Abstract:
A hybrid of the pneumatic and hydraulic actuators for combining pneumatically powered actuation with incompressible and controllable hydraulic damping in order to achieve smooth displacement, rapid stopping and steady and accurate positioning of the hybrid actuator in which hydraulic damping of a pneumatic actuator is obtained through utilizing positive-displacement hydraulic actuator means with zero volumetric differential.

Description:
This is a Div. of Ser. No. 09/470,733 filed Dec. 23, 1999 Pat. No. 6,481,335. 
    
    
     BACKGROUND OF THE INVENTION 
     The present invention relates to hybrid devices of the pneumatic and positive-displacement hydraulic actuators generally named “hydropneumatic actuator”. A hydropneumatic actuator per the present invention has a broad spectrum of applications in many industrial fields, and can be used for actuating a variety of machine parts and objects. More particularly, this invention relates to improvements in pneumatic actuators utilizing positive-displacement zero volumetric differential hydraulic dampening means for achieving smooth displacement, rapid stopping and steady, and accurate positioning of the actuator. 
     Pneumatic actuators (piston-cylinders, rotary actuators, etc.) are generally advantageous in respect to low purchase and operation cost over positive-displacement hydraulic actuators. The simplicity of using one centralized station producing compressed air (which in some instances is capable of supplying a whole plant with air power), cheap of-the-shelf pneumatic hardware and means of control (such as hoses, fittings, switches, valves, etc.) makes pneumatics almost a plug-in technology. 
     Pneumatic actuators, however, have certain disadvantages. For example, they suffer rapid accelerations (which normally happens at the beginning of actuation) and “creeping” (when the compressed air is cut off, but the actuator keeps moving). These effects are attributed to the compressibilty of air. Using pneumatic actuators it is very difficult to achieve accurate control of speed and displacement, or maintain a steady position of an actuator. In fact, achieving the quality of motion and position control equivalent or even any close to the quality of motion and position control routinely achievable by positive-displacement hydraulic systems is practically unrealistic. 
     Positive-displacement hydraulic actuators, on the other hand, offer an excellent motion and position control, but the cost of hydraulic systems as well as the maintenance of hydraulics is high. In addition, most hydraulic systems require individual pump stations, which makes them even more expensive and further complicates the their usage. 
     The present invention offers an inexpensive hybrid actuator that allows to combine the advantages of the pneumatic and positive-displacement hydraulic actuation. The present invention gives a viable alternative to those areas of the industry where the need in accurate control of motion and position is contradicted by a low cost requirement. 
     It is known in the art to utilize positive-displacement hydraulic actuators in combination with pneumatic actuators. In such hybrids a displacement that takes place in a pneumatic actuator is being translated into a displacement of a positive-displacement hydraulic actuator filled with dampening fluid, thus causing a flow of dampening fluid in the hydraulic actuator. The accurate control of motion and position is then achieved through controlling the flow of dampening fluid using a variety of optional valve means and their combinations. 
     U.S. Pat. No. 2,624,318 to B. Walder, et al. shows a pneumatic cylinder with a hollow piston rod serving as a housing unit for a hydraulic actuator containing dampening fluid which travels from one side of the hydraulic actuator plunger to the other. 
     This invention uses a single rod hydraulic actuator for dampening the pneumatic cylinder. The obvious disadvantage of such an arrangement is the presence of a volumetric differential in the dampening cylinder (that is natural for single rod hydraulic actuators). To compensate for the volumetric differential of the dampening hydraulic actuator the device is equipped with an additional expendable reservoir for receiving, containing and returning back to the system differential volumes of dampening fluid. 
     U.S. Pat. No. 3,146,680 to James F. Hutter, et al. shows a hydraulically controlled pneumatic cylinder with a hollow piston rod utilized as the housing unit of a single rod hydraulic actuator. The hollow piston rod of the pneumatic cylinder is filled with oil. The two chambers of the hydraulic actuator are connected through an oil reservoir with a floating cover and a valve means that allow to control the oil flow between the two chambers of the cylinder. 
     Similar to the first prior art described, this invention uses a single rod hydraulic actuator (with a natural volumetric differential), and an expandable oil reservoir to compensate for the volumetric differential of the hydraulic actuator. 
     The expandable reservoirs used in both cases are in essence a form of a hydraulic accumulator means and, thus, are equipped with some type of a built-in spring (mechanical, pneumatic, etc.) that makes them expandable. At the same time, the built-in spring reintroduces the main disadvantage of a true pneumatic actuator—compressibility of the media. Therefore, the utilization of expandable reservoirs defeats the very object or minimizes the extend of improvement attempted by the prior arts described above. 
     In addition, the complex switches and valve means utilized to control the fluid transfer between the chambers of the hydraulic actuator and through the expandable reservoirs complicate such hybrid actuators, making them more expensive, and less reliable. 
     U.S. Pat. No. 3,313,214 to Nathan Ackerman shows a hydropneumatic feed—a hydrid of pneumatic and single rod hydraulic cylinders. This hydropneumatic feed also includes a spring-loaded fluid reservoir of an expandable nature so to compensate for the volumetric differential of the single rod hydraulic cylinder, which is built into a piston rod of the pneumatic cylinder. Therefore, this hydrid shall suffer the same disadvantages as the prior arts discussed above. 
     U.S. Pat. No. 3,678,805 to Henry Walter Weyman shows a pneumatic cylinder assembly incorporated with single rod hydraulic dampening. In this invention a built-in spring-loaded fluid reservoir of an expandable nature is also used to compensate for the volumetric differential of the single rod dampening hydraulic cylinder. 
     U.S. Pat. No. 5,735,187 to Bert Harju shows a pneumatic cylinder with an integrated hydraulic control system and a single rod hydraulic dampening cylinder. The arrangement of this invention does not show any special means to compensate for the volumetric differential natural to a single rod hydraulic cylinder. Thus, in order for the hybrid cylinder to be functional the single rod hydraulic actuator shall be partially filled with dampening fluid. In fact, the total volume of the dampening hydraulic fluid shall be no greater than the full volume of the small chamber of the single rod hydraulic dampening cylinder. Therefore, the larger chamber of the hydraulic actuator per this invention will develop a vacuum gauge pressure at all positions of the plunger except the terminal position at which the plunger is fully retracted. Due to the presence of a vacuum gauge pressure in one of the chambers the arrangement of this invention will suffer the same disadvantage of media compressibility as all the prior arts discussed above. 
     The concept of a hybrid of positive-displacement hydraulic and pneumatic actuators was practically utilized in commercially available devices named “Cyl-Check” by Allenair Corporation. The “Cyl-Check” design arrangement, however, uses single rod hydraulic dampening cylinders and spring-loaded fluid reservoirs as well, to compensate for a volumetric differential of the single rod dampening hydraulic actuators. 
     Whatever the precise merits, features and advantages of the above cited references, all of them suffer the same main disadvantage attributed to the use of dampening hydraulic actuators with positive volumetric differential. Thus, none of them achieve or fulfill the goal of providing an inexpensive technology which combines the advantages separately inherent to pneumatic and positive-displacement hydraulic actuation. 
     SUMMARY OF THE INVENTION 
     It is therefore, a principle object of the present invention to provide a hydropneumatic actuator capable of smooth actuation which speed and positioning can be controlled with high level of accuracy. 
     Another object of the present invention is to provide a free of “creeping” and rapid speed changes hydropneumatic actuator powered by compressed gasses and yet. 
     It is also an object of the present invention to provide an inexpensive and reliable hydropneumatic actuator. 
     Yet another object of the present invention is to provide a hydropneumatic actuator capable of rapid and accurate stops in any required position. 
     The present invention achieves the forgoing objectives by the use of pneumatic actuators combined with a positive-displacement hydraulic dampening means with zero volumetric differential (such as double rod hydraulic actuators with constant diameter of the rod on both sides of the piston, bellows with equal volumetric to linear displacement ratios, etc.) which allows dampening fluid transfer between its chambers without producing vacuum as well as excessive amounts of dampening fluid (that would require additional spring-loaded fluid reservoirs of an expandable nature). 
     Such hydropneumatic actuators are simple by design, and inexpensive due to the small number of components from which they can be constructed. The majority the components can be mass produced or off-the-shelf items. 
     Further objects and advantages of this invention will become apparent from the consideration of the drawings and ensuing description. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 a  shows a longitudinal sectional view of a hydropneumatic actuator according to a first embodiment of the present invention. 
     FIG. 1 b  shows a partial enlarged view (of the area encircled on FIG. 1 a ) of the first embodiment of the present invention. 
     FIG. 2 shows a longitudinal sectional view of a hydropneumatic actuator of a second embodiment according to the present invention. 
     FIG. 3 a  shows a longitudinal sectional view of a hydropneumatic actuator according to a third embodiment of the present invention. 
     FIG. 3 b  shows a partial enlarged view (of the area encircled on FIG. 3 a ) of the third embodiment of the present invention. 
     FIG. 4 shows a longitudinal sectional view of a hydropneumatic actuator according to a fourth embodiment of the present invention. 
     FIG. 5 shows a longitudinal sectional view of a hydropneumatic actuator illustrating a possible design arrangement of positive-displacement hydraulic dampening means according to a fifth embodiment of the present invention. 
     FIG. 6 a  shows a longitudinal sectional view of a hydropneumatic actuator according to a sixth embodiment of the present invention. 
     FIG. 6 b  shows a partial enlarged view (of the area encircled on FIG. 6 a ) of the sixth embodiment of the present invention. 
     FIG. 7 a  shows an isometric view of a hydropneumatic actuator of a seventh embodiment according to the present invention. 
