Joint for making a robotic arm

Abstract

A joint for the construction of a robotic arm consisting of a plurality of segments (1, 10) mated to each other, having opposite ends in mutual engagement and longitudinal grooves (8) for control cables (6), has: a pair of helical tooth sectors (11, 12, 101, 102) obtained in each of the opposite ends of said segments (1, 10), for the articulation of a segment with the mating segment, each helical tooth sector (11, 12, 101, 102) having an axis of rotation; a pair of mechanical retaining members, for the rotary coupling of the helical tooth sectors (11, 12, 101, 102) of mating segments; a plurality of pulley pins (4) orthogonally integral with the helical tooth sectors (11, 12, 101, 102), and a plurality of pulleys (5) supported by said pins (4) per pulley; control cables (6), running along said longitudinal grooves (8) and on said plurality of pulleys (5).

Description

Description Title of Invention: JOINT FOR MAKING A ROBOTIC ARM |Technical Field

[0001] The present invention relates to a joint for making a robotic arm. In particular, the invention concerns a mechanical joint that allows the mutual rotation of two distinct robotic arm segments. The operating principle of the mechanical joint is based on the rolling of two mutually tangent circles belonging to said two distinct segments.Background Art

[0002] This operating principle is already present in the prior art.

[0003] EP3459473A1 describes a medical instrument whose robotic arm has a terminal segment supporting a plier-shaped tool, the terminal segment and the plier-shaped tool being equipped with pairs of interlocking teeth facing each other. The teeth of each pair are separated by a groove, into which a web of the tool is at least partially inserted. This web is intended to stabilize or guide the tool during its rotation. The teeth are straight-toothed, and the terminal segment and plier-shaped tool are held together by external control cables. The web and the external control cables make the joint bulky and are unreliable in granting stability to the joint. The joint is only intended to connect the robotic arm to the plier- shaped tool.

[0004] A robotic arm with a terminal segment and an end tool, shaped like a gripper, both being equipped with respective narrow, mutually engaged, straight-toothed segments, facing each other, is disclosed in US 7101363 B2. According to this patent, the connection between the terminal segment and the tool is stabilized by external connecting rods mounted on the axes of connecting pulleys: this arrangement makes the joint cumbersome. As with the first document cited, the joint is only provided for the connection of the robotic arm to the tool.

[0005] US 2014 / 0257331 A1 describes laparoscopic surgical devices including a first member having a first gear, a second member having a second gear corresponding to the first gear, a connection member configured to connect the first member and the second member; first and second wire mounting pieces respectively at the first and second members, a first wire wound on the first wiremounting pieces so as to be pulled upon receiving a first drive force; and a second wire wound on the second wire mounting pieces so as to be pulled upon receiving a second drive force. The drive unit is configured to selectively transmit the first and second amplified driving forces to a respective one the first member and the second member to cause tilting of the first member and the second member.

[0006] US 2016 / 0051274 A1 discloses a device having a shaft, a tool portion including a first arm and a second arm, and a split rolling joint including a first curved portion and a second curved portion. The second curved portion may be coupled to the shaft. The first curved portion may include a first split portion and a second split portion. The first split portion may be coupled to the first arm. The second split portion may be coupled to the second arm. At least one of the first split portion and the second split portion may be configured to roll with respect to the second curved portion such that at least one of the first arm and the second arm can move towards or away from each other.Summary of Invention

[0007] An object of the invention is to provide a robotic arm joint capable of compensating for axial forces, i.e. , those acting along the joint's rotation axis, without requiring the use of arrangements and means to keep aligned the teeth.

[0008] A further object of the invention is to provide a robotic arm joint with a central opening for the passage of cables in order to reach a terminal tool mounted on the tip of the robotic arm.

[0009] Yet another object of the invention is to provide a joint that allows the robotic arm to be actuated with precision, in virtue of the purely rolling motion performed in the joint, i.e., without any sliding and with zero play.

[0010] Finally, another object of the invention is to reduce the size of a robotic arm joint and, therefore, its dimensions.

