Abstract:
In the present invention are disclosed a step type ratchet wheel mechanism and a turning switch with step type ratchet wheel mechanism, wherein comprising: camshaft circular disc, on its end surface is disposed at least one groove, on its rim is disposed at least one positioning slot; driving cam, on its end surface is disposed at least one groove, on its rim is disposed at least one angular shape tooth; first pawl and second pawl; one resilient element is contained in the chamber, which is formed from two corresponding grooves respectively disposed on the end surfaces of camshaft circular disc and driving cam. When said camshaft circular disc is at a control-position, first pawl falls into one positioning slot of camshaft circular disc; when said driving cam is being turned toward next control-position, said two grooves will be staggered, said resilient element is compressed; when said driving cam is turned to the next control-position, one angular shape tooth will push first pawl out from said positioning slot, the released resilient element will cause said camshaft circular disc turning to the next control-position, and then second pawl will fall into another positioning slot of camshaft circular disc. In use of the present invention, the acted force is even, the operation is steady, the hand handle is comfortable, and furthermore, the phenomenon of hung-up point between two adjacent control-positions also may be avoided.

Description:
RELATED APPLICATIONS 
     The present application is based on, and claims priority from, Chinese Application No. 200810210099.2, filed Aug. 22, 2008, the disclosure of which is hereby incorporated by reference herein in its entirety. 
     FIELD OF THE ART 
     The present invention relates to a ratchet wheel mechanism and a turning switch, especially relates to a step type ratchet wheel mechanism and a turning switch with step type ratchet wheel mechanism. 
     BACKGROUND OF THE ART 
     Turning switch is a common switch configuration. The ratchet wheel positioning mechanism will help turning switch to effect the mechanical configuration of turning switch implementing switchover from one control-position to next control-position and then instantly to lock the mechanical configuration at the next control-position, when there are several control positions needed to be controlled by a turning switch. 
     Generally, the ratchet wheel mechanism of turning switch has two main functions: Non-returning and positioning function, i.e. to prevent turning switch from coming back to its previous control-position and to lock turning switch at a certain control-position in turning operation; Snap-jumpiness function to indicate the turning switch already being turned to position, i.e. when the turning switch is turned to a certain control-position, the switch configuration may send out a snap or a jumpiness to cause operator be able to distinctly perceive the turning switch already being turned to an expected position in order to prevent the operator from stopping the turning operation before achieving next switch control-position or from continuing the turning operation after already achieving an expected switch control-position. 
     Now, a description about the functions of a ratchet wheel mechanism of the prior art in turning switch is made through  FIGS. 1A to 1E . 
       FIG. 1A  is a schematic diagram to show said ratchet wheel mechanism  100  at still (initial) position, wherein comprising: ratchet wheel  110  co-axial with camshaft and pawl device  120 . Ratchet wheel  110  has 6 ratchet teeth  111  ( 111 . A ,  111 . B ,  111 . C ,  111 . D ,  111 . E ,  111 . F ) to divide the circular rim into six equal segments. Pawl device  120  has two transversal pawl arms  121  ( 121 . A ,  121 . B ) symmetrically disposed along height direction (relative to the axis of camshaft), on two transversal pawl arms  121  ( 121 . A  and  121 . B ) respectively exists a pawl  122  ( 122 . A ,  122 . B ), they are symmetrically disposed along height direction, transversal pawl arms  121  and pawls  122  are made from resilient material, such as plastic, etc. Ratchet wheel  110  and pawl device  120  may be made from Nylon. As shown in  FIG. 1A , ratchet wheel  110  and pawl device  120  are matched each other at a certain control-position. Saying concretely, at this control-position, upper ratchet pawl  122 . A  is between two adjacent ratchet teeth  111 . A  and  111 . B , lower ratchet pawl  122 . B  is between two adjacent ratchet teeth  111 . D  and  111 . E . So that ratchet wheel  110  will be locked at this control-position. As shown in  FIG. 1A , ratchet teeth  111  ( 111 . A ,  111 . B ,  111 . C ,  111 . D ,  111 . E ,  111 . F ) and pawls  122  ( 122 . A ,  122 . B ) are circular-arc shape. 
       FIG. 1B  shows said ratchet wheel  110  starting to be being turned from still (initial) position shown in  FIG. 1A  toward next control-position. As shown in  FIG. 1B , when the operator turns the knob (not shown in the Figure) counterclockwise, which is disposed at one end of ratchet wheel  110 , ratchet wheel  110  starts to turn counterclockwise resulted in ratchet tooth  111 . B  also being turned. In this time, the circular-arc shape surface of ratchet tooth  111 . B  will act an outward thrust on the circular-arc shape surface of pawl  122 . A  at their contact place, then due to the elasticity of transversal pawl arm  121 . A , upper pawl  122 . A  moves outward and resulted in that an outward elastic bending deformation of transversal pawl arm  121 . A  will occur along with the outward movement of upper pawl  122 . A . Similarly, when the counterclockwise turning of ratchet wheel  110  causes ratchet tooth  111 . E  to turn, the circular-arc shape surface of ratchet tooth  111 . E  will act an outward thrust on the circular-arc shape surface of lower pawl  122 . B  at their contact place, then due to the elasticity of transversal pawl arm  121 . B , lower pawl  122 . B  moves outward resulted in that an outward elastic bending deformation of transversal pawl arm  121 . B  will occur along with the outward movement of lower pawl  122 . B . As shown in  FIG. 1B , for the interactions between both the circular-arc shape surfaces of upper pawl  122 . A  and ratchet tooth  111 . B  and between both the circular-arc shape surfaces of lower pawl  122 . B  and ratchet tooth  111 . E , so that when the top points of the circular-arc shape surfaces of upper pawl  122 . A  and lower pawl  122 . B  respectively approach to the top points of the circular-arc shape surfaces of ratchet tooth  111 . B  and ratchet tooth  111 . E , if knob is loosen by the operator (or the operator does not apply any force to knob), the resilient forces respectively produced by the elastic bending deformation of transversal pawl arm  121 . A  and by that of arm  121 . B  will compel ratchet tooth  111 . B  and ratchet tooth  111 . E  still to comeback to their respective original control-position. Namely, in this time the operator has to act force continuously to turn ratchet wheel  110  and cannot stop. 