     FIG. 7 b  shows an isometric view of an exploded assembly with encircled broken-out section exposing the internal structure per the seventh embodiment of the present invention. 
     FIG. 7 c  is another isometric view of the same exploded assembly per the seventh embodiment of the present invention (shown from the side unexposed on FIGS. 7 a - 7   b ). 
     FIG. 7 d  shows a partial enlarged view (of the area encircled on FIG. 7 b ) of the seventh embodiment of the present invention. 
     FIG. 8 is an isometric view of a hydropneumatic actuator of an eighth embodiment according to the present invention. 
     FIG. 9 is another isometric view of the same hydropneumatic actuator per the eighth embodiment of the present invention (shown without the front cover and with a broken-out section of the housing unit to indicate the internal structure of the pneumatic elements of the actuator). 
     FIG. 10 is another isometric view of the same hydropneumatic actuator per the eighth embodiment of the present invention (shown with yet another broken-out section of the housing unit to indicate the internal structure of the hydraulic elements of the actuator). 
     FIG. 11 is another isometric view of the same hydropneumatic actuator per the eighth embodiment of the present invention (shown with two broken-out sections of the housing unit to indicate the internal structure of the hydraulic channels and details hidden on FIGS.  9  and  10 ). 
     FIG. 12 a  is an isometric view of a hydropneumatic actuator of a ninth embodiment according to the present invention shown with a broken-out section of the housing unit, to indicate the internal structure of the hydraulic and mechanical elements of the actuator. 
     FIG. 12 b  shows a partial enlarged view (of the area encircled on FIG. 12 a ) of the ninth embodiment of the present invention. 
     FIG. 13 a  shows a longitudinal sectional view of a hydropneumatic actuator according to a tenth embodiment of the present invention. 
     FIG. 13 b  shows a partial enlarged view of an eleventh embodiment of a hydropneumatic actuator similar to the tenth embodiment but with different type of dampening fluid flow governor means. 
     FIG. 13 c  shows a partial enlarged view of a twelfth embodiment of a hydropneumatic actuator similar to the tenth embodiment but with yet different type of dampening fluid flow governor means. 
     FIG. 14 shows a longitudinal sectional view of a hydropneumatic actuator according to a thirteenth embodiment of the present invention. 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     FIG. 1 a  and FIG. 1 b  show a longitudinal sectional view of a hydropneumatic actuator according the first embodiment of the present invention and a partial enlarged sectional view of the circled area on the same sectional view. 
     The hydropneumatic actuator shown on FIG. 1 a  and FIG. 1 b  is generally constructed of a pneumatic actuator  3  (which according to the first embodiment of the present invention is presented by a pneumatic cylinder), a positive-displacement hydraulic actuator (which according to the first embodiment of the present invention is presented by a hydraulic actuator built into the pneumatic actuator  3 ) in the following referred to as “hydraulic actuator”, a dampening fluid path  24   a  (shown on FIG. 1 b ), and a dampening fluid flow governor means  27  (shown on FIG. 1 b ). 
     The pneumatic actuator  3  is further comprised of a pneumatic actuator housing unit, composed of a hollow cylindrical body  6 , a front closure  9 , fixedly mounted at the front end of the hollow cylindrical body  6 , a rear closure  12 , fixedly mounted at the rear end of the hollow cylindrical body  6 , and a pneumatic actuator actuation means  15  (which according the first embodiment of the present invention is presented by a cylindrical plunger formed with a rod  18 ) slidably disposed inside the hollow cylindrical body  6 . 
     The pneumatic actuator actuation means  15  divides the active volume of the chamber inside the hollow cylindrical body  6  into two chambers: chamber  45   a  and chamber  45   b.    
     The front closure  9  is formed with an air channel  39 . The rear closure  12  is formed with an air channel  42 . Through the air channels  39  and  42  compressed air can be provided to the chambers  45   a  and  45   b  respectively, to power the pneumatic actuator actuation means  15 . 
     The rod  18  of the pneumatic actuator  3  is formed hollow with an axial cylindrical bore which allows the rod  18  to serve a function of a body for a hydraulic actuator housing unit. 
     The hydraulic actuator housing unit further includes a hydraulic actuator front closure  33  (fixedly mounted inside the axial cylindrical bore of the rod  18 ) and a hydraulic actuator rear closure  36  (fixedly mounted at the rear end of the axial cylindrical bore inside the rod  18 ). 
     Thus, the hydraulic actuator housing unit is composed of the hollow rod  18  assembled together with the hydraulic actuator front closure  33  and the hydraulic actuator rear closure  36 . 
     The hydraulic actuator further comprises a hydraulic actuator actuation means  21  which, according to the first embodiment of the present invention, is presented by a cylindrical plunger formed with a double rod  30 . The hydraulic actuator actuation means  21  is slidably disposed within the axial cylindrical bore inside the rod  18 , whereby, the hydraulic actuator actuation means  21  divides the chamber inside the hollow hydraulic actuator housing unit into a first hydraulic chamber  48   a  and a second hydraulic chamber  48   b.  In the following, the total volume of the first hydraulic chamber and the second hydraulic chamber will be referred to as “active volume” of the hydraulic actuator. 
     The double rod  30  has a constant diameter, which is equal on both sides of the hydraulic actuator actuation means  21 . This allows to achieve an equal displacement area of the hydraulic actuator actuation means  21  in both hydraulic chambers,  48   a  and  48   b,  of the hydraulic actuator. The design arrangement such as described provides conditions under which the volume of dampening fluid displaced from one hydraulic chamber of the hydraulic actuator is always equal to the volume of dampening fluid received by the opposite hydraulic chamber of the hydraulic actuator. In the following such conditions will be referred to as “zero volumetric differential”. 
     The front closure  33  and rear closure  36  of the hydraulic actuator are formed with channels (not shown) for filling the active volume of the hydraulic actuator and all the adjacent hydraulic cavities with a suitable dampening fluid. The active volume of the hydraulic actuator and all the adjacent hydraulic cavities are completely filled with dampening fluid and sealed with sealing means (not shown). 
     Hydropneumatic actuator, in accordance with the first embodiment of this invention, further includes the dampening fluid path  24   a  formed as a bore through the hydraulic actuator actuation means  21  which provides a channel for dampening fluid corresponding between the first and the second hydraulic chambers ( 48   a  and  48   b  respectively) during the operation of the hydraulic actuator. 
     Further, hydropneumatic actuator of the first embodiment includes the dampening fluid flow governor means  27  installed in series with the dampening fluid path  24   a  in the way of the flow of dampening fluid corresponding between the hydraulic chambers  48   a  and  48   b  in either direction. The governor means  27  impedes the rate of dampening fluid flow between the chambers  48   a  and  48   b  during hydraulic actuator operation, and thus, provides control over dampening fluid transfer. According to the design arrangement of the first embodiment of the present invention, the function of the dampening fluid flow governor means  27  is carried by a permanent orifice  51  (shown on FIG. 1 b ). 
     To enable the transfer of the displacement generated by the pneumatic actuator into the displacement of the hydraulic actuator, the pneumatic and the hydraulic actuators of the first embodiment are coupled. In accordance with the first embodiment of this invention the housing unit of the hydraulic actuator housing unit is being coupled with the pneumatic actuator actuating means due to the fact that pneumatic actuator actuation means  15  formed with a rod  18  is hollow and simultaneously serves the function of the body of the hydraulic actuator housing unit. Further, the hydraulic actuator actuating means  21  are being coupled with the pneumatic actuator housing unit through the rear end of the double rod  30  of the hydraulic actuator actuation means  21  being fixedly connected to the rear closure  12  of the pneumatic actuator  3  (for example, by threaded fastener means as shown on FIG. 1 a ). According to the first embodiment, the connection between the double rod  30  and the rear closure  12  is being sealed to prevent leakage of compressed air from the chamber  45   b  of the pneumatic actuator  3 . 
     The type of connection and sealing should not be construed as limitations on the scope of the invention. In fact it is widely optional (for example the sealing can be done with o-rings, air tight clamping means, sealing compounds, or by pressing, swaging, gluing, welding, brazing, etc.) 
     The front end of the double rod  30  is free to move inside the rod  18  of the pneumatic actuator  3 . 
     When compressed air is let into the channel  39  and further to the chamber  45   a  it causes the pneumatic actuator actuation means  15  to move rearward. Respectively, when compressed air is let into the channel  42  and further to the chamber  45   b  it causes the pneumatic actuator actuation means  15  to move forward. The hollow rod  18 , as a solid part of the pneumatic actuator actuation means  15 , moves with the pneumatic actuator actuation means  15 , and, simultaneously, as a solid part of the hydraulic actuator housing unit makes a displacement with respect to the hydraulic actuator actuation means  21 . The hydraulic actuator actuation means  21 , being fixedly connected to the rear closure  12  through the double rod  30 , therefore, remain stationary with respect to the pneumatic actuator housing unit. 
     During the displacement of the rod  18  with respect to the hydraulic actuator actuation means  21  the dampening fluid contained in the active volume of the hydraulic actuator is being effectively redistributed between the first and the second hydraulic chambers,  48   a  and  48   b,  of the hydraulic actuator. The dampening fluid transfer occurs through the dampening fluid path  24   a  and the dampening fluid flow governor means  27 , whereby dampening of the pneumatic actuator rapid speed changes takes place. 
     Due to the zero volumetric differential of the hydraulic actuator, the volume of dampening fluid displaced from one of the hydraulic chambers ( 48   a  or  48   b ) and receptively received by the other hydraulic chamber ( 48   b  or  48   a ) of the hydraulic actuator always remains even. Whereby, the hydropneumatic actuator per the present invention provides hydraulic dampening by a self-contained, completely filled with fluid hydraulic actuator that is inherently free from the compressibility effect, and therefore, simultaneously offers the advantages of creeping free smooth displacement, steady positioning and simplicity of design. 
