Abstract:
An actuating device for regulating a control mechanism which is subject to a force against the direction of regulation. The actuating device includes a drive device which has a drive shaft and is connected in a moveable manner to a rotating spindle, by which means an actuating element can be axially displaced in the direction of regulation, in a housing receiving the device. The aim of the invention is to improve one such actuating device in such a way that actuation of the control mechanism is guaranteed in a constructively simple and cost-effective manner. In order to achieve this, the drive device comprises at least two electric motors which can respectively be actuated and controlled for the rotation of the drive shaft.

Description:
BACKGROUND OF THE INVENTION 
     The invention relates to an actuating device for regulating a control mechanism which is subjected to a force against the direction of regulation. Said actuating device comprises a drive device which has a drive shaft and is connected in a moveable manner to a rotating spindle, by which means an actuating element can be axially displaced in the direction of regulation, in a housing receiving the device. 
     Such an actuating device is, for example, known from EP 1 024 422. Such actuating devices are used especially for regulating control devices such as valves, throttle devices and other control mechanisms, especially in applications in oil and gas production. The actuating device is used for maritime and terrestrial locations which may be remote or have difficult access. By displacing the actuating element using the rotating spindle, a valve, for example, is closed or appropriately opened as a control device. Generally in this connection, such a valve is subjected to a force in the direction of the open position, produced by a spring element or similar. To regulate the rotating spindle, it is connected in a movable manner to a drive shaft which is driven by a drive device for regulating the rotating spindle and correspondingly the actuating element in the regulation direction. The actuating device comprises a device housing in which essentially all parts of the actuating device are accommodated and protected against harsh ambient effects in appropriate regions of deployment of the actuating device. 
     Generally, the point of use of such actuating devices is positioned remotely to the associated monitoring and motor control device and additionally it is usually difficult to access, such as for example, with maritime oil and gas production in which the actuating device and the associated control device are located on the sea bed. In order to be able to operate the control device even during a failure or with insufficient effect from the actuating device, a second independent actuating device can be assigned to the same control device. This means that with the failure of one actuating device the other one is employed and remotely operated appropriate to the actuation of the control device. 
     The constructive complexity and financial cost for the arrangement of two actuating devices for only one control device is quite high. In addition, in this case both actuating devices must be maintained and installed at the location of use, whereby often insufficient space is available. 
     The object of the application is therefore to improve an actuating device of the type mentioned at the beginning such that actuation of the control device is ensured in a constructively simple and less expensive manner. 
     U.S. Pat. No. 4,179,944 shows an actuating device with a drive shaft for driving a throttle. The drive shaft is arranged displaceable within a guide sleeve, whereby suitable balls are provided between these two as a bearing. The drive shaft can be withdrawn by rotating a motor and fed forward by rotating a second motor. Appropriate armature windings are provided for both motors and an additional device for fixing a spindle nut is provided between the motors. 
     In the normal operating mode the armature windings of the motors are separate from one another, whereby a suitable locking pin engages the spindle nut. With the occurrence of a fault, one motor rotates in the clockwise direction and the other motor in the counter-clockwise direction so that the corresponding armature windings move towards one another to move the locking pin into a release position. Then, the spindle nut can move in the longitudinal direction of the drive shaft. 
     Accordingly, both motors are not used to mutually substitute one another, to move the drive shaft in both directions of rotation or, should the occasion arise, to drive the drive shaft together in both directions of rotation. 
     The object of the application is therefore to improve an actuating device of the type mentioned at the beginning such that actuation of the control device is ensured in a constructively simple and less expensive manner. 
     BRIEF SUMMARY OF THE PREFERRED EMBODIMENTS 
     The object is solved according to the invention in that the drive device comprises at least two independent electric motors which can respectively be actuated and controlled for the rotation of the drive shaft. 
     Through the use of at least two electric motors it is ensured that with the failure of one motor the other one continues to drive the drive shaft in order to move the rotating spindle and the actuating element appropriately in the regulating direction. All other parts of the actuating device are present in the usual numbers and only the number of electric motors is doubled. According to the invention, a second drive shaft is also not needed on which the second electric motor acts and through which it controls the rotating spindle and actuating element. As a consequence, overall the actuating device according to the invention is in its dimensions essentially unchanged with respect to the previously known actuating device. Alternatively, both motors are used simultaneously, if, for example, a higher driving force is needed. 
