EP3271613A1

EP3271613A1 - Movement transmission device, in particular for a robot arm

Info

Publication number: EP3271613A1
Application number: EP16718391.2A
Authority: EP
Inventors: Franck Olivier LORIOT
Original assignee: Mip Robotics
Current assignee: Mip Robotics
Priority date: 2015-03-16
Filing date: 2016-03-14
Publication date: 2018-01-24
Also published as: CN107667234A; FR3033862B1; US20180079072A1; FR3033861A1; CN107667234B; JP2018512550A; US10307907B2; JP6781444B2; FR3033862A1

Abstract

The device comprises a shaft 4, a notched mobile member - for example a wheel 1 - and at least three arms 2.1, 2.2, 2.3 that together transmit movement between the shaft 4 and the mobile member. Each arm is hinged to two eccentric bearings 3, 3' that hold same parallel to said arm, regardless of the rotational angle of the shaft 4 with which they rotate synchronously. Each arm engages with the notches of the wheel 1 during at least a portion of the cyclic motion of same, by means of at least one tooth 7 of the arm, in such a way as to ensure mutual displacement. The bearings 3, 3' are arranged such that at least one of the arms engages with the mobile member, regardless of the rotational angle of the shaft 4. Said device can be used for producing low-clearance speed reducers.

Description

Motion transmission device, in particular for robot arms

The invention relates to a motion transmission device, in particular for a robot arm.

The reduction ratios between an electric motor and a robot arm are of the order of 1/100 - typically from 1/50 to 1/200 - with an engine speed of 3000 rpm, ie 50 t / s and the arm 0.5 t / s.

Most current robots use cycloid-type gearboxes having a toothed gear mounted in a ring gear and having very similar numbers of teeth, for example 80 teeth and 79 teeth. The crown has an internal toothing and the wheel an external toothing. In order to obtain a gearbox with low backlash, which is reversible and resistant to wear, the teeth must be made of very hard metal and be machined with great precision. The ring having an internal toothing is particularly difficult to machine and involves a significant cost. The high selling price of the robots is mainly due to the cost of the gearboxes, a standard robot being composed of 6 reducers.

Furthermore, it is known from US 5,351,568 a speed reducer comprising a ring gear and four arms mounted inside the ring on the same eccentric lobe of a shaft. The arms are evenly distributed inside the ring and have at least one tooth at their end opposite to the eccentric axis to cooperate with the toothing of the ring. A respective pivoting lever is articulated to each arm to describe to his teeth an elliptical cyclic movement when the shaft rotates, the swinging lever angularly and imposing on the arm a cyclical movement during which it changes orientation. During the cyclic elliptical movement, the teeth of the arm engage the teeth of the crown and rotate in a given direction, then disengage and return back and so on. The arms engage the teeth of the crown successively due to their mounting on the same eccentric lobe and their regular distribution inside the crown. DE 312164 discloses a similar device, but wherein each arm is slidably and pivotally guided relative to a fixed point instead of being guided by a pivoting lever.

The devices of these two documents have the particular disadvantage that the elliptical cyclic movement of the end of the arms complicates both the definition of the shape of the teeth of the arms and the crown at their interface and their machining. In addition, they also use a crown with internal teeth.

It is still known from EP 155 497 A1 a reducer comprising two crowns provided with notches regularly distributed on their circumference and a rotor provided with three radial arms and mounted on an eccentric driven by a motor shaft. Each arm comprises pins for successively cooperating with the notches of a respective ring, one of the rings defining a support member for the corresponding pin to drive the other ring pivoted by the corresponding pin, each arm changing orientation during the cyclic engagement and release movement of the pin pairs with the notches of the crowns. Due to the even distribution of the arms around the rotor axis, the cyclic engagement and disengagement movement of the pin pairs of each arm with the notches of the crowns is offset from those of the other arms. It also provides for several rotors with three arms each mounted on another eccentric integral with the motor shaft, the eccentrics being offset angularly relative to each other around the motor shaft. This device has the disadvantage of being particularly complex and expensive since it requires two rings and one or more rotors with three arms. In addition, there is significant friction between the pins and notches crowns that are detrimental. Moreover, it is difficult to provide a reduced game in the transmission of the movement.