     While the above description contains many specificities, these should not be construed as limitations on the scope of this invention, but rather as an exemplification of one preferred embodiment thereof. Many variations are possible even within the scope of the first embodiment general design arrangement. For example, the permanent orifice that performs the function of the dampening fluid flow governor means  27  can be substituted by a combination of a shut-off valve and a permanent orifice, which would allow the hydropneumatic actuator to make sudden and steady stops and high accuracy positioning. Another example would be the utilization of a valve with external analog or digital control of the orifice, in which case an additional speed control would become possible. 
     FIG. 2 shows a longitudinal sectional view of a hydropneumatic actuator according the second embodiment of the present invention. 
     The hydropneumatic actuator per the second embodiment of the present invention is generally constructed of a pneumatic actuator  3 , two positive displacement hydraulic actuators built into pneumatic actuator  3 , three dampening fluid paths  24   b,    24   c  and  24   d,  and a dampening fluid flow governor means  27 . 
     The pneumatic actuator  3  is further composed of a pneumatic actuator housing unit which comprises a hollow cylindrical body  6 , a front closure  9 , fixedly mounted at the front end of the hollow cylindrical body  6 , a rear closure  12 , fixedly mounted at the rear end of the hollow cylindrical body  6 , and pneumatic actuator actuation means  15  (formed as a cylindrical plunger) with a rod  18 . The pneumatic actuator actuation means  15  is slidably disposed within the hollow cylindrical body  6  and divides the active volume inside the hollow cylindrical body  6  into two chambers  45   a  and  45   b.    
     The front closure  9  is formed with an air channel  39 , and the rear closure  12  is formed with an air channel  42 . The channels allow compressed air to be provided to the chambers  45   a  and  45   b  respectively to power the pneumatic actuator actuation means  15 . 
     According to the second embodiment the pneumatic actuator actuation means  15  are formed with two cylindrical bores parallel to the main axis of the rod  18 , with each bore forming a cylindrical body for one hydraulic actuator. 
     Each one of the two hydraulic actuators is further comprised of a hydraulic actuator front closure  33  (fixedly mounted at the front end of the cylindrical body inside the pneumatic actuator actuation means  15 ), and a hydraulic actuator rear closure  36  (fixedly mounted at the rear end of the cylindrical body inside the pneumatic actuator actuation means  15 ). 
     The pneumatic actuator actuation means  15 , assembled with the two hydraulic actuator front closures  33  and the two hydraulic actuator rear closures  36  composes two hydraulic actuator housing units for two positive displacement hydraulic actuators. 
     Each one of the two hydraulic actuators further comprises one hydraulic actuator actuation means  21  (which according to the second embodiment of the present invention is presented by a cylindrical plunger formed with a double rod  30 ) each slidably disposed within one of the two cylindrical bores inside the pneumatic actuator actuation means  15 . Each hydraulic actuator actuation means  21  divides active volume of the hydraulic actuator housing unit it has been placed in into a first hydraulic chamber  48   a  and a second hydraulic chamber  48   b.    
     Each double rod  30  has a diameter equal on both sides of the hydraulic actuator actuation means  21 , whereby each of the two hydraulic actuators is a zero volumetric differential hydraulic actuator. 
     The hydraulic actuator closures  33  and  36  are formed with channels (not shown) for filling the total active volume of the two hydraulic actuators and all adjacent hydraulic cavities with a suitable dampening fluid. The first and the second hydraulic chambers  48   a  and  48   b  of each hydraulic actuator and all adjacent hydraulic cavities are completely filled with dampening fluid and sealed with sealing means (not shown). 
     In accordance with the second embodiment of this invention, the pneumatic actuator actuation means  15  are formed with the three dampening fluid paths  24   b,    24   c  and  24   d.  The dampening fluid path  24   c  is formed for connecting together the two first hydraulic chambers  48   a  of both hydraulic actuators. The channel  24   d  is formed for connecting together the two second hydraulic chambers  48   b  of both hydraulic actuators. The channel  24   b  is formed for connecting together the two first hydraulic chambers  48   a  with the two second hydraulic chambers  48   b  of both hydraulic actuators. 
     The pneumatic actuator actuation means  15  further comprises a dampening fluid flow governor means  27  placed in the way of the dampening fluid corresponding between the two first hydraulic chambers  48   a  and the two second hydraulic chambers  48   b.  Per the second embodiment of the present invention, the dampening fluid flow governor means  27  is an adjustable needle valve  57  that allows for fine adjustment to the rate of dampening fluid flow. 
     Each double rod  30  is fixedly clamped between the front closure  9  and the rear closure  12  of the pneumatic actuator. Thus, both of the hydraulic actuator actuation means remain stationary with respect to the pneumatic actuator housing unit. 
     When compressed air is let into the channel  39  and further to the chamber  45   a  it causes the pneumatic actuator actuation means  15  to move rearward. Respectively, when compressed air is let into the channel  42  and further to the chamber  45   b  it causes the pneumatic actuator actuation means  15  to move forward. Being at the same time a part of the hydraulic actuator housing unit with movement in either direction, the pneumatic actuator actuation means  15  make a correspondent displacement with respect to the two hydraulic actuator actuation means  21  (which are stationary with respect to the pneumatic actuator housing unit). During this displacement the dampening fluid contained in the active volume of the two hydraulic actuators is being effectively redistributed between the two first and the two second hydraulic chambers,  48   a  and  48   b,  of the hydraulic actuators. The dampening fluid transfer occurs through the dampening fluid paths  24   b,    24   c  and  24   d,  and the dampening fluid flow governor means  27 , whereby dampening of the pneumatic actuator&#39;s rapid speed changes takes place. 
     Due to the zero volumetric differential of the two hydraulic actuators, the volume of dampening fluid displaced by the two first (second) hydraulic chambers  48   a  ( 48   b ) and receptively received by the two second (first) hydraulic chambers  48   b  ( 48   a ) of the hydraulic actuators always remains even. Whereby, the hydropneumatic actuator per the second embodiment of the present invention provides hydraulic dampening by a self-contained, completely filled with fluid hydraulic actuator that is inherently free from the compressibility effect and, therefore, offers the advantages of smooth and free of creeping displacement, steady positioning and simplicity of design all at the same time. 
     FIG. 3 a  and FIG. 3 b  show a longitudinal sectional view of a hydropneumatic actuator per the third embodiment of the present invention. 
     The hydropneumatic actuator of the third embodiment is generally comprised of a pneumatic actuator  3 , a hydraulic actuator, a dampening fluid path  24   e,  and a dampening fluid flow governor means  27 . 
     The pneumatic actuator  3  is further composed of a pneumatic actuator housing unit that further comprises a hollow cylindrical body  6 , a front closure  9 , fixedly mounted at the front end of the hollow cylindrical body  6 , a rear closure  12  fixedly mounted at the rear end of the hollow cylindrical body  6 , and a pneumatic actuator actuation means  15  (formed as a cylindrical plunger) with a rod  18 . The pneumatic actuator actuation means  15  are slidably disposed inside the hollow cylindrical body  6  and divide the active volume inside the pneumatic actuator housing unit into chamber  45   a  and chamber  45   b.    
     The front closure  9  is formed with an air channel  39 , and the rear closure  12  is formed with an air channel  42 . Through the channels  39  and  42  compressed air can be provided to the chambers  45   a  and  45   b  respectively, to power the pneumatic actuator actuation means  15 . 
     The hydraulic actuator is further composed of a hydraulic actuator housing unit and a hydraulic actuator actuation means  21  with a double rod  30 . The hydraulic actuator housing unit is further comprised of a hollow cylindrical body  60 , a front closure  33 , fixedly mounted at the front end of the hollow cylindrical body  60 , and a rear closure  36 , fixedly mounted at the rear end of the hollow cylindrical body  60 . The hydraulic actuator actuation means  21  is slidably disposed inside the hollow cylindrical body  60  and divide the active volume of the hydraulic actuator housing unit into a first hydraulic chamber  48   a  and a second hydraulic chamber  48   b.    
     The double rod  30  has the same diameter on both sides of the hydraulic actuator actuation means  21 , which makes a zero volumetric differential hydraulic actuator. 
     The hydraulic actuator is mounted alongside the pneumatic actuator  3  with the hydraulic actuator housing unit fixedly clamped to the pneumatic actuator housing unit with a bracket means  66  and a fastener means  69  in a such manner that the main axis of the rod  18  and the main axis the double rod  30  are parallel to each other. 
     The end of the rod  18  is fixedly connected to the front end of the double rod  30  with a bracket means  75  and threaded fastener means  72  and  78  so to allow only simultaneous linear displacement of both the pneumatic actuator and hydraulic actuator actuation means  15  and the hydraulic actuator actuation means  21 . 
     The dampening fluid path  24   e  is formed with an inlet (not shown) for filling the active volume of the hydraulic actuator and all the adjacent hydraulic cavities with a suitable dampening fluid. The dampening fluid path  24   e  connects the first hydraulic chamber  48   a  with the second hydraulic chamber  48   b.  Both, the first hydraulic chamber  48   a  and the second hydraulic chamber  48   b  and all the adjacent hydraulic cavities are completely filled with dampening fluid and sealed with sealing means (not shown). 
     The dampening fluid flow governor means  27  is placed in the dampening fluid path  24   e  in the way of the dampening fluid corresponding between the hydraulic chambers  48   a  and  48   b.  Per the third embodiment of the present invention a pneumatically controlled shut-off valve  63  and an adjustable needle valve  57  connected in series carry the function of the dampening fluid flow governor means  27 . The shut-off valve is utilized to enable an accurate positioning control in addition to the adjustable dampening provided by the needle valve  57 . 
