PATENT DOCUMENT

Abstract:
This invention relates to a novel helical dual-center engagement converting mechanism and its applications in fluid-powered actuation system, more particularly to a highly reliable, simple, powerful and balanced and less expensive helical rotary actuator. This actuator comprises a self-balanced linear/rotary dual-center engagement converter, compact porting systems and easy manufacturing modules and various bodies and shaft interface with other components. This actuator also provides a rotary position control and backlash eliminating mechanism to meet various requirements with lighter weight, smaller size and higher accuracy of position and can be interfaced with different machines, such as subsea valves, earthmoving equipment, construction equipment, lifting equipment, landing gears, militarily equipment and medical devices, robotic and artificial leg and arm joints.

Full Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application claims the benefit of provisional patent application Ser No. 61/404,430 filed on Oct. 1, 2010 by Jianchao Shu 
    
    
     FEDERALLY SPONSORED RESEARCH 
     No 
     SEQUENCE LISTING OR PROGRAM 
     No 
     BACKGROUND 
     This invention relates to a novel helical dual-center engagement converting mechanism and its applications in fluid-powered actuation system, more particularly to a highly reliable, simple, powerful and balanced and less expensive helical rotary actuator. This actuator comprises a self-balanced linear/rotary dual-center engagement converter, compact porting systems, easy manufacturing modules, various body configuration and shaft interfaces with other components. This actuator also provides a rotary position control and backlash eliminating mechanism to meet high precision requirements with lighter weight, smaller size and higher accuracy of position and can be interfaced with different machines, such as subsea valves, earthmoving equipment, construction equipment, lifting equipment, landing gears, militarily equipment and robotic and medical devices, artificial arm and leg joints. 
     Conventional fluid-powered helical actuators have been used in many industries for years, it is based on an old helical linear/rotary converter mechanism and includes a cylindrically shaped housing and two moving parts: a shaft and an annular piston. Helical spline teeth machined on the shaft engage a matching complement of splines on an inside diameter of the piston, an outside diameter of the piston carries a second set of helical splines that engages a ring gear integral with the housing. While conventional linear pistons with pivot joint, the rack and pinion and vane actuators still have majority market share over the helical rotary actuators, the reason is that conventional fluid-powered helical rotary actuators have many unsolved problems and disadvantages; (1) low efficiency, about 60%-70% efficiency for helical rotary actuator is in comparison with that of 90 to 98% for the rack and pinion or vane actuators, so it prevents the actuator from low pressure applications, there are fewer helical pneumatic actuators in the market in comparison with rack and pinion and vane actuators, it not only wastes lot of materials and energy but also can not be used for limited space or restrict weight applications (2) high unbalanced thrust, the unbalanced thrust is still an unsolved problem, it requires more internal parts to balance the thrust, so length of actuator becomes very longer, size of the actuator becomes bigger even there are some balanced helical actuators in the prior art, none of the trials has been commercial success (3) backlashes, due to cumulative clearances of two sets of helical teeth engagements, it increases the impact on the teeth and reduces the accuracy of moving position, life of actuator, some efforts were made in the prior art, but none of trials has been commercial success (4) high stress concentration on cylindrical bodies with helical teeth either by pinging, welding or integrating, it has been struggled for years to seek the solution, under high pressure 3000-5000 psi, the root of helical teeth on cylindrical body generates high stress concentration, this structural problem not only reduces the load capacity and increase the actuator size and weights, but also it can cause sudden break down based on Paris law and is considered to be unreliable and unsafe for critical operations where linear piston with pivot joint devices which have the same rotation function still play a key role in earthmoving equipment and landing gears (5) restrict installation position, most helical actuators are designed for either vertical or horizontal position, they are not suitable for any position between them, due to lack of proper structure and bearing (6) lack of position control, due to lack of control of rotary position and fail to close or open function, it prevents the actuator from critical applications such as military equipment, robotic devices and valve control (7) lack of interface function, most of the actuator bodies are cylindrical shape, such a shape is difficult for three dimensional joint (8) low reliability, according to Failure Modes and Effects Analysis (FMEA), a piston with internal and external helical teeth has the highest severity, with lack of redundancy, the conventional helical actuator never can compete with linear piston with pivot joint in critical applications like landing gears (9) structural inferiority (a) most cylindrical body can not sustain high structural bending load and compression load, it prevent it from those applications like rotation with high bending or compression (b) material incomparability, since material requirement of mechanical property for body is very different from that of teeth, for the body, it requires high strength, ductile, while for the teeth, high hardness and wearing resistance are the key requirements, since the helical teethes are a part of the body, so most designs are to put the body strength first and to scarify teeth design, as a result the teeth with soft surface will be damaged first or wore out fast even with hydraulic fluid (10) difficult and expensive manufacturing, it is difficult and expensive to make helical teeth, specially internal helical teeth or internal splines on the body as an integral part, it not only makes the manufacturing process more difficult if not impossible, it is impossible to replace the teeth alone, since there is no modulization design in the actuator, conventional actuator manufacturing require large inventory for each size actuator (11) inlet and outlet ports are far away and not standardized, so it is difficult to connect the ports, especially in case of counterbalanced valve is required, additional tube and adapter is needed, it not only increase cost but also reduce reliability, any addition joint adapter and tube can cause leak. 
     In order to overcome the disadvantages or solve the problems of the conventional fluid-powered helical rotary actuators, many efforts have been made in the prior arts. There are four approaches to improve the conventional helical actuators in the prior arts, but those approaches work against each other within a limited scope. 
     The first approach is to improve the conversion mechanism. U.S. Pat. No. 3,255,806 to Kenneth H. Meyer (1966), U.S. Pat. No. 4,089,229 to James Leonard Geraci (1978) show a approach is to use a number of keys and keyway to prevent the piston sleeve from rotation under linear force, this conversion mechanism did work, but there were two drawbacks, one is to waste large internal body space due to the keyway, the other is to cause high stress concentration on the body, under 3000-5000 psi pressure, such stress condition is unsafe and prohibited, likewise other actuators are provided with splined design to prevent the piston from rotation for valve actuations, in addition, it is expensive to make, so many other solutions came out like U.S. Pat. No. 1,056,616 to C. E Wright (1913), U.S. Pat. No. 6,793,194 B1 to Joseph Grinberg (2004) the approach is to use two bars to prevent piston sleeve from rotation, the drawback is to waste a large interior housing space and it is restricted to smaller actuator applications, finally current widely acceptable helical actuator is shown in U.S. Pat. No. 3,393,610 to R. O. Aarvold (1966) disclosed a device with a pair helical gearing means between a housing and a shaft in an opposite direction, but it did not prevent the piston rotation, rather it is used as medium to generate a reaction torque between the housing and the shaft and in turn to rotate the shaft, the drawback is to waste internal space and more energy to rotate the piston and increase backlash and cost, a desirable design for this conversion mechanism is that only rotary part should be a rotary shaft, not a body or a piston, moreover the additional rotation will wear bearings and o rings faster and more than under a linear movement only, in addition the arrangement greatly restricts an engaged diameter of the piston, as a result, the output torque is greatly reduced, again, high stress concentration on the body still exists, even it become more difficulty to manufacture with internal and external teeth in a piston. 
     The second approach is to balance thrust force and ease consequences of the unbalanced forces on helical actuators, U.S. Pat. No. 3,255,806 to Kenneth H. Meyer (1966) shows an actuator with two actuator assembled in an opposite teeth and direction, the design become more difficulty for machining the keyways on the longer body, other effort made is shown on U.S. Pat. No. 4,745,847 to Julian D. Voss (1988) discloses a new design with four parts; a shaft, a housing, a linear piston, a rotation piston, it causes more leak paths and make the actuators more complicated and less reliable, finally U.S. Pat. No. 3,393,610 to R. O. Aarvold (1966) shows two sets of helical teeth in an opposite direction on a piston, it balances the thrust force on the piston but not on the shaft or housing, this arrangement causes a constant tension on the piston during linear/rotary converting, so the piston is subject to torsion well as tension while the load is still applied to shaft and housing, as a result the size of piston is increased while the housing and shaft are underused, so far there is no successful full balance design in the market. 
     The third approach is to simplify the manufacturing process, there is few development in the field, the most internal helical teeth are as an integral part of a housing or shaft, few welding process or pining process have been tried, but for the current pressure vessel safety standards, those practices under 3000-5000 psi pressure are considered to be unsafe, so stronger, heaver body or shaft with a integral helical teeth are only the solution for now, there is no improvement in the filed 
     The fourth approach is to ease the backlash and improve performances of the actuator, a typical example is shown in U.S. Pat. No. 2,791,128 to Howard M. Geyer (1957) and U.S. Pat. No. 4,858,486 to Paul P. Meyer (1989), a complex mechanical adjustable devices are introduced, but in most applications, such a design is considered to be impractical or too costly due to inherent disadvantage of clearance of two set of helical teeth, the fundamental adjustment mechanism is still unchanged. 
     So the fluid-powered actuation industry has long sought means of improving the performance of fluid-powered actuation system, eliminating the unbalanced thrust increate efficiency, increate integrity of the body strength, and increasing reliability and accuracy rotary position with less cost. 
     In conclusion, insofar as I am aware, no fluid-powered actuation system formerly developed provides higher system performances with a modularization structure, less parts, highly efficient, versatile, reliable, easy manufacturing at low cost. 
     SUMMARY 
     This invention provides a simple, highly reliable, modular, compact, efficient and balanced rotary actuator. This actuator comprises a novel and improved helical linear/rotary converting modules, compact porting systems and shaft/body interface modules and is much simpler for manufacturing and assembly. It is constructed as converting modules and shaft/body modules, which are easily connected to various components. It also provides rotary position controllers for 90, 180 or 360 degrees with no backlash and lighter weight, smaller space and higher accuracy of position and can be used for a combination device of a hinge and rotary actuator or a rotary actuator either under high axial load or gravity load between vertical and horizontal positions, or for quick cycle, high vibration, quick opening or closing applications and other critical applications to replace linear pistons with pivot joint devices or landing gears for aircraft or artificial or robotic leg and arm joints 
     The helical linear/rotary converting module can be constructed as a body, a converting unit and a shaft, the converting unit can be constructed as one piston having a two-center linear engagement means and a helical rotary engagement means with the body and the shaft, the two-center linear engagement means is constructed as a pair of a centric and eccentric section which are engaged with a centric bore and eccentric bore between the converting piston and the body or shaft, the helical rotary engagement means is constructed with a pair of helical converting means which includes spline teeth engagement, spline groove/pin and teeth engagement with balls between the converting piston and the body or the converting piston and the shaft, the converting unit can be constructed as two pistons have two pairs of the linear engagement means and rotary engagement means located and moved in an opposite direction. The body can be constructed as one piece a body or two piece split bodies, while shaft can be constructed as one pieces part with helical rotary converting means or two-center linear converting means or multiple pieces parts. The actuator includes various shapes of bodies for different applications. 
     The actuator can be constructed with various shape of bodies, the spherical shape of the body is constructed for supporting high axial load both on the shaft or body or installed between vertical and horizontal positions and sustain high bending and compression loads or with robotic and artificial arm and leg joints, other shape of body is provided with one end closed and other end opened for operating rotary valve, finally a split body is constructed to receive large engaged diameter of piston with smaller end shaft or large spring to generate return force. 
     The actuator can be constructed with position control devices. One of the feature is to combine a vane actuator and helical actuator as one unit, it not only eliminate backlash but increase output torque and improve the accuracy of rotary position, other is to provide two hard adjustable hard stop in both ends of rotation of 90, 180, 270 or 360 degree. In the manufacturing of the actuator, this invention provides other joint method to separate helical teeth from shaft or body, so the helical teeth can be manufactured replaced easily at low cost. 
     Accordingly, besides objects and advantages of the present invention described in the above patent, several objects and advantages of the present invention are:
     (a) To provide a highly efficient linear/rotary converting mechanism with less energy, maxim output torque and fewer components.   (b) To provide a linear/rotary converting mechanism with less stress concentration, so the mechanism can be more reliable, compact and still robust for critical applications   (c) To provide a fluid-powered actuation system with highly optimal division of functions among the modular members in a balanced manner, so such a system allows a user to have higher integrity of a system with fewer components and reduce a system space, leakage and manufacturing and replacement cost   (d) To provide a directly coupling means for an actuator and other components so as to eliminate adapters, reduce the space for their connection.   (e) To provide a fully balanced means for an actuator, so the actuator is constructed with more powerful and reliable mechanism with less weight, parts and cost.   (f) To provide a fluid-powered actuation system with actuator, which has less displaced fluid volumes on both sides of pistons, so the energy loss can be reduced to a minimum level   (g) To provide an internal porting means for a fluid-powered actuation system, the system is not subject to external tube corrosion and breakdown and has quick response time and can be either connected through a shaft or body.   (h) To provide a fluid-powered actuator with high holding torque, so it is not susceptible to vibration and more stable and can be used in applications of high vibration, quick cycle.   (i) To provide a fluid-powered actuation system with gravity balance mechanism, so the actuator can be used between vertical and horizontal positions.   (j) To provide a fluid-powered actuation system without backlash, so the system becomes more stable and accurate at pre-setting position   (k) To provide a fluid-powered actuation system with highly reliable, inherently redundant, intrinsically safe control functions, so the system can be used for critical applications such as military operation, medical emergence care/device and aircraft landing gears   (l) To provide a produced-friendly, fluid-powered actuation modules with simple, flexible structures, easy manufacturing and process and various size and material selection, the modules require simple manufacturing process and flexible construction methods for different applications, so a manufacturer for the system can easily implement rapid product development and outsourcing at lower cost   (m) To provide a linear-rotary converting device with compact, adaptable rotary shaft and body. Therefore, the devices can use as a combination of a hinge joint and rotary actuator for robotic or artificial arm and leg joints.   

