Abstract:
A converter for converting mechanical energy into hydraulic energy and a robot implementing the converter are disclosed. The converter includes a shaft rotated about a first axis relative to a casing, a hub defining a bore about a second axis, the shaft rotating in the bore. The first axis is parallel to the second axis, and a distance between the first axis and second axis defines an eccentricity. At least two pistons are movably disposed in radial housings of the shaft with the at least two pistons bearing against the bore. Movement of the pistons feed a hydraulic fluid into one of two annular grooves of the casing arranged in an arc of a circle about the first axis, and the hub is configured to translate along a third axis to modify the value of the eccentricity between two extreme values.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application is a National Stage of International patent application PCT/EP2009/053553, filed on Mar. 25, 2009, which claims priority to foreign French patent application No. FR 08 51943, filed on Mar. 26, 2008, the disclosures of which are incorporated by reference in their entirety. 
     BACKGROUND 
     The invention relates to a converter for converting mechanical energy into hydraulic energy and to a robot implementing said converter. The invention can be particularly used in the production of humanoid robots in which autonomy is to be improved. 
     Such robots are equipped with actuating mechanisms that allow the different parts of the robot to be moved. These mechanisms connect a power source providing mechanical energy such as, for example, an electric, hydraulic or pneumatic motor, to a load. In other words, an actuating mechanism transmits mechanical power between a motor and a load. 
     An essential parameter of an actuating mechanism is its transmission ratio which is chosen so as to adapt a nominal working point of the load to that of the motor. In a known actuating mechanism in which the transmission ratio is constant, formed for example from a set of gears, the choice of the ratio is limited to discrete values and changing the ratio necessitates complicated devices such as a gearbox to adapt the transmission ratio. Now, in robotic applications, the working point of the loads is generally highly variable. If the reduction ratio is constant, this means that the motor must be dimensioned for the most unfavorable circumstances in which the load is used. 
     Devices exist which allow the transmission ratio to be varied continuously but these are complicated and their performance is often poor. Belt speed reducers are known, for example, whose transmission ratio is varied as a function of the speed of the motor by means of inertia masses. 
     The above-described actuating devices are bulky, heavy and complex, which is disadvantageous for robotic applications. 
     Moreover, of the abovementioned motors, electric motors are well suited only to high speeds and low torques. In robotic applications, the opposite situation is common: low speed and high torque. The use of electric motors for low speeds entails high reduction ratios that are thus complicated to achieve. 
     As is known, in robotic applications, a central hydraulic power unit is used that is connected to different joints to be driven by lines transporting a pressurized fluid. When the robot includes a large number of actuators, the network of lines becomes complex. Moreover, the hydraulic power unit must provide to all the joints the maximum pressure required by the joint that is subject to the greatest demand. 
     SUMMARY OF THE INVENTION 
     The invention aims to overcome all or some of the abovementioned problems by providing an actuating mechanism that converts the mechanical energy supplied by a motor into hydraulic energy used by a load, for example in the form of a cylinder allowing a movable part of a robot to be moved. It is understood that the invention is not limited to the field of robotics. The invention can be applied in any field where an actuating mechanism needs to be optimized. More precisely, the invention provides a converter for converting mechanical energy into hydraulic energy which can be decentralized, in other words associated with a single load. The converter then supplies only the hydraulic power required by the load. 
     To this end, the subject of the invention is a converter for converting mechanical energy into hydraulic energy, including a shaft rotated by mechanical energy about a first axis relative to a casing, a hub comprising a bore formed about a second axis, the shaft rotating in the bore, the two axes being parallel and a distance between the axes forming an excentricity, at least two pistons each capable of movement in a radial housing of the shaft, the housings guiding the pistons, the pistons bearing against the bore, characterized in that the movement of the pistons feeds a hydraulic fluid into two annular grooves of the casing, the grooves being arranged in an arc of a circle about the first axis, the hydraulic energy being generated by a pressure difference of the fluid present between the two grooves, and in that the hub is capable of translation along a third axis perpendicular to the first two axes in order to modify the value of the excentricity between two extreme values, one being positive and the other being negative, so as to generate an inversion of the fluid pressures in the grooves while maintaining the same rotation direction for the shaft. 
     One of the grooves forms the inlet and the other forms the discharge of the converter. Inverting the fluid pressures between the grooves has the effect of switching the roles of the grooves between inlet and discharge while maintaining the same rotation direction for the shaft. 
     The subject of the invention is also a robot including multiple independent joints moved by hydraulic energy, characterized in that it also includes the same number of converters according to the invention as there are independent joints, each converter being associated with one joint. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The invention will be better understood and other advantages will become apparent upon reading the detailed description of several alternative embodiments given by way of example, which description is illustrated by the attached drawings, in which: 
         FIG. 1  shows a cross section of an embodiment of a converter according to the invention; 
         FIG. 2  shows elements that carry out the pumping of a hydraulic fluid, for the converter in  FIG. 1 ; 
         FIG. 3  shows an alternative embodiment of the elements shown in  FIG. 2 ; 
         FIG. 4  shows fluid inlet and discharge orifices of the converter; 
         FIG. 5  shows means for modifying an excentricity of the converter; 
         FIG. 6  shows a hydraulic diagram of a valve of the converter; 
         FIGS. 7   a  and  7   b  show two positions of the means for modifying the excentricity; 
         FIG. 8  shows a hydraulic diagram of a distributor of a first alternative embodiment of the converter; 
         FIGS. 9 and 10  show an embodiment of the distributor in  FIG. 8 ; these two figures are cross sections along perpendicular planes; 
         FIGS. 11   a  to  11   g  show different positions of a movable part of the distributor of the first embodiment; 
         FIGS. 12   a  and  12   b  show a hydraulic diagram of two distributors of a second alternative embodiment of the converter; 
         FIGS. 13 and 14  show an embodiment of the distributors in  FIGS. 12   a  and  12   b;    
         FIGS. 15   a  to  15   g  show different positions of a movable part of the first distributor of the second alternative embodiment; 
         FIGS. 16   a  and  16   b  show different positions of a movable part of the second distributor of the second alternative embodiment. 