       FIG. 1C  is a schematic diagram of a typical ratchet wheel mechanism when a cam is turned just to hung-up point to show said ratchet wheel  110  at the position shown in  FIG. 1D  being turned continuously toward next control-position. At the position shown in  FIG. 1B , the operator continuously turns ratchet wheel  110  counterclockwise, upper pawl  122 . A  continuously moves outward to cause the elastic bending deformation of transversal pawl arm  121 . A  continuously increasing, then the top point of circular-arc shape surface of upper pawl  122 . A  coincides with the top point of circular-arc shape surface of ratchet tooth  111 . B . Similarly, lower pawl  122 . B  continuously moves outward to cause the elastic bending deformation of transversal pawl arm  121 . B  continuously increasing along with the counterclockwise turning of ratchet wheel  110 , then the top point of circular-arc shape surface of lower pawl  122 . B  coincides with the top point of circular-arc shape surface of ratchet tooth  111 . E . At this time, the outward elastic bending deformation of two transversal pawl arms  121  ( 121 . A  and  121 . B ) increases to maximum. For the resilient forces respectively acted on the top point of the circular-arc shape surfaces of ratchet teeth  111 . B  and  111 . E  by the top point of the circular-arc shape surface of upper pawl  122 . A  and by the top point of the circular-arc shape surface of lower pawl  122 . B  just pass through the center of ratchet wheel  110 , so they cannot yield turning moment for ratchet wheel  110 . When the top points of the circular-arc shape surfaces of upper pawl  122 . A  and lower pawl  122 . B  respectively coincide with the top point of the circular-arc shape surface of ratchet tooth  111 . B  and with that of ratchet tooth  111 . E , if knob is loosen by the operator (or the operator does not apply any force to knob), ratchet wheel  110  will stop at this position and keep in equilibrium, notwithstanding this position is not the expected next control-position, i.e. ratchet wheel  110  keeps in equilibrium and stop at a wrong position. Such phenomenon means there exists a hung-up point between two adjacent switch control-positions, and then to cause the turning switch bringing control failure. 
       FIG. 1D  is a schematic diagram of a typical ratchet wheel mechanism after a cam going over hung-up point to show said ratchet wheel  110  at the position shown in  FIG. 1C  continuously being turned toward next control-position. At the position shown in  FIG. 1B , the operator continuously turns ratchet wheel  110  counterclockwise, transversal pawl arm  121 . A  starts to move inward, then to cause upper pawl  122 . A  moving toward next control-position. Similarly, transversal pawl arm  121 . B  also moves inward along with the counterclockwise turning of ratchet wheel  110 , then to cause lower pawl  122 . B  moving toward next control-position. For the interactions between both the circular-arc shape surfaces of upper pawl  122 . A  and ratchet tooth  111 . B  and between both the circular-arc shape surfaces of lower pawl  122 . B  and ratchet tooth  111 . E , so that when the top points of the circular-arc shape surfaces of upper pawl  122 . A  and lower pawl  122 . B  respectively somewhat depart from the top points of the circular-arc shape surfaces of ratchet tooth  111 . B  and ratchet tooth  111 . E , even though in this time the force acted on the knob is decreased (or no force acted on the knob), the resilient force produced by the elastic deformation of transversal pawl arms  121 . A  and  121 . B  yet will help to push ratchet teeth  111 . B  and  111 . E  (or push teeth  111 . B  and  111 . E  directly by resilient force itself) to next control-position, i.e. ratchet wheel  110  may be turned through a smaller force acted by the operator (or the operator does not act any force). 
       FIG. 1E  is a schematic diagram of a typical ratchet wheel mechanism when a cam turning 60° to show said ratchet wheel  110  at the position shown in  FIG. 1E  continuously being turned to achieve next control-position. As shown in  FIG. 1E , ratchet wheel  110  and pawl device  120  are matched each other at the next control-position. Saying concretely, at this control-position upper pawl  122 . A  is between ratchet teeth  111 . B  and  111 . C ; lower pawl  122 . B  is between ratchet teeth  111 . E  and  111 . F . So that ratchet wheel is locked at the next control-position. 
     The ratchet wheel mechanism introduced above has following shortcomings: (1) Ratchet wheel may stop at a hung-up point between two adjacent switch control-positions, then to cause control failure occurring for the turning switch, the phenomenon of hung-up point especially is able to occur, if a large angle is included between two adjacent ratchet teeth (such as not less than 60°). (2) The ratchet wheel mechanism, introduced above, has a low working efficiency, for the frictional force existing among the contact surfaces of ratchet teeth of ratchet wheel and pawls. (3) More larger turning moment is needed for the turning switch having more loops to control, hand handle in operation also is not comfortable; Furthermore, the applied force is uneven and the operation is unsteady due to the interference of interior electricity-conductive contact spring of the turning switch. 