The invention aims to at least partially overcome the disadvantages of the prior art. According to one aspect, the object of the invention is to propose a motion transmission device that is most often in the form of a gearbox - preferably with a gear ratio greater than 1/50 and reversible, providing good accuracy thanks to a low gear game in the transmission of movement, as well as limited friction.

For this purpose, the invention proposes a device for transmitting motion comprising:

a shaft rotatably mounted about its longitudinal axis,

a movable member having at least one succession of notches,

at least three arms for transmitting together the movement between the shaft and the movable member,

in which :

each arm is provided with at least one tooth to cooperate with the notches of the movable member,

each arm is articulated on a first eccentric bearing with respect to a first axis around which the bearing is rotatably mounted, the first bearing and the shaft being linked together to rotate in synchronism,

the movable member and each arm are mechanically guided so that:

o The arm describes a cyclic movement for each turn of the first bearing on which it is articulated, and that

the arm is engaged with the movable member during at least part of the cyclic movement by engagement of the at least one tooth of the arm with a notch of the movable member so that the displacement of one causes the movement of the other,

wherein the first bearings are arranged so that there is at least one arm engaged with the movable member regardless of the angle of rotation of the shaft and wherein each arm is further articulated on a second eccentric bearing relative to a second axis about which the second bearing is rotatably mounted to maintain the arm parallel to itself regardless of the rotation angle of the shaft.

It will be understood that for each arm, the first axis and the second axis are parallel and at a distance from one another, the first bearing and the second bearing having the same eccentricity with respect to their respective axis of rotation. Therefore, when the shaft rotates, every point of each arm describes a circular path due to the eccentricity of its bearings. The radius of the circular path corresponds to the eccentricity distance of its bearings to their respective axis of rotation. The fact that the path of the at least one tooth of each arm is circular together with the constant orientation of the arms advantageously simplifies the shape of the teeth of the arms and the movable member at their interface and therefore their machining, and provides better accuracy due to reduced clearance in motion transmission, as well as limited friction.

Preferably, the first bearings and the second bearings all have the same eccentricity with respect to their respective axis of rotation.

The dependent claims define other preferred embodiments of the invention.

Other features and advantages of the invention will appear on reading the following description of preferred embodiments of the invention, given by way of example and with reference to the appended drawing.

Figures 1 to 7 illustrate the basic operating principle of the invention in the case of a notched wheel. Figure 1 shows an arm in the position where its tooth 7 is fully engaged in a notch of a wheel. Figure 2 shows the arm in the position where the tooth 7 is completely clear of the notches of a wheel. Figures 3 to 7 show the different positions taken by the arm in its cyclic movement around the axis of the shaft 4. During a movement around the axis of the shaft 4, the tooth 7 of the arm progressively enters a notch and disengages from it.

FIG. 8 represents an embodiment of the invention with three arms 2.1, 2.2, 2.3 (in the following, these arms are also referenced indistinctly by reference numeral 2) and a notched wheel, the positions of the notches on the periphery being shifted to three levels corresponding to the positions of the three arms. Figure 9 shows another embodiment with a notch wheel in which the notches are aligned and where against the teeth 7 of the arms 2 are offset with respect to each other.

Figure 10 illustrates the three arms 2 in the case of use with a wheel with aligned notches as that of Figure 9. The teeth 7 of the arms 2 are offset relative to each other. In this arrangement, the axes of the shaft 4 and that of the secondary shaft 5 are in the same plane as the axis of rotation 8 of the wheel 1.

FIG. 11 illustrates the shaft 4 with eccentric bearings 3.1, 3.2, 3.3 (also indistinctly referred to hereinafter by the reference numeral 3) angularly offset relative to one another.

Figure 12 illustrates an alternative to the embodiment of Figure 9, but wherein the tooth 7 of each arm is arranged on another of its sides.

Figure 13 illustrates an embodiment of the invention with a crown with internal notches.