     Due to the rigid connection between the rod  18  and the double rod  30  the hydraulic actuator actuation means  21  actuates simultaneously with the pneumatic actuator actuation means  15 . During actuation the hydraulic actuator actuation means  21  forces the transfer of dampening fluid between the first and second hydraulic chambers  48   a  and  48   b.  The dampening fluid transfer between the chambers  48   a  and  48   b  takes place through the dampening fluid path  24   e  and the dampening fluid flow governor means  27 , where hydraulic locking and dampening of the pneumatic actuator  3  effectively occur. 
     Utilization of the hydraulic actuator with zero volumetric differential allows for hydraulic locking and dampening with a self-contained hydraulic actuator free from the compressibility effect and, thus, offering the advantages of smooth and free of creeping displacement, steady positioning and design simplicity. 
     FIG. 4 shows a longitudinal sectional view of a hydropneumatic actuator per the fourth embodiment of the present invention. 
     The hydropneumatic actuator of the fourth embodiment is generally comprised of a pneumatic actuator  3 , a hydraulic actuator, a dampening fluid path  24   f,  and a dampening fluid flow governor means  27 . 
     The pneumatic actuator  3  is further composed of a pneumatic actuator housing unit that comprises a hollow cylindrical body  6 , a front closure  9 , fixedly mounted at the front end of the hollow cylindrical body  6 , a rear closure  12 , fixedly mounted at the rear end of the hollow cylindrical body  6 , and a pneumatic actuator actuation means  15  (formed as a plunger) with a rod  18 . The pneumatic actuator actuation means  15  is slidably disposed inside the hollow cylindrical body  6  and divide the chamber of the pneumatic actuator housing unit into chamber  45   a  and chamber  45   b.    
     The front closure  9  is formed with air channel  39 , and the rear closure  12  is formed with air channel  42  through which compressed air can be provided to the chambers  45   a  and  45   b  respectively to power the pneumatic actuator actuation means  15 . 
     According to the fourth embodiment of the present invention the hydraulic actuator is mounted externally in line with the pneumatic actuator  3 . The hydraulic actuator is further composed of a hydraulic actuator housing unit and a hydraulic actuator actuation means  21  formed with a double rod  30 . The hydraulic actuator housing unit is further comprised of a hollow cylindrical body  60 , a front closure  33 , fixedly mounted at the front end of the hollow cylindrical body  60 , and a rear closure  38 , fixedly mounted at the rear end of the hollow cylindrical body  60 . 
     The hydraulic actuator actuation means  21  is slidably disposed inside the hollow cylindrical body  60 , and divides active volume of the hydraulic actuator into a first hydraulic chamber  48   a  and a second hydraulic chamber  48   b.    
     The double rod  30  has a constant diameter equal on both sides of the hydraulic actuator actuation means  21 , which makes the hydraulic actuator a zero volumetric differential hydraulic actuator. 
     The hydraulic actuator front closure  33  is fixedly connected to pneumatic actuator rear closure  12  with a plurality of threaded fastener means  81 . 
     The front end of the double rod  30  of the hydraulic actuator air-tightly extends through the axial hole in the center of the rear closure  12 , and fixedly connected to the rear end of the pneumatic actuator actuation means  15  to allow only simultaneous linear displacements of both the pneumatic actuator actuation means  15  and the hydraulic actuator actuation means  21 . 
     This type of connection should not be construed as limitations on the scope of the present invention. In fact, it is widely optional. For example, the connection can be also made by clamping, pressing, swaging, gluing, welding, brazing, using threaded fasteners, etc. 
     The dampening fluid path  24   f  is formed with an inlet (not shown) for filling the active volume of the hydraulic actuator and all of the adjacent hydraulic cavities with a suitable dampening fluid, and provides a connection between the first hydraulic chamber  48   a  and the second hydraulic chamber  48   b.  Both, the first hydraulic chamber  48   a  and the second hydraulic chamber  48   b  and all adjacent hydraulic cavities are completely filled with dampening fluid and sealed with sealing means (not shown). 
     The dampening fluid flow governor means  27  is placed in dampening fluid path  24   f  in the way of the dampening fluid corresponding between the hydraulic chambers  48   a  and  48   b.  Per the fourth embodiment of the present invention a pneumatically controlled shut-off valve  63  carries the function of the dampening fluid flow governor means  27 . The shut-off valve  63  is utilized to enable accurate positioning control. 
     Due to the rigid connection between the rod  18  and the double rod  30  the hydraulic actuator actuation means  21  actuate simultaneously with the pneumatic actuator actuation means  15 . During actuation the hydraulic actuator actuation means  21  effectively force transfer of the dampening fluid between the first and the second hydraulic chambers  48   a  and  48   b.  The dampening fluid transfer between the chambers  48   a  and  48   b  takes place through the dampening fluid path  24   f  and the dampening fluid flow governor means  27  where hydraulic locking and dampening of the pneumatic actuator  3  effectively occurs. 
     Utilization of the hydraulic actuator with zero volumetric differential allows for hydraulic locking and dampening with a self-contained hydraulic actuator free from the compressibility effect and, thus, offering the advantages of smooth and free of creeping displacement, steady positioning and design simplicity. 
     FIG. 5 shows a longitudinal sectional view of a hydropneumatic actuator per the fifth embodiment of the present invention. As it will become apparent from the ensuing description, in the fifth embodiment of the present invention the function of the positive-displacement dampening hydraulic actuator with zero volumetric differential is carried by a different type of positive-displacement device. 
     The hydropneumatic actuator per the fifth embodiment is generally comprised of a pneumatic actuator  3 , a hydraulic actuator, a dampening fluid path  24   g,  and dampening fluid flow governor means  27 . 
     The pneumatic actuator  3  is further composed of a pneumatic actuator housing unit that is comprised of a hollow cylindrical body  6 , a front closure  9  fixedly mounted at the front end of the hollow cylindrical body  6 , a rear closure  12  fixedly mounted at the rear end of the hollow cylindrical body  6 , and pneumatic actuator actuation means  15  (formed as a cylindrical plunger) with a rod  18 . The pneumatic actuator actuation means  15  is slidably disposed inside the hollow cylindrical body  6  and divide the chamber inside the pneumatic actuator housing unit into a chamber  45   a  and a chamber  45   b.    
     The front closure  9  is formed with the air channel  39 , and the rear closure  12  is formed with the air channel  42 . Through the air channels  39  and  42  compressed air can be provided to the chambers  45   a  and  45   b  respectively to actuate the pneumatic actuator actuation means  15 . 
     The front closure  9  is further formed with a first hydraulic channel  84 , and the rear closure  12  is further formed with a second hydraulic channel  87 . As it will become apparent from the ensuing description, the first and the second hydraulic channels  84  and  87  allow the front and the rear closures  9  and  12  to form a hydraulic actuator housing unit. 
     The hydraulic actuator comprises the hydraulic actuator housing unit and two hydraulic actuator actuation means  90  and  93 . According to the fifth embodiment of the present invention the hydraulic actuator actuation means  90  and  93  are formed of bellows made out of a suitable material (metallic, plastic, composition, etc.) each with one sealed terminal end in contact with the pneumatic actuator actuation means  15  and one open inlet end. The open inlet end of the hydraulic actuator actuation means  90  is air-tightly assembled (for example by gluing, welding, brazing, etc.) to the front closure  9  in such manner that the hydraulic channel  84  is connected to the first hydraulic chamber  48   a  of the hydraulic actuator actuation means  90 . The open inlet end of the hydraulic actuator actuation means  93  is air-tightly assembled (for example by gluing, welding, brazing, etc.) to the front closure  12  in such manner that the hydraulic channel  87  is connected to the first hydraulic chamber  48   b  of the hydraulic actuator actuation means  93 . 
     The dampening fluid path  24   g  is formed with an inlet (not shown) for filling the active volume of the hydraulic actuator and all adjacent hydraulic cavities with a suitable dampening fluid. The dampening fluid path  24   g  provides a connection between the first hydraulic chamber  48   a  and the second hydraulic chamber  48   b.  Both, the first hydraulic chamber  48   a  and the second hydraulic chamber  48   b  and all adjacent hydraulic cavities are completely filled with dampening fluid and sealed with sealing means (not shown). 
     The dampening fluid flow governor means  27  are placed in the middle of the dampening fluid path  24   g  in the way of the dampening fluid corresponding between the first and second hydraulic chambers  48   a  and  48   b.  Per the fifth embodiment of the present invention the dampening fluid flow governor means  27  is an electrically controlled shut-off valve  64 , which enables the hydropneumatic actuator of the fifth embodiment to make rapid and accurate stops in any required position. 
     In order to achieve zero volumetric differential of the hydraulic actuator the hydraulic actuator actuation means  90  and  93  are constructed so to have equal volumetric to linear displacement ratios that can be mathematically described by the following equation:            V     48      a         l     48      a         =       V     48      b         l     48      b                                
     Where: 
     V 48a —a volumetric change of the first hydraulic chamber  48   a;    
     I 48a —a linear displacement of the hydraulic actuator actuation means  90 ; 
     V 48b —a volumetric change of the second hydraulic chamber  48   b  associated with the volumetric change V 48a  of the first hydraulic chamber  48   a;    
     I 48b —a linear displacement of the hydraulic actuator actuation means  93  associated with the linear displacement I 48a  of the hydraulic actuator actuation means  90 . 
     Both hydraulic actuator actuation means  90  and  93  remain in perpetual contact with the pneumatic actuator actuation means  15 . 