     BRIEF DESCRIPTION OF THE INVENTION 
     Aiming to solving above problem, the object of the present invention is to provide a ratchet wheel mechanism, wherein comprising: 
     Camshaft circular disc, on the fore end surface of said camshaft circular disc is disposed at least one groove, on the rim of said camshaft circular disc are disposed several positioning slots; 
     Driving cam, on the end surface of said driving cam is disposed at least one groove corresponding to that on the front surface of said camshaft circular disc, on the rim of driving cam are disposed several angular shape teeth; 
     First pawl and second pawl; 
     After the fore end surface of said camshaft circular disc and the end surface of driving cam are gathered together face to face, the groove(s) on camshaft circular disc and the groove(s) on driving cam will form at least one empty chamber in which at least one resilient element is placed; 
     When said camshaft circular disc is at a control-position, first pawl falls into a positioning slot to lock said camshaft circular disc at this control-position; 
     When said driving cam starts to be being turned toward next control-position, said camshaft circular disc keeps at its position not varying, thus the groove on camshaft circular disc and the groove on said driving cam are staggered each other to compress the resilient element to store resilient potential energy therein; 
     When said camshaft circular disc is turned to the next control-position, one angular shape tooth pushes said first pawl out from one positioning slot, resilient element pushes camshaft circular disc to turn to the next control-position, second pawl falls into another positioning slot of said camshaft circular disc to lock said camshaft circular disc at the next control-position. 
     The present invention also provides a turning switch with aforesaid ratchet wheel mechanism as said above. 
     In present invention, the implementation of switchover to cause the turning switch from current control-position to next control-position may be carried out through user to turn driving cam by knob. When driving cam starts to be turned, camshaft circular disc keeps in its position not turning for one positioning slot of camshaft circular disc is locked by one pawl, thus interior spring is compressed to store resilient potential energy. When driving cam is turned a predetermined angle counterclockwise, one pawl will be pushed out from one positioning slot by one angular shape tooth of driving cam, and then the resilient potential energy will be released from interior spring to push camshaft circular disc turning a predetermined angle counterclockwise; thus another pawl will fall into another positioning slot to send out a snap, the knob also will cause user to feel a jumpiness. Additionally, because the user only acts force to compress interior spring before driving cam starts to be turned, and then driving cam is pushed to turn by interior spring, so that in turning operation of driving cam, the acted force is even, the operation is steady, user feels a comfortable hand handle, the phenomenon of hung-up point between two adjacent control-positions also may be avoided. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1A  shows said ratchet wheel mechanism  100  at still (initial) position; 
         FIG. 1B  shows said ratchet wheel  110  starting to be turned from still (initial) position toward next control-position; 
         FIG. 1C  is a schematic diagram of a typical ratchet wheel mechanism when a cam is turned just to hung-up point; 
         FIG. 1D  is a schematic diagram of a typical ratchet wheel mechanism after a cam going over hung-up point 
         FIG. 1E  is a schematic diagram of a typical ratchet wheel mechanism when a cam turning 60° counterclockwise; 
         FIG. 2A  is a perspective view of components: camshaft mechanism  201  and executive mechanism  202  of step type ratchet wheel mechanism  200  of the present invention; 
         FIG. 2B  is an assembly perspective view of components: camshaft mechanism  201  and executive mechanism  202  of step type ratchet wheel mechanism  200  of the present invention; 
         FIG. 2C  is an assembly perspective view of camshaft  201 , executive mechanism  202  and pawl devices ( 250  and  260 ) in step type ratchet wheel mechanism  200 ; 
         FIG. 2D  is a schematic diagram of pawl arm of the present invention; 
         FIG. 2E  is an elevation of executive mechanism  202  viewed from E direction; 
         FIG. 2F  is an elevation of camshaft circular disc  220  viewed from F direction; 
         FIG. 2G  is a partial sectional view of camshaft circular disc  220  and driving cam  208  of the present invention, when they are assembled together; 
         FIG. 3A  is a perspective view of turning switch  300  of the present invention; 
         FIG. 3B  is a sectional view of turning switch of the present invention along line A-A in  FIG. 3A ; 
         FIG. 3C  is two sectional views of turning switch of the present invention along lines D-D and F-F in  FIG. 3A ; 
         FIG. 4A  shows the circumstance of relative position between camshaft circular disc  200  and driving cam  208 , when turning switch is at initial position; 
         FIG. 4B  shows the circumstance of relative position between camshaft circular disc  200  and driving cam  208 , after driving cam  208  is turned an angle counterclockwise; 
         FIG. 4C  shows the circumstance of relative position between camshaft circular disc  200  and driving cam  208 , after driving cam  208  is continuously turned an angle counterclockwise; 
         FIG. 4D  shows the circumstance of relative position between camshaft circular disc  200  and driving cam  208 , when driving cam  208  is continuously turned to 60° counterclockwise; 
         FIGS. 5A-5C  show the position relation among positioning slot on camshaft circular disc  220 , angular shape teeth on driving cam  208  and two pawls, when step angles are 30°, 45° and 60°. 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     The meanings of element (or component) reference numbers used in the drawings of the present invention are as follows: 
     Ratchet wheel mechanism  100 : ratchet wheel  100 , ratchet teeth  111 , pawl devices  120 , transversal pawl arms  121  and pawls  122 ; 
     Ratchet wheel mechanism  200 : camshaft mechanism  201 , executive mechanism  202 , circular ring  205  for assembling knob, executive circular disc  206 , circular prominence  207 , driving cam  208 , sector shape groove  211 , positioning slot  212 , interior spring  213 , camshaft  215 , camshaft circular disc  220  (its function is equivalent to aforesaid ratchet wheel  110  co-axial with camshaft), sector shape groove  222 , empty chamber  231 , angular shape teeth  235 , upper pawl device  250 , exterior spring  251 , pawl arm  252 , pins  253  and  254 , upper pawl  255 , lower pawl device  260 , exterior spring  261 , pawl arm  262 , pins  263  and  264 , lower pawl  265 ; 
     Turning switch  300 : housing  301 , switch contact sheets  302 , upper housing  311 , lower housing  312 , grooves  321  and  322 , electricity-conductive plates  341  and  342 , electricity-conductive contactors  343  and  344 , electricity-conductive bridge  345 , springs  346  and  347 , electricity-conductive plates  351  and  352 , electricity-conductive contactors  353  and  354 , electricity-conductive bridge  355 , springs  356  and  357 . 