Fig. 14 illustrates an embodiment in which the teeth of the arms will not engage in the same notch of the wheel when the shaft will rotate, but in notches adjacent to or spaced about the circumference of the wheel, such as represented by FIG. 19. This embodiment has the advantage of increasing the contact surface between the faces of the teeth and the faces of the notches and thus offers the possibility of using a wheel of smaller thickness while keeping a important contact surface.

Figures 15 to 18 illustrate the shape of the parts in the embodiment illustrated in Figure 14.

Figure 20 illustrates an embodiment of the invention with a rack. Figure 21 illustrates an embodiment in which the arms 2.1, 2.2, 2.3 have many teeth, here, 44 teeth per arm. The high number of teeth on each arm allows a better progressiveness of the movement transmission, since at any time, some teeth will be partially engaged in the notches and at least one fully engaged.

Figure 22 shows the embodiment of Figure 21 by hiding the wheel so that the teeth of the three arms are visible.

Figure 23 shows the embodiment of Figure 21 showing only the shafts 4 and 5 and their bearings to show the eccentricity of the bearings and their identical arrangement on the shafts 4 and 5.

Figure 24 shows an embodiment similar to that of Figure 21 in the sense that the arms 2.1, 2.2, 2.3 have many teeth. In this case, the arms form a complete ring around the movable member. The two shafts 4 and 5 are arranged on either side of the movable member. Figure 25 shows the embodiment of Figure 24 by hiding the movable member to show the arrangement of the teeth on the arms.

Figure 26 illustrates another aspect of the invention where the teeth of the arms 2 are held in a defined direction. The arms 2, being articulated on a bearing of the shaft 4, have a groove which can slide on a nipple 14 fixed relative to the axes of the movable member 1 and the shaft 4. A single arm is shown in FIG. 26 to facilitate the understanding of the drawing, but, as in the devices described in connection with the other figures, there are at least three arms superimposed with at least one tooth each so that there is always at least one tooth engaged in a notch of the wheel due to the angular offset of their respective bearing around the shaft 4.

With reference to FIGS. 1 to 7, the basic principle of the invention will be explained in the case of a notched wheel provided on its outer circumference, but which also applies to the case of a notched crown formed on its inner circumferential surface or for the case of a rack. As can be seen in FIG. 1, the gearbox comprises a wheel 1 provided with an output shaft (not shown in FIGS. 1 to 7), a shaft 4 and an arm 2 for transmitting motion between 4 and the wheel 1. The wheel 1 has a series of notches in its outer surface. The number of notches depends on the desired reduction ratio, for example 80 notches for a ratio of 1/80. The arm 2 is mounted on a cylindrical bearing 3 of the shaft 4, preferably by means of a ball bearing 6 or a smooth ring. The cylindrical bearing 3 has a slight eccentricity with respect to the axis of rotation of the shaft 4. The part 2 comprises a tooth 7 which engages in the notches of the wheel 1. The part 2 is mounted on a bearing cylindrical 3 'of a secondary shaft 5, preferably also via a ball bearing 6 or a smooth ring. The axis of rotation 10 of the secondary shaft 5 is parallel to the axis of rotation 9 of the shaft 4. This cylindrical bearing 3 'of the secondary axis 5 has the same eccentricity as the cylindrical bearing 3. shaft 4 and the axis 5 rotate in synchronism, the part 2 will always be oriented in the same direction. In the case of Figure 1, the part 2 will always be oriented in the vertical direction as the tooth 7 at its base. When the shaft 4 rotates, any point of the part 2 describes a circular path due to the eccentricity of the cylindrical bearing 3, the radius of the circular path corresponding to the eccentricity distance of the cylindrical bearing 3 to the axis of rotation of the shaft 4.

The wheel 1 is mounted so as to rotate about an axis 8 located in the center thereof. When the shaft 4 will make a turn, the tooth 7 of the part 2 will enter a notch of the wheel 1 and drive the wheel in rotation on a peripheral distance which will be a little less than the eccentric diameter of the part 3 by relative to the shaft 4. During the rotation of the shaft 4, the tooth of the part 2 will emerge from the notch.