     
    
    
     For greater clarity, the same elements carry the same reference numerals in the different figures. 
     DETAILED DESCRIPTION 
     The converter shown in  FIG. 1  receives mechanical energy in the form of a rotational movement of a shaft  10  driven by a motor  11 , for example a DC electric motor. The motor  11  rotates at a constant rotational speed, which makes it possible to optimize its operation. The shaft  10  is connected to the motor  11  by a coupling  12 . It is also possible to dispense with the coupling  12  by forming stator windings of the motor  11  directly on the shaft  10 . The shaft  10  rotates about an axis  13  relative to a casing  14  that is closed at the ends of the shaft  10  by two covers  15  and  16 . In each cover  15  and  16 , a rolling bearing  17  and  18 , respectively, effects the guiding, limits the friction between the shaft  10  and the assembly formed by the casing  14  and the covers  15  and  16 , and seals the converter. 
       FIG. 2  shows elements of the converter that effect the pumping of a hydraulic fluid. To this end, the converter includes a hub  20  comprising a bore  21  formed about a second axis  22 . The shaft  10  rotates in the bore  21 . The two axes  13  and  22  are parallel and a distance between the axes  13  and  22  forms an excentricity E. 
     The converter includes at least two pistons each capable of movement in a radial housing of the shaft. It is possible to implement the invention for a converter in which the pistons are parallelepipedal vanes. In the example shown, the housings are cylinders and three pistons  23 ,  24  and  25  each move in a cylinder  26 ,  27  and  28 , respectively. One end of each piston bears against the bore  21 . The shaft  10  includes at least two channels that extend parallel to the axis  13 . The two channels  29  and  30  can be seen in  FIG. 2 . The cylinder  26  opens into the channel  29  and the cylinders  27  and  28  open into the channel  30 . The number of pistons per channel can be increased until they occupy the entire volume of the shaft  10  lying inside the bore  21 . 
     The pistons are advantageously arranged in a quincunx pattern about the axis  13 . In other words, between two adjoining channels, the longitudinal position along the axis  13  of a cylinder opening into a first channel is interposed between the longitudinal positions of two adjacent cylinders of the second channel. This arrangement makes it possible to maximize the number of pistons for a given bore  21 . The arrangement improves the dynamic balance of the shaft  10  and of its pistons when the shaft  10  is rotating. The arrangement also reduces the variation in the radial forces on the shaft  10  as a function of the angle of rotation of the shaft  10 . 
     The movement of the pistons  23 ,  24  and  25  feeds a hydraulic fluid into the channels  29  and  30 . More precisely, in the relative position of the shaft  10  and the hub  20  shown in  FIG. 2 , the pistons  24  and  25  are in a position termed top dead center and the piston  24  is in a position termed bottom dead center. When the shaft  10  rotates about its axis  13 , the pistons  23  to  25  move in their respective cylinder between their two dead centers. This movement feeds the fluid present into the part of the cylinders  26 ,  27  and  28  communicating with the channels  29  and  30 . Each channel  29  and  30  is closed off at one of its ends by a cap  31 , which can be seen in  FIG. 1 , and communicates with inlet and discharge orifices at its other end, which orifices will be described later. 
       FIG. 3  shows an alternative embodiment of the elements shown in  FIG. 2 , in which embodiment the pistons  23 ,  24  and  25  are replaced by balls  32  to  35 . The diameter of the balls matches the internal diameter of the corresponding cylinders. In the description that follows, the term piston will be used indiscriminately to refer to cylindrical pistons as shown in  FIG. 2  or balls as shown in  FIG. 3 . The use of balls does not allow as good a sealing of the fluid in the cylinders owing to the reduced contact surface area between balls and cylinders. The performance of the converter is reduced as a result. Nevertheless, the alternative embodiment employing balls is much less expensive to produce. 
     The hub  20  advantageously forms an inner ring of a rolling bearing  36 , for example a needle bearing. The hub  20  can thus rotate together with the shaft  10  and so limit the friction of the pistons against the bore  21 . 
       FIG. 4  shows fluid inlet and discharge orifices of the converter in cross section along a plane perpendicular to that of  FIGS. 1 to 3 . More precisely, the shaft  10  includes ten longitudinal channels, including the channels  29  and  30 . The casing  14  includes two annular grooves  40  and  41  in the shape of an arc of a circle about the axis  13  and each communicating alternately with the channels of the shaft  10 . The groove  40 , for example, admits the fluid to the channels facing it and, similarly, the groove  41  discharges the fluid to the channels facing it. Each of the grooves  40  and  41  communicates with a connecting socket  42  and  43 , respectively, that makes it possible to supply a load associated with the converter either directly or via a distributor which will be described below. For a given excentricity E, the converter operates as a positive displacement pump with a constant output, assuming that the rotational speed of the shaft  10  is constant. The hydraulic energy generated by the converter is caused by a pressure difference of the fluid present between the two grooves  40  and  41 . Two seals  44  and  45 , which can be seen in  FIG. 1  and are, for example, lip seals, can be placed one on either side of the grooves  40  and  41  along the shaft  10  in order to seal the two grooves  40  and  41 . 