     An especially simple and space-saving arrangement can be seen in that the electric motors are arranged one behind the other in the longitudinal direction of the drive shaft. 
     In order to be able to control each of the electric motors individually and essentially independently of one another, a dedicated motor control device can be assigned to each motor. The said motor control device contains a suitable microprocessor, memory devices and similar devices. Each of the electric motors can be operated according to requirements through an appropriate software program using the microprocessor. 
     In order to achieve a very accurate motion control with high reliability and high efficiency of the electric motors, the said motors can be realized as servomotors. 
     In order to obtain a bearing mechanism of high quality and high efficiency which is at the same time reversible in its movement in a simple manner, a rotating sleeve can be driven by a drive shaft via a transmission device, the said rotating sleeve being rotationally rigidly connected to a ball nut of a feed device, whereby the rotating spindle formed as a recirculating ball spindle for movement in the regulating direction is rotationally supported in the ball nut. In this way the drive force of the electric motors is transferred to the ball nut via the rotating sleeve. The said ball nut rotates together with the rotating sleeve and with the suitable rotation the recirculating ball spindle is moved in the regulating direction and consequently also the actuating element. It is also possible that instead of the previously described ball screw drive a roller screw drive is analogously applied. 
     In order to prevent reactions by the control device, which is subjected to force in the direction opposite to the regulating direction, via the actuating element and rotating spindle or recirculating ball spindle on the electric motors, the rotating sleeve can be fixed by a first spiral spring opposing a feed rotational direction on a ring flange rotationally rigidly arranged in the device housing. The feed rotational direction corresponds here to a rotation of the recirculating ball spindle for the regulation of the actuating element or the rotating spindle in the regulating direction. 
     A constructively simple way of arranging such a ring flange can be seen in that the said ring flange sticks out from a transverse wall in the device housing essentially coaxially to the drive shaft or to the rotating sleeve. 
     In order to enable resetting of the actuating element in the direction opposing the regulating direction despite this when the control of the actuating device fails, a retaining sleeve can be rotationally rigidly connected at one of its ends to the transverse wall, whereby the retaining sleeve is rotationally rigidly connected at its other end via a second spiral spring to a guide sleeve in the direction opposite to the feed rotational direction, the actuating element connected to the recirculating ball spindle being supported for longitudinal displacement, but rotationally rigidly in the said guide sleeve. If this second spiral spring is released during a failure of the usually provided control for the actuating device, the guide sleeve can rotate in the direction opposite to the feed rotational direction due to the force which is transferred via the actuating element and which is acting on the control device to be actuated. Through this rotation the rotating spindle is turned back in the recirculating ball nut also in the direction opposite to the regulating direction until the actuating element is again arranged in its initial position. 
     In this connection, in order to prevent the actuating element itself from being rotated in the direction opposite to the regulating direction when being displaced, a spindle head for mutual connection can be arranged between the said actuating element and the recirculating ball spindle. The actuating element is decoupled with regard to rotation from the recirculating ball spindle by this spindle head. 
     In order to enable appropriate guidance and retention with regard to the guide sleeve as mentioned above, the spindle head can comprise at least one guide element protruding radially outwards, which engages a longitudinal guide running in the guide sleeve in the regulating direction. 
     In order to wind up the second spiral spring for the rotationally rigid connection of the retaining sleeve and guide sleeve sufficiently tightly on them, the said spring can be drive-connected to at least one electric motor. A sufficiently rotationally rigid connection between the retaining sleeve and the guide sleeve is produced by suitable actuation of the electric motor for winding up the spiral spring, especially before regulation of the recirculating ball spindle and actuating element. 
     In order to be able to accommodate the appropriate electric motor at a convenient point within the device housing, the electric motor can be drive-connected to a clamping sleeve from which a dog protrudes radially inwards which can be motion-connected to essentially one end of the second spiral spring. Due to the arrangement of the clamping sleeve, the electric motor can be located remotely with respect to the second spiral spring. Here, the arrangement is preferably realized such that a space available in the device housing is optimally used. 