Figures 2 to 7 show the different positions of the tooth 7 relative to the notches of the wheel 1. When the cylindrical bearing 3 due to its eccentricity is opposite the wheel 1, the tooth 7 is completely clear of the notches : cf. Fig. 2. Gradually, when the shaft 4 will turn, the tooth, while remaining vertical, will move closer to the wheel and enter a notch: cf. Figs.3 and 4. When the shaft 4 has made a rotation of 180 ° and that the bearing 3 will be oriented towards the wheel 1, the tooth 7 will be entered at the maximum in the notch: cf. Fig.5. It may be noted that at this moment, a rotation of the axis 4 will cause a movement of the arm 2 on a circular trajectory but which will be tangent to a fictitious circle centered on the axis of rotation of the wheel 1 (this tangent being horizontal in the case of Figures 1 to 7). The circular movement of the tooth 7 and the circular motion of the notch of the wheel 1 will both be almost identical. The drive of the wheel 1 by the tooth 7 will therefore be with very little friction and therefore with a mechanical efficiency of almost 100%. It may also be noted that because of this transmission with little friction and the presence of a ball bearing or other or a sliding bearing at the shaft 4, if the shaft 4 is free to rotate and if we exert a torque on the wheel, the pressure force of the edge of the notch on the tooth 7 will cause rotation of the shaft 4. This feature will make possible the reversibility of the movement, that is to say the possibility of rotating the shaft 4 by rotating the wheel 1. The rotational speed is then multiplied by the number of notches of the wheel 1.

During the rotation of the shaft 4, the tooth 7 will emerge from the notch: cf. Figs 6 and 7. In this case, the wheel 1 is no longer driven by the arm 2 and it could therefore rotate freely about its axis 8. To avoid this and so that the wheel 1 is always positioned precisely by at least one tooth engaged in one of its notches, it is advantageous to stack at least three wheels 1 with notches mounted on the same axis and rigidly assembled, and at least three arms 2 each having at least one tooth 7 and driven by the shaft 4, and arrange them so that at any point of the rotation of the shaft 4, there is at least one tooth 7 engaged in a notch of a wheel 1.

Figure 8 shows such an arrangement. The wheel comprises three parts 1.1, 1.2, 1.3 which are assembled together in a fixed manner. It is mounted so as to rotate about its axis 8. The notches of the three parts 1.1, 1.2, 1.3 are shifted. The arms 2.1, 2.2, 2.3 for transmitting motion between the shaft 4 and the wheel 1 - namely three arms 2 described above - each comprise a tooth 7 and are each mounted on a respective eccentric bearing 3 of the shaft 4 These bearings 3 are angularly offset around the axis of rotation of the shaft 4 preferably so regular. Thus, they are shifted by about 120 ° in the case of a system with three teeth 7 and three wheels 1, of 90 ° in the case of a system with four teeth 7 and four wheels 1, etc. The value of the eccentricity to the axis of rotation of the shaft 4 is the same for the different bearings. The shaft 4 thus has a crankshaft shape with at least three bearings 3.1, 3.2, 3.3 as illustrated in FIG. 11. This is also the case of the secondary shaft 5 (this is visible for another embodiment of embodiment in Figure 23 where the bearings of the shaft 5 are referenced 3 M, 3 '.2, 3' .3). During the rotation of the shaft 4, each tooth will fit into a notch of the wheel that corresponds to it. When a tooth comes off its notch, another tooth from another room engages in the notch of the wheel facing it. For example, with a system with three teeth whose trajectories are offset by 120 °, it can be guaranteed that there will always be a tooth engaged in a notch of one of the wheels. And since at any time there will be a tooth engaged in a notch of the corresponding wheel, all three wheels will always be positioned in a determined manner. When the tree has made a turn, all three wheels will have turned the value of a notch. In the case where the wheels each have 100 notches, for a turn of the shaft 4 the wheel will have turned the value of a notch is 1/100 of a turn. The device then behaves like a speed reducer with a reduction ratio of 1/100.

The fact that the arms 2.1, 2.2, 2.3 are mounted on crankshaft bearings offset at the same angle causes the shaft 4 and the secondary shaft 5 to be mechanically connected and will rotate together in synchronism without any external device ensuring the constant orientation of the arms 2. It is also possible to use either one of the two shafts as drive shaft, and the other as a secondary shaft.