     When the pneumatic actuator actuation means  15  moves forward it compresses the hydraulic actuator actuation means  90 , and causes a negative linear displacement I 48a  of the hydraulic actuator actuation means  90  and a corresponding displacement of dampening fluid from the first hydraulic chamber  48   a.    
     The volume of dampening fluid displaced by the first hydraulic chamber  48   a  is equal to the associated volumetric increase V 48b  of the second hydraulic chamber  48   b  of the hydraulic actuator actuation means  93  due to the intake of the dampening fluid displaced by the first hydraulic chamber  48   a.    
     The associated volumetric increase V 48b  results in the corresponding positive linear displacement I 48b  of the hydraulic actuator actuation means  93 , which, by the absolute value is equal to the absolute value of the original negative linear displacement I 48a  of the hydraulic actuator actuation means  90 . 
     When the pneumatic actuator actuation means  15  moves rearward it compresses the hydraulic actuator actuation means  93 , and causes a negative linear displacement I 48b  of the hydraulic actuator actuation means  93  and a corresponding displacement of dampening fluid from the second hydraulic chamber  48   b.    
     The volume of dampening fluid displaced by the second hydraulic chamber  48   b  is equal to the associated volumetric increase V 48a  of the first hydraulic chamber  48   a  of the hydraulic actuator actuation means  90  due to the intake of the dampening fluid displaced by the second hydraulic chamber  48   b.    
     The associated volumetric increase V 48a  results in the corresponding positive linear displacement I 48a  of the hydraulic actuator actuation means  90 , which is, by the absolute value, equal to the original negative linear displacement I 48b  of the hydraulic actuator actuation means  93 . 
     Taking into consideration the above equation, it becomes apparent that with any direction and amount of linear displacement by the pneumatic actuator actuation means  15  the volume of dampening fluid expelled by deflated hydraulic actuator actuation means ( 90  or  93 ) will always remain equal to the volume of dampening fluid received by the inflated hydraulic actuator actuation means ( 93  or  90 ). 
     These conditions allow to maintain a volumetric balance of dampening fluid transferred between the first and second hydraulic chambers ( 48   a  and  48   b ) of the hydraulic actuator, or, in other words, make the hydraulic actuator utilized by the fifth embodiment of this invention a zero volumetric differential hydraulic actuator. 
     During dampening fluid transfer between the hydraulic chambers  48   a  and  48   b  the hydraulic dampening effectively occurs in the dampening fluid flow governor means  27 . The utilization of the hydraulic actuator with zero volumetric differential allows to achieve hydraulic locking and dampening with a self-contained hydraulic actuator that is free from the compressibility effect, and thus, offers the advantages of smooth and free of creeping displacement, steady positioning and design simplicity. 
     FIG. 6 a  and FIG. 6 b  show a longitudinal sectional view of a hydropneumatic actuator per the sixth embodiment of the present invention. 
     The hydropneumatic actuator per the sixth embodiment is generally comprised of a pneumatic actuator  3 , a hydraulic actuator, a dampening fluid path  24   h,  and dampening fluid flow governor means  27 . 
     The pneumatic actuator  3  is further composed of a pneumatic actuator actuation means  15  (formed as a cylindrical plunger) with a rod  18 , and a pneumatic actuator housing unit that is comprised of a hollow cylindrical body  6 , a front closure  9 , fixedly mounted at the front end of the hollow cylindrical body  6 , a rear closure  12 , fixedly mounted at the rear end of the hollow cylindrical body  6 . The pneumatic actuator actuation means  15  are slidably disposed inside the hollow cylindrical body  6  and divide the active volume of the chamber inside the pneumatic actuator housing unit into chamber  45   a  and chamber  45   b.    
     The front closure  9  is formed with an air channel  39 , and the rear closure  12  is formed with an air channel  42 . Through the air channels  39  and  42  compressed air can be provided to the chambers  45   a  and  45   b  respectively to power the pneumatic actuator. 
     The hydraulic actuator comprises a hydraulic actuator housing unit and hydraulic actuator actuation means  21 , which according to the sixth embodiment of the present invention, is presented by a thin flexible diaphragm made out of a suitable material (metallic, plastic, composition, etc.) with a detached double rod  30 . The double rod  30  of the hydraulic actuator actuation means  21  has a constant diameter equal on both sides of the diaphragm. 
     The hydraulic actuator housing unit is further composed of a shell  96 , and the rear closure  12  of the pneumatic actuator  3 . The shell  96  is formed with a cylindrical depression that faces the rear closure  12 . The rear closure  12  has an external rear surface formed with an identical cylindrical depression the diameter of which is equal to the diameter of the cylindrical depression of the shell  96 . The shell  96  and the rear closure  12  form the hydraulic actuator housing unit by being held together with fastener means (not shown). 
     The hydraulic actuator actuation means  21  is disposed and fixedly compressed between the shell  96  and the rear closure  12 , and thus, seals the perimeter of the two incorporated cylindrical depressions of the shell  96  and of the rear closure  12 , whereby the hydraulic actuator actuation means  21  divide the hydraulic chamber formed by the two cylindrical depressions into a first hydraulic chamber  48   a  and a second hydraulic chamber  48   b.    
     The shell  96  is further formed with an axial hole through which air-tightly extends the rear end of the double rod  30 . 
     The equal diameter of the rear closure&#39;s  12  and the shell&#39;s  96  cylindrical depressions together with the equal diameter of the double rod  30  on both sides of the hydraulic actuator actuation means  21 , and a negligible small thickness of the hydraulic actuator actuation means  21  allow to obtain conditions of a hydraulic actuator with zero volumetric differential. 
     The rear closure  12  is further formed with a first segment of the dampening fluid path  24   h , and an inlet  102  for filling the hydraulic chamber of the hydraulic actuator and all the adjacent hydraulic cavities with a suitable dampening fluid. 
     The shell  96  is further formed with a second segment of the dampening fluid path  24   h.    
     The first and the second segments of the dampening fluid path  24   h  are connected through a dampening fluid flow governor means  27  built into the shell  96 , and together form the dampening fluid flow path  24   h . Per the sixth embodiment of the present invention the function of the dampening fluid flow governor means  27  is carried by a pneumatically controlled shut-off valve  63  and a permanent orifice  51  connected in series. 
     Both, the first hydraulic chamber  48   a  and the second hydraulic chamber  48   b  and all the adjacent hydraulic cavities are completely filled with dampening fluid and sealed with sealing means  105 , which, per the sixth embodiment of the present invention, is an airtight threaded plug. 
     The front end of the double rod  30  air-tightly extends through the axial hole of the rear closure  12  of the pneumatic actuator  3 . Further, the front end of the double rod  30  is fixedly connected to pneumatic actuator actuation means  15  to enable simultaneous linear displacements of pneumatic actuator actuation means  15  and hydraulic actuator actuation means  21 . During actuation the pneumatic actuator actuation means  15  through the hydraulic actuator actuation means  21  effectively force transfer of the dampening fluid between the first and second hydraulic chambers  48   a  and  48   b , and therefore, provide dampening of the pneumatic actuator. 
     FIGS. 7 a - 7   d  show isometric views of a rotary type hydropneumatic actuator according to the seventh embodiment of the present invention. 
     The hydropneumatic actuator per the seventh embodiment of the present invention generally comprises a pneumatic actuator  3  (shown on FIG. 7 a ) a hydraulic actuator, a dampening fluid path  24   i  (shown on FIG. 7 b  and FIG. 7 d ), and a dampening fluid flow governor means  27  (shown on FIG. 7 b  and FIG. 7 d ). 
     The pneumatic actuator  3  is composed of a pneumatic actuator housing unit (which further comprises of a body  111 , a front closure  114  and a rear closure  117 ), and a pneumatic actuator actuation means  15 . 
     The body  111  is a formed parallelepiped with an internal axial through cut, which is shaped as a cylindrical hole with two inwardly propagated identical triangular ribs  120   a  and  120   b  (shown on FIG. 7 b  and FIG. 7 c ). The ribs  120   a  and  120   b  are positioned diametrically opposite to each other. 
     The front closure  114  is fixedly mounted at the front end of the body  111 , and the rear closure  117  is fixedly mounted at the rear end of the body  111 . Both, the front closure  114  and the rear closure  117  are assembled to the body  111  with four identical fastener means  123 . 
     The pneumatic actuator actuation means  15  are formed of a rotor  126  (shown on FIG. 7 b  and FIG. 7 c ) with a shaft  129 . 
     The rotor  126  is slidably disposed inside said axial through cut of the body  111  (so to allow rotational reciprocation of the rotor  126  inside the body  111 ), whereby the space inside the pneumatic actuator housing unit is divided by the rotor  126  and the two ribs  120   a  and  120   b  into chambers  132   a ,  132   b ,  132   c , and  132   d  (shown on FIG. 7 b  and FIG. 7 c ). The chambers  132   a ,  132   b ,  132   c , and  132   d  are slidably sealed from each other with sealing means (not shown). Types and design arrangements of the sealing means are not limited by the scope of this invention; for instance, they can be served by polymer gaskets, elastic fins, etc. 
     The body  111  is further formed with channels  141  and  144  (shown in FIG. 7 c ). Through the channels  141  and  144  compressed air can be provided to the chambers  132   b  and  132   a  respective to power 
     Thus, the body  111  with the channels  141  and  144 , the front closure  114  and the rear closure  17 , the four fastener means  123 , and the rotor  126  with the shaft  129  form said pneumatic actuator  3  with two pneumatic working chambers  132   a  and  132   b.    
     According to the seventh embodiment of the present invention, the described above housing unit of the pneumatic actuator  3  and the pneumatic actuator actuation means  15  simultaneously serve functions of a housing unit for the hydraulic actuator and a hydraulic actuator actuation means subsequently. 