     Associating with the drawings below is carried out a further description of the present invention. 
       FIG. 2A  is a perspective view of components: camshaft mechanism  201  and executive mechanism  202  of step type ratchet wheel mechanism  200  of the present invention. As shown in  FIG. 2A , step type camshaft mechanism  200  of the present invention comprises: camshaft mechanism  201  and executive mechanism  202 .The components of camshaft mechanism  200  in  FIG. 2A  are viewed from rear end of camshaft mechanism  201  (or viewed from fore end of executive mechanism  202 ), i.e. viewed along direction indicated as arrowhead E. Camshaft mechanism  201  comprises camshaft  215 , on and along which are disposed a plurality of cams ( 12  cams shown in the Figure) used to control the connection and disconnection mechanism of a plurality of switch contact sheets  302  ( 12  groups of switch contact sheets, see  FIG. 3A ). Camshaft mechanism  201  has a camshaft circular disc  220  (driven disc) with thickness We. On the rim of camshaft circular disc are evenly distributed  3  positioning slots (positioning slots  212 . A ,  212 . B  and  212 . C , taking 120° as angular spacing). Camshaft  215  (driven shaft) is connected with the rear surface of camshaft circular disc  220 . 
     As shown in  FIG. 2A , executive mechanism  202  comprises: an executive circular disc  206  (driving disc), on the rear surface of executive circular disc  206  is jointed a circular ring  205  used for assembling the knob of turning switch (not shown in the Figure). On the fore surface of executive circular disc  206  exists a circular prominence  207 ; on circular prominence  207  exists a protruded driving cam  208  (with thickness W 2 ). The radius of inner root circle of driving cam  208  is R 1 ; the radius of outer top circle of driving cam  208  is R 2 . On the rim of inner root circle are evenly distributed 3 angular shape teeth (angular shape teeth  235 . A ,  235 . B  and  235 . C  taking 120° as angular spacing). On driving cam  208  are symmetrically arranged two sector shape grooves having a semicircular section. These two symmetrical sector shape grooves are used respectively to contain a resilient element. The resilient element preferably is spring, it may be called as interior spring  213 . In diametrical direction, half of interior spring  213  is just put into sector shape groove  222 , another half of interior spring  213  is just put into sector shape groove  221  arranged on camshaft circular disc  220  (see  FIG. 2B ). Sector shape groove  222  and sector shape groove  221  are gathered together to form an empty chamber used to contain entire interior spring  213  (see  FIG. 2G ). 
       FIG. 2B  is an assembly perspective view of components: camshaft mechanism  201 , executive mechanism  202  and pawl devices ( 250  and  260 ) of step type ratchet wheel mechanism  200  of the present invention. As shown in  FIG. 2B , the components of ratchet wheel mechanism  200  are viewed along a direction from fore end of camshaft mechanism  201  (or from rear end of executive mechanism  202 ) (along direction indicated as arrowhead F). As shown in  FIG. 2B , on the fore-end surface of camshaft circular disc  220  are symmetrically arranged two sector shape grooves  211  with semicircular section. These two symmetrical sector shape grooves  211  are respectively used to contain the interior springs  213 . In diametrical direction, half of interior spring  213  is just put into sector shape groove  211 ; another half of interior spring  213  is just put into sector shape groove  222  arranged on driving cam  208  (see  FIG. 2A ). Sector shape groove  222  and sector shape groove  221  are gathered together to form an empty chamber used to contain entire interior spring  213  (see  FIG. 2G ). 
     In  FIG. 2B , ratchet mechanism  200  further comprises: two pawl devices, i.e. upper pawl device  250  and lower pawl device  260 . Upper pawl device  250  includes: exterior spring  251 , pawl arm  252 , pins  253  and  254 ; lower pawl device  260  includes: exterior spring  261 , pawl arm  262 , pins  263  and  264 . The bent downward portions at the fore ends of pawl arms  252  and  262  respectively are pawl  255  and pawl  265  (see  FIG. 2D ); the thickness of pawl  255  and pawl  265  is suitable for inserting the pawl into positioning slot  212  of camshaft circular disc  220 . The width W of pawls  255  and  265  is larger than the thickness W 1  of camshaft circular disc  220 , so that in width direction of pawl  255  or  265  still exists residual portion after pawl  255  or  265  falls into positioning slot  212 , this residual portion will rest on the rim of driving cam  208 . Namely, when camshaft circular disc  220  and driving cam  208  are assembled together face to face, pawl  255  (or pawl  265 ) may rest on the rim of camshaft circular disc  220  (or fall into positioning slot of camshaft circular disc  220 ) and simultaneously rest on the rim of driving cam  208 .In  FIG. 2B , in circular ring  205  for assembling knob exists an assembling hole  270  and a fixed key  271 , assembling hole  270  and fixed key  271  are used to assemble knob of turning switch (not shown in Figure). 