     The hub  20  can move in translation along an axis  46  perpendicular to the axes  13  and  22  in order to modify the value of the excentricity E between two extreme values, one being positive and the other being negative. In order to move the hub  20  in translation, an outer ring  47  of the rolling bearing  36  is integral with a carriage  48  capable of moving along the axis  46  in order to modify the value of the excentricity E. Assuming that the rotational speed of the shaft  10  is constant, when the excentricity E is zero, in other words when the axes  13  and  22  coincide, the pistons are stationary in their respective cylinder and the converter delivers no fluid output. When the value of the excentricity E is increased in a first direction along the axis  46 , the output of the converter increases. On the other hand, when the value of the excentricity E is increased in a second direction opposite to the first, the output of the converter becomes negative. In other words, the groove  40  switches from inlet to discharge and vice versa for the groove  41 . Varying the excentricity E between a positive value and a negative value makes it possible to reverse the inlet and discharge roles of the converter without having to reverse the direction of rotation of the motor  11  to do so. Adjusting the excentricity E makes it possible to use a motor that is very simple to control in order to rotate the shaft  10 . This motor can rotate at an almost constant speed without any precise speed control, which simplifies the control of said motor. With this type of motor, the converter output is adjusted just by varying the excentricity E. The inlet/discharge reversal is made much more quickly by varying the excentricity E than by reversing the direction of rotation of the motor owing to the very low inertia of the carriage  48  compared with that of the conventional motor and pump assembly. 
     It is of course possible, if necessary, to adjust both the excentricity E of the converter and the speed of the motor in its operating range. 
       FIG. 5  is a cross sectional view of the converter along a plane parallel to the plane of  FIG. 1 . In order to move the carriage  48  in translation along the axis  46 , the converter includes two pistons  50  and  51  integral with the casing  14 . The pistons  50  and  51  guide and move the carriage  14  along the axis  46 . A chamber  52  and  53 , respectively, is formed on either side of the carriage  48 , between the pistons  50  and  51  and the carriage  48 . A differential pressure of a fluid between the two chambers  52  and  53  allows the carriage  48  to be moved in order to modify the excentricity E of the converter. 
     To this end, the converter includes a valve  55  controlling the movement of the carriage  48  by means of a pressure difference of a hydraulic fluid. 
     A hydraulic diagram of the valve  55  is shown in  FIG. 6 . The valve  55  forms a hydraulic distributor supplied by the fluid moving the carriage  48 . A high pressure of this fluid is labeled P and a low pressure is labeled T in  FIG. 6 . The distributor can assume three positions. In a central position  55   a , neither of the two chambers  52  and  53  is supplied with the fluid. In a position  55   c , shown on the right-hand side in  FIG. 6 , the chamber  53  receives the low pressure T and the chamber  52  receives the high pressure P. In a position  55   b , shown on the left-hand side in  FIG. 6 , the chamber  52  receives the low pressure T and the chamber  53  receives the high pressure P. 
     The valve  55  is advantageously formed in the carriage  48 . All the channels supplying the chambers  52  and  53  from the valve  55  are thus formed in the carriage  48 , which frees up space in the casing  14 . The converter is thus more compact. 
     The valve  55  includes a bore  56  formed in the slide  48 . The bore is made along an axis  57  parallel to the axis  46 . The diameter of the bore  56  is constant. The valve  55  includes a rod  58  which can slide inside the bore  56 . The outer surface of the rod  58  is formed from alternating cylindrical shapes of a small diameter d and of a large diameter D that extend along the axis  57 . A series of five cylindrical shapes is arranged along the axis  57 . These shapes have, in order, the diameters D, d, D, d and D. The diameter D is matched to the internal diameter of the bore  56 . Two communication chambers  59  and  60  are formed between the bore  56  and the shapes of diameter d. Five channels  61  to  65  formed in the bore  56  enable the fluid to communicate with the chambers  59  and  60 . The channels  61  and  65  are connected to the low-pressure fluid T. The channel  62  is connected to the chamber  52 . The channel  63  is connected to the high-pressure fluid P and the channel  64  is connected to the chamber  53 . 
       FIGS. 7   a  and  7   b  show two positions of the rod  58  inside the bore  56 . The two chambers  52  and  53  communicate permanently with the communication chambers  59  and  60 , respectively, and the movement of the rod  58  makes it possible to connect each communication chamber  59  and  60  either with the high-pressure fluid P present in the channel  63  or with the low-pressure fluid T present in the channels  61  and  65 . 
     In  FIG. 7   a , the position shown as  55   a  is termed the position of equilibrium as neither the high-pressure fluid nor the low-pressure fluid communicates with the chambers  52  and  53 . In this position the excentricity E remains constant. More precisely, the three cylindrical shapes of diameter D block the low-pressure channels  61  and  65  and the high-pressure channel  63 . The chambers  52  and  53  communicate only with the communication chambers  59  and  60 , respectively, with access to neither the high-pressure fluid nor the low-pressure fluid. 