     The hydraulic actuator of the seventh embodiment is composed of a hydraulic actuator housing unit (sheared with pneumatic actuator), and a pneumatic actuator actuation means  15  (sheared with pneumatic actuator as well). 
     The dampening fluid path  24   i  (shown on FIG. 7 b  and FIG. 7 d ) and the dampening fluid flow governor means  27  are assembled in a governor means block  108 , which is formed with two ports: a port  153  and a port  156  (shown on FIG. 7 b , FIG. 7 c  and FIG. 7 d ). The dampening fluid path  24   a  connects the ports  153  and  156  together through the governor means  27 . The governor means block  108  is mounted onto the body  111  with four identical fastener means  159 . 
     The body  111  is further formed with a channel  147  (shown on FIG. 7 b  and FIG. 7 c ) with the first end of the channel  147  connected to the chamber  132   c , which is by essence a first hydraulic chamber, and the second end of the channel  147  connected to the port  153  of the governor means block  108 , and a channel  150  (shown on FIG. 7 b ) with the first end of the channel  150  connected to the chamber  132   d , which is by essence a second hydraulic chamber, and the second end of the channel  150  connected to the port  153  of the governor means block  108 . 
     The body  111  is further formed with an inlet (not shown) for filling the chambers  132   c  and  132   d , and all adjacent hydraulic cavities with a suitable dampening fluid. Thus, the chamber  132   c  carries the function of the first hydraulic chamber and the chamber  132   d  carries the function of the second hydraulic chamber. The first hydraulic chamber  132   c , the second hydraulic chamber  132   d , and all adjacent hydraulic cavities are completely filled with dampening fluid and sealed with sealing means (not shown). 
     The assembly of the body  111 , formed with the channels  147  and  150 , the front closure  114 , the rear closure  117 , the four fastener means  123 , and the rotor  126 , formed with the shaft  129 , further composes said hydraulic actuator. 
     The design arrangement of the seventh embodiment, in which the rotor  126  and the axial through cut of the body  111  are of symmetrical geometry, allows to form a hydraulic actuator with zero volumetric differential in which the volume of dampening fluid displaced from one chamber ( 132   c  or  132   d ) is always equal to the volume of dampening fluid received by the opposite chamber ( 132   d  or  132   c ). 
     When compressed air is let into the channel  141  and further into the chamber  132   b  it causes rotor  126 , which at this moment carries the function of pneumatic actuator actuation means, to rotate counterclockwise. And, respectively, when compressed air is let into the channel  144  and further into the chamber  132   a  it causes the rotor  126  to rotate clockwise. During the counterclockwise rotation the rotor  126  (which at the same time carries the function of hydraulic actuator actuation means) simultaneously causes dampening fluid transfer from the second hydraulic chamber  132   d  to the first hydraulic chamber  132   c . During the clockwise rotation, the rotor  126  causes reverse direction transfer of dampening fluid. 
     During dampening fluid transfer between the hydraulic chambers  132   c  and  132   d  dampening fluid passes through the dampening fluid flow governor means  27   a , whereby takes place dampening of the rapid speed changes and creeping that naturally occur in the pneumatically powered rotor  126 . 
     The hydropneumatic actuators encompassed in all the above embodiments represent only one type design arrangement with which the novel concept of the present invention is utilized. This is a type of design arrangement in which any relative displacement of a pneumatic actuator housing unit with respect to a pneumatic actuator actuation means is directly translated into an equal relative displacement of a hydraulic actuator housing unit with respect to a hydraulic actuator actuation means. 
     FIGS. 8-11 show four different isometric views of a hydropneumatic actuator according to the eighth embodiment of the present invention. 
     In the hydropneumatic actuator of the to eighth embodiment the novel concept of the present invention is utilized in combination with such a design arrangement in which a displacement occurring in pneumatic actuator translated proportionally into a displacement of hydraulic actuator using mechanical transmission means. 
     The hydropneumatic actuator per the eighth embodiment of this invention generally comprises a pneumatic actuator  3 , a hydraulic actuator, a dampening fluid path  24   j  (partially shown on FIG.  11 ), and a dampening fluid flow governor means  27  (shown on FIG.  11 ). The pneumatic actuator  3 , according to the eighth embodiment of this invention, is comprised of a pneumatic actuator housing unit and pneumatic actuator actuation means (shown on FIG.  9 ). 
     The pneumatic actuator housing unit is further comprised of a body  165 , a pneumatic front plug  168 , a pneumatic rear plug  171  (shown on FIG.  9  and FIG.  10 ). The pneumatic actuator actuation means is further comprised of two pistons  174   a  and  174   b  fixedly connected through a gear rack  177  (shown on FIG.  9  and FIG. 10) positioned between them, and a rod  180 . 
     As shown on FIG. 9, the body  165  is formed with a first cylindrical through bore threaded at both ends. The pneumatic actuator actuation means is slidably disposed inside said first cylindrical bore. 
     The pneumatic front plug  168  and the pneumatic rear plug  171  are air-tightly threaded into the threaded ends of the first bore, whereby two pneumatic chambers  183   a  and  183   b  are formed inside the pneumatic actuator housing unit. 
     The body  165  is further formed with channels  186   a  and  186   b . Through the channel  186   a  compressed air can be provided to the chamber  183   a , and through the channel  186   b  compressed air can be provided to the chamber  183   b  to actuate the pneumatic actuator actuation means. 
     The hydraulic actuator, according to the eighth embodiment of this invention, is comprised of a hydraulic actuator housing unit and a hydraulic actuator actuation means, (shown on FIG.  10  and FIG.  11 ). The hydraulic actuator housing unit is further comprised of a body  165  (shared with pneumatic actuator), a hydraulic plug  189   a  (shown on FIG.  10  and FIG.  11 ), and a hydraulic plug  189   b  (shown on FIG.  10 ). The hydraulic actuator actuation means is further comprised of two identical pistons  192   a  and  192   b  fixedly connected through a gear rack  195  (shown on FIG.  10  and FIG. 11) positioned between them. 
     As shown on FIG.  10  and FIG. 11, the body  165  is further formed with a second cylindrical through bore threaded at both ends. The hydraulic actuator actuation means are slidably disposed inside said second cylindrical bore, and hydraulic plugs  189   a  and  189   b  are air-tightly threaded into the threaded ends of the second bore, whereby a first hydraulic chamber  198   a  and a second hydraulic chamber  198   b  are formed inside the hydraulic actuator housing unit. 
     The dampening fluid path  24   j  (partially shown on FIG. 11) comprises two symmetrical hydraulic channels formed in the body  165 . The first hydraulic channel (shown on FIG. 11) connects the first hydraulic port  201   a  to the first hydraulic chamber  198   a . The second hydraulic channel (not shown) connects the second hydraulic port  201   b  to the second hydraulic chamber  198   b.    
     The first hydraulic port  201   a  and the second hydraulic port  201   b  are interconnected through the dampening fluid flow governor means  27  (shown on FIG.  11 ). Per the eighth embodiment of the present invention, the dampening fluid flow governor means  27  is an adjustable needle valve  57  that allows for fine adjustment to the rate of dampening fluid flow. 
     The body  165  is further formed with an inlet  204  (shown on FIG.  10  and FIG. 11) for filling the first and the second hydraulic chambers  198   a  and  198   b , and all adjacent cavities with a suitable dampening fluid. The first hydraulic chamber  198   a , second hydraulic chamber  198   b , and all adjacent cavities are completely filled with dampening fluid and sealed with sealing means  207 . 
     The design arrangement of the eighth embodiment of the present invention, in which the two pistons  192   a  and  192   b  have the same outer diameter and active displacement area, allows to form a hydraulic actuator with zero volumetric differential. 
     The function of the mechanical transmission means of the eighth embodiment of the present invention is carried by a rack-and gear drive (shown on FIGS.  9 - 11 ), which is composed of said gear rack  177 , said gear rack  195 , a gear wheel  210 , a gear wheel  213 , and a shaft  216  (on which both gear wheels  210  and  213  are fixedly mounted). The shaft  216  is supported in the body  165  (for example with two bushings). 
     The gear rack  177 , being a solid of part of the pneumatic actuator actuation means, is mechanically coupled to the gear wheel  210  and further through the shaft  216  and the gear wheel  213  is mechanically coupled to the gear rack  195 , which is a solid of part of the hydraulic actuator actuation means. Thus, the described chain provides translation of the pneumatic actuator actuation means displacement into the hydraulic actuator actuation means displacement at a constant ratio determined by the ratio of the mechanical transmission means used. 
     The main goal of mechanical transmission means utilization is to minimize the stroke of hydraulic actuator actuation means, dimensions of the required hydraulic actuator, and therefore, the overall dimensions of the hydropneumatic actuator according to this invention. The additional benefits of having the mechanical transmission means is the possibility of obtaining multiple forms of actuation by the same hydropneumatic actuator. 
     When compressed air is let into the channel  186   a  and further into the chamber  192   a , or into the channel  186   b  and then into the chamber  192   b  it causes linear displacement of the pneumatic actuator actuation means. Further, through the gear rack  177  coupled to the gear wheel  210  the linear displacement of the pneumatic actuator actuation means is translated into rotary displacement of the shaft  216 . From the shaft  216  through the gear wheel  213  and the gear rack  195  coupled to the gear wheel  213  the rotary displacement is further translated into linear displacement of the hydraulic actuator actuation means. The linear displacement of the hydraulic actuator actuation means causes dampening fluid transfer between the hydraulic chambers  192   a  and  192   b  of the hydraulic actuator. 