       FIG. 2C  is an assembly perspective view of camshaft  201 , executive mechanism  202  and pawl devices ( 250  and  260 ) in step type ratchet wheel mechanism  200 . As shown in  FIG. 2C , camshaft mechanism  201 , executive mechanism  202  and pawl devices ( 250  and  260 ) already were assembled together. In this time, camshaft circular disc  220  of camshaft mechanism  201  and driving cam  208  of executive mechanism  202  are assembled together face to face, and to cause two sector shape grooves  211  on the end surface of camshaft circular disc  220  and two sector shape grooves  222  on the end surface of driving cam  208  able to be correspondingly gathered together to form two empty chambers  231  for containing their respective interior spring  213  (as shown in State  1  of  FIG. 2G ). Furthermore, for the width W of pawl  255  and pawl  265  is approximately equal to the sum of thickness W 1  of camshaft circular disc  220  and thickness W 2  of driving cam  208 , thus pawl ( 255  or  265 ) may rest on the rim of camshaft circular disc  220  (or fall into positioning slot  212  of camshaft circular disc  220 ) and simultaneously rest on the rim of driving cam  208 . 
       FIG. 2D  is a schematic diagram of pawl arm of the present invention. The bent downward portions at the fore ends of pawl arms  252  and  262  respectively form pawl  255  and pawl  265 . The width of pawls  255  and  265  is W. 
       FIG. 2E  is an elevation of executive mechanism  202  viewed along a direction indicated as arrowhead E.  FIG. 2F  is an elevation of camshaft circular disc  220  viewed along a direction indicated as arrowhead F. As shown in  FIG. 2E , the radius of inner root circle of driving cam  208  is denoted as R 1 , radius of outer top circle of driving cam  208  as R 2 , and the top points of 3 angular shape teeth  235 . A ,  235 . B  and  235 . C  inscribe in the outer top circle of driving cam  208 . As shown in  FIG. 2F , the distance from the bottom of positioning slot  212  of camshaft circular disc  220  to the center of camshaft circular disc  220  is denoted as R 3 , the radius of camshaft circular disc  220  as R 4 . Following relation exists among R 1 , R 2 , R 3  and R 4 : the radius R 1  of inner root circle of driving cam  208  is equal (or approximately equal) to the distance R 3  from the bottom of positioning slot  212  of camshaft circular disc  220  to the center of camshaft circular disc  220 ; the radius R 2  of outer top circle of driving cam  208  is equal to (or slightly larger than) radius R 4  of camshaft circular disc  220 . Obviously, radius R 2  of outer top circle of driving cam  208  is larger than radius R 1  of inner root circle of driving cam  208 ; radius R 4  of camshaft circular disc  220  is larger than the distance R 3  from the bottom of positioning slot  212  of camshaft circular disc  220  to the center of camshaft circular disc  220 ; radius R 4  of camshaft circular disc  220  is larger than radius R 1  of inner root circle of driving cam  208 . As shown in  FIG. 2E , the symmetrical axis of two sector shape groves  222  on driving cam  208  is denoted as L 1 , the angle included between L 1  and line passing through the top point of angular shape tooth  235 . B  and the center of camshaft is 60°. As shown in  FIG. 2F , the symmetrical axis of two sector shape groves  211  on camshaft circular disc  220  is denoted as L 2 , L 2  also is the symmetrical axis of positioning slot  212 . A . Thus when sector shape groove  222  coincides with sector shape groove  211 , namely L 1  coincides with L 2 , the angle included between angular shape tooth  235 . A  and positioning slot  212 . A  is about 60° (step angle is 60°). 
       FIG. 2G  is a partial sectional view of camshaft circular disc  220  and driving cam  208  of the present invention, which are assembled together. When executive mechanism  202  and camshaft mechanism  201  are assembled together (see  FIG. 2C ), sector shape groove  211  on camshaft circular disc  220  and sector shape groove  222  on driving cam  208  are gathered together to form empty chamber  231  for containing interior spring  213  (as shown in State  1 ). In sate  1 , interior spring is in free state, i.e. not compressed; or for working reliably, interior spring  213  may be somewhat pre-compressed. 
     In State  2 , driving cam  208  is turned counterclockwise, but camshaft circular disc  220  keeps in still state (because pawl  255  or  265  is inserted in positioning slot  212  on camshaft circular disc  220 ), thus sector shape groove  211  and sector shape groove  222  are staggered each other resulted in that interior spring  213  is compressed and resilient potential energy is stored in interior spring. In this time, the force acted by interior spring  213  (as shown in Figure its direction is to the left) will form a counterclockwise moment for camshaft circular disc  220 . 
     In State  3 , when driving cam  208  is turned to 60° counterclockwise, Pawl  255  (or pawl  265 ) is pushed out from positioning slot  212  on camshaft circular disc  220 , then the resilient potential energy stored in interior spring  213  is released to cause camshaft circular disc being turned 60° counterclockwise resulted in that sector shape groove  211  on camshaft circular disc  220  and sector shape groove  222  on driving cam  208  are gathered together over again, then to form an entire empty chamber  231  as shown in State  1  (the detailed operational process, see the description about  FIG. 4A  and  FIG. 4D ). 
       FIG. 3A  is a perspective view of turning switch  300  of the present invention. Turning switch  300  has a housing  301  composed of upper housing  311  and lower housing  312 . Ratchet wheel mechanism  200  shown in  FIG. 2C  (comprising camshaft mechanism  201 , executive mechanism  202 , and pawl devices  250  and  260 ) is assembled between upper housing  311  and lower housing  312 . On upper housing  311  and on lower housing  312  are respectively disposed 6 groups (12 pieces) of switch contact sheets  302 , (i.e. in a total of 12 groups, 24 pieces of switch contact sheets). Under the control of a relevant cam, each group of switch contact sheets may be electrically connected or disconnected, for example, switch contact sheets  302 . a  and  302 . A form one group, switch contact sheets  302 . g  and  302 .G form another one group. 