     Still further objects and advantages will become apparent from study of the following description and the accompanying drawings. 
    
    
     
       DRAWINGS 
       Drawing Figures 
         FIG. 1  is an exploded, quarter cut view of a helical linear/rotary converting mechanism constructed in accordance with this invention. 
         FIG. 2  is a front view of helical linear/rotary converting mechanism of  FIG. 1 . 
         FIG. 3  is a side view of helical linear/rotary converting mechanism of  FIG. 1 . 
         FIG. 4  is a cross sectional views of helical linear/rotary converting mechanism of  FIG. 2  along line A-A. 
         FIG. 5  is an exploded, quarter cut view of an alternative embodiment of helical linear/rotary converting mechanism of  FIG. 1 . 
         FIG. 6  is an exploded, quarter cut view of an alternative embodiment of helical linear/rotary converting mechanism of  FIG. 1 . 
         FIG. 7  is an exploded, quarter cut view of an alternative embodiment of helical linear/rotary converting mechanism of  FIG. 1 . 
         FIG. 8  is an exploded, quarter cut view of an alternative embodiment of helical linear/rotary converting mechanism of  FIG. 1 . 
         FIG. 9  is an exploded, quarter cut view of an alternative embodiment of helical linear/rotary converting mechanism of  FIG. 1 . 
         FIG. 10  is an exploded, quarter cut view of a helical rotary actuator embodiment of the helical linear/rotary converting mechanism of  FIG. 8 . 
         FIG. 11  is a front view of the helical rotary actuator of  FIG. 10 . 
         FIG. 12  is a cross sectional view of the helical rotary actuator of  FIG. 11 .
     Along line B-B.   

