WO2017144954A1 - Six degrees of freedom parallel mechanism - Google Patents

Six degrees of freedom parallel mechanism Download PDF

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Publication number
WO2017144954A1
WO2017144954A1 PCT/IB2016/051066 IB2016051066W WO2017144954A1 WO 2017144954 A1 WO2017144954 A1 WO 2017144954A1 IB 2016051066 W IB2016051066 W IB 2016051066W WO 2017144954 A1 WO2017144954 A1 WO 2017144954A1
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WO
WIPO (PCT)
Prior art keywords
plurality
linkages
joints
parallel mechanism
joint
Prior art date
Application number
PCT/IB2016/051066
Other languages
French (fr)
Inventor
Mohsen AFROUGH
Original Assignee
Afrough Mohsen
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Publication date
Application filed by Afrough Mohsen filed Critical Afrough Mohsen
Priority to PCT/IB2016/051066 priority Critical patent/WO2017144954A1/en
Publication of WO2017144954A1 publication Critical patent/WO2017144954A1/en

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    • BPERFORMING OPERATIONS; TRANSPORTING
    • B25HAND TOOLS; PORTABLE POWER-DRIVEN TOOLS; MANIPULATORS
    • B25JMANIPULATORS; CHAMBERS PROVIDED WITH MANIPULATION DEVICES
    • B25J9/00Programme-controlled manipulators
    • B25J9/003Programme-controlled manipulators having parallel kinematics
    • B25J9/0063Programme-controlled manipulators having parallel kinematics with kinematics chains having an universal joint at the base

Abstract

The parallel mechanism herein comprises a base portion, a moving bracket, and a plurality of at least three linkages each consisting of an upper arm, a lower arm and a universal joint 15. Where one end of the plurality of the linkages are connected to the base portion through a plurality of double revolute joints and the other ends are connected to the moving bracket through a plurality of universal joints or double revolute joints. The mechanism makes it possible to attain the dexterity of six degree of freedom positioning of the moving bracket with respect to the base portion, in spite of the limited number of only at least three linkages. Higher dexterity of the mechanism allows its application in further additional tasks like robotic assembly cells, welding of complex form work objects, surgery robots and, material handling of objects with complex shapes.

Description

Six Degrees of Freedom Parallel Mechanism

The present invention relates to parallel mechanisms and in particular to a six degrees of freedom parallel mechanism that can provide quick and precise manipulation capabilities.

There is always a demand for increasing speed and accuracy of industrial robots. Parallel mechanisms have been a good candidate for development of fast industrial robots. In a conventional parallel mechanism, a moving bracket is connected to a base portion through a plurality of linkages. The actuators of a parallel mechanism can be located on the stationary base portion. Since the actuators are not placed on the linkage joints. The mass of the moving parts of the mechanism can be lowered resulting in high speed of movement.

The earliest parallel mechanisms included six parallel linkages with linear actuators that could position a bracket with six degrees of freedom. Later, more variations of parallel mechanisms have been developed that include rotary actuators and comprise three or more parallel linkages.

Lowering the number of parallel linkages not only reduces the problems of interference or collision of linkages, but also decreases the mass of the moving parts. This allows faster movements. However, by decreasing the number of linkages, also the number of degrees of freedom of the mechanism reduces. This results in less dexterity of the robot. While three or four degrees of freedom are enough for most of pick and place tasks, there are many applications that require more dexterity.

There have been solutions for increasing the dexterity of the robot for example by providing additional degrees of freedoms through adding additional motors on the moving bracket or by adding a rotating shaft to transfer additional rotation to the end effector or by adding additional mechanisms to the main configuration of the parallel mechanism.

The present invention provides a solution for attaining dexterity of full six degrees of freedom in a parallel mechanism with only at least three linkages. In this regard, both advantages of a reduced number of linkages and higher dexterity of the robot based on this mechanism are achieved.

The present invention provides a parallel mechanism comprising only three or more parallel linkages which enables positioning of a bracket with six degrees of freedom. Therefore, the mechanism provides high dexterity by enabling six degrees of freedom positioning of the bracket. Since the number of linkages can be lowered down to three linkages, the mechanism provides the advantages of low number of linkages including less conflict of the linkages and faster movement due to less mass of moving parts. In this way the mechanism provides both the advantages of reducing the number of linkages and dexterity of six degrees of freedom mechanisms.

The parallel mechanism consists of a fixed portion, a moving bracket, a plurality of at least three linkages each comprising two arms connected to each other through a plurality of universal joints. The plurality of linkages are connected to the fixed portion through a plurality of double perpendicular axes revolute joints. The other side of the plurality of the linkages are connected to the moving bracket through double perpendicular revolute joints or a universal joint.

Rotary actuators can be connected to the revolute joints on the fixed portion. The embodiment enables positioning of the bracket with three translational and three rotational degrees of freedom with respect to the fixed portion. A key difference between the present invention and conventional parallel mechanisms is that here each linkage possesses two rotatory actuators. Two motors can be connected to each linkage at the fixed portion that insert not only a rotational but also a torsional torque on each linkage. As a result, a sum of only three linkages is enough for providing six degrees of freedom.