[0011] The objects are achieved by the invention, which discloses a joint for making a robotic arm consisting of a plurality of interconnected segments, having opposite ends in mutual engagement and longitudinal grooves for control cables, the joint being characterized by comprising:- at least one pair of helical toothed sectors obtained in each of the opposite ends of said segments, for articulating a segment with the mated segment, each helical toothed sector having an axis of rotation,- a pair of mechanical retaining members, for the rotary coupling of the helical toothed sectors of mated segments,- a plurality of pulley pins orthogonally integral with the helical toothed sectors, and a plurality of pulleys supported by said pulley pins, and- driving wires, running along said longitudinal grooves and on said plurality of pulleys.Brief Description of Drawings

[0012] Further characteristics and advantages of the present invention will become most clear from the indicative, and therefore non-limiting, description of embodiments of a joint to be used in a robotic arm as illustrated in the accompanying drawings in which:

[0013] [Fig.1 ] Figure 1 is a plan view of a first embodiment of a joint according to the present invention;

[0014] [Fig.2] Figure 2 is a cross-section view along the lines A-A in Figure 1 ;

[0015] [Fig.3] Figure 3 is a plan view similar to that one in Figure 2, but with robotic arm sectors being rotated;

[0016] [Fig.4] Figure 4 is a schematic top view wherein the joint in Figure 1 has parts removed;

[0017] [Fig.5] Figure 5 is a central cross-sectioned perspective view of the joint in Figure 4;

[0018] [Fig.6] Figure 6 is a diagrammatic enlarged view of a central part of the crosssectioned zones in Figure 5 to highlight the forces acting between the herringbone or V-shaped teeth of the joint sectors;

[0019] [Fig. 7] Figure 7 is a perspective centrally cross-sectioned view of Figure 4;

[0020] [Fig. 8] Figure 8 is a diagrammatic perspective view of a robotic arm made with a plurality of joints according to the first embodiment of the present invention;

[0021] [Fig. 9] Figure 9 is a partial diagrammatic perspective view of a robotic arm that uses joints according to the first embodiment of the present invention and a plier-shaped tool;

[0022] [Fig. 10] Figure 10 is a longitudinal cross-section view of a second embodiment of a joint according to the present invention;

[0023] [Fig. 11] Figure 11 is a longitudinal 90° rotated cross-section view of the joint in Figure 10;

[0024] [Fig. 12] Figure 12 is a 45° rotated view of a joint with helicoidal teeth sectors of the second embodiment;

[0025] [Fig. 13] Figure 13 is a side view corresponding to the cross-section in Figure 11 ;

[0026] [Fig. 14] Figure 14 is a side view corresponding to the that one in Figure 12;

[0027] [Fig. 15] Figure 15 is a left side view of the joint in Figure 14;

[0028] [Fig. 16] Figure 16 is a cross-section according to the lines B-B in Figure 15; and

[0029] [Fig. 17] Figure 17 is a cross-section according to the lines C-C in Figure 15.Description of Embodiments

[0030] Reference is initially made to Figures 1 and 2, which are a plan view of a first embodiment of a joint according to the present invention and, respectively, a section taken along lines A-A in Figure 1.

[0031] As shown below, a joint for the construction of a robotic arm is made up of a plurality of interconnected segments indicated by 1 and 10. The robotic joint segments have shapes and sizes that vary according to their functions; here they are represented as simple cylindrical portions. According to the invention, the joints have opposite ends that are mutually engaged by a pair of sectors 11 , 12, and 101 , 102. These sectors have helical teeth and are formed respectively in each of the opposite ends of the segments 1 , 10. The sectors 11 , 12, and 101 , 102 allow the articulation of the segment 1 with the conjugated segment 10 and therefore allow the rotation with one degree of freedom of the segment 1 and segment 10 around rotation axes corresponding to those of the connecting rodpins 2, 20. The connecting rod pins 2, 20 are inserted into through holes formed transversely in the respective sectors 11 , 12, and 101 , 102. The connecting rod pins 2, 20 are connected at their ends by a pair of opposite external connecting rods 3, 30, functioning as mechanical retaining members.

[0032] See also Figure 4, which is a schematic top view with parts removed of the joint shown in Figure 1 . In Figure 4, the connecting rods 3, 30 are replaced by the forces F, F', and F", F'", reciprocally exchanged along them.