         FIG. 13  is a cross sectional view of the helical rotary actuator of  FIG. 11 .
     Along line C-C.   

         FIG. 14  is a detail view of the helical rotary actuator of  FIG. 13 .
     Along cycle of F.   

         FIG. 15  is an exploded, quarter cut view of an alternative embodiment of helical rotary actuator of  FIG. 10 . 
         FIG. 16  is a front view of the helical rotary actuator of  FIG. 15 . 
         FIG. 17  is a cross sectional view of the helical rotary actuator of  FIG. 16 .
     along line E-E.   

         FIG. 18  is a cross view of the helical rotary actuator of  FIG. 16 .
     along line D-D.   

         FIG. 19  is an isometric view of the helical rotary actuator of  FIG. 16 . 
         FIG. 20  is an exploded, quarter cut view of an alternative embodiment of helical rotary actuator of  FIG. 10 . 
         FIG. 21  is a detail view of the helical rotary actuator of  FIG. 20 .
     along cycle of A   

         FIG. 22  is a front view of a subassembly of  FIG. 20 . 
         FIG. 23  is a side view of the subassembly of  FIG. 22 . 
         FIG. 24  is a cross sectional view of the subassembly of  FIG. 22  along line F-F. 
         FIG. 25  is a cross sectional view of the subassembly of  FIG. 22  along line G-G. 
         FIG. 26  is an exploded, quarter cut view of an alternative embodiment of helical rotary actuator of  FIG. 10 . 
         FIG. 27  is a front view of the helical rotary actuator of  FIG. 26 . 
         FIG. 28  is a cross sectional view of the helical rotary actuator of  FIG. 27  along line I-I. 
         FIG. 29  is a cross sectional view of the helical rotary actuator of  FIG. 27  along line H-H. 
         FIG. 30  is an exploded, quarter cut view of an alternative embodiment of helical rotary actuator of  FIG. 10 . 
         FIG. 31  is a front view of the helical rotary actuator of  FIG. 30 . 
         FIG. 32  is a cross sectional view of the helical rotary actuator of  FIG. 31  along line K-K. 
         FIG. 33  is a cross sectional view of the helical rotary actuator of  FIG. 30  along line J-J. 
         FIG. 34  is an exploded view of an alternative embodiment of helical rotary actuator of  FIG. 30 . 
         FIG. 35  is a front view of the helical rotary actuator of  FIG. 34 . 
         FIG. 36  is a cross sectional view of the helical rotary actuator of  FIG. 35  along line L-L. 
         FIG. 37  is an exploded, quarter cut view of an alternative embodiment of helical linear/rotary converting mechanism of  FIG. 5 . 
         FIG. 38  is an exploded view of an alternative embodiment of helical linear/rotary converting mechanism of  FIG. 9 . 
         FIG. 39  is an exploded, quarter cut view of an alternative embodiment of shaft of  FIG. 8 . 
         FIG. 40  is an exploded, quarter cut view of an alternative embodiment shaft of  FIG. 9 . 
     
    
    
     
       
         
               
             
               
               
               
               
             
           
               
                   
               
               
                 Reference Number In Drawing 
               
               
                   
               
             
             
               
                   
               
             
          
           
               
                 10 
                 Single Helical Converter 
                 20 
                 Double Helical converter a, b, f 
               
               
                   
                 a, b, c, d, e, f, h 
                   
                   
               
               
                 11 
                 body a, b, c, d 
                 21 
                 Body, a, b, f 
               
               
                 12 
                 Converting piston, a, b, c, d 
                 22, 22′ 
                 Converting piston a, b, f 
               
               
                 13 
                 Shaft, a, b, c, d, e, f, g, h 
                 23 
                 Shaft, a, b, f 
               
               
                 14 
                 Centric section, a, b, c, d 
                 24 
                 Centric section a, b, f 
               
               
                 15 
                 Eccentric section, a, b, c, d 
                 25, 25′ 
                 Eccentric section a, b, f 
               
               
                 16 
                 Centric bore, a, b, c, d 
                 26, 26′ 
                 Centric bore a, b, f 
               
               
                 17 
                 Eccentric bore a, b, c, d 
                 27, 27′ 
                 Eccentric bore a, b, f 
               
               
                 18 
                 Helical internal teeth, a, b ,d 
                 28, 28′ 
                 Helical internal teeth a, b, f 
               
               
                 19 
                 helical external teeth, a, b, d 
                 29, 29′ 
                 Helical external teeth a, b, f 
               
               
                 18 
                 Helical groove, c 
                   
                   
               
               
                 19 
                 Helical groove pin, c, 
                   
                   
               
               
                 1 
                 Support ring e, f, g, h 
                 9 
                 Retaining ring g 
               
               
                 4 
                 Centric section, e, f, g, h 
                 2 
                 Helical teeth ring, e, f, g, h 
               
               
                 5 
                 Eccentric section, e, f, g, h 
                 3 
                 Shaft e, f, g, h 
               
               
                 6 
                 Centric bore e, f, g, h 
                 7 
                 Eccentric bore, e, f, g, h 
               
               
                   
                   
                 8 
                 Set of Balls 
               
               
                 100 
                 Helical Actuator, a, b, c, d, e, g 
                   
                   
               
               
                 A 
                 port, 1, 2, 3, 4, 5, 6, 7 
                 130″, 130 
                 Converting piston 
               
               
                 B 
                 Port, 1, 2, 3, 4, 5, 6, 7 
                 131′, 131 
                 Groove 
               
               
                 101′, 101 
                 Body, 
                 132′, 132 
                 Centric section 
               
               
                 102′, 102 
                 Centric bore, 
                 133′, 133 
                 Eccentric section 
               
               
                 103′, 103 
                 Eccentric bore 
                 134′, 134 
                 Internal helical teeth 
               
               
                 104′, 104 
                 body end 
                 135′, 135 
                 External helical teeth 
               
               
                 105 
                 Horizontal Passageway 
                 136′, 136 
                 Piston inward surface 
               
               
                 106 
                 Spherical external surface 
                 137′, 137 
                 Piston outward surface 
               
               
                 107 
                 Cylindrical External surface 
                 138′, 138 
                 Link hole 
               
               
                 108′, 108 
                 Groove 
                 139′, 139 
                 bore 
               
               
                 109′, 109 
                 End Vertical surface 
                   
                   
               
               
                 110′, 110 
                 End Horizontal surface 
                 150 
                 Spherical Cover 
               
               
                 111 
                 End Spherical surface 
                 151 
                 Spherical internal surface 
               
               
                 112 
                 Out-vertical surface 
                 152 
                 Out-Vertical surface 
               
               
                 113 
                 Horizontal surface 
                 153 
                 Horizontal surface 
               
               
                 117 
                 Inter-vertical surface 
                 154 
                 Spherical external surface 
               
               
                 120 
                 Center chamber 
                 155 
                 End Vertical surface 
               
               
                 121′, 121 
                 Side chamber, 
                 156 
                 Shaft hole 
               