     In order to be able to arrange the actuating device suitably compact and with small outer dimensions, the clamping sleeve can be rotationally supported on an external side of the retaining sleeve and on an external side of a ring flange which engages in the device housing, whereby the ring flange protrudes from an inner side of a housing cover. 
     A simple type of drive connection between the electric motor and clamping sleeve can be seen in that the electric motor drives a gearwheel which engages teeth on especially one end of the clamping sleeve. 
     In order to achieve redundancy also in connection with the drive of the clamping sleeve, another electric motor can be arranged, especially diametrically opposed to the first electric motor, through which a gearwheel that meshes with the teeth can be driven. In this way the clamping sleeve can be alternatively driven by the first or second electric motor and especially with the failure of one electric motor the other one is used. 
     In order to be able to still release the second spiral spring with the failure of both electric motors, a torsion spring can be arranged between the clamping sleeve and ring flange, the said torsion spring being able to be tensed during the rotation of the clamping sleeve for winding up the second spiral spring. If therefore the clamping sleeve is no longer held by one of the electric motors during the failure of its electrical supply in such a position in which the second spiral spring is wound up, the torsion spring rotates back the clamping sleeve at least so far that the second spiral spring is relieved for the release of the rotationally rigid connection between the retaining sleeve and the guide sleeve. 
     In order to be able to finely and accurately control the rotation of the clamping sleeve, the first and second electric motors can be stepper motors. 
     In order to supply the motors of the actuating device with electricity also independently of one another at least two separate electrical connections are arranged on the device housing and especially on the housing cover adjacent to the electric motors. The appropriate voltage supply as well as the data interchange or interchange of control signals can be implemented via these electrical connections. Each of the electrical connections can be provided for one of the electrical motors, i.e. servomotors. In this connection it is also possible that each of the electrical connections is assigned to a stepper motor. A further possibility is also the provision of separate electrical connections for the stepper motors. 
     According to the invention, there is the possibility that the two electric motors can be controlled independently of one another for the separate drive of the drive shaft. In this case it is practicable to operate one of the electric motors in the idling mode when the other drives the drive shaft. 
     However, in order to be able to transfer a higher torque to the drive shaft when necessary and therefore to displace the actuating element in the regulating direction with a higher force, both electric motors (servomotors) can be operated simultaneously. 
     In this case, in order to prevent the motors from rotating the drive shaft with a phase displacement due, for example, to different motor characteristics or due to the formation of the separate electrical supply for both motors instead of providing mutual support during simultaneous operation, the servomotors can be especially synchronized by software via their associated motor control devices. 
     A simple type of synchronization and control can be seen in that one servomotor is used as the master and the other as the slave. 
     It can be seen as being advantageous, especially for the transmission of a high torque if each of the servomotors is a direct current motor. 
     For the further monitoring of the actuating device according to the invention, especially remotely from said actuating device, a position sensor can be assigned to the drive shaft. With the said sensor it can be found, for example, how far the actuating element has been regulated, whether it has returned to its initial position, etc. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       In the following an advantageous embodiment of the invention is explained in more detail and described based on the enclosed figures in the drawing. 
       The following are shown: 
         FIG. 1  shows a basic illustration of the actuating device according to the invention with two separate electric motors and associated control device; 
         FIG. 2  shows a front view of a housing cover of the actuating device according to the invention; 
         FIG. 3  shows a cross-section along the line Ill—Ill from  FIG. 2 , and 
         FIG. 4  shows a cross-section along the line IV—IV from  FIG. 2 . 
     
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
       FIG. 1  shows the basic principle of the actuating device  1  according to the invention with two separate electric motors  8 ,  9  as drive device  3 . The electric motors  8 ,  9  are realized as direct current servomotors and are both used, where necessary, independently of one another for rotating a drive shaft  2 . As shown in the following figures, when the drive shaft  2  is rotated, a rotating spindle  4  is displaced in the regulating direction  6  and accordingly an actuating element  5  connected to it is also displaced. The actuating element  5  is used, for example, for closing or opening a valve as control device (not shown) to be actuated by the actuating device  1 . 
