in particular the sleeve insert.  
           [0029]    In order to also cock the return spring by means of the tensioning sleeve, an additional cam may be provided in a way as to protrude inward in an essentialy radial sense from the inside of the tensioning sleeve and to make contact with a coil end of the torsional-type return spring. Specifically, the respective other end of the volute spring is locked in position on the rigidly mounted component.  
           [0030]    To at least partially enclose the actuator element along the direction of the advance movement, the enclosure lid may be provided with an outer sleeve that is located opposite the sleeve insert and surrounds the actuator element.  
           [0031]    To prevent water, dirt etc from penetrating into the outer sleeve, the free end of the latter can be equipped with a preferably detachable end cap that is provided with an exit opening for the essentially rod-shaped actuator element. The actuator element may have a polygonal or round cross section.  
           [0032]    For an attenuation of the movement of the actuator element the outer sleeve may be at least partly filled with a fluid and at least one displacement element may protrude laterally from the actuator element within the outer sleeve.  
           [0033]    One particularly effective yet simple displacement element may be a displacement disk radially extending outward from the actuator element and provided with at least one fluid-conducting aperture.  
           [0034]    For facilitated maintenance and accessibility of the actuator system the enclosure may be composed of at least two detachably connected enclosure sections. In this context, for the purpose of replacing or easily repairing the motor-drive-unit, one of the enclosure sections may essentially constitute an enclosure end section housing the motor-drive assembly.  
           [0035]    As an example of a simple approach to attaching the actuator system according to this invention to a corresponding control device, link-up hardware is provided directly on an outside surface of the enclosure in the area of the enclosure lid, allowing the attachment and detachment of a control device. 
       
    
    
       [0036]    The following describes in more detail advantageous design examples of this invention with the aid of the figures in the attached drawings in which:  
         [0037]    [0037]FIG. 1 is a longitudinal section through the actuator system according to this invention, attached to a control device;  
         [0038]    [0038]FIG. 2 shows a longitudinal section through the actuator system per FIG. 1 along the intersecting line II-II in FIG. 3;  
         [0039]    [0039]FIG. 3 is a front view of the actuator system per FIG. 2;  
         [0040]    [0040]FIG. 4 is a sectional view along the line IV-IV in FIG. 3;  
         [0041]    [0041]FIG. 5 is a front view, analogous to FIG. 3, of a second design example of an actuator system according to this invention; and  
         [0042]    [0042]FIG. 6 is a sectional view along the line VI-VI in FIG. 5. 
     
    
       [0043]    The illustration in FIG. 1 depicts a section through an actuator system  1  according to this invention, laterally flanged to a control device  3  in the form of a gate valve. The actuator system  1  includes a system enclosure  4  in the axial direction  66  of which an actuator element  7  is slide-mounted to permit shifting between an extended position  70  and a retracted position  71 . At the end of the actuator system  1  facing the control device  3  the actuator element  7  can be extended so as to shift a valve slide  68 . At least one return spring  67  on the side of the control device  3  opposite the actuator system  1  is subjected to a pressure load in the reset direction  74 .  
         [0044]    The system enclosure  4  is detachably fastened to a flange housing  69  of the control device  3  by means of fasteners  64 . Inside the flange housing  69  the actuator element  7  and the valve slide  68  can be moved in the shift direction  2 . In the extended position  70  of the actuator element  7  the valve slide  68  is shifted within the control device  3  to a point where it exposes a valve gate  72  in the slide bore  73  of the valve slide  68 . In its retracted position  71  the valve slide  68  closes the valve gate  72 .  
         [0045]    Connected at the end of the system enclosure  4  opposite the control device  3  is a cable  79  used for controlling the actuator system and for data transfer.  
         [0046]    [0046]FIG. 2 depicts a longitudinal section through the actuator system  1 . In the upper half of FIG. 2 the actuator element  7  is shown in its retracted position  71 , in the lower half separated by the axial line  66  the actuator element  7  is shown in its extended position  70  as in FIG. 1.  