               
                 122′, 122 
                 Helical internal teeth right 
                 157 
                 Inter-Vertical surface 
               
               
                 123′, 123 
                 Helical internal teeth left 
                 158 
                 Flat cover 
               
               
                 124 
                 Spherical external surface 
                 159 
                 O ring groove 
               
               
                 125 
                 Thread hold 
                   
                   
               
               
                 126 
                 Bolt hole 
                 170 
                 Vane cover 
               
               
                 127 
                 hole 
                 171 
                 Vane 
               
               
                 128 
                 hole 
                 172 
                 Piston land 
               
               
                 129 
                 O ring groove 
                 173 
                 Inward port 
               
               
                 140 
                 Shaft 
                 174 
                 Outward port 
               
               
                 141′, 141 
                 External helical teeth, 
                 175 
                 vane Key 
               
               
                 142 
                   
                 176 
                 Middle ring 
               
               
                 143 
                 Centric section 
                 177 
                 hole 
               
               
                 144 
                 Eccentric section 
                 178 
                 Inside surface 
               
               
                 145′, 145 
                 end 
                 179 
                 Outside surface 
               
               
                 146 
                 keyway 
                 197 
                 Link port 
               
               
                 147 
                 center hole 
                 198 
                 recess 
               
               
                 148′, 148 
                 Side hole 
                 180 
                 Conical step 
               
               
                 160 
                 O ring 
                 181 
                 Conical surface 
               
               
                 161 
                 O ring 
                 182 
                 Conical surface 
               
               
                 162 
                 O ring 
                 183 
                 Vane chamber 
               
               
                 163 
                 O ring 
                 184 
                 Vane chamber 
               
               
                 164 
                 O ring 
                 185′, 185 
                 Slot 
               
               
                 165 
                 Spherical bearing 
                 186 
                 plug 
               
               
                 166 
                 bolt 
                 187 
                 setscrew 
               
               
                 190 
                 Spherical supporter 
                 188 
                 Flat screw 
               
               
                 191 
                 Shell plate 
                 189 
                 spring 
               
               
                 192 
                 Recess surface 
                 195 
                 Vane land 
               
               
                 193 
                 Thread hole 
                 196 
                 groove 
               
               
                   
               
             
          
         
       
     