     The servomotors  8 ,  9  are each electrically connected to a dedicated motor control device  11  or  12 . These devices comprise appropriately a microprocessor, a memory device and other components necessary for the control. An appropriate software program for controlling the servomotors is held in the motor control devices. 
     Each of the motor control devices  11 ,  12  can be separately connected to the actuating device  1  via suitable connections  44 ,  45  (see for example  FIG. 2 ). In addition, each of the motor control devices  11 ,  12  is connected to a suitable voltage supply. 
       FIG. 2  shows a front view of a housing cover  46  of a device housing  7 , see  FIGS. 3 and 4 , of the actuating device  1  according to the invention. The housing cover  46  can also be realized as the end of a subhousing, see  FIGS. 3 and 4 , which can be releasably connected to the rest of the device housing  7 . 
     In the housing cover  46  especially the connections  44 ,  45  for the electrical supply and control of the servomotors  8 ,  9  are arranged. A smaller cover  48  is arranged centrally with respect to the housing cover  46 , the said smaller cover covering a pot-shaped protrusion of the housing cover  46 , see again  FIGS. 3 and 4 , in which a position sensor  47  is located. 
       FIG. 3  shows a section along the line III-IIIl and  FIG. 4  shows a section along the line IV—IV from  FIG. 2 . 
     In the following the actuating device  1  according to the invention is described based on both of the  FIGS. 3 and 4 . 
     The two servomotors  8 ,  9  of the drive device  3  are arranged in the longitudinal direction  10  of the drive shaft  2  one behind the other. The drive shaft  2  extends adjacent to the position sensor  47 . The said sensor is used to measure rotation of the drive shaft  2  and therefore for the determination of a feed of the actuating element  5  in the regulating direction  6 . 
     The drive shaft  2  terminates in a transmission device  13 , which, for example, can be realized as a so-called flex-spline gearbox without classical gearwheels. A rotating sleeve  14  is rotated by the drive shaft  2  via the transmission device  13 , the said rotating sleeve being rotationally rigidly connected to a ball nut  15  as part of a feed device  16 . A further part of the feed device  16  is formed by the rotating spindle  4  which is realized as a recirculating ball spindle. 
     A spindle head  25  is arranged on one end of the rotating spindle  4  which protrudes from the ball nut  15 . The actuating element  5  is connected to the said spindle head on its side opposite the rotating spindle  4 . The rotating sleeve  14  is rotationally supported in the ball bearing  49  with respect to a retaining sleeve  20  which surrounds the rotating sleeve. The rotating sleeve  14  is inserted into a ring flange  18  at its end facing the transmission device  13 . 
     A first spiral spring  17  is wound up on the outer sides of the ring flange  18  and the rotating sleeve  14 . The said spring is used to provide the rotationally rigid connection of the ring flange  18  and the rotating sleeve  14  in a rotational direction opposite to the feed rotational direction of the rotating sleeve  14 , i.e. the direction of rotation through which both the rotating spindle  4  and also the actuation element  5  are displaced in the regulating direction  6 . 
     The ring flange  18  protrudes essentially coaxially to the drive shaft  2 , respectively rotating spindle  4  from a transverse wall  19 . The said wall is arranged in the region of the device housing  7  where it is releasably connected to the subhousing  51 . 
     A retaining sleeve  20  is rotationally rigidly connected to the transverse wall  19  radially outwards relative to the ring flange  18 , see especially  FIG. 3 . The rotationally rigid connection is realized by screwing one end  21  of the retaining sleeve  20  to the transverse wall  19 . The retaining sleeve  20  extends up to its end  22  which faces away the transverse wall  19 . The said retaining sleeve is rotationally supported relative to a guide sleeve  24  on this said end via a ball bearing  53 . A second spiral spring  23  is wound up on the outsides of both the retaining sleeve and also the guide sleeve  24 . 
     The guide sleeve  24  extends to a housing cover  36  through which the actuating element  5  is passed. The guide sleeve  24  exhibits longitudinal guides  27  running in the regulating direction  6  and in which guide elements  26  engage. The said guide elements protrude outwards radially from the spindle head  25 . 