     In  FIG. 7   b , the rod  58  is moved to the left in the figure. This is position  55   b . The central cylindrical shape of diameter D frees up access to the channel  63  and the high-pressure fluid P communicates with the communication chamber  60 . Similarly, the left-hand cylindrical shape D frees up access to the channel  61 . The low-pressure fluid T communicates with the communication chamber  59  and the chamber  52 . The carriage  48  moves to the left. A movement of the carriage  48  in the opposite direction is possible with a movement of the rod  58  to the right in order to reach the position  55   c.    
     The movement of the rod  58  is, for example, effected by means of a winding  70  supplied with a control electric current. A core  71  integral with the rod  58  moves in the winding  70  as a function of the control current. 
     Another advantage linked with forming the valve  55  in the carriage  48  is the creation of an automatic control of the excentricity E of the carriage  48  relative to the control. 
     More precisely, a movement of the rod  58  by the value of the desired excentricity E relative to the casing  14  brings certain channels  61 ,  63  or  65  into communication with the corresponding communication chambers  59  and  60 . When the carriage  48  reaches the desired excentricity E, the relative position of the rod  58  with respect to the carriage  48  causes the rod  58  to assume the position  55   a , shown in  FIG. 7   a , without there being any need for a new control to be applied to the winding  70 . 
     The converter comprises a sensor  72  that allows its excentricity E to be determined. To this end, the sensor  72  measures the position of the rod  58  relative to the casing  14 . When the rod  58  is in its position of equilibrium, that shown in  FIG. 7   a , the measurement made by the sensor  72  is the position of the carriage  48 . When the rod  58  is in one of its extreme positions, as shown in  FIG. 7   b , the measurement made by the sensor  72  is the position of the carriage  48  plus the movement of the rod  58  relative to the carriage  48 . The movement of the rod  58  relative to the carriage  48  is relatively fleeting. Indeed, the valve  55  quickly resumes its central position  55   a  after a control is applied to the winding  70 . As a first approximation, it can therefore be considered that the sensor  72  measures the excentricity E of the converter. This excentricity E is proportional to the output of the converter and hence to the speed of movement of a load moved by the fluid delivered by the converter. 
     Moreover, knowing the variation in the acceleration of the load, which is referred to as “jerk”, is important when the converter is applied to the production of a humanoid robot in order to mimic the working of the human body. Indeed, it has been observed that human beings tend to minimize any jerking in their movements. Knowing the variation in the acceleration of the load makes it possible, in a control strategy of the converter, to control the jerk and thus mimic human behavior. 
     The converter advantageously comprises means for determining the acceleration of the output of the converter from the control of the valve  55 . More precisely, the variation in the position of the rod  58  is proportional to the control signal applied to the winding  70 . The control signal is thus proportional to the acceleration of the load. By varying the control signal over time, the acceleration of the output of the converter, or the jerk, is thus obtained. 
     An LVDT (Linear Variable Differential Transformer) sensor is, for example, used. 
     The fluid used to move the carriage  48  can originate from a source outside the converter. This solution makes it possible to simplify the supply to the valve  55  by using an external source in which the high and low pressures P and T have constant pressures. This solution nevertheless has the disadvantage of requiring additional lines to supply the valve  55  with fluid. In order to overcome this problem, the pressure prevailing in the grooves  40  and  41  is used to move the carriage  48 . This improves the independence of the converter with respect to its surroundings. 
     To this end, the converter comprises a distributor  75  to bring the high-pressure inlet P of the valve  55  into communication with the groove  40  or  41  in which the pressure of the fluid is greatest and to bring the low-pressure inlet T of the valve  55  into communication with the groove  40  or  41  in which the pressure of the fluid is lowest. 
     To aid understanding of the operation of the distributor  75 , an electrical analogy can be made with the hydraulic functioning of the distributor  75 . In this analogy, the pressure delivered by the grooves  40  and  41  is compared to an alternating voltage since the excentricity E can be positive or negative. The distributor  75  then behaves like a voltage rectifier allowing the valve  55  to be supplied between positive and negative electrical terminals of the rectifier. 
       FIG. 8  shows a hydraulic diagram of the distributor  75  supplied by the fluid present in the groove  40  and by the fluid present in the groove  41 . The distributor  75  can assume three positions. In a central position  75   a , the excentricity E is zero and the pressure of the fluid in the groove  40  is equal to the pressure of the fluid in the groove  41 . In this position, the distributor  75  connects the groove  40  to the inlet P of the valve  55  and the groove  41  to the inlet T of the valve  55 . A load  76  supplied by the converter is shown in the form of a dual-action cylinder comprising two chambers  77  and  78 . In the central position  75   a , neither of the chambers of the load  76  is supplied. When the excentricity E is modified in such a way that the pressure in the groove  41  is greater than the pressure in the groove  40 , the distributor  75  moves into a second position labeled  75   b  in which the groove  40  is connected to the low-pressure inlet T and the groove  41  is connected to the high-pressure inlet P of the valve  55 . The pressure difference between the two grooves  40  and  41  is created by pumping means  79  of the converter including, notably, the pistons  23  to  25  described above. Furthermore, in the position  75   b , the chamber  77  of the load  76  is connected to the groove  41  and the chamber  78  is connected to a reservoir  80  of fluid labeled R. On the other hand, when the excentricity E is modified in such a way that the pressure in the groove  40  is greater than the pressure in the groove  41 , the distributor  75  moves into a third position labeled  75   c  in which the groove  41  is connected to the low-pressure inlet T and the groove  40  is connected to the high-pressure inlet P of the valve  55 . Furthermore, in the position  75   c , the chamber  78  of the load  76  is connected to the groove  40  and the chamber  77  is connected to a reservoir  80  of fluid labeled R in  FIG. 8 . The distributor  75  does not use any external energy source for its movements. Indeed, it is the pressure of the fluid present in the grooves  40  and  41  that allows the distributor to move from one position to another. 