       FIG. 3B  is a sectional view of turning switch of the present invention along line A-A in  FIG. 3A . As shown in  FIG. 3B , ratchet mechanism  200  (comprising camshaft mechanism  201 , executive mechanism  202 , and pawl devices  250  and  260 ) is assembled and installed between upper housing  311  and lower housing  312  of turning switch. When assembling and installing, camshaft mechanism  201 , executive mechanism  202 , and pawl devices  250  and  260  are firstly assembled together (see  FIG. 2C ), then upper housing  311  and lower housing  312  are gathered together, thus camshaft mechanism  201 , executive mechanism  202 , and pawl devices  250  and  260  may be installed and fixed in the housing  301  of turning switch. Executive mechanism  202  is assembled in the fore portion of housing  301  of turning switch; camshaft mechanism  201  passes through the middle and the rear portion of housing  301  of turning switch. 
     On upper housing  311  and on lower housing  312  respectively exists semicircular groove  321  and semicircular groove  322 . When semicircular groove  321  and semicircular groove  322  are gathered together, a space will be formed just to contain executive circular disc  206  on executive mechanism  202 ; groove wall  313  and circular prominence  207  are arranged face to face. The fit clearance between housing  301  (i.e. upper housing  311  and lower housing  312 ) and camshaft mechanism  201  and the fit clearance between housing  301  (i.e. upper housing  311  and lower housing  312 ) and executive mechanism  202  have to meet the requirement allowing camshaft mechanism  201  and executive mechanism  202  able to turn successfully in housing  301 . When camshaft  215  is turned, the cams disposed on the camshaft may control the connection and disconnection mechanism of said 12 groups of switch contact sheets  302 . When executive mechanism  202  is turned, camshaft mechanism  201  may be driven to turn by the resilient force of interior spring  213 . Because the width W of upper pawl  255  and lower pawl  265  is equal or approximately equal to the sum of thickness W 1  of camshaft circular disc  220  and thickness W 2  of driving cam  208 , so that upper pawl  255  and lower pawl  265  may rest on the rim of driving cam  208  and simultaneously rest on the rim of camshaft circular disc  220  (or fall into positioning slot  212  of camshaft circular disc  220 ). 
       FIG. 3C  are two sectional views of turning switch of the present invention along lines D-D and F-F in  FIG. 3A , used to show the control mechanism of switch contact sheets. Through taking these two sectional views as examples, the working principle about how to control the connection and disconnection of two corresponding groups of switch contact sheets by two cams on camshaft is described. For other cams to control the connection and disconnection of other corresponding groups of switch contact sheets, the working principle just described above also is valid. 
     As shown in  FIG. 3C , in control mechanism of switch contact sheets is disposed an electricity-conductive bridge  345  ( 355 ), on which exists a bow-shape protruded portion, so that in a period during a cam is turned 360°, a portion of the cam may push the bow-shape protruded portion of electricity-conductive bridge  345  ( 355 ) in a certain angular range, and other portion of the cam may depart from the bow-shape protruded portion of electricity-conductive bridge  345  ( 355 ) in other angular range. Two electricity-conduct contactors  343  and  344  ( 353  and  354 ) are respectively disposed at one end of electricity-conductive bridge  345  ( 355 ), two springs  346  and  347  ( 356  and  357 ) are disposed respectively at the back of each electricity-conduct contactors and installed on housing. Two electricity-conductive plates  341  and  342  ( 351  and  352 ), which are connected respectively with two pieces (a group) of switch contact sheets, are respectively disposed beneath one of electricity-conduct contactors  343  and  344  ( 353  and  354 ). Therefore, when the cam does not contact the bow-shape protruded portion of electricity-conductive bridge  345  ( 355 ), the resilient force of springs  346  and  347  ( 356  and  357 ) will press electricity-conductive contactors  343  and  344  ( 353  and  354 ) tightly against electricity-conductive plates  341  and  342  ( 351  and  352 ), so that an open circuit of electric appliance, which is across said electricity-conductive contactors, will be electrically connected to become a closed circuit. When the cam pushes the bow-shape protruded portion of electricity-conductive bridge  345  ( 355 ), the thrust of the cam may conquer the resilient force of springs  346  and  347  ( 356  and  357 ) to cause electricity-conductive contactors  343  and  344  ( 353  and  354 ) departing respectively from electricity-conductive plates  341  and  342  ( 351  and  352 ), so that a closed circuit of electric appliance, which is across said electricity-conductive contactors, will be electrically disconnected to become an opened circuit. 
     Here, the housing and the cams are insulators; electricity-conducive plates, electricity-conductive contactors and electricity-conductive bridges all are conductors. 
     As shown in F-F section, switch contact sheets  302 . k  and  302 .K in lower housing are in electricity-connection state. The current flows in turn through switch contact sheet  302 . k , electricity-conducive plate  351 , electricity-conductive contactor  353 , electricity-conductive bridge  355 , electricity-conductive contactor  354 , electricity-conducive plate  352 , and finally to switch contact sheet  302 .K. In this time, from F-F section it may be seen that a cam on camshaft  215  does not contact with electricity-conductive bridge  355 , between them exists a gap. Through electricity-conductive contactors  353  and  354 , springs  356  and  357  may press two ends of electricity-conductive bridge  355  respectively tightly against electricity-conductive plates  351  and  352 , so that an electric connection is set up between contact sheets  302 . k  and  302 .K. 