     DESCRIPTION 
       FIGS. 1-4  illustrate a helical linear/rotary converting mechanism  10   a  constructed in accordance with the present invention. The mechanism  10   a  comprises a body  11   a , a converting piston  12   a  and a shaft  13   a  for converting reciprocal movements of piston  12   a  to rotary movements of shaft  13   a . Body  11   a  includes a centric bore  16   a  and an eccentric bore  17   a  parallel to centric bore  16   a , converting piston  12   a  is movably disposed in body  11   a  and has a centric section  14   a  engaged with centric bore  16   a  and an eccentric section  15   a  engaged with eccentric bore  17   a , shaft  13   a  movably positioned in converting piston  12   a  has external helical teeth  19   a , converting piston  12   a  has an internal helical teeth  18   a  engaged with external helical teeth  19   a    
     Referring to  FIG. 5 , a helical linear/rotary converting mechanism  10   b  based on mechanism  10   a  comprises a body  11   b , a converting piston  12   b  and a shaft  13   b  for converting reciprocal movements of piston  12   b  to rotary movements of shaft  13   b . Body  11   b  includes internal helical teeth  18   b , converting piston  12   b  is movably disposed in body  11   b  and has external helical teeth  19   a  engaged with internal helical teeth  18   b , shaft  13   b  movably disposed in converting piston  12   b  has a centric section  14   b  and an eccentric section  15   b  parallel to centric section  14   b , converting piston  12   b  has a centric bore  16   b  engaged with centric section  14   b  and an eccentric bore  17   b  engaged with eccentric section  15   b.    
     Referring to  FIG. 6 , a helical linear/rotary converting mechanism  10   c  based on mechanism  10   a  comprises a body  11   c , a converting piston  12   c  and a shaft  13   c  for converting reciprocal movements to rotary movements. Body  11   c  includes a centric bore  16   c  and an eccentric bore  17   c  parallel to centric bore  16   c , converting piston  12   c  is movably disposed in body  11   c  and has a centric section  14   c  engaged with centric bore  16   c  and an eccentric section  15   c  engaged with eccentric bore  17   c , shaft  13   c  movably positioned in converting piston  12   c  has a pin  19   c , converting piston  12   c  has a helical grooves  18   c  engaged with pin  19   c.    
     Referring to  FIG. 7 , a helical linear/rotary converting mechanism  10   d  based on mechanism  10   a  comprises a body  11   d , a set of balls  8 , a converting piston  12   d  and a shaft  13   d  for converting reciprocal movements to rotary movements. Body  11   d  includes a centric bore  16   d  and an eccentric bore  17   d  parallel to centric bore  16   d , converting piston  12   d  is movably disposed in body  11   d  and has a centric section  14   d  engaged with centric bore  16   d  and an eccentric section  15   d  engaged with eccentric bore  17   d , shaft  13   d  movably positioned in converting piston  12   d  has external helical teeth  19   d , converting piston  12   d  has internal helical teeth  18   d  engaged with helical teethes  18   d  by means of balls  8 . 
     Referring to  FIG. 8 , a helical linear/rotary converting mechanism  20   a  based on mechanism  10   a  comprises a body  21   a , two converting pistons  22   a , 22   a ′ and a shaft  23   a  for converting reciprocal movements to rotary movements. Body  21   a  includes two centric bores  26   a ,  26   a ′ and an eccentric bore  27   a  parallel to centric bores  26   a ,  26   a ′, converting piston  22   a  is movably disposed in a left side of body  21   a  and has internal left helical teeth  28   a , a centric section  24   a  engaged with centric bore  26   a  and an eccentric section  25   a  engaged with eccentric bore  27   a , converting piston  22   a ′ is movably disposed in a right side of body  21   a  and has internal right helical teeth  28   a ′, a centric section  24   a ′ engaged with centric bore  26   a ′ and an eccentric section  25   a ′ engaged with eccentric bore  27   a , shaft  23   a  is movably positioned in converting pistons  22   a , 22   a ′ and has external left helical teeth  29   a  engaged with helical teeth  28   a  and external right helical teeth  29   a ′ engaged with teeth  28   a′.    
     Referring to  FIG. 9 , a helical linear/rotary converting mechanism  20   b  based on mechanism  20   a  comprises a body  21   b , converting pistons  22   b , 22   b ′ and a shaft  23   b  for converting reciprocal movements to rotary movements. Body  21   b  includes internal left helical teeth  28   b  and internal right helical teeth  28   b ′ in an opposite direction, converting piston  22   b  is movably disposed in a left side of body  21   b  and has a centric bore  26   b , an eccentric bore  27   b  and external helical left teeth  29   b  engaged with teeth  28   b , while converting piston  22   b ′ is movably disposed in a right side of body  21   b  and has a centric bore  26   b ′, an eccentric bore  27   b ′ and external helical right teeth  29   b ′ engaged with teeth  28   b ′, shaft  23   b  is movably disposed in pistons  22   b , 22   b ′ and has eccentric sections  25   b , 25   b ′ in an opposite direction and a centric section  24   b  engaged with bore  26   b  and bore  26   b ′, eccentric section  25   b  is engaged with bore  27   b , while eccentric section  25   b ′ is engaged with bore  27   b′.    
       FIGS. 10-14  illustrate a fluid powered helical rotary actuator  100   a  based on helical linear/rotary converting mechanism  20   a  constructed in accordance with the present invention. The actuator  100   a  comprises a body  101   a  having an eccentric bore  103   a , two centric bores  102   a , 102   a ′ and pistons  130   a , 130   a ′, a shaft  140   a  is movably disposed in pistons  130   a , 130   a ′, body  101   a  is covered by a spherical cover  150   a  and a flat cover  158   a  and has standard ports A 1 , B 1  which includes port size and distance between port A 1 , B 1  and respectively connected to a pressurized fluid and a sink fluid (not shown), the actuator  100   a  is provided for rotary movements. 
     Pistons  130   a , 130   a ′ are axially opposed and respectively have sections  132   a ,  133   a  movably engaged with bores  102   a ,  103   a  and sections  132   a ′,  133   a ′ movably engaged with bores  102   a ′,  103   a  in an opposite direction. Pistons  130   a , 130   a ′ also include internal helical teeth  134   a , 134   a ′ in inner surfaces to operatively engage with sections  141   a , 141   a ′ of the shaft  140   a , a center chamber  120   a  is provided between inward surfaces  136   a ,  136   a ′ and bore  103   a  and is connected to port B 1  and to grooves  131   a , 131   a ′ through gaps between teeth  134   a  and  141   a , teeth  134   a ′ and  141   a ′ and link holes  138   a , 138   a ′, while side chambers  121   a , 121   a ′ are defined respectively by cover  150   a , an outward surface  137   a  and bore  102   a  and by cover  158   a , an outward surface  137   a ′ and bore  102   a ′ and connected to port A 1  through a passageway  105  and grooves  108   a , 108   a′.    
     Cover  150   a  is mounted on a left side of shaft  140   a  and has a first vertical surface  152   a , spherical surface  151   a , a second vertical surface  157   a  and a horizontal surface  153   a  with an o ring groove  159   a , body  101   a  has a first vertical surface  112   a , a spherical surface  111   a , a second vertical surface  117   a  with an o ring groove  129   a  and horizontal surface  110   a , a spherical bearing  165   a  is placed between surfaces  151   a  and  111   a  for providing a bearing and a seal, while o-rings  160   a  and  161   a  are respectively placed in groove  129   a  and groove  159   a  for providing a vertical seal and a horizontal seal between cover  150   a  and body  101   a.    
     Referring to  FIGS. 15-19 , a fluid powered helical rotary actuator  100   b  based on fluid powered helical rotary actuator  100   a  comprises a spherical body  101   b , pistons  130   b , 130   b ′, a shaft  140   b  is movably disposed in pistons  130   b , 130   b ′, body  101   b  is covered by two spherical covers  150   b ,  150   b ′ and has standard ports A 2 , B 2  which includes port size and distance between port A 2 , B 2  and respectively connected to a pressurized fluid and a sink fluid (not shown), there are other optional ports A 3 , B 3  respectively connected to a pressurized fluid and a sink fluid (not shown), the actuator  100   b  is provided for rotary movements. 
     A center chamber  120   b  is connected to port B 2  through hole  147   b , while side chambers  121   b ,  124   b ′ are connected to port A 2  through holes  148   b , 148   b ′ and grooves  108   b , 108   b ′. Covers  150   b , 150   b ′ are mounted respectively on a left side and a right side of shaft  140   b , a holder  190   b  has a cylindrical bar extended to shell  191   b  with a spherical recess  192   b  to receive actuator  100   b  for securing a pre-set position, holes  193   b  and thread holes  125   b  are provided for bolting between actuator  100   b  and holder  190   b.    
     Referring to  FIG. 20-25 , a fluid powered helical rotary actuator  100   c  based on fluid powered helical rotary actuator  100   a  comprises a body  101   c , pistons  130   c , 130   c ′, two vanes  171   c  and two vane covers  170   c , a shaft  140   c  is movably disposed in pistons  130   c , 130   c ′, vanes  171   c  and vane covers  170   c , body  101   c  is covered by two covers  158   c ,  158   c ′ and has standard ports A 4 , B 4  which includes size port and distance between ports A 4 , B 4  respectively connected to a pressurized fluid and a sink fluid (not shown). the actuator  100   c  is provided for rotary movements. 
     Pistons  130   c , 130   c ′ are axially opposed, movably disposed in body  101   c  since the left piston  130   c  is as the same as the right piston  130   c ′, only the left side piston is described here, two vane chambers  183   c  and  184   c  are defined by piston  130   c , vane cover  170   c , vane  171   c , a vane land  195   c  of vane  171   c  and a piston land  172   c  of piston  130   c , a center chamber  120   c  is connected to vane chamber  183   c  through gaps between shaft  140   c  and piston  130   c , radial hole  138   c  and axial hole  173   c  and a slot  185   c ′, while a side chamber  121   c  is connected to chamber  184   c  through hole  174   c , slot  185   c , vane  171   c  is coupled with shaft  140   c  by keyway 146   c  and key  175   c.    