     The converter advantageously includes means so that, when the fluid pressure between the chambers  52  and  53  is equalized, the excentricity E of the converter is not zero. These means comprise, for example, a spring situated in one of the chambers  52  or  53  and which tends to exert a force between the carriage  48  and the relevant piston  50  or  51 . This spring is useful when the converter is started up. Indeed, the central position  75   a  is a position of equilibrium obtained for a zero excentricity E. Beyond this position, in the absence of the abovementioned means, the movement of the rod  58  could cause no movement of the carriage  48 . By shifting the position of equilibrium of the carriage  48 , this risk is avoided at start-up. 
     In mechanisms using hydraulic fluids, attempts are generally made to minimize leakages as much as possible so as to prevent fluid from escaping from the mechanism and to improve its performance. In the present invention, it is accepted that leakages occur in the different hydraulic functions of the converter such as, for example, the pumping means  79 , the valve  55  and the distributor  75 . By accepting that leakages will occur inside the converter, any impacts or, more generally, unforeseen forces that may arise on the load  76 , can be damped. This damping makes it possible to mimic human behavior in the case of the converter being implemented in a humanoid robot. To this end, provision may be made for leakages internal to the converter to be adjusted to suit. 
     The converter advantageously includes means for recycling any internal fluid leakages that take place, notably during pumping. These leakages are collected in an internal hydraulic space  82  labeled PE in  FIG. 8 . The internal hydraulic space  82  is situated inside the casing  14 , notably on either side of the carriage  48 . 
     To this end, the distributor  75  includes means so that, when it leaves its central position  75   a , the groove in which the pressure is lowest, here the groove  41 , is connected to the internal hydraulic space  82  collecting internal leakages of the converter as long as the channels supplying the load  76  remain closed off by the distributor  75 . 
     Continuing the electrical analogy introduced above, the rectifier, which represents the distributor, can be illustrated as a diode bridge in which the threshold voltages are different: an increased threshold voltage toward a negative voltage representing reduced pressure, and a reduced threshold voltage toward a positive voltage representing excess pressure. Leakages are recycled as long as the alternating voltage is less than the threshold voltage. In the hydraulic diagram in  FIG. 8 , the means for recycling leakages cannot be seen as the internal hydraulic space  82  is connected to one of the grooves only in the central position  75   a.    
       FIGS. 9 and 10  show an embodiment of a distributor that makes it possible both to supply the valve  55  and recycle the leakages. The distributor  75  includes a movable part, termed a throttle valve  85 , that can freely rotate about the axis  13  inside the casing  14 . The throttle valve  85  has the shape of a flat disk. The throttle valve  85  is guided in rotation between an annular cavity  86  of the casing  14  and a complementary annular shape of the throttle valve  85 . The annular cavity  86  is limited by two faces  87  and  88  of the casing  14  that are perpendicular to the axis  13 . The face  88  belongs to the cover  16 . The groove  40  communicates with orifices  90   a ,  90   b ,  90   c  and  90   d  of the face  87  and the groove  41  communicates with orifices  91   a ,  91   b ,  91   c  and  91   d  of the face  87 . The channels  61  and  65 , forming the low-pressure inlet T of the valve  55 , communicate with an orifice  92  of the face  88  and the channel  63  forming the high-pressure inlet P of the valve  55  communicates with an orifice  93  of the face  88 . The fluid reservoir  80  communicates with an orifice  94  of the face  88 . Two orifices  95  and  96  situated on the face  88  form outlets of the converter that allow the load  76  to be supplied. Furthermore, to recycle the leakages, the face  87  includes an orifice  97  that can be seen in  FIGS. 11   a  to  11   g  communicating with the internal hydraulic space  82 . 
     The casing  14  includes an abutment  100  limiting the rotation of the throttle valve  85 . The throttle valve  85  includes an annular groove  101 , the ends  102  and  103  of which can bear against the abutment  100 . The bearing of one of the ends  102  or  103  against the abutment  100  depends on the pressure difference of the fluid present in the grooves  40  and  41 . By way of example, around the central position  75   a , the throttle valve  85  can cover an angular sector of + or −22.5° about the axis  13 . 
     The throttle valve  85  includes multiple annular counterbores communicating with the fluid issuing from the grooves  40  and  41 . On a large diameter of the throttle valve  85  a counterbore  105  is permanently situated opposite the orifice  90   d . On a large diameter of the throttle valve  85  a counterbore  106  is permanently situated opposite the orifice  91   d . On a small diameter of the throttle valve  85  two counterbores  107  and  108  are permanently situated opposite the orifices  90   b  and  90   c . On a small diameter of the throttle valve  85  two counterbores  109  and  110  are permanently situated opposite the orifices  91   b  and  91   c . “Permanently situated” is understood to mean that the counterbore and the orifice in question face each other in all positions of the throttle valve  85  in its rotational movements about the axis  13 . In other words, the counterbores  105 ,  107  and  108  contain fluid at the pressure in the groove  40  and the counterbores  106 ,  109  and  110  contain fluid at the pressure in the groove  41 . 