         [0047]    The two-part system enclosure  4  consists of enclosure sections  62  and  63 . The enclosure section  63  constitutes an enclosure end part which is removably attached to the other enclosure section  62  by means of the fastening device  64 . A corresponding fastening device  64  is located at the exit end  29  of the system enclosure  4  opposite the enclosure end section  63 .  
         [0048]    The enclosure section  63  houses an electric motor  14  constituting part of a motor-drive assembly  19 . A positional sensor  26  at one end serves to detect the longitudinal position of the spindle  5 . Opposite the exit end  29  of the system enclosure  4  the positional sensor  26  protrudes from the enclosure end section  63  and is positioned inside a sensor cap  76  that is detachably connected to the enclosure end section  63 .  
         [0049]    The electric motor  14  connects to a drive assembly  17  constituting its companion part of the motor-drive unit and consisting for instance of a so-called flex-spine drive without the traditional gears. The motor-drive unit  19  is attached to an annular disk  18  which extends horizontally across the inside of the system enclosure  4 , while the drive assembly  17  is at least in part set in a corresponding central circular opening in the annular disk.  
         [0050]    On the side  20  of the annular disk  18  facing away from the electric motor  14 , the disk is provided with a ring extension  21  in which a connecting sleeve  22  is pivot-mounted. The end  23  of the connecting sleeve  22  is rotatably connected to the drive assembly  17  while at its opposite end  24  it is removably attached to a ball nut  16 . The rotating spindle in the form of a ball screw  15  is suspended in the ball nut  16  in a way as to permit movement in the axial direction  66 , i.e. in the shift direction  2 . In the direction toward the ball screw  16  the connecting sleeve  22  features a series of sections with a progressively larger diameter, with its end  23  having the smallest diameter connected to the drive assembly  17 . The combination of ball nut, rotating spindle  15  and motor-drive unit  19  constitutes an advance mechanism  6  for the actuator element  7 .  
         [0051]    Located in the connecting sleeve  22  is the rotating spindle  5 , illustrated in the upper half of FIG. 2 in its fully retracted position in the connecting sleeve  22  while in the lower half it is shown in its maximum extended position from the connecting sleeve  22 .  
         [0052]    Situated between the connecting sleeve  22  and the ring extension  21  is a volute spring  25  as shown. It permits a rotation of the connecting sleeve  22  in the advance direction  11  while preventing any rotation in the reverse direction.  
         [0053]    A rotary mount  28 , indicated in the usual manner by a square or rectangle with diagonal lines, is located between the connecting sleeve  22  and the ring extension  21 .  
         [0054]    The connecting sleeve  22  is surrounded by a casing  27  one end of which is rigidly but detachably mounted on the annular disk  18 . At its opposite end the casing  27  has an end section  40  constituting a circular flange  9  which surrounds the ball nut  16 . In the direction of the exit end  29  of the system enclosure  4  the circular flange  9  connects to a rotating sleeve  8  whose end facing the circular flange  9  features an end section  39 . The end section  39  and the circular flange  9  have the same outside diameter  41  and  42 , respectively. A volute spring  10  is wound onto the end section  39  and the circular flange  9 , respectively, rigidly connecting the casing  27  and the rotating sleeve  8  when the ball nut  16  turns in the advance direction  11 . The rotating sleeve  8  extends all the way to the enclosure lid  43  mounted in the exit opening  29  of the system enclosure  4 . On its inside, the enclosure lid is provided with a sleeve insert  45  which surrounds the rotating sleeve and in which the rotating sleeve is pivot-mounted on a rotary mount  28 . By way of additional rotary bearings  28  at its other end, the rotating sleeve  8  is pivot-mounted on the circular flange  9  of the casing  27 . The actuator element  7  extends through a guide bore  44  in the center of the enclosure lid  43 . At its end  38  on the side of the rotating spindle  5 , the actuator element  7  is connected to a rotary mount  37 . At the end  34  of the rotating spindle  5  the rotary mount  37  is removably attached to and constitutes a separable part of a spindle head  35 , supporting the rotating spindle on its side  36  opposite the spindle. Radially protruding from the rotary mount  37  are two mutually opposite guide lugs  32 ,  33  which engage in corresponding guide slots  30 ,  31  in the rotating sleeve  8  and are guided by these slots in an axial direction  66 . By engaging in the guide slots, the guide lugs cause the rotary mount  37  and thus the rotating spindle  5  and the rotating sleeve  8  to be rigidly connected to one another.  