     Referring to  FIG. 26-29 , a fluid powered helical rotary actuator  100   d  based on fluid powered helical rotary actuator  20   a  comprises a body  101   d  having a left closed end except a shaft hole  127   d  and a right end with a centric bore  102   d  to receive a middle ring  176   d , pistons  130   d , 130   d ′, a shaft  140   d  is movably disposed in pistons  130   d , 130   d ′ and middle ring  176   d , body  101   d  is covered by cover  158   d  and has standard ports A 5 , B 5  which includes port size and distance between ports A 5  and B 5  respectively connected to a pressurized fluid and a sink fluid (not shown), the actuator  100   d  is provided for rotary movements. 
     Middle ring  176   d  is axially placed between pistons  130   d , 130   d ′ and has a centric outside surface  179   d  and an eccentric inside surface  178   d . Pistons  130   d , 130   d ′ have respectively centric sections  132   d , 132   d ′ engaged with bore  102   d  and eccentric sections  133   d , 133   d ′ engaged with eccentric surface  178   d . Pistons  130   d , 130   d ′ also include internal helical teeth  134   d , 134   d ′ in inner surfaces to operatively engage with external helical teeth  141   d , 141   d ′ of the shaft  140   d . Middle ring  176   d  also includes three radial holes  177   d , 177   d ′ and is secured by two screws  187   d  through holes  177   d , conical tips of two screws  187   d  are engaged with conical surfaces of  182   d , 182   d ′ for controlling inward positions of pistons  103   d , 103   d ′, two screws  188   d  are threaded through cover  158   d  for controlling outward positions of piston of  130   d , hole  176   d ′ is linked between port B 5  and inside surface  178   d.    
     Referring to  FIG. 30-33 , a fluid powered helical rotary actuator  100   e  based on fluid powered helical rotary actuator  100   a  comprises a pair of split bodies  101   e , 101   e ′ to receive a middle ring  176   e  and pistons  130   e , 130   e ′, bodies  101   e , 101   e ′ respectively have centric bores  102   e , 102   e ′ and eccentric bores  103   e , 103   e ′, pistons  130   e , 130   e ′ are axially opposed and respectively have sections  132   e , 133   e  engaged with bores  102   e , 103   e  and sections  132   e ′, 133   e ′ engaged with bores  102   e ′,  103   e ′, a shaft  140   e  is movably disposed in pistons  130   e , 130   e ′ and middle ring  176   e , split bodies  101   e , 101   e ′ are secured by four of bolts  166   e  and sealed by o-ring  164   e , bodies  101   e , 101   e ′ have standard ports A 6 , B 6  which includes size port and distance between port A 6 , B 6  respectively connected to a pressurized fluid and a sink fluid (not shown), the actuator  100   e  is provided for rotary movements. 
     Pistons  130   e , 130   e ′ are axially opposed, movably disposed in bodies  101   e , 101   e ′, a center chamber  120   e  is connected to port B 6 , while side chamber  121   e , 121   e ′ are connected to port A 6  through a passageway  105   e  and grooves  108   e , 108   e ′, body  101   e  has two holes  128   e , two screws  187   e  are respectively threaded through holes  128   e  and engaged with conical surfaces  181   e , 181   e ′ defined by ring  176   e  and piston  130   e  for controlling an inward position of pistons of  130   e , 130   e ′, screws  188   e  are threaded through cover  158   e  for controlling outward positions of piston  130   e  and are secured by plugs  186   e.    
     Referring to  FIG. 34-36 , a fluid powered helical rotary actuator  100   g  based on fluid powered helical rotary actuator  100   e  comprises a pair of split bodies  101   g , 101   g ′, spring set  189   g , pistons  130   g , 130   g ′, a shaft  140   g  is movably disposed in pistons  130   g , 130   g ′ and a spring set  189   g , split bodies  101   g , 101   g ′ are secured by four of bolts  166   g  and sealed by o-ring  164   g , the pair of split bodies  101   g , 101   g ′ has standard ports A 7 , B 7  which includes size of port and distance between ports A 7 ,B 7  respectively connected to a pressurized fluid and a sink fluid (not shown), the actuator  100   g  is provided for rotary movements. 
     Bodies  101   g , 101   g ′ respectively have centric bores  102   g , 102   g ′ and eccentric bores  103   g , 103   g ′, pistons  130   g , 130   g ′ are axially opposed and have respectively sections  132   g , 133   g  and sections  132   g ′, 133   g ′ engaged with bores  102   g ,  103   g  and bores  102   g ′ and  103   g ′, the spring set  189   g  is placed between pistons  130   g  and  130   g ′ for spring return. 
     Referring to  FIG. 37 , a helical linear/rotary converting mechanism  10   e  based on  10   b  of  FIG. 5  comprises a body  11   e , a support ring  1   e , a converting piston  12   e  and a shaft  13   e  for converting linear movements to rotary movements. Body  11   e  has a centric bore  6   e  and an eccentric bore  7   e , support ring  1   e  has a section  4   e  engaged with bore  6   e  and an eccentric section  5   e  engaged with bore  7   e  and internal helical teeth  18   e.    
     Referring to  FIG. 38 , a helical linear/rotary converting mechanism  20   f  based on  20   b  of  FIG. 9  comprises a body  21   f , a support ring  1   f , converting pistons  22   f , 22   f ′ and a shaft  23   f  for converting linear movements to rotary movements. Body  21   f  has a centric bore  6   f  and an eccentric bore  7   f , support ring  1   f  has a section  4   f  engaged with bore  6   f  and an eccentric section  5   f  engaged with bore  7   f  and helical teeth  28   f ,  28   f′.    
     Referring to  FIG. 39 , a shaft assembly  13   g  based on  20   a  of  FIG. 8  comprises a pair of teeth rings  2   g , 2   g ′ two retaining rings  9   g  and a shaft  3   g , shaft  3   g  has a left centric sections  5   g  with a left groove  196   g  and a right centric section  5   g ′ with a right groove  196   g ′ and an eccentric section  4   g , teeth rings  2   g , 2   g ′ have bores  6   g  and  6   g ′ movably engaged with sections  4   g  and bores  7   g , 7   g ′ movably engaged with section  5   g , 5   g ′, teeth rings  2   g , 2   g ′ placed on both ends of shaft  3   g  are secured by two retaining rings  9   g  respectively disposed in grooves  196   a , 196   a′.    
     Referring to  FIG. 40 , a shaft assembly  13   h  based on  20   a  of  FIG. 8  comprises a shaft  3   h  and a teeth ring  2   h , shaft  3   h  has an eccentric section  5   h  and an centric section  4   h , teeth ring  2   h  has a centric bore  6   h  engaged with sections  4   h  and an eccentric bores  7   h  engaged with section  5   h.    
     Operations 
     For the mechanisms  10   a , assume that piston  12   a  is inserted into body  11   a  by engaging between sections  14   a , 15   a , and bores  16   a , 17   a  with a clearance fit, then shaft  13   a  is inserted into piston  12   a  by engaging between helical teeth  19   a  and helical teeth  18   s  with a clearance fit, piston  12   a  tends to rotate under axial force, but since there is an offset between bores  16   a , 17 , the offset only allows piston  12   a  to move linearly but prevents piston  12   a  from rotation, as a result, the helical teeth  18   a  on piston  12   a  forces helical teeth  19   a  as well as the shaft  13   a  to rotate, in case of mechanisms  10   c ,  10   d , only difference is the helical converting means. 
     For the mechanisms  10   b , assume that piston  12   b  is inserted into body  11   b  by engaging between helical teeth  19   b  and helical teeth  18   b  with a clearance fit then shaft  13   b  is inserted into piston  12   b  by engaging between sections  14   b , 15   b , and bores  16   b , 17   b  with a clearance fit, piston  12   b  rotates under axial forces, since there is an offset between bores  16   b ,  17   b , as a result, the offset force shaft  130   b  to rotate along with the piston  12   b.    
     For mechanisms  20   a , assume that shaft  23   a  is inserted into body  21   a , then piston  22   a  is inserted into ring  21   a  from the left side by engaging between sections  24   a ,  25   a , and bores  26   a , 27   a  with a clearance fit and between helical left teeth  29   a  and left helical teeth  28   a , then piston  22   a ′ is inserted into body  21   a  from the right side by engaging between sections  24   a ′,  25   a ′ and bores  26   a ′, 27   a  with a clearance fit and between right helical teeth  29   a ′ and right helical teeth  28   a ′, two equal but opposite forces are applied inwardly and outwardly to piston  22   a  and  22   a ′, piston  22   a  tends to rotate under axial forces, but since there is an offset between bores  26   a , 27   a , the offset only allow piston  22   a  to move linearly but prevents piston  22   a  from rotation, as a result, the helical teeth  28   a  on piston  22   a  forces helical teeth  29   a  as well as the shaft  23   a  to rotate clockwise, while piston  22   a ′ tends to rotate under axial forces, but since there is an offset between bores  26   a ′, 27   a ′, the offset allows piston  22   a ′ to move linearly but prevents piston  22   a ′ from rotation, as a result, the helical teeth  28   a ′ on piston  22   a ′ forces helical teeth  29   a ′ as well as shaft  23   a  rotate the clockwise due to opposite direction between teethes of  29   a , 28   a  and  29   a ′, 28   a ′, so the axial forces balances on shaft  23   a.    
     For the mechanisms  20   b , the balance mechanism is the same as the mechanism  20   a , while the operation is the same as mechanism  10   b    
     For actuator  100   a , assume that shaft  140   a  is inserted into body  101   a , then piston  130   a  is inserted into body  101   a  from the left side by engaging between sections  132   a , 133   a , and bores  102   a , 103   a  with a clearance fit and between helical teeth  134   a  and helical teeth  141   a , then piston  130   a ′ is inserted into body  101   a  from the right side by engaging between sections  132   a ′, 133   a ′ and bores  102   a ′, 103   a  with a clearance fit and between helical teeth  134   a ′ and helical teeth  141   a′.    