These and other aspects of the embodiments herein will be better understood when considered in conjunction with the following description and the accompanying drawings. It should be understood, however, that the following descriptions, while indicating preferred embodiments and numerous specific details thereof, are given by way of illustration and not of limitation. Changes and modifications may be made within the scope of the embodiments herein without departing from the spirit thereof, and the embodiments herein include all such modifications.

Lowering the number of parallel linkages not only reduces the problems of interference or collision of linkages, but also decreases the mass of the moving parts. This allows faster movements. However, by decreasing the number of linkages in conventional parallel mechanisms, also the number of degrees of freedom of the mechanism reduces. This results in less dexterity of the robot. While three or four degrees of freedom are enough for most of pick and place tasks, there are many applications that require more dexterity.

The present invention provides a solution for attaining dexterity of full six degrees of freedom in a parallel mechanism with only at least three linkages. In this regard, both advantages of a reduced number of linkages and higher dexterity of the robot based on this mechanism are achieved.

A key difference between the present invention and conventional parallel mechanisms is that here each linkage possesses two rotatory actuators. Two motors can be connected to each linkage at the fixed portion that insert not only a rotational but also a torsional torque on each linkage. As a result, a sum of only three linkages is enough for providing six degrees of freedom.

This mechanism provides both advantages of reduced number of linkages and higher dexterity of the robot based on this mechanism.

The reduced number of linkages results in decreasing the mass of the moving parts so that higher accelerations and faster motion are attainable. In the same time interference or collision of the linkages is reduced which provides more flexibility of the mechanism and better accessibility of the workspace.

The higher dexterity of the robot based on this mechanism due to full six degrees of freedom positioning of the moving bracket, enables application of the robot in various tasks which require higher dexterity, like assembly tasks, welding tasks, surgery etc.

Fig.1

shows a schematic view of general configuration of the parallel mechanism according to the first embodiment.

Fig. 2

shows a schematic view of general configuration of the parallel mechanism according to the second embodiment.

Fig. 3

shows a schematic view of general configuration of the parallel mechanism according to a modification of the first embodiment with Persian joints on each linkage and Cardan joints for connection of the linkages to the moving bracket. Six motors are connected to the revolute joints on the base portion that enable six degrees of freedom positioning of the moving bracket.

Fig. 4

shows a partial view of the mechanism showing the placement of actuators according to the configuration of Fig. 3.

Fig. 5

shows a schematic view of general configuration of the parallel mechanism according to another modification of the first embodiment with Persian joints on each linkage and Cardan joints for connection of the linkages to the moving bracket. Six motors are connected to the revolute joints on the base portion that enable six degrees of freedom positioning of the moving bracket.

Fig. 6

shows a partial view of the mechanism showing the placement of actuators according to the configuration of Fig. 5.

Fig. 7

shows a partial view of the mechanism illustrating an arrangement of the connection of the lower arms to the moving bracket using Cardan or double revolute joints with perpendicular joint axes.

In the following detailed description, a reference is made to the accompanying drawings that form a part thereof, and in which the specific embodiments that may be practiced are shown by way of illustration. These embodiments are described in sufficient detail in order to enable those skilled in the art to practice the embodiments and it is to be understood that the mechanical, logical or other changes may be made without departing from the scope of the embodiments. Therefore, the following detailed description is not to be taken in a limiting sense.

The various embodiments herein provide a parallel mechanism which allows positioning and moving a bracket with respect to a fixed portion hereinafter called base portion. A description of the embodiments is presented here with respect to the drawings of figures. In order to simplify the description, the same numbers are assigned to the components of embodiments in all figures.

The parallel mechanism consists of a fixed portion, a moving bracket, a plurality of at least three linkages each comprising two arms connected to each other through a plurality of universal joints. The plurality of linkages are connected to the fixed portion through a plurality of double perpendicular axes revolute joints. The other side of the plurality of the linkages are connected to the moving bracket through double perpendicular revolute joints or a universal joint.

As shown in Fig.1 and Fig. 2 a fixed base portion 11, is connected through rotary joints 12 and 13 to at least three linkages. The rotation axes of each pair of joints 12 and 13 of are configured perpendicular to each other. Each linkage comprises two arms, upper arm 14 and lower arm 16, which are connected to each other through a universal joint 15. The universal joint 15 can be a Cardan joint or Persian joint or other types of universal joint that allow transferring torsional rotations as well as the joint forces from upper arm 14 to lower arm 16. Each of lower arms 16 is connected through a universal joint 17 to the moving bracket 18. The universal joint 17 can be a Cardan joint or Persian joint or double revolute joints with perpendicular axes or other types of universal joint.