The amount of eccentricity of the crankshaft bearings on the shaft 4 and on the secondary axis 5 is accurately calculated so that the teeth are well in front of a notch when they come into contact with the wheel. Despite a very low eccentricity, for example 0.6mm for a gear ratio 1/100 with notched wheels diameter 100 mm, the fact that the moving parts are mounted with ball bearings, roller or needle or rings or plain bearings eliminates friction and allows reversibility. That is to say that if one exerts a torque on the wheels 1, it will cause a rotation of the shaft 4, if, of course, nothing is opposed to its movement.

It should be noted that the presence of at least three arms 2 mounted on the bearings 3 of the shaft 4 and also mounted on the bearings 3 'of the secondary shaft 5, because the bearings have an identical eccentricity on the two shafts, because these bearings are offset angularly relative to each other with angles less than 180 °, because these angular offsets are identical on the shaft 4 and the shaft secondary 5, allows a transmission of movement between the shaft 4 and the secondary shaft 5.

Arrangements of rooms other than that of Figure 8 are possible.

Figure 9 illustrates an embodiment where the wheel 1 has a series of notches aligned from top to bottom. So that there is always at least one tooth engaged in a notch, the teeth 7 of the arms 2 are offset laterally depending on the position of their bearings 3, as shown in FIG.

In FIGS. 12 and 13, for the sake of clarity, only a wheel, a tooth and an arm carrying the tooth have been drawn, but in fact there are at least three superimposed ones.

In Figure 12, the shaft 4 and the secondary shaft 5 are disposed equidistant from the wheel. The positions of the shafts 4 and 5 relative to the axis 8 of the wheel 1 have no influence on the operation, they can be arbitrary.

In Figure 13, the notches are inside a ring 11 which is hollow and the motor and secondary shafts are located inside said ring.

In all cases, the secondary shaft and shaft rotate in synchronism to ensure a constant orientation of the arms 2 which bear one or more teeth 7. And there are at least three superposed pieces 2 with at least three teeth and three wheels so that there is always a tooth engaged in a notch.

The fact that there is only one cutting operation and that it takes place on the outside of the wheels which is easily accessible, makes the manufacture of this type of reducer easier and therefore more economical.

Another possibility of construction consists in using a wheel 1 which is thinner and whose thickness is less than the total thickness of the arms 2 as in the embodiment illustrated by FIGS. 14 to 19. In this case, the teeth 7 of the three or more arms 2 fit into notches contiguous or adjacent to the wheel 1. The disposition of the teeth and the wheel can be seen in FIG. 19. FIG. 15 shows an exploded view, the parts not having to their place, but correctly oriented relative to each other. Each arm 2 has a tooth referenced respectively 7.1, 7.2, 7.3. Figure 16 shows the same parts in their place in the reducer, their teeth being nested so that the three teeth are well in front of the notches of the wheel. The operating principle remains the same. The arms 2 are always in rotation guided by the rolling bearings. The teeth of the three arms 2 enter the notches of the wheel so that at least one tooth is always engaged in a notch of the wheel. Figure 17 shows one of the side arms 2, and the tooth protrudes upward in this case. Figure 18 shows the three arms 2 assembled, and in the central part, that is to say in the area that includes the thickness of the piece 2.2 of the medium, the three teeth are present. It is in this area that the teeth will return in the notches of the wheel. Figure 19 shows the three teeth facing three adjacent slots of the wheel. This construction with a thinner wheel will be simpler to manufacture, so cheaper. It will also be lighter.