         [0055]    On its outside opposite the sleeve insert  45 , the enclosure lid  43  is provided with an outer sleeve  55  which surrounds the actuator element  7 . The free end  56  of the outer sleeve  55  is sealed off by an end cap  57 . The actuator element  7  can be extended through an exit hole  58  in the end cap  57 . In its retracted position  71  the free end of the actuator element  7  is essentially flush with the outside surface of the end cap  57 . The outer sleeve  55  is filled with a fluid, not shown. The fluid serves to attenuate the movement of the actuator element  7  which is provided with a radially protruding displacement disk  60  acting as the displacement element  59 . The displacement disk  60  is perforated with fluid-conducting apertures  61  which serve to attenuate the movement of the actuator element  7  especially in the direction of its extended position  70 .  
         [0056]    At one of its coil ends  51 , the volute spring  10  makes contact with a cam  49  located on an inside surface  50  of a tensioning sleeve  13 . The ends of the tensioning sleeve  13  are pivot-mounted in rotary mounts  28  on the outside  47  of the sleeve insert  45  and, respectively, on the outside  46  of the casing  27 . At its end mounted on the casing  27 , the tensioning sleeve  13  is provided with a radially inward-pointing terminal flange  77  with an internal gear rim. This toothed rim engages in a gear  78  that is turned by a tensioning motor  48 . The tensioning motor  48  is positioned between the casing  27  and the system enclosure  4  and can be controlled independent of the electric motor  14  for turning the tensioning sleeve  13 .  
         [0057]    A return spring  52  in the form of a torsion spring is connected at one end to the sleeve insert  45 . Its other coil end  54  makes contact with a cam  53  which protrudes from the inside  50  of the tensioning sleeve  13 . When the tensioning motor  48  turns the tensioning sleeve  13 , it tensions the return spring  52 , producing the necessary return force for the tensioning sleeve  13 .  
         [0058]    The combination of tensioning motor  48 , tensioning sleeve  13 , volute spring  10  and return spring  52  constitutes an emergency release unit  12  which causes the actuator element  7  to be automatically reset into its retracted position  71  in the event of an electric-power failure in the actuator system  1 .  
         [0059]    [0059]FIG. 3 is a frontal illustration of the actuator system  1  per FIG. 2 viewed in the direction of the enclosure end section  63  and the sensor cap  76 . FIG. 2 represents a sectional view along the line II-II in FIG. 3. Four compensators  75 , shown in more detail in FIG. 4, are mounted in a concentric arrangement around the positional sensor  26  per FIG. 3. FIG. 4 represents a section along the line IV-IV in FIG. 3.  
         [0060]    The compensators  75  are positioned in the enclosure end section  63  in a radial configuration relative to the electric motor  14 . These compensators serve to compensate for volume and pressure variations relative to a complete oil filling of the actuator system, i.e. they compensate for volume changes due to system actuation and to temperature fluctuations.  
         [0061]    [0061]FIG. 5 is an illustration, analogous to FIG. 3, of a second design example of an actuator system  1  according to this invention. Four compensators  75  are mounted in a concentric arrangement relative to the positional sensor  26 .  
         [0062]    [0062]FIG. 6 represents a sectional view along the line VI-VI in FIG. 5. For a description of the second design example of the actuator system  1 , reference is made to FIG. 2, with identical components bearing identical reference numbers which latter will be mentioned only as required.  
         [0063]    The second design example of the actuator system  1  essentially differs from the first in that the sleeve insert  45  protrudes less deeply into the system enclosure  4 . As another difference, the positional sensor  26  is recessed into the enclosure end section  63  and the opening accommodating the positional sensor can be sealed relative to the outside of the enclosure end section  63  by a flush-mounted sensor cap  76 .  
         [0064]    Furthermore, the electric motor  14  is of smaller dimensions since the second design version of the actuator system  1  according to this invention is intended for less demanding performance requirements.  