     During dampening fluid transfer between the hydraulic chambers  192   a  and  192   b  dampening fluid passes through the dampening fluid flow governor means  27 , whereby dampening of rapid speed changes and creeping naturally occurring in the pneumatic actuator takes place. 
     FIG. 12 a  and FIG. 12 b  show an isometric view of a hydropneumatic actuator according to the ninth embodiment of the present invention. 
     The design arrangement of the ninth embodiment is generally similar to the design arrangement of the eighth embodiment for which reason the part of the arrangement identical to the one described above is not show on FIG. 12 a  and FIG. 12 b.    
     The hydropneumatic actuator per the ninth embodiment of this invention generally comprises a pneumatic actuator  3 , a hydraulic actuator, and dampening fluid path and a dampening fluid flow governor means  27 . The dampening fluid path of the ninth embodiment is combined with the dampening fluid flow governor means  27 . 
     The pneumatic actuator  3 , according to the ninth embodiment of this invention, is comprised of a pneumatic actuator housing unit and pneumatic actuator actuation means (not shown) identical to the pneumatic actuator actuation means of the eighth embodiment (shown on FIG.  9 ). The pneumatic actuator housing unit is further comprised of a body  165 , a pneumatic front plug  168 , and a pneumatic rear plug  174  identical to the pneumatic rear plug  171  of the eighth embodiment. 
     The pneumatic actuator actuation means is fixedly connected to a gear rack  177 , which is further mechanically coupled to a gear wheel  210  and further through the shaft  216  and the gear wheel  213  mechanically coupled to the gear rack  195 . 
     The hydraulic actuator of the ninth embodiment is composed of a hydraulic actuator housing unit and a hydraulic actuator actuation means  21  formed with a double rod  30 . The hydraulic actuator housing unit is further comprised of a hollow cylindrical body  60  formed with the gear rack  195 , and a rear closure (not shown) fixedly mounted at the rear end of the hollow cylindrical body  60 . The hydraulic actuator actuation means  21  is slidably disposed inside the hollow cylindrical body  60  and divide the active volume of the hydraulic actuator housing unit into a first hydraulic chamber  48   a  and a second hydraulic chamber  48   b.    
     The double rod  30  has the same diameter on both sides of the hydraulic actuator actuation means  21  therefore is a zero volumetric differential hydraulic actuator. 
     The front end and the rear end of the double rod  30  are fixedly clamped between a front closure and a rear closure of the hydraulic actuator ( 186   a  and  186   b  respectively) threaded into the body  165 . Thus, the hydraulic actuator actuation means  21  remains fixedly joined with the pneumatic actuator housing unit described. 
     According to the ninth embodiment of the present invention, the function of the dampening fluid flow governor means  27  is carried by a permanent orifice  51  formed as a small diameter bore drilled through the hydraulic actuator actuation means  21 . Simultaneously the permanent orifice  51  serves the function of the dampening fluid path allowing the dampening fluid to communicate between the two hydraulic chambers  48   a  and  48   b.    
     The body  165  is further formed with channels  186   a  and  186   b . Through the channels  186   a  and  186   b  compressed air can be provided to actuate the pneumatic actuator actuation means. 
     The hollow cylindrical body  60  is formed with an inlet (not shown) for filling the first and the second hydraulic chambers  48   a  and  48   b , and all adjacent cavities with a suitable dampening fluid. The first hydraulic chamber  48   a , second hydraulic chamber  48   b , and all adjacent cavities are completely filled with dampening fluid and sealed with sealing means (not shown). 
     The pneumatic actuator actuation means of the ninth embodiment is mechanically coupled with the hydraulic actuator housing unit. The function of the mechanical transmission means of the ninth embodiment of the present invention is carried by a rack-and gear drive composed of the gear rack  177 , said gear rack  195 , a gear wheel  210 , a gear wheel  213 , and a shaft  216  (on which both gear wheels  210  and  213  are fixedly mounted). The shaft  216  is supported in the housing unit  165  (for example with two bushings). 
     When compressed air is let into the channel  186   a  with simultaneous exhaust provided form the channel  186   b , or into the channel  186   b  with simultaneous exhaust provided from the channel  186   a , it causes linear displacement of the pneumatic actuator actuation means fixedly attached to the gear rack  177 . Further, the linear displacement of the gear rack  177  is being translated into rotary displacement of the gear wheel  210  mechanically coupled with the gear rack  177 . The rotary displacement of the gear wheel  210  is further being translated into rotary displacement of the shaft  216 , and yet further from the shaft  216  through the gear wheel  213  into linear displacement of the gear rack  195  coupled to the gear wheel  213 . 
     This linear displacement of the gear rack  195  and, therefore, of the hydraulic actuator housing unit occurring with respect to the hydraulic actuator actuation means causes dampening fluid transfer between the hydraulic chambers  48   a  and  48   b  of the hydraulic actuator. 
     During dampening fluid transfer between the hydraulic chambers  48   a  and  48   b  dampening fluid passes through the dampening fluid flow governor means  27 , whereby dampening of rapid speed changes and creeping takes place. 
     Naturally, the design arrangement of the ninth embodiment as well as all of the above embodiments is not intended to limit the present invention. For example, different types of lever motion mechanisms for instance such as cam-shaft mechanisms, etc. could be optionally utilized for mechanical transmission means. The shaft  216  such as shown on FIGS. 8,  9 ,  10 ,  11 ,  12   a  and  12   b  of the eighth and ninth embodiments could be fixedly connected to a rotor of a dampening rotary hydraulic actuator with zero volumetric differential. 
     FIG. 13 a  shows a longitudinal sectional view of a hydropneumatic actuator according to a tenth embodiment of the present invention. 
     The hydropneumatic actuator shown on FIG. 13 a  is generally constructed of linear pneumatic actuator  3 , a linear positive-displacement hydraulic actuator, a dampening fluid path combined of dampening fluid path segments  24   k ,  24   l ,  24   m ,  24   n ,  24   o ,  24   p ,  24   q  and a dampening fluid flow governor means  27 . 
     The pneumatic actuator  3  is further comprised of a pneumatic actuator housing unit, composed of a hollow cylindrical body  6 , a front closure  9 , fixedly mounted at the front end of the hollow cylindrical body  6 , a rear closure  12 , fixedly mounted at the rear end of the hollow cylindrical body  6 , and a pneumatic actuator actuation means is presented by a cylindrical plunger formed with a rod  18  slidably disposed inside the hollow cylindrical body  6 . 
     The pneumatic actuator actuation means  15  divides the active volume of the chamber inside the hollow cylindrical body  6  into two chambers: chamber  45   a  and chamber  45   b.    
     The front closure  9  is formed with an air channel  39 . The rear closure  12  is formed with an air channel  42 . Through the air channels  39  and  42  compressed air can be provided to the chambers  45   a  and  45   b  respectively, to power the pneumatic actuator actuation means  15 . 
     The rod  18  of the pneumatic actuator  3  is formed hollow with an axial cylindrical bore which allows the rod  18  to serve a function of a body for a hydraulic actuator housing unit disposed inside pneumatic actuator. 
     The hydraulic actuator housing unit further includes a hydraulic actuator front closure  33  (fixedly mounted inside the axial cylindrical bore of the rod  18 ), and a hydraulic actuator rear closure  36  (fixedly mounted a the rear end of the axial cylindrical bore inside the rod  18 ). 
     Thus, the hydraulic actuator housing unit is composed of the hollow rod  18  assembled together with the hydraulic actuator front closure  33  and the hydraulic actuator rear closure  36 . 
     The hydraulic actuator further comprises a hydraulic actuator actuation means  21  presented by a cylindrical plunger formed with double rod  30 . The hydraulic actuator actuation means  21  is slidably disposed within the axial cylindrical bore inside the rod  18 , whereby the hydraulic actuator actuation means  21  divides the volume inside the hollow hydraulic actuator housing unit into a first hydraulic chamber  48   a  and a second hydraulic chamber  48   b.    
     The double rod  30  has a constant outside diameter, equal on both sides of the hydraulic actuator actuation means  21 , which allows to achieve the conditions of zero volumetric differential. 
     The rear segment of the double rod  30  of the tenth embodiment is formed with an axial bore extending slightly beyond the level of hydraulic actuator actuation means  21 . The axial bore is formed with a smaller diameter at the end to be engaged in a sealing press-fit with a front end of a tubular member  219 . At the rear end of the tubular member  219  is rigidly engaged with a plug  222 . The plug  222  is simultaneously engaged with the inlet end of the axial bore in the rod  30 . Both engagements: between the plug  222  and the tubular member  219 , and the plug  222  and the inlet end of the axial bore in the rod  30  are hydraulically sealed. Such an arrangement allows to form two distinct segments for dampening fluid path: segment  24   l , presented by the inner bore of the tubular member  219 , and segment  24   p  presented by the annular duct formed by the gap between the inner surface of the axial bore in the rod  30  and the external surface of the tubular member  219 . 
     The rod  30  is further formed with a dampening fluid path segment  24   k  and a dampening fluid path segment  24   q . The dampening fluid path segment  24   k  provides a hydraulic path to the first hydraulic chamber  48   a . The dampening fluid path segment  24   q  provides a hydraulic path to the first hydraulic chamber  48   b.    
     Hydropneumatic actuator, in accordance with the tenth embodiment of this invention, further includes the dampening fluid path segment  24   o , which provides connection with the segment  24   p.    
     It will be appreciated that the external disposition of the dampening fluid flow governor means  27  with respect to the linear positive-displacement hydraulic actuator is desirable in such instances when a plurality of actuator models is intended on the base of one standard core sub-assembly. The standard core sub-assembly comprised of the linear pneumatic actuator  3 , the linear positive-displacement hydraulic actuator, and the dampening fluid path combined of dampening fluid path segments  24   k ,  24   l ,  24   o ,  24   p ,  24   q  remains unchanged, and the variations of actuator models is achieved by a variety of external interchangeably detachable modules containing different dampening fluid flow governor means  27 . 