[0033] The helical toothed sectors 11 , 12 of the robotic arm segment 1 have herringbone or V-shaped teeth 33 designed to engage with the herringbone or V- shaped teeth 34 of the helical toothed sectors 101 , 102 of the mating segment 10.

[0034] The helical toothed sectors 11 , 12, 101 , 102 are coupled to each other by the connecting rod pins 2, 20 and the connecting rods 3, 30, not shown in Figure 4 because they have been replaced by the arrows F, F' and F", F'", as mentioned above.

[0035] Figure 4 also shows a plurality of pulley pins, generally indicated by 4. The pulley pins 4 are integral with the helical toothed sectors 11 , 12, and 101 , 102 and are parallel to the connecting rod pins 2, 20. The pulley pins 4 support a plurality of pulleys, generally indicated as 5. Control cables or tendons, generally indicated as 6, run across the plurality of pulleys 5. The pulleys 5 and the control cables 6, shown in more detail below, allow the mutual rotation of the robotic arm segments 1 , 10 thanks to the helical toothed sectors 11 , 12 and 101 , 102, preferably herringbone-shaped, as shown in Figure 3, which is a plan view similar to Figure 2, but with the robotic arm segments rotated.

[0036] Connecting rods 3, 30 are used to ensure the correct compression of the two segments 1 , 10. Their function is to keep compact the two main bodies during motion. In the actuation of the joint, connecting rod 3 describes a circumference of radius R, where R equals the center distance of the two pins 2, 20. This distance remains unchanged by virtue of the pure rolling motion principle imparted to the joint.

[0037] Reference is made also to Figures 5 and 6, which are a centrally sectioned perspective view of the joint in Figure 4 and, respectively, an enlarged schematicview of a central portion of the sectioned areas in Figure 5 to highlight the forces acting between the herringbone teeth, for example, of sectors 12 and 102 of the joint. The herringbone teeth are not marked with a reference number. The arrows, generically indicated as G, schematically indicate the forces exchanged between the teeth. The perfectly balanced G-forces, thanks to the herringbone shape of the teeth, allow for a joint that does not require additional support elements for the toothed sectors.

[0038] Figure 7 shows a perspective centrally cross-sectioned view of Figure 4. The mating segments 1 , 10 have respective helical toothed sectors 11 , 101 machined as a single piece with the respective mating segments 1 , 10 of the robotic arm.The rotation axis coincides with the axis of the pins 2, 20 per connecting rod. The connecting rods are not visible in Figure 7. The pins 2, 20 pass through holes generally indicated as 7, machined in sectors 11 and 101.

[0039] The pulley pins 4, integral with the helical-toothed sectors 11 , 101 , parallel to the connecting rod pins 2, 20, support the pulleys 5, on which the control cables 6 run, passing along grooves machined in the segments 1 , 10 of the robotic arm. These grooves are generically indicated as 8. The control cables 6 are operated in a conventional manner that requires no further explanation.

[0040] From the preceding description, it is clear that the choice of using a pair of helical-toothed sectors in the joint between mating segments creates a gap between the mating segments that allows the passage of cables or similar in the middle of the joint.

[0041] The choice of herringbone or V-shaped teeth ensures pure rolling motion, that avoids sliding between the contact surfaces, and the absence of backlash in the gear, as well as prevents relative translation between the connected parts without requiring other restraints.

[0042] The actuation system chosen for the tendon-type joint movement using control cables provides a lightweight structure for the joint and the robotic arm into which the joint is integrated. The aforementioned joint characteristics are reflected in the actuation system, with the absence of backlash in the transmission, the precision of actuation, and the rigidity of the joint itself, as well as its resistance to loads.

[0043] The actuation system for the single joint consists of a pair of tendons or control cables that are passed through the joint itself through a winding system.

[0044] The use of pulleys allows for the amplification of the input force, which is primarily used for the actuation of a robotic joint.

[0045] The first embodiment features a set of three pulleys, six for each degree of freedom, capable of providing a mechanical advantage equal to a factor equal to the number of tendon sections, considering the arrangement shown in Figure 7.

[0046] This configuration allows for lifting a load that is four times heavier than the applied force, effectively illustrating the practical application of mechanical advantage through the use of pulleys. This allows for significant energy savings and greater efficiency in heavy lifting operations, making the system particularly useful in industrial and engineering applications.