More generally, the device has the following preferred characteristics. The shaft 4 and the secondary shaft 5 have at least three bearings 3 with the same eccentricity, and the bearings are spaced apart from each other, about the axes of rotation of their shafts, by angles less than 180 °, allowing the transmission of the rotational movement of the shaft 4 to the secondary shaft 5. The shaft 4 and the secondary shaft 5 are held in a specific position, in the same mechanical assembly, by ball bearings, roller or needle, or rings or plain bearings, so that their axes are parallel and they can rotate about their axis, the shaft 4 is connected to a source of mechanical energy and the secondary shaft 5 is not connected The speed reducer comprises at least three arms 2, the shape of the teeth, in relief, corresponds to the shape of the notches, recessed, of the movable member. The speed reducer comprises at least three arms 2 whose teeth 7 can engage in notches of a movable member 1, the angular offset of the bearings of the shaft 4 and the secondary shaft 5 implies that for all angle of rotation of the shaft 4, there is at least one tooth of an arm 2 engaged in a notch of the movable member 1. According to another embodiment, the wheel 1 is replaced by a rack as is illustrated in FIG. 20. In this case, a rotary movement of the shaft 4 is transformed into a linear movement of the rack. When the shaft 4 turns, the relative position of the motor with respect to the rack will be displaced by the value of the distance between two notches of the rack.

According to another embodiment illustrated by FIGS. 21 to 23, the arms - cf. 2.1, 2.2, 2.3 - may have many teeth that correspond to the notches of the wheel 1. As for the previous embodiments, the teeth of the arms gradually engage in the notches of the wheel and provide continuity in the positioning of the wheel. The position of the teeth on the arms is such that they are arranged in a circular manner, which would correspond to a portion of a crown that would have a diameter -preferentially identical for each arm -a little larger than the diameter of the organ mobile. For example, if the movable member, which comes here as a wheel, has 60 notches on its periphery, then the teeth of the arms would form a portion of a ring having 61 teeth arranged on a diameter a little larger than that of the wheel, in a ratio of 61 divided by 60. The device will have in this case a reduction ratio of 1/60. When the motor shaft makes a turn, a shift occurs and the same tooth will not reengage in the same notch of the wheel, but in another notch offset one or more notches from the original one. The direction of the offset is related to the direction of rotation of the trees 4 and 5. Fig. 21 shows the three arms 2.1, 2.2, 2.3 mounted on the shafts 4 and 5 and whose multiple teeth are, in certain positions, engaged in the notches of the wheel 1. Fig. 22 shows the three arms 2.1, 2.2, 2.3 mounted on the shafts 4 and 5, but here the wheel is not shown so as to reveal the plurality of teeth on the arms. Figure 23 shows the shafts 4 and 5 without the wheel 1 and the arms 2 to show the eccentricity of the bearings 3.1, 3.2, 3.3 of the shaft 4 and bearings 3'.1, 3'.2, 3 '. 3 and their identical arrangement on the shafts 4 and 5. The operation of the teeth, in this embodiment is similar to that of a gear comprising a complete ring gear with an internal toothing and meshing with a wheel having a number of teeth slightly smaller. In this case, the shape of the most suitable teeth is similar to that of involute gears, whereas when the arms have only one tooth, their shape is preferentially square. The advantages of this embodiment with many teeth are:

a better progressivity of the transmission of the force since several teeth are in contact with their corresponding notches at the same moment;

a limitation of the friction, since at any moment there is a tooth completely engaged in its notch and that at this moment their trajectories are tangent;

a homokinetic transmission whereas in the case of a one-tooth gearbox, there is a slight difference in transmission ratio between the motor where a tooth comes into contact with its notch and the moment when it is completely engaged, because that the trajectory of the tooth and that of the notch are not tangent at the moment of their contact, while their trajectory are tangent when the tooth is fully engaged in the notch;

- Compared to a cycloid reducer, the one described above allows to use a hollow output shaft of large diameter, which allows to pass cables and pipes that will be subject to minor movements during the rotation of the output shaft of the gearbox only if they were placed away from the axis of rotation;

in this embodiment, the operation of machining the teeth of the arms is facilitated because the access of bulky tools such as grinding wheels is possible on a crown portion while it is not for a complete crown.

It is also possible to increase the number of teeth of the arms until making a complete crown. This embodiment is illustrated in FIGS. 24 and 25. The most advantageous arrangement then consists in placing the shafts 4 and 5 at a distance from each other on each side of the wheel 1. The large distance between the shafts will guarantee good stability. In this embodiment, the arms 2.1, 2.2, 2.3 are always in engagement with the wheel 1. This embodiment provides the same advantages as the embodiment of FIG. 21 in an even more pronounced manner: - very good progressivity;

- very good resistance to wear since teeth of each arm are engaged permanently;

homokinetic transmission;

- hollow shaft of large diameter;

the motor shaft and the secondary shaft are remote from the axis of the output shaft and it is possible to support them by bearings at both ends, which improves their rigidity. This is not possible for cycloid type reducers whose outer ring is in the form of a bell.