     In  FIG. 9 , the throttle valve  85  is shown in the central position  75   a . In its rotation about the axis  13 , the throttle valve  85  allows or closes off the passage of the fluid between orifices in the face  87  and orifices in the face  88 . The different positions that the throttle valve  85  can assume, as well as the communications between orifices, are shown in  FIGS. 11   a  to  11   g.    
       FIG. 11   a  shows the throttle valve  85  in the central position  75   a . In this position, the orifices  95  and  96  allowing the load  76  to be supplied are closed off by the solid parts  113  and  114  of the throttle valve  85  situated respectively between the counterbores  107  and  108 , on the one hand, and  109  and  110 , on the other hand. The orifices  92  and  93  communicate partly with the counterbores  108  and  109 , respectively, such that the valve  55  is supplied. The orifice  94  connected to the reservoir  80  communicates with the counterbore  106  and the orifice  97  allowing the leakages to be recycled is completely closed off. The end  102  is at an angular position of 22.5° relative to the abutment  100 . 
       FIG. 11   b  shows the throttle valve  85  in a position in which the pressure of the fluid in the groove  41  is slightly greater than that of the fluid present in the groove  40 . As in  FIG. 11   a , the orifices  95  and  96  allowing the load  76  to be supplied are closed off by the solid parts  113  and  114  of the throttle valve  85 . The orifices  92  and  93  communicate partly with the counterbores  108  and  109 , respectively, such that the valve  55  is supplied. The orifice  94  connected to the reservoir  80  communicates with the counterbore  106 . The orifice  97  allowing the leakages to be recycled communicates partly with the counterbore  105  via an orifice  120  traversing the bottom of the counterbore  105 . As a consequence, the fluid contained in the internal hydraulic space  82  communicates with the groove  40  which is at a reduced pressure. The content of the internal hydraulic space  82  is drawn by the pumping of the converter into the reservoir  80 . The position of the throttle valve  85  shown in  FIG. 11   b  is an intermediate one between the position  75   a  and  75   c b . The end  102  is at an angular position of 26.32° relative to the abutment  100 . 
       FIG. 11   c  shows the throttle valve  85  in a position in which it is moved from the position in  FIG. 11   a  toward the position  75   b  in such a way that the orifices  97  and  120  are completely facing each other and the recycling of the leakages is at its maximum. The position of the throttle valve  85  shown in  FIG. 11   c  is an intermediate one between the position in  FIG. 11   b  and the position  75   b . The end  102  is at an angular position of 29.32° relative to the abutment  100 . 
       FIG. 11   d  shows the throttle valve  85  in a position in which it is moved between the position in  FIG. 11   b  and the position  75   b  in such a way that the orifices  97  and  120  no longer face each other. The leakages are no longer sucked up. In this position, the orifices  95  and  96  allowing the load  76  to be supplied are still closed off by solid parts  113  and  114  of the throttle valve  85 . Attempts are made to suck up the leakages as long as the converter is not supplying the load  76 . The end  102  is at an angular position of 33.32° relative to the abutment  100 . 
       FIG. 11   e  shows the throttle valve  85  almost in the position  75   b . In this position, the orifices  95  and  96  allowing the load  76  to be supplied come into communication with the counterbores  107  and  110 , respectively, and the orifice  94  comes into communication with the counterbore  105  so as to supply the load between the highest pressure delivered by the converter and the reservoir  80 . The end  102  is at an angular position of 37.32° relative to the abutment  100 . 
     In the position  75   b , not shown, the end  103  comes into contact with the abutment  100  and the orifices  95  and  96  allowing the load  76  to be supplied are completely in communication with the counterbores  107  and  110 , respectively. The orifice  94  is also completely in communication with the counterbore  105 . 
       FIG. 11   f  shows the throttle valve  85  in an intermediate position between the central position  75   a  shown in  FIG. 11   a  and the position  75   c . In this position, the orifices  95  and  96  allowing the load  76  to be supplied come into communication with the counterbores  108  and  109 , respectively, and the orifice  94  remains in communication with the counterbore  106  so as to supply the load  76  between the high pressure delivered by the converter and the reservoir  80 . The end  102  is at an angular position of 20.5° relative to the abutment  100 . In this position, the orifices  92  and  93  are not completely closed off so as to allow the valve  55  to be supplied. 
     In the position  75   c , shown in  FIG. 11   g , the end  102  comes into contact with the abutment  100  and the orifices  95  and  96  allowing the load  76  to be supplied are completely in communication with the counterbores  108  and  109 , respectively. The orifice  94  is also completely in communication with the counterbore  106 . The orifices  92  and  93  supplying the valve  55  communicate with the counterbores  110  and  107 , respectively. 