[0047] Overall, the joint is extremely lightweight, highly precise, and robust, as well as resistant to high loads in proportion to the implemented actuation system. The joint according to the present invention can be integrated into any robotic solution that requires lightweight and electronics protection.

[0048] The joint construction is compatible with additive 3D printing techniques such as SLA and DMSL, which also use less robust materials, such as PLA (polylactic acid bioplastic) and PETG-CFR (carbon fiber-reinforced polyethylene terephthalate).

[0049] Figures 8 and 9 show, by way of example, applications of the joint according to the present invention in robotic arms.

[0050] Specifically, Figure 8 is a schematic perspective view of a robotic arm constructed with a plurality of joints according to the present invention, and Figure 9 is a partial schematic perspective view of a robotic arm using joints according to the present invention and a plier-shaped tool.

[0051] Reference is made now to Figures 10 and 11 , which are longitudinal sections, rotated 90° relative to each other, of a second embodiment of a joint according to the present invention. In this embodiment, a single joint is shown between an end portion 200 of a robotic arm and an adjacent portion 201 . In Figures 10 and 11 , it is sufficient to note that the same helical tooth sectors indicated by 202 and 203are used in mutual engagement. To enable this engagement, actuation tendons 13 and 130 and compression tendons 14, 140 are used as mechanical retaining members. The drive tendons 13, 130, which are controlled by the adjacent portion 201 , allow rotation of the end portion 200 to which they are attached. The compression tendons 14, 140 hold the helical toothed sectors 202, 203 together, performing a function similar to that of the connecting rods 3, 30 of the first embodiment. The compression tendons 14, 140 wrap around pins generally indicated as 15 in Figure 12, which is a 45° rotated view of a joint with helical toothed sectors of the second embodiment. The helical toothed sectors identical to those of the first embodiment are indicated as 11 , 12, 101 , and 102.

[0052] Reference is made now to Figure 15, which is a left side view of the joint in Figure 14, and to Figures 16 and 17, which are sections along lines B-B and C-C of Figure 15, respectively. There are shown the actuation tendon 13, and compression tendons 16, 160, which are formed in a ring, unlike the compression tendons 14, 140 described above.

[0053] The second embodiment of the joint serves to demonstrate that the mechanical holding member can be designed as a simple ring, useful for replacing a connecting rod that is undoubtedly heavier and, therefore, less advantageous for the robotic arm.

Claims

Claims

1. . A joint for making a robotic arm consisting of a plurality of segments (1, 10) that are mated to each other, the segments having opposite ends in mutual engagement and longitudinal grooves (8) for driving wires (6), the joint being characterised in that it comprises:- at least one pair of helical toothed sectors (11, 12, 101, 102) obtained in each of the opposite ends of said segments (1, 10), for articulating a segment with the mated segment, each helical toothed sector (11, 12, 101, 102) having an axis of rotation,- a pair of mechanical retaining members, for the rotary coupling of the helical toothed sectors (11, 12, 101, 102) of mated segments,- a plurality of pulley pins (4) orthogonally integral with the helical toothed sectors (11, 12, 101, 102), and a plurality of pulleys (5) supported by said pulley pins (4), and- driving wires (6), running along said longitudinal grooves (8) and on said plurality of pulleys (5).

2. 2. The joint according to claim 1, wherein each helical tooth sector (11, 12, 101, 102) has herringbone or V-shaped teeth (9) suitable for engaging with the herringbone or V-shaped teeth (9) of the helical toothed sector (11, 12, 101, 102) of the mated segment.

3. 3. The joint according to claim 1, wherein the helical toothed sectors obtained in the opposite ends of said segments (1, 10) are two and are coupled to each other by means of said pulley pins (4).

4. 4. The joint according to claim 1 wherein the pair of mechanical retaining members is represented by a pair of connecting rods (3, 30) and connecting rod pins (2, 20) passing along said rotation axis of each toothed sector (11, 12, 101, 102), for the rotary coupling of the helical toothed sectors (11, 12, 101, 102) of mated segments.

5. 5. The joint according to claim 1 wherein the pair of mechanical retaining members is represented by a pair of compression tendons (14, 140;16, 160) placed along the contact direction of the helical toothed sectors (11, 12, 101, 102) of mated segments.

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