Devices with one or two arms mounted on shafts with eccentric bearings are known. For example, FR 2,833,673 A1 discloses a device where there is only one ring mounted on two eccentric and whose movement in synchronism is provided by three toothed wheels. The use of gear wheels which have by construction a game necessary for their operation that the gear as a whole has a relatively large game. The advantage of the present invention comes from the use of three or more arms and bearings shifted by less than 180 ° which ensure the identity of the movement between the two shafts without additional device such as gears or transmissions by wheels and belts, and which have an excellent accuracy because of the game of operation can be very low since this game can come only bearings or bearings.

In another embodiment which is opposite to that of FIGS. 24 and 25, the arms each consist of a toothed wheel having teeth distributed over their entire outer circumference to engage the notches of a movable member made in the form of a crown. inside which the notches are distributed circumferentially. Each of the wheels is thus mounted on a first eccentric bearing of the shaft 4 and a second eccentric bearing of the shaft 5 so as to remain parallel to itself regardless of the angle of rotation of the shafts 4, 5.

In general, it will be noted that embodiments using no ring gear both for the arms and for the movable member - which can then be in the form of a toothed wheel or rack - allow a very easy manufacturing. This ease of manufacture is further increased in the case where the arms 2 each have only one tooth 7 or a limited number of teeth 7.

Of course, the present invention is not limited to the examples and to the embodiment described and shown, but it is capable of numerous variants accessible to those skilled in the art.

According to another aspect, the invention also proposes a device for transmitting motion, comprising:

a shaft rotatably mounted about its longitudinal axis, a movable member having a succession of notches,

a plurality of arms for transmitting together motion between the shaft and the movable member,

in which :

each arm is articulated on an eccentric bearing relative to an axis about which the bearing is rotatably mounted, the bearing and the shaft being linked together to rotate in synchronism,

the movable member and each arm are mechanically guided so that the arm describes a cyclic movement for each revolution of the eccentric bearing on which it is articulated, the cyclic motion comprising successively:

a phase during which certain teeth of the arm are free to grip with the movable member, and

a phase during which these same teeth of the arm are engaged with the movable member by engagement of the at least one tooth of the arm with a notch of the movable member so that the displacement of the one causes the displacement of the other, wherein the eccentric bearings are angularly offset about their axis relative to one another so that there is at least one arm engaged with the movable member regardless of the rotation angle of the shaft and wherein each arm has an element for mechanically guiding the arm together with the bearing on which the arm is mounted during all the cyclic movement.

The angular offset eccentric bearings and the use of the same element of the arm used to guide it mechanically throughout the cyclic movement together with the bearing on which it is mounted has several advantages. It makes it possible to simplify in particular the member for transmitting motion between the shaft and the movable member by not requiring it to have three radial arms as in the case in EPI 55497. In addition, the movable member may be different. a crown with internal teeth as is the case in US 5,351,568, DE 312164 and EP155497.

According to preferred embodiments, the invention according to this aspect further comprises the following features:

each arm is mechanically guided by a nipple sliding in a slot or a groove during all the cyclic movement;

the eccentric bearings are arranged on the shaft;

the angular offset between any two successive stages is less than 180; the bearings are staggered angularly with each other regularly around their axis of rotation; the at least one tooth of the arms cooperate with the same succession of notches, the movable member has several successions of notches arranged side by side, the notches of each being offset from the notches of the other and the at least one tooth each arm cooperating with another of the successions of notches;

the arms are mounted on the bearings by ball or needle bearings or plain bushings;

the movable member is a rack guided in translation;

the movable member is a wheel rotatably mounted about its central axis and on which the notches are arranged circumferentially;

the movable member is a ring rotatably mounted about its central axis and inside which the notches are arranged circumferentially;

the device forms a speed reducer whose shaft is the input and whose reduction ratio is preferably at least 1/50.