         [0065]    [0065]FIG. 6 shows the actuator element  7  in its retracted position  71  whereby, as can also be seen in FIG. 2, its end is flush with the outside surface of the end cap  57 .  
         [0066]    By way of example and similar to FIG. 2, the system enclosure  4  is provided on its outside  65  with suitable fastening devices  64  which serve to connect the enclosure end section  63  with the enclosure section  62  and the enclosure section  62  for instance with the flange housing  69  per FIG. 1.  
         [0067]    With the aid of the attached figures, the following will briefly explain the mode of operation of the actuator system  1  according to this invention.  
         [0068]    The actuator element  7  is moved into the shift position  2  by operating the electric motor  14  which, by way of the drive assembly  17 , turns the connecting sleeve  22  and, rigidly connected to the latter, the ball nut  16 . As the ball nut turns, the rotating spindle  5  or ball screw  15  is moved in an axial direction in the process of which, by way of the rotary mount  37  at its end  34 , it moves the actuator element  7  in the direction of the extended position  70 .  
         [0069]    At the same time, or before that, the tensioning motor  48  turns the gear  78  and with it the tensioning sleeve  13 . The cams  49  and  53  respectively cause the volute spring  10  to be relaxed and the return spring  52  to be tensioned. Specifically, the volute spring  10 , by virtue of its intrinsic coiling strength, wraps around the rotating sleeve  8  and the casing  27 , thus rigidly connecting these components. The return spring  52  is tensioned by the rotation of the tensioning sleeve  13 .  
         [0070]    The connection between the rotating sleeve  8  and the casing  27  prevents the ball screw  5  from turning backward. The corresponding return-pressure energy is transferred to the system enclosure  4  via the casing  27 .  
         [0071]    If and when the tensioning motor  48 , designed as a step motor, is fed a corresponding holding current, it will hold its position, as will the tensioning sleeve  13 . The return spring  52  stores energy which tries to turn the tensioning sleeve  13  back against the holding force of the tensioning motor  48 .  
         [0072]    In the extended position  70  of the actuator element  7  the valve gate  72  per FIG. 1 is open, allowing gas, oil or similar exploration or extraction to take place.  
         [0073]    The corresponding longitudinal movement of the rotating spindle  5  is monitored by the positional sensor  26 .  
         [0074]    If the valve gate  72  is to be closed, the holding force of the tensioning motor  48  is brought down by appropriate controls. This will then release the volute spring  10 , enabling the rotating sleeve  8 , powered by the return energy of the return spring  52 , to rotate in the opposite direction relative to the casing  27 . By virtue of the rigid connection between the rotating sleeve  8  and the rotating spindle  5 , provided by the guide slots  30 ,  31  and guide lugs  32 ,  33 , the rotating spindle and ball nut  16  can reverse direction toward the electric motor  14 , whereby the actuator element  7 , connected to the rotating spindle, is shifted back into its retracted position  71 . A major factor in this context is the return force applied by the return spring  67  per FIG. 1 on the actuator element  7  since it is essentially this force that resets both the actuator element  7  and the rotating spindle  5 . The return spring  52  essentially serves only the purpose of turning back the tensioning sleeve  13  and correspondingly releasing the volute spring  10 .  
         [0075]    In the event of a power failure as well, the holding force in the tensioning motor  48  subsides, causing an emergency closure of the actuator system  1  due to the action of the emergency release unit  12  composed of the return spring  52 , volute spring  10  and tensioning sleeve  13 . As described further above, the return spring  52  turns the tensioning sleeve  13  back, releasing the volute spring  10 , so that the rotating sleeve  8  can then rotate relative to the casing  27 . The remainder of the closing process takes place in the same way as in a normal closing operation of the actuator system  1 .  
         [0076]    It is thus possible to operate and close a corresponding valve without an extraneous control and electric power-supply system.  
         [0077]    The actuator system  1  described above is particularly suitable for use in the oil, gas, refinery or chemical industry where remote-controlled actuation of a pressure-regulating or shut-off valve or the like in remote and/or dangerous locales is desirable. The emergency release unit  12  according to this invention can be employed not only in conjunction with the aforementioned flex spline drive without traditional gears but also with other, conventional drive systems, production motors and standard clutch/brake combinations.