     As shown in D-D section, switch contact sheets  302 . b  and  302 .B in upper housing are in electric-disconnection state. Because in uplifting process of electricity-conductive bridge  345  due to a cam on camshaft  215  pushing electricity-conductive bridge  345  upward, springs  346  and  347  are compressed. In this time, electricity-conductive contactors  343  and  344  will depart respectively from electricity-conductive plates  341  and  342  to cause electric-disconnection being set up between switch contact sheets  302 . b  and  302 .B. 
       FIGS. 4A ,  4 B,  4 C and  4 D are some sectional views used to concretely introduce the working principle about turning switch to be turned from a control-position to next control-position. At different control-position, the groups of switch contact sheets will set up different electrically connected circuit as a closed loop for electric appliance. 
     Although in fact, the switchover work is implemented by the interaction from camshaft mechanism  201  and executive mechanism  202 , which are coupled together, for more distinctly to introduce the working principle, in  FIG. 3B  yet are provided two sectional views along lines B-B and C-C to show the change of relative position of camshaft circular disc  220  and driving cam  208  in practical work. From B-B section the change of relative position of driving cam  208  may be distinctly observed; from C-C section the change of relative position of camshaft circular disc  220  may be distinctly observed 
       FIG. 4A  shows the circumstance of relative position of camshaft circular disc  220  and driving cam  208  when turning switch is at initial position. As shown in C-C section of  FIG. 4A  (i.e. sectional view along line C-C in  FIG. 3A ), upper pawl device  250  include upper pawl arm  252 , upper pawl  255 , which is at fore end of upper pawl arm  252 ; through pin  253  upper pawl arm  252  may be rotatablely assembled on upper housing  311 . One end of exterior spring  251  clasps upper pawl arm  252 , another end clasps pin  254 , pin  254  is fixed on upper housing  311 . Similarly, lower pawl arm  262  may be rotatablely assembled on lower housing  312  by pin  263 , one end of exterior spring  261  clasps lower pawl arm  262 , another end clasps pin  264 , pin  264  is fixed on lower housing  312 . Exterior springs  251  and  261  apply pre-tensile force (or offset force) respectively to pawl arm  252  and to pawl arm  262  resulted in that pawls  255  and  265  respectively have a tendency to move toward the center of camshaft. Therefore, once a positioning slot  212  rotates to a position where pawl  255  or  265  exists, pawl  255  or  265  will speedily fall into positioning slot  212 . 
     As shown in C-C section of  FIG. 4A  (i.e. sectional view along line C-C in  FIG. 3A ), when turning switch is at initial position, pawl  255  on upper pawl device  250  falls into positioning slot  212   A  to lock camshaft mechanism  201  unable to rotate; pawl  265  on lower pawl device  260  is at an intermediate position between positioning slots  212 . B  and  212 . C . It should be noted that: in width direction only a portion of pawl  255  falls into positioning slot  212 , the residual portion of pawl  255  will rest on the rim of driving cam  208  (see pawl  255  in B-B section). 
     As shown in B-B section  FIG. 4A  (i.e. sectional view along line B-B in  FIG. 3A ), when turning switch is at initial position, in width direction a portion of upper pawl  255  rests on the rim of driving cam  208  and at an intermediate position between angular shape teeth  235 . A  and  235 . B ; In width direction a portion of lower pawl  265  rests on the top of angular shape tooth  235 . C  of driving cam  208 . 
     When turning switch is at initial position as shown in  FIG. 4A , sector shape groove  211  on camshaft circular disc  220  and sector shape groove  222  on driving cam  208  are fully gathered together to form an empty chamber, in this case that the interior spring  213  contained in the empty chamber is not compressed and in free state, as shown in State  1  of  FIG. 2G   
     Pawl arm also may be a resilient metal sheet made from shape memory alloy. In this case, the resilient metal sheet is directly fixed on housing, thus exterior spring may be omitted, but the pawl at the fore end of pawl arm is preset into positioning slot  212 . 
       FIG. 4B  shows the circumstance of relative position of camshaft circular disc  220  and driving cam  208  after driving cam  208  is turned an angle counterclockwise. As shown in C-C section of  FIG. 4B  (i.e. sectional view along line C-C in  FIG. 3A ), for pawl  255  falls into positioning slot  212   A  to cause camshaft mechanism  201  being locked, so camshaft circular disc  220  keeps at its position not varying. As shown in B-B section of  FIG. 4B  (i.e. sectional view along line B-B in  FIG. 3A ), when driving cam  208  is turned about 30° counterclockwise, because camshaft circular disc  220  keeps at its position not varying, sector shape groove  211  and sector shape groove  222  are staggered each other, interior spring  213  starts to be compressed and to store a certain quantity of potential energy as shown in State  2  of  FIG. 2G . When driving cam  208  is being turned counterclockwise, angular shape tooth  235 . A  will be gradually close to pawl  255 , then pawl  255 , which already fell in positioning slot  212 . A , also gradually approaches the going-up slant surface on driving cam  208  (for radius R 2  of outer top circle of driving cam  208  is larger than radius R 1  of inner root circle of driving cam  208 ). Then pawl  255 , which formerly fell in positioning slot  212 . A , will be gradually pushed out from positioning slot  212 . A  by the going-up slant surface. 
     In B-B section of  FIG. 4B , pawl  265  rests on the rim of camshaft circular disc  220 , for radius R 4  of camshaft circular disc  200  is larger than radius R 1  of inner root circle of driving cam  208 , thus between pawl  265  and driving cam  208  remains a gap, therefore no roadblock will interfere the turning of driving cam  208 . 