     The converter advantageously comprises means for storing the hydraulic energy in a pressurized reservoir  119 . The storage can take place when the load  76  has to remain stationary. In an application as a humanoid robot, the use of a load such as a cylinder for moving, for example, an ankle follows an operating cycle in which rest periods alternate with working periods. It is possible to simulate the walking of the robot and thus predefine a cyclic ratio between the working periods and the rest periods of the ankle. The storage of hydraulic energy takes place during the rest periods and it is possible to dimension the pressurized reservoir  119  as a function of a cyclic ratio between the working periods and the rest periods of the cylinder. 
     The pressurized reservoir  119  is advantageously shared by several converters of the robot. Converters can be chosen in which the working periods do not overlap in time and, for example, converters in which the cycles are opposite. This is, for example, the case with the two ankles of the robot. Thus, when one of the converters stores energy in the reservoir  119 , another converter associated with the same reservoir  119  uses this energy. The dimensions of the shared reservoir  119  can thus be reduced. 
     An alternative embodiment allowing an example of means for storing hydraulic energy to be illustrated is shown with the aid of  FIGS. 12   a  and  12   b  for a hydraulic diagram,  FIGS. 13 and 14  for an embodiment,  FIGS. 15   a  to  15   g  for the different positions of a throttle valve of a first distributor  120  and  FIGS. 16   a  and  16   b  for the different positions of a throttle valve of a second distributor  121 . 
     The distributor  120 , like the distributor  75 , is supplied by the grooves  40  and  41  and supplies the chambers  77  and  78  of the load  76 , the valve  55  via its high-pressure inlet P and low-pressure inlet T. The distributor  120  can assume three positions  120   a ,  120   b  and  120   c . The position  120   a  is identical to the position  75   a.    
     In the position  120   b , the pressure in the groove  41  is greater than that in the groove  40 . The high-pressure inlet P and low-pressure inlet T of the valve  55  are, as for the position  75   b , supplied by the grooves  41  and  40 , respectively. Similarly, as for the position  75   b , the chamber  77  is supplied by the groove  41 . However, unlike the distributor  75 , in the position  120   b , the chamber  78  is connected to the reservoir  80  without any link to the pumping means  79  and the groove  40  draws the fluid into the pressurized reservoir  119 . A check valve  122  ensures that the pressure of the pressurized reservoir  119  is never less than the pressure of the reservoir  80  which is, for example, maintained at atmospheric pressure. 
     In the position  120   c , the pressure of the groove  40  is greater than that of the groove  41 . The high-pressure inlet P and low-pressure inlet T of the valve  55  are, as for the position  75   c , supplied by the grooves  40  and  41 , respectively. On the other hand, the load  76  and the reservoirs  80  and  119  are not connected directly to the distributor  120  but via the distributor  121 , the hydraulic diagram of which is shown in  FIG. 12   b.    
     The distributor  121  can assume two positions,  121   a , termed the rest position, and  121   b , termed the active position. The distributor  121  is controlled by an external actuator  122 , for example an electric actuator. In the absence of any control of the actuator  122 , the distributor  121  is returned to its rest position by means of a spring  123 . 
     In the position  121   a , the two chambers  77  and  78  of the load  76  are isolated and the pumping means  79  draw fluid into the reservoir  80  in order to increase the pressure of the pressurized reservoir  119 . 
     The actuator  122  is activated when it is desired to move the load in the direction represented by an arrow  124 . When the actuator  122  is activated, the distributor  121  assumes the position  121   b , the chamber  77  is connected to the reservoir  80  and the pumping means  79  draw fluid from the pressurized reservoir  119  to supply the chamber  78 . The pressure difference between the two chambers  77  and  78  is thus equal to the sum of the pressure difference between the two reservoirs  80  and  119  and the pressure difference obtained by the pumping means  79 . Thus, when the load  76  is at rest, energy can be stored by increasing the pressure of the pressurized reservoir  119 . This stored energy is recovered when the load  76  is moved either in the position  120   b  or in the position  120   c , these two positions being associated with the position  121   b . When all the stored energy has been consumed, the pressure of the reservoir  119  becomes equal to that of the reservoir  80  and the operation of the converter reverts to that of the alternative embodiment implementing the distributor  75 . 
     To form the storage means, the distributor  120  includes a throttle valve  130 , freely rotatable about the axis  13  inside the casing  14 . The throttle valve  130 , like the throttle valve  85 , is guided in rotation in an annular cavity  131  of the casing  14 . The annular cavity  131  is limited by two faces  132  and  133  of the casing  14  that are perpendicular to the axis  13 . The throttle valve  130  is shown in different positions in  FIGS. 15   a  to  15   g.    
     Like the distributor  75 , the distributor  120  allows the high-pressure inlet P of the valve  55  to be brought into communication with the groove  40  or  41  in which the pressure of the fluid is greatest and the low-pressure inlet T of the valve  55  to be brought into communication with the groove  40  or  41  in which the pressure of the fluid is lowest. To this end, the distributor includes orifices  135  and  136  connected to the channel  63 , forming the high-pressure inlet P of the valve  55 , for the orifice  135 , and to the channels  61  and  65 , forming the low-pressure inlet T of the valve  55 , for the orifice  136 . As a function of the rotation of the throttle valve  130 , the orifices  135  and  136  communicate either with counterbores  137  and  138  connected to the groove  40  via the orifice  90   a  or with counterbores  139  and  140  connected to the groove  41  via the orifice  91   a.    
     The distributor  120  also makes it possible to bring the chambers  77  and  78  of the load  76  into communication with the grooves  40  and  41  via the distributor  121  when the latter is in its position  121   b . To simplify the description of the distributor  120 , it is assumed below that the distributor  121  is in its position  121   b , in other words without the storage of any energy. 