The device of the invention according to this aspect can also advantageously be used to transmit the rotary movement of a motor to a joint of a robot arm or to move an element of a machine from the rotary movement of an engine .

Claims

A motion transmission device, comprising:

a shaft (4) rotatably mounted about its longitudinal axis,

- a movable member (1; 11; 12) having at least one succession of notches, at least three arms (2.1, 2.2, 2.3) for transmitting together the movement between the shaft and the movable member,

in which :

each arm is provided with at least one tooth (7) to cooperate with the notches of the movable member,

each arm is articulated on a first bearing (3.1; 3.2; 3.3) eccentric with respect to a first axis (9) around which the bearing is rotatably mounted, the first bearing and the shaft (4) being interconnected to rotate in synchronism, the movable member (1) and each arm are mechanically guided so that:

the arm is in engagement with the movable member during at least part of the cyclic movement by engagement of the at least one tooth of the arm with a notch of the movable member so that the displacement of the one causes the displacement of the other,

in which the first bearings (3.1; 3.2; 3.3) are arranged so that there is at least one arm (2.1, 2.2, 2.3) engaged with the movable member regardless of the angle of rotation of the shaft and wherein each arm is further hinged to a second eccentric bearing (3 ') with respect to a second axis (10) about which the second bearing is rotatably mounted to maintain the arm parallel to itself regardless of the angle of rotation of the shaft (4).

2. Device according to claim 1, wherein the cyclic movement of each arm (2.1, 2.2, 2.3) comprises successively:

a phase during which the arm is free to grip with the movable member, and o a phase during which the arm is engaged with the movable member by engagement of the at least one tooth of the arm with a notch of the movable member so that the displacement of one causes the movement of the other.

3. Device according to claim 1 or 2, wherein the first bearings (3.1;

3.2; 3.3) are arranged on the shaft (4) and the second bearings (3 ') are arranged on the same second shaft (5).

4. Device according to any one of claims 1 to 3, wherein the first bearings (3), respectively the second bearings (3 '), are angularly offset from each other about their respective axis of rotation (9; 10).

5. Device according to claim 4, wherein the angular offset between any first two successive bearings, respectively any second two successive stages, is less than 180 °, the first bearings, respectively the second bearings, being preferably angularly offset from each other. in a regular manner around their respective axis of rotation (9; 10).

6. Device according to any one of claims 1 to 5, wherein the at least one tooth of the arms cooperate with the same succession of notches.

7. Device according to any one of claims 1 to 5, wherein the movable member has several successions of notches (1.1, 1.2, 1.3) arranged side by side, the notches of each being offset from the notches of the other and the at least one tooth of each arm (2.1, 2.2, 2.3) cooperating with another of the successions of notches.

8. Device according to any one of claims 1 to 7, wherein the arms are mounted on the first bearings and the second bearings by ball bearings, roller or needle or rings or plain bearings.

9. Device according to any one of claims 1 to 8, wherein the movable member is either a rack (12) guided in translation or a ring (11) rotatably mounted about its central axis and inside. from which the notches are circumferentially arranged.

10. Device according to any one of claims 1 to 8, wherein the movable member is a wheel (1) rotatably mounted about its central axis (8) and on which the notches are arranged circumferentially.

11. Device according to claim 10, wherein the arms each have a plurality of teeth arranged on a circular portion so as to form a ring gear portion.

12. Device according to claim 10 or 11, wherein the arms each have a plurality of teeth so that the operation of the teeth is similar to that of a gear comprising a complete crown with an internal toothing and meshing with the wheel having a smaller number of teeth.

13. Device according to claim 10, wherein each arm comprises a ring gear inside which are distributed teeth over its entire circumference to cooperate with the notches of the movable member, each tooth being successively engaged, then disengaged in a notch of the movable member during the cyclic movement of the arm.

14. Device according to any one of claims 10 to 13, which forms a speed reducer whose shaft (4) is the input and whose reduction ratio is preferably at least 1/50.

15. Use of a device according to any one of claims 1 to 14 for transmitting the rotary motion of a motor to a joint of a robot arm or for moving an element of a machine from the rotary motion of a machine. 'a motor.