     In accordance with the tenth embodiment of this invention the detachable module is composed of a governor means housing  225  formed with dampening fluid path segments  24   m ,  24   n  and having the dampening fluid flow governor means  27  presented by a permanent orifice  51  disposed between them. The detachable module is fastened to the rear closure  12  with fasteners means (not shown). 
     The governor means housing  225  is formed with channels (not shown) for filling the active volume of the hydraulic actuator, all dampening fluid path segments  24   k ,  24   l ,  24   m ,  24   n ,  24   o ,  24   p ,  24   q  and all the adjacent hydraulic cavities with a suitable dampening fluid. The active volume of the hydraulic actuator and all the adjacent hydraulic cavities are completely filled with dampening fluid and sealed with sealing means (not shown). 
     To convert the displacement generated by the pneumatic actuator into the displacement of the hydraulic actuator, the pneumatic and the hydraulic actuators are coupled. In accordance with the tenth embodiment of this invention the housing unit of the hydraulic actuator is being coupled with the pneumatic actuator actuating means due to the fact that pneumatic actuator actuation means  15  formed with a rod  18  is made hollow and simultaneously performs the function of a body for the hydraulic actuator housing unit. Further, the hydraulic actuator actuating means  21  are being coupled with the pneumatic actuator housing unit through the rear end of the double rod  30  of the hydraulic actuator actuation means  21  being sealably connected to the rear closure  12  of the pneumatic actuator  3  and secured with a retainer  228  as shown on FIG. 13 a.    
     The front end of the double rod  30  is free to move inside the rod  18  of the pneumatic actuator  3 . 
     When compressed air is let into the channel  39  and further to the chamber  45   a  it causes the pneumatic actuator actuation means  15  to move rearward. Respectively, when compressed air is let into the channel  42  and further to the chamber  45   b  it causes the pneumatic actuator actuation means  15  to move forward. 
     The hollow rod  18 , as a solid part of the pneumatic actuator actuation means  15 , moves with the pneumatic actuator actuation means  15 , and, simultaneously, as a solid part of the hydraulic actuator housing unit makes a displacement with respect to the hydraulic actuator actuation means  21 . The hydraulic actuator actuation means  21 , being fixedly connected to the rear closure  12  through the double rod  30 , therefore, remain stationary with respect to the pneumatic actuator housing unit. 
     During the displacement of the rod  18  with respect to the hydraulic actuator actuation means  21  the dampening fluid contained in the active volume of the hydraulic actuator is being effectively redistributed between the first and the second hydraulic chambers,  48   a  and  48   b , of the hydraulic actuator. For example, when the pneumatic actuator actuation means  15  moves forward the dampening fluid is being forced from the second hydraulic chamber  48   b  through the dampening fluid path segment  24   q  and then subsequently through the dampening fluid path segments  24   p ,  24   o ,  24   n , passing the permanent orifice  51 , whereby dampening takes place, and further through the dampening fluid path segments  24   m ,  24   l ,  24   k  into the first hydraulic chamber  48   a.    
     FIG. 13 b  shows a partial enlarged view of the eleventh embodiment. The eleventh embodiment of the present invention by essence is a modified version analogous to the tenth embodiment described above, however having detachable module equipped with an adjustable needle valve  57  for dampening fluid flow governor means  27 . The needle valve  57  allows fine manual adjustment to the dampening rate. 
     FIG. 13 c  shows a partial enlarged view of the twelfth embodiment of the present invention, which by essence is yet another modified version analogous to the tenth embodiment described above, however equipped with a detachable module including a combination of a shut-off valve  64  and a permanent orifice  51  for dampening fluid flow governor means  27 . 
     In terms of the principle of operation, the actuator of the eleventh and twelfth embodiments, shown on FIG. 13 b  and FIG. 13 c , remain analogous to the actuator of the tenth embodiment, shown on FIG. 13 a.    
     FIG. 14 shows a longitudinal sectional view of a hydropneumatic actuator according to a thirteenth embodiment of the present invention. 
     The hydropneumatic actuator shown on FIG. 14 is yet another design arrangement for a hydropneumatic actuator with a hydraulic actuator disposed inside of a pneumatic actuator and dampening fluid flow governor means disposed externally to hydraulic actuator actuating means. The hydropneumatic actuator per the thirteenth embodiment of the present invention generally comprises a pneumatic actuator  3  a hydraulic actuator, a dampening fluid path  24   r , and a dampening fluid flow governor means  27 . 
     The pneumatic actuator  3  is further comprised of a pneumatic actuator housing unit, composed of a hollow cylindrical body  6 , a front closure  9 , fixedly mounted at the front end of the hollow cylindrical body  6 , a rear closure  12 , fixedly mounted at the rear end of the hollow cylindrical body  6 , and two fixedly joint pneumatic actuator actuation means  15   a  and  15   b  (presented by two cylindrical plungers) movably disposed inside the hollow cylindrical body  6  and thus dividing the active volume of the chamber inside the hollow cylindrical body  6  into three chambers. 
     Chambers  45   a  and  45   b  are two of the three the chambers inside the hollow cylindrical body  6 . Functionally these chambers are the chambers of the pneumatic actuator  3 . They are adjacent to the front closure  9  and the rear closure  12  respectively. 
     The front closure  9  is formed with an air channel  39 . The rear closure  12  is formed with an air channel  42 . Through the air channels  39  and  42  compressed air can be provided into the chambers  45   a  and  45   b  respectively, to power the pneumatic actuator actuation means  15   a  and  15   b . The pneumatic actuator actuation means  15   a  is formed with a front rod  18  (serving the function of a rod for the pneumatic actuator  3 ) and a rear rod  30  (allowing to fixedly joint together the pneumatic actuator actuation means  15   a  and  15   b ). 
     The hydraulic actuator of the thirteenth embodiment is composed of a hydraulic actuator housing unit and the two hydraulic actuator actuation means  15   a  and  15   b  (shared with the pneumatic actuator  3 ). 
     The hydraulic actuator housing unit further consists of the hollow cylindrical body  6  (shared with the pneumatic actuator  3 ) and a dividing member  231 . 
     Thus the housing unit of the pneumatic actuator  3  simultaneously serves the functions of a housing unit for the hydraulic actuator, and the pneumatic actuator actuation means  15   a  and  15   b  simultaneously serve the functions of a hydraulic actuator actuation means. 
     The rear rod  30  extends through the dividing member  231  in sealing engagement, thus allowing the dividing member  231  to further divide the last of the three chambers (located in the middle of the hollow cylindrical body  6 ) into a first hydraulic chamber  48   a  and a second hydraulic chamber  48   b . In the described arrangement the total volume of the chambers  48   a  and  48   b  remains constant regardless of the axial position of the hydraulic actuator actuation means  15   a  and  15   b , therefore, the dampening hydraulic actuator of the thirteenth embodiment is a true zero volumetric differential hydraulic actuator. 
     In accordance with the thirteenth embodiment of this invention, the hydropneumatic actuator further includes the dampening fluid path  24   r  formed as a bore through the dividing member  231 , which provides a channel for dampening fluid to correspond between the first and the second hydraulic chambers  48   a  and  48   b  during the operation. The chambers  48   a  and  48   b  of the hydraulic actuator and all the adjacent hydraulic cavities are completely filled with dampening fluid and sealed with sealing means (not shown). 
     Further, the hydropneumatic actuator of the thirteenth embodiment includes the dampening fluid flow governor means  27  installed in series with the dampening fluid path  24   r  in the way of the flow of dampening fluid corresponding between the hydraulic chambers  48   a  and  48   b  to govern the flow rate of dampening fluid during operation. According to the design arrangement of the thirteenth embodiment, the function of the dampening fluid flow governor means  27  is carried by an adjustable needle valve  57 . 
     When compressed air is let into the channel  39  and further to the chamber  45   a  it causes the pneumatic actuator actuation means  15   a  to move rearward. Respectively, when compressed air is let into the channel  42  and further to the chamber  45   b  it causes the pneumatic actuator actuation means  15   b  to more forward. During such displacements of the pneumatic actuator actuation means  15   a  and  15   b  the dampening fluid contained in the chambers  48   a  and  48   b  of the hydraulic actuator is being effectively redistributed between the hydraulic chambers  48   a  and  48  of the hydraulic actuator, whereby hydraulic dampening takes place. For example, when the pneumatic actuator actuation means  15   a  and  15   b  moves forward the dampening fluid is being forced from the second hydraulic chamber  48   b  through the dampening fluid path  24   r  and the adjustable needle valve  57  into the first hydraulic chamber  48   b.    
     Naturally, the above instances should not be construed as limitations on the scope of this invention. The devices such as permanent orifices, needle valves, as well as any other types of valves with different types of control, and different varieties of combinations of such devices could be optionally utilized for the dampening fluid flow governor means depending on technical specifications for particular applications. 
     The hydropneumatic actuator according to the present invention can be also equipped with different types of transducers (linear displacement transducers for determining position of the pneumatic actuator actuation means and forming positional feedback, speed transducers, acceleration transducers, load transducer, etc.) and combinations of them. Many other elements of the hydropneumatic actuator according to the present invention in relation with specifics applications will be obvious to those skilled in the art. 
     Therefore, the foregoing is considered as illustrative only of the principles of the present invention, and, since numerous modifications will readily occur to those skilled in the art, it is not desired to limit the invention to the exact construction and operation shown and described.