     Port A 1  and port B 1  are respectively connected to a pressurized fluid source/a fluid sink (not shown), there is no movement of the piston  130   a , 130   a ′ or that of shaft  140   a . When a pressurized flow fluid is allowed to enter to chamber  121   a , 121   a ′ through port A 1 , then spilt into two flows into passageways  105   a , then into grooves  108   a , 108   a ′, the flow fluids provide sufficient pressure against pistons  130   a ,  103   a ′ from outward surfaces  137   a , 137   a ′, while fluids in chambers  120   a  through B 1  connected to the fluid sink have a lower pressure, so pressure differentials generate two equal but opposite forces against pistons  130   a , 130   a ′ inwardly and cause inward movements of two pistons  130   a , 130   a ′ in a synchronized manner, so shaft  140   a  is balanced in the axial direction, because of offset engagement between body  101   a  and piston  130   a , 130   a ′, piston  130   a , 130   a ′ are only allowed to move linearly, as a result, the helical teeth  134   a  on piston  130   a  and teeth  134   a ′ in piston  130   a ′ force helical teeth  141   a ,  141   a ′ as well as the shaft  140   a  to rotate clockwise. On the contrary, when the connections of ports A 1  and port B 1  with the fluid source/the fluid sink are switched, the conditions of flow fluids are reversed, shaft  140   a  is rotated anti-clockwise. 
     For the actuator  100   a  installed in between vertical and horizontal positions, the gravity force or an external axial force is applied to cover  150   a  and shaft  140   a , in turn cover  150   a  will distribute the load into bearing  165   a  and body  101   a  evenly due to the spherical surface engagement, then shaft  140   a  distribute the torsion evenly to two pistons  130   a , 130   a ′ due to the balanced arrangement of pistons  1301   a , 130   a′.    
     For actuator  100   b , it can be used as a combination of a hinge and an actuator, actuator  100   b  can installed in any position and sustain great bending as well as axial force due to spherical shape of body and cover which can cancel out most of non axial force, it also can be easily used for connecting other dimensional rotary device. 
     For actuator  100   c , when a backlash is not allowed, actuator  100   c  can be used, by nature a vane actuator has no backlash, actuator  100   c  based on  100   a  can be modified by adding two the same vane actuators on both ends of pistons  130   c , 103   c ′. Ports A 4 ,B 4  are respectively connected to a pressurized fluid source/a fluid sink (not shown), there is no movement of the pistons  130   c , 130   c ′, or that of shaft  140   c . When a pressurized flow fluid is allowed to enter to chamber  121   c , 121   c ′ through port A 4 , then spilt into two flows into passageways  105   c , then through hole  174   c , slot  185   c  into vane chamber  184   c , the flow fluids provide sufficient pressure against land  195   c  which is keyed with shaft  140   c  by key  175   c  and keyway  146   c , while low pressure fluids in vane chambers  183   c  enters chamber  120   c  through holes  173   c , 138   c  and engagement gaps between shaft  140   c  and piston  130   c , in turn, chamber  120   c  is connected to the fluid sink, so pressure differentials forces lands  195   c  as well as shaft  140   c  to rotate clockwise. On the contrary, when the connections of ports A 4  and port B 4  with the fluid source/the fluid sink are switched, the conditions of flow fluids are reversed, shaft  140   c  is rotated anti-clockwise. 
     For actuator  100   d  which can be used when precision rotary position is required, piston  130   d , 130   d  are placed in center of body  101   d , two screws  187   d  are threaded in holes  128   d , 177   d  with conical tips engaged with both conical surfaces  182   d , 182   d ′, by rotating the screw  182   d , 182   d ′, inward movement of pistons  130   d , 130   d ′ are controlled to a preset position, on the outward sides, two flat tip screws  188   d  are threaded through cover  158   d , by rotating the screw  188   d , 188   d ′, outward movement of pistons  130   d , 130   d ′ are controlled for a pre-set position of shaft  140   d.    
     For actuator  100   e , assume that ring  176   e  is pressed into piston  130   e , then two pistons  130   e , 130   e ′ are placed from both ends of shaft  140   e , then two bodies  101   e , 101   e ′ are placed from both ends of shaft  140   e  by aligning up between hole  128   e , conical surfaces  181   d , 182   d  and secured by bolts  166   e . Port A 6  and port B 6  are respectively connected to a pressurized fluid source/a fluid sink (not shown), there is no movement of the piston  130   e , 130   e ′ or that of shaft  140   e . When a pressurized flow fluid is allowed to enter to chamber  121   e , 121   e ′ through port A 6 , then spilt into two flows into passageways  105   e , then into grooves  108   e , 108   e ′, the flow fluids provide sufficient pressure against pistons  130   e ,  130   e ′, while fluids in chambers  120   e  through port B 6  connected to the fluid sink have a lower pressure, so pressure differentials move pistons  130   e , 130   e ′ inwardly in a synchronized manner then make shaft  140   e  to rotate clockwise. On the contrary, when the connections of ports A 6  and port B 6  with the fluid source/the fluid sink are switched, the conditions of flow fluids are reversed, shaft  140   e  is rotated anti-clockwise. 
     For actuator  100   g  which can be used for single acting application, top and bottom is interchangeable for fail closed and fail open of valve control without changing any part, assume that one set of springs  189   g  is placed into shaft  140   g , then two pistons  130   g , 130   g ′ are placed from both ends of shaft  140   g , then two bodies  101   g , 101   g ′ are placed from both ends of shaft  140   g  and secured by bolts  166   g . Port A 7  and port B 7  are respectively connected to a pressurized fluid source/a fluid sink (not shown), there is no movement of the piston  130   g , 130   g ′ or that of shaft  140   e . When a pressurized flow fluid is allowed to enter to chamber  121   g , 121   g ′ through port A 7 , then split into two flows into passageways  105   g , then into grooves  108   g , 108   g ′, the flow fluids provide sufficient pressure against pistons  130   g , 130   g ′, while fluids in chambers  120   g  through port B 7  connected to the fluid sink have a lower pressure, so pressure differentials move pistons  130   g , 130   g ′ inwardly in a synchronized manner then make shaft  140   g  to rotate clockwise and compress springs  189   g . On the contrary, when the connections of ports A 7  loses pressure, the pressure differentials disappears, the compressed springs force pistons  130   g , 130   g ′ to move outward and make shaft  140   g  rotated anti-clockwise. 
     Advantages 
     From the description above, a number of advantage of some embodiments of my helical rotary actuator become evident:
     (1) high efficiency, with double effective areas of pistons, balance design, this embodiment increase the efficiency of helical rotary actuator from about 60%-70% to 85-95, with less materials and weights, smaller size, it opens the door to the low pressure pneumatic actuators market against rack and pinion and vane actuators   (2) a balanced thrust, the thrust is fully balanced on the shaft without any bearing under both inward and outward pressures, so under no time, the piston bears any external axial load, both the body and shaft take external side or axial loads evenly, so the piston can generates more torque than any helical actuator and last longer, the other benefit is vibration proof, due to left and right pistons work in an opposite direction, any axial movement will not change rotation position of shaft as long as there is no the relative position change between the left and right positions.   (3) no backlashes, first the dual center engagement does not add any axial clearance, second the left helical teeth and right helical teeth works against each other and cancel out any clearance in the axial direction, finally the piston with the vane actuator completely eliminate any backlashes structurally   (4) No high stress concentration on the body, with the dual center engagement, the body no longer has high stress concentration on the wall without the teeth or shape spline, it greatly reduce the wall thickness of the body and increase safety of the body and meet the pressure vessel standards for critical applications   (5) free installation position, with spherical joint between body and cover, balanced thrust, the invention provides an actuator which can be installed between any position between vertical and horizontal positions.   (6) precision position control, with conical and flat surfaces engagements devices, both inward and outward positions are fully controlled, now this actuator can be used for a critical applications such as military equipment, robotic devices and valve control   (7) versatile interface functions, most of the actuator bodies are cylindrical shape, such a shape is difficult for three dimensional joint   (8) high reliability, without high stress concentration on the body, high tension on the piston and balanced thrust on the shaft, this actuator has highest safety design over all existing helical rotary actuators, in addition, the dual independent pistons, porting systems provide redundant functions, if a left piston fails, the right piston still functions independently, it can be used for airplane landing gears or linear piston with pivot joint in the construction machines or lift equipment.   (9) optimized structural design (a) spherical body can sustain high structural bending and compression loads, it can be used for stand-along or combine with additional actuator for 2 D or 3 D position control (b) material comparability with design, now material for body can be different from that of teeth rings for design or application purpose, so teeth ring can be heat treated or hardened, while body can be ductile with anti wearing coating in ID wearing resistance, so it sustains high pressure on body and high compression and wearing on ID surface and does not scarify any design requirement and greatly increase the life of the product.   (10) Easy and low cost manufacturing, the dual-center mechanism with two pair of simple cyclical bore/sections engagements greatly reduce manufacturing and assembly cost and time at least by 50%, an axial distance adjustment becomes much easy, most of all, helical teeth ring can be replaced without replacing the body or shaft, with middle ring with eccentric surfaces, even the offset machining becomes simpler, moreover, teeth ring can be pre-made, only left is ID or OD,   (11) Standard input and out port, the novel internal port system makes standardized the port size and distance between inlet port and outlet port possible, it reduces adaptor and tube, but also increases the reliability of the connection, the ports can be directly connected with counterbalanced valve, two way to four way solenoid valve without tube or adaptors.   