     The distributor  120  includes an orifice  141  communicating either with the counterbore  138  so that the orifice  141  communicates with the groove  40  (see  FIG. 15   g ), or with a counterbore  145  so that the orifice  141  communicates with the reservoir  80  via an orifice  146  of the casing  14  (see  FIG. 15   e ). The distributor  120  also includes an orifice  142  communicating either with the counterbore  140  so that the orifice  142  communicates with the groove  41  (see  FIG. 15   e ), or with a counterbore  143  so that the orifice  142  communicates with the reservoir  80  via an orifice  144  of the casing  14  (see  FIG. 15   g ). 
     The pumping of the fluid from the pressurized reservoir  119  takes place by bringing an orifice  150  of the casing  14  into communication either with a counterbore  151  of the throttle valve  130  connected to the groove  40  (see  FIG. 15   e ), or with a counterbore  152  of the throttle valve  130  connected to the groove  41  (see  FIG. 15   g ). 
     Like the distributor  75 , the distributor  120  allows the leakages contained in the internal hydraulic space  82  to be recycled by being drawn into the reservoir  80 . The recycling is effected between the central position in  FIG. 15   a  and the extreme position in  FIG. 15   e . The recycling is illustrated in the positions of the throttle valve  130  which are shown in  FIGS. 15   b ,  15   c  and  15   d . In these positions, the load  76  is isolated and the orifices  141  and  142  communicate neither with the grooves  40  and  41  via the counterbores  138  and  140  nor with the reservoir  80  via the counterbores  143  or  145 . 
     The positions of the throttle valve  130  which are shown in  FIGS. 15   b ,  15   c  and  15   d  correspond to the central position  120   a  in  FIG. 12   a . The pumping means  79  draw out the fluid contained in the internal hydraulic space  82  to deliver it into the reservoir  80 . The internal hydraulic space  82  is connected to the groove  40  which is at a lower pressure than that of the groove  41 . This link is made by bringing an orifice  157  of one of the faces of the casing  14  connected to the internal hydraulic space  82  into communication with a counterbore  158  of the throttle valve  130  connected to the groove  40 . Furthermore, the reservoir  80  is connected to the groove  41 . This link is made by bringing an orifice  159  of one of the faces of the casing  14  connected to the groove  41  into communication with a counterbore  160  of the throttle valve  130 .  FIG. 15   b  represents the beginning of the recycling of the leakages in the rotation of the throttle valve  130 , moving away from the central position  120   a .  FIG. 15   c  represents the maximum sucking up of the leakages. In  FIG. 15   c , the orifice  157  is completely opposite the counterbore  158  and the orifice  159  is completely opposite the counterbore  160 .  FIG. 15   d  shows the end of the sucking up of the leakages before the load  76  is supplied. 
     The distributor  121  can be formed by means of a throttle valve  170  rotating about the axis  13  inside an annular cavity  171  of the casing  14 .  FIGS. 16   a  and  16   b  show two positions of the throttle valve  170  corresponding respectively to the positions  121   a  and  121   b  defined on the hydraulic diagram in  FIG. 12   b . The throttle valve  170  includes several elongated slots that allow orifices situated on opposite faces closing the annular cavity  171  perpendicularly to the axis  13  to be brought into communication. The spring  123 , arranged between the casing  14  and the throttle valve  170 , tends to return the throttle valve  170  into its position in  FIG. 16   a.    
     In the position  121   a  ( FIG. 16   a ) an elongated slot  175  brings the reservoir  80  into communication with an outlet S 1  of the distributor  120 . In the position  121   b  ( FIG. 16   b ), a solid part  176  of the throttle valve  170  prevents this communication. 
     In the position  121   a  an elongated slot  177  brings the chamber  77  of the load  76  into communication with an outlet S 2  of the distributor  120 . In the position  121   b , a solid part  178  of the throttle valve  170  prevents this communication. 
     In the position  121   a  an elongated slot  179  brings the chamber  78  of the load  76  into communication with an outlet S 3  of the distributor  120 . In the position  121   b , a solid part  180  of the throttle valve  170  prevents this communication. 
     In the position  121   a  an elongated slot  181  brings the pressurized reservoir  119  into communication with an outlet S 4  of the distributor  120 . In the position  121   b , a solid part  182  of the throttle valve  170  prevents this communication. 
     In the position  121   b  an elongated slot  183  brings the pressurized reservoir  119  into communication with the outlet S 3  of the distributor  120 . In the position  121   a , a solid part  184  of the throttle valve  170  prevents this communication. 
     In the position  121   b  an elongated slot  185  brings the reservoir  80  into communication with the outlet S 4  of the distributor  120 . In the position  121   a , a solid part  186  of the throttle valve  170  prevents this communication. 
     The distributor  121  is controlled by the actuator  122  only in the position  120   c  of the distributor  120 . It is possible to use the pressures P and T to rotate the throttle valve  170  about the axis  13  and overcome the force of the spring  123 . To this end, the distributor  121  includes a chamber  190  formed in the casing  14  allowing the fluid entering this chamber to push a finger  191  of the throttle valve  170 . The distributor  121  also includes a valve that can be arranged in a space  192  of the casing  14 . The valve allows the inlet of the fluid to the chamber  190 .