     In the region of the longitudinal guides  27  the guide sleeve  24  is inserted into a ring flange  34  which protrudes from an inner side  35  of the housing cover  36 . A clamping sleeve  29  is rotationally supported by suitable bearings on an external side  33  of the ring flange  34  and on an external side  32  of the retaining sleeve  20 . The clamping sleeve  29  is releasably connected at its end  39  facing the drive device  3  by screwing to a toothed ring  42 . The toothed ring  42  exhibits inner teeth as tooth system  38  which engages the gearwheels  37 ,  41 . The gearwheel  37  can be rotated by a first electric motor  28  and the other gearwheel  41  by a second electric motor. The electric motors  28 ,  40  are realized as stepper motors. 
     A dog  30  protrudes radially inwards approximately centrally to the clamping sleeve  29  and said dog can be coupled to one end  31  of the second spiral spring  23 , so that, depending on the rotation of the rotating sleeve  14 , the second spiral spring  23  can be wound up more or less on the retaining sleeve  20  and the guide sleeve  24 . 
     A torsion spring  43  is arranged between the clamping sleeve  29  and ring flange  34 . The said spring can be clamped between the ring flange  34  and the rotating sleeve  14  when the clamping sleeve  29  is rotated for winding up the second spiral spring  23 . 
     In the following the function of the actuating device according to the invention is briefly explained based on the enclosed figures. 
     Since the servomotors  8 ,  9  are mounted on the drive shaft  2 , they can be used singly as well as in combination. Single application occurs especially when one of the servomotors  8 ,  9  is to replace the other one. Common actuation of both servomotors  8 ,  9  is especially then provided when a higher torque is to be transferred onto the drive shaft  2 , which may amount to twice the torque which can be transferred by one servomotor. 
     Both servomotors  8 ,  9  are connected via separate feed cables, see the connections  44 ,  45 , and the partially illustrated connection line  50 , to their respective motor control devices  11 ,  12 . One of the servomotors  8 ,  9 , or both motors can be actuated and controlled via these control devices and separate electrical supplies to the motor control device and also to the servomotors. 
     The motor control devices  11 ,  12  are especially formed in that one of the servomotors is wired as the master and the other as the slave and synchronization of both motors to the common drive of the drive shaft  2  occurs by software. 
     The electric motors  28 ,  40 , formed as stepper motors, are also arranged double in order to substitute one of the stepper motors with failure, damage or a similar condition. Also in this case, the control of the stepper motors occurs independently of one another over dedicated feed cables and dedicated motor control devices. 
     Otherwise the actuating device according to the invention functions as follows: 
     The ball nut  15  is rotated through the rotating sleeve  14  by rotating the drive shaft  2 . Since the said ball nut is fixed in the axial direction relative to the device housing  7 , the rotating spindle  4  is displaced in the regulating direction  6  when the ball nut  15  is rotated. The actuating element  5  is also displaced at the same time as the rotating spindle  4 , because the said actuating element is connected to the rotating spindle  4  via the spindle head  25 . The displacement of the actuating element  5  can be measured via the position sensor  47 . 
     The force applied to the actuating element from the direction of the control device, which is not illustrated, in the opposite direction to the regulating direction  6  is transferred via the first spiral spring  17  from the rotating sleeve  14  to the ring flange  18  and therefore to the housing  7 . 
     For resetting the actuating element  5  in the opposite direction to the regulating direction  6 , the second spiral spring  23  is released via the dog  30 , the said spiral spring holding the guide sleeve  24  with the retaining sleeve  20  rotationally rigid in the direction opposite to the feed rotational direction. With the second spiral spring  23  released, the guide sleeve  24  can rotate in the direction opposite the feed rotational direction, whereby the rotation onto the guide sleeve  24  is transferred via the guide elements  26  of the spindle head  25  corresponding to the reverse rotation of the rotating spindle. 
     If due to the failure of both stepper motors  28 ,  40  a release of the second spiral spring  23  is not possible, the release of the spiral spring  23  occurs through the torsion spring  43 , which was tensed on winding up the second spiral spring  23  for the rotationally rigid connection of the guide sleeve  24  and retaining sleeve  20  between the clamping sleeve  29  and the ring flange  34 .