     CONCLUSION, RAMIFICATIONS AND SCOPE 
     The dual-center engagement mechanism in helical rotary actuator completely changes the rotary/linear converting concept and provides breakthrough performances and advantages over all existing rotary actuators (1) simplicity, two simple cylindrical engagement with an offset, but magically much better than the conventional helical actuators either have complicated dual internal and external helical teeth on piston or external spline and internal helical on the piston, more effective areas for axial forces than that of conventional helical actuators, the double center engagement can be arranged as example of mechanism  20   a , A left offset+A center+A right offset, so the left offset can be balanced the right left offset within the body under axial forces, or A centric+An offset+A centric, such a arrangement can reduce machining, or simple a centric bore with middle ring with a centric OD and an eccentric ID like mechanism  100   d  (2) robust, there is no detrimental features on the body, two cylindrical engagement convert the torsion from the piston to compression, such a compression structure greatly increase the body ability for holding the torque than any other methods on the conventional helical actuators while no space waste for keyway or helical or spline teeth or seals, in case of high cycle operation, there is no one location standing high impact force on the body unlike the conventional helical actuator, the impact force can enlarged the small fraction on teeth on the body and cause body buster. (3) compact, since there is no external helical teeth, the internal teeth diameter on piston can be made bigger with the size of the conventional helical piston, since there is no keyway or spline teeth, the seal groove can be on any place on the piston, it reduce at 50% length of the conventional helical actuator requires. (4) synergy, without the dual-center engagement mechanism, no full thrust balance can succeed, as the readers look back the history of helical actuator, as it evolves, no truly balance structure has been succeed, the reason is that the conventional helical actuator without an axial balance mechanism is already too longer at least twice as longer than that of the dual-center engagement mechanism actuator, if other half is added, it will be at four time longer than the dual-center engagement mechanism actuator, it is away beyond design scope in term of strength, stability and concentricity, and it is difficult to make, with dual-center engagement mechanism, fully balance helical actuator is about the same as the conventional one piston helical actuator 
     Each of embodiments of the present invention provides each advantage, each unique solution and each special modular structure to solve each problem existing for very long time, there are three interface elements, body where to hold, shaft where to rotate, fluid port where to get energy for operation, with all existing problem in mind (1) mechanism  100   a  is used as a hinge with rotary actuator in many lift equipment and deal with installation issue between vertical and horizontal positions, it provide a novel sandwich three seals, vertical o ring and horizontal o ring and conical or spherical bearing, which made out soft metals like bronze, or engineering plastics like peek to provide a seal between the cover and the body and, a bearing function to shift the load from the cover and shaft to the body to the body, the triple seals secure a sound sealing function in any rotation position between vertical and horizontal positions, when it is installed in vertical position, or a horizontal position or between the vertical seal or horizontal seal with no or a bit effect of gravity for seal due to spherical or conical engagement between the cover and body, while spherical bearing play a key to swift gravity load to the body as well for hard seal (2) mechanism  100   b  dealt with adaptability issue, it is used for providing 360 degree rotation, it is breakthrough in term of usage, it can sustain very high compression load or bending load, three of them combine can provide any three dimension position due to the spherical joint between cover and body, it can be used as robotic arm joint to replace linear piston with a pivot joint device or artificial arm or leg joint with a linear piston arm or leg, it can be used as a self motored hydraulic wheel for at 360 degree rotation (3) mechanism  100   c  dealt with backlash issue, the backlash causes loss of control of position, damage of output shaft or other piston or body and weakens joint between actuator and other connected part and is a nightmare for control engineers, with a conventional helical actuator, it is impossible to eliminate the backlash, or loss motion, because two sets of clearance between the body and piston, piston and shaft are caused by one piece of the piston, but with this embodiment, the two teeth engagements are separated by two pistons, there is no cumulative clearance, moreover actuator  100   c  solves the problem by adding two vane actuator on both sides, by nature, vane actuator has no backlash, the helical actuator provide a converting, rigid torque, the torque is not susceptible to an inlet pressure frustrations, while the vane actuator provides a soft direct torque without converting or delay, when the actuator start to rotate the shaft, a combination soft and rigid torques provides a smooth, backlash free rotation movement, by changing size of hole  174   c  vane torque can be either reduced or increased, moreover the vane actuator can be used as a damper when actuator acts too fast, this combination of vane actuation and two pistons arrangement solution surpass all previous efforts (4) mechanism  100   d  is used for applications like rotary valve actuation, it is required a body bottom connection with a valve for precision position, inward position control is provided with a pair of conical tips of screws, outward position are controlled by two flat tip screws, since the piston is not rotated unlike conventional helical actuator (5) mechanism  100   e  is used for lager torque output with limited axial space and precision position, with split bodies, the diameter of helical teeth can be made much larger without wasting lot material, since they are symmetric, it reduce the casting or forging mould cost, other application is used for spring return, it saves lot of money by reducing haft the spring sets in comparison with the conventional helical actuator with spring return devices, specially in subsea rotary valve applications, light weight, easy installation, versatility are the key requirements for a diver to install a valve system, the other advantage is top and button of connection can be interchanged for fail closed or fail open applications without changing any part. 
     Although the description above contains many specifications, these should not be construed as limiting the scope of the invention but as merely providing illustration of some of the presently preferred embodiments of this invention. 
     Thus, the scope of the invention should be determined by the appended claims and their legal equivalents, rather than by the examples given.