       FIG. 4C  shows the circumstance of relative position of camshaft circular disc  220  and driving cam  208  after driving cam  208  is continuously turned an angle counterclockwise. As shown in B-B section of  FIG. 4C  (i.e. sectional view along line B-B in  FIG. 3A ), after driving cam is turned about 55° counterclockwise, pawl  255  in positioning slot  212 . A  gradually approaches the top point of the going-up slant surface of driving cam  208  (i.e. the top of angular shape tooth  212 . A ), in this time, going-up slant surface pushes pawl  255  almost but not completely out from positioning slot  212 . A . Therefore, camshaft circular disc  220  yet keeps in its original position not varying, sector shape groove  211  and sector shape groove  222  are further staggered each other, and interior spring  213  also is further compressed. 
       FIG. 4D  shows the circumstance of relative position of camshaft circular disc  220  and driving cam  208 , when driving cam  208  is continuously turned to 60° counterclockwise. 
     As shown in B-B section of  FIG. 4D  (i.e. sectional view along line B-B in  FIG. 3A ), when driving cam  208  is turned 60° (a step angle), upper pawl  255  is just at the top of angular shape tooth  235 . A , thus upper pawl  255 , which formerly fell in positioning slot  212 . A , is pushed completely out from positioning slot  212 . A . 
     As shown in C-C section of  FIG. 4D  (i.e. sectional view along line C-C in  FIG. 3B ), camshaft circular disc  220  is turned counterclockwise by the pushing of resilient force of compressed interior spring  213 , as for the circumstance when upper pawl  255  at the top of angular shape tooth  235 . A , see B-B section of  FIG. 4D . When camshaft circular disc  220  is turned 60° counterclockwise, under the action of pulling force of exterior spring  261 , lower pawl  265  falls into positioning slot  212 . B  and sends out a silvery snap, then the turning of camshaft circular disc  220  is stopped. Interior spring  213  comes back to its free state (or maybe in a state being somewhat pre-compressed) as shown in State  3  of  FIG. 2G . 
     In this time, in B-B section of  FIG. 4D  (i.e. sectional view along line B-B in  FIG. 3B ), upper pawl  255  is at the top of angular shape tooth  235 . A , lower pawl  265  is at an intermediate position between angular shape teeth  235 . B  and  235 . C  of driving cam  208 ; In C-C section of  FIG. 4D  (i.e. sectional view along line C-C in  FIG. 3B ), upper pawl  255  is at an intermediate position between positioning slots  212 . A  and  212 . C , lower pawl  265  falls into positioning slot  212 . B . 
     If driving cam  208  is again turned 60° counterclockwise toward next position, angular shape teeth  235 . B  of driving cam  208  will push lower pawl  265  out from positioning slot  212 . B . Once lower pawl  265  is pushed out from positioning slot  212 . B , due to driving of the resilient force of interior spring  213 , then camshaft circular disc  220  will be turned 60° counterclockwise, upper pawl  255  falls into positioning slot  212 . C , lower pawl  265  is at an intermediate position between angular shape teeth  235 . B  and  235 . A . Namely, camshaft circular disc  208  is turned  1200  counterclockwise every time, upper pawl  255  and lower pawl  265  in turn will fall into positioning slot  212  ( 212 . A ,  212 . B , or  212 . C ) a time. 
     As embodiment to describe the principle of the present invention in detail, the step angle in the present invention is taken as 60° (i.e. six times of step equal to 360°). Even though the step angle is changed, the principle yet will keep correct and able to get same effect of the present invention if the number of positioning slots on camshaft circular disc  220 , the number of angular shape teeth on driving cam  208 , and the angle included between lower pawl  265  and vertical line are changed correspondingly and suitably. 
       FIGS. 5A to 5C  shows the positional relation among the positioning slots on camshaft circular disc  220 , angular shape teeth on driving cam  208  and two paws, when step angle is taken as 30°, 45° and 90° respectively. 
     As shown in  FIG. 5A , when step angle is taken as 30° (i.e. 12 times of step equal to 360°), the number of positioning slots on camshaft circular disc  220  is 6, the number of angular shape teeth on driving cam  208  is 6, in assembly the angular shape tooth on driving cam  208  and the positioning slot on camshaft circular disc  220  are staggered an angle of 30°; the angle included between lower pawl  265  and vertical line is 30°. Under such a condition, driving cam  208  is turned 30° every time; there exists one of pawls to fall into positioning slot. 
     As shown in  FIG. 5B , when step angle is taken as 45° (i.e. 8 times of step equal to 360°), the number of positioning slots on camshaft circular disc  220  is 4, the number of angular shape teeth on driving cam  208  is 4, in assembly the angular shape tooth on driving cam  208  and the positioning slot on camshaft circular disc  220  are staggered an angle of 45°; the angle included between lower pawl  265  and vertical line is 45°. Under such a condition, driving cam  208  is turned 45° every time; there exists one of pawls to fall into positioning slot. 
     As shown in  FIG. 5C , when step angle is taken as 90° (i.e. 4 times of step equal to 360°), the number of positioning slots on camshaft circular disc  220  is 2, the number of angular shape teeth on driving cam  208  is 2, in assembly the angular shape tooth on driving cam  208  and the positioning slot on camshaft circular disc  220  are staggered an angle of 90°; the angle included between lower pawl  265  and vertical line is 90°. Under such a condition, driving cam  208  is turned 90° every time; there exists one of pawls to fall into positioning slot. 
     Additionally, in the embodiment of the present invention, the ratchet mechanism of the present invention is used for turning switch. As known by those skilled in the art, the ratchet mechanism of the present invention also may be widely used for other occasions where the function of non-returning and positioning is needed (such as used for encoder).