Rotary joints 12 and 13 on the base portion can be driven by rotary actuators. In this way each upper arm 14 can be driven by two rotary actuators. Unlike other conventional parallel mechanisms, here two actuators are connected to each linkage. Therefore each linkage possesses two independent joint rotations. And a combination of at least three linkages is enough for providing six independent joint rotations.

Fig. 3 shows a configuration of the parallel mechanism with the actuators connected to the joints on the base portion. Actuators 131 rotates the upper arm 14 about the joint 13. Actuators 121 are directly connected to joint 12 which results in rotation of upper arm 14 about its longitudinal axis. The actuator 121 is installed on the part 132 which also comprises joints 12 and 13. Since the part 132 rotates about the axis of joint 13, the actuator 121 also moves with it. In this way the actuator 121 is not fixed in this configuration.

A close view of the placement of actuators in this configuration is shown in Fig. 4. As shown actuator 131 rotates part 132 and therefore upper arm 14 about joint 13. In this way, the upper arm 14 rotates upward or downward. This movement pushes the joint 15 and accordingly the lower arm 16 up or down. Actuator 121 inserts a torsional torque on the upper arm 14. The torsional torque is transferred through universal joint 15 to the lower arm. In this way, each lower arm 16 receives two different motions: a translational motion according to the movement of joint 15 due to rotation of joint 13 and a torsional rotation about its longitudinal axis due to rotation of joint 12.

Another configuration for placement of the actuators on the base portion is shown in Fig. 5. In this configuration actuator 131 directly rotates the part 132 and therefore the upper arm about axis of joint 13. Whereas, the rotation of actuator 121 is transferred to the upper arm 14 via a combination of bevel gears 122 and 123. A close view of the placement of actuators in this configuration is shown in Fig. 6. The advantage of this configuration is that the actuator 121 is also fixed on the base portion. I this way both of the actuators are fixed on the base portion.

In both configurations of Fig. 3 and Fig. 5 each of the upper arms numbered 14 is connected to one of the lower arms numbered 16 through a universal joint numbered 15. The universal joint 15 in this figure is a Persian joint, however other types of universal joint can also be used here. Use of a constant velocity universal joint with a higher cross over angle like Persian joint as shown in Fig. 3 is advantageous in the sense that it allows higher bending angles between upper arm 14 and lower arm 16. In this way a larger working envelope and workspace for a robot based on this parallel mechanism can be attained. The lower arms are connected to the moving bracket 18 via double perpendicular rotary joints or Cardan joints numbered 17.

A close view of the moving bracket 18 and its connections to the plurality of lower arms is shown in Fig. 7. The connection to each of the lower arms comprises two revolute joints with perpendicular joint axes 171 and 172, which together comprise the Cardan joint 17.

Parallel mechanisms have already been used in design of fast pick and place robots. Regarding the dexterity of this invention, it can be used in various further additional tasks. Robotic assembly cells, welding of complex form work objects, surgery robots and, material handling of objects with complex shapes are examples of applications of this invention.

Patent Literature

European Patent “Parallel Mechanism” Patent No. EP2133181A2

European Patent “Parallel Mechanism” Patent No. EP2602068A1

European Patent “Parallel link robot system” Patent No. EP2623270A2

European Patent “Parallel Link Robot” Patent No. EP2789432A1

US Patent “Parallel Robot” Patent No. US5333514

US Patent “Parallel Mechanism” Patent No. US6330837

US Patent “Parallel Robot” Patent No. US8418579B2

US Patent “Parallel Robot” Patent No. US8424411B2

US Patent “Parallel Link Robot” Patent No. US20110097184A1

US Patent “Parallel Mechanism having Three Dimensional Translation and One Dimensional Rotation” Patent No. US20120227532A1

US Patent “Universal Joint Mechanism” Patent No. US20120094775

Non Patent Literature

Majid Yaghoubi, Ali Jafary, Seyed Saeid Mohtasebi, "Design, simulation and evaluation of a new universal joint with intersecting angle up to 100 degrees for farm machineries," Australian Journal of Agricultural Engineering, AJAE 1(4):149-152 (2010)

Claims (9)

  1. A parallel mechanism comprising a base portion 11, a moving bracket 18, a plurality of at least three linkages each consisting of an upper arm 14, a lower arm 16 and a universal joint 15. Where one end of the plurality of the linkages are connected to the base portion through a plurality of double revolute joints 12 and 13 and the other end of the plurality of the linkages are connected to the moving bracket through a plurality of universal joints 17 or a plurality of double revolute joints 171 and 172.
  2. The parallel mechanism according to claim 1 wherein two revolute joints 12 and 13 with perpendicular joint axes connect each upper arm 14 to the base portion.
  3. The parallel mechanism according to claim 1 wherein two revolute joints 171 and 172 with perpendicular joint axes connect the lower arm to the moving bracket.
  4. The parallel mechanism according to claim 1 wherein each pair of the upper arm 14 and lower arm 16 are respectively connected to the input and output shafts of a universal joint 15.
  5. The parallel mechanism according to claim 1 wherein the joint connecting each pair of the upper arm 14 and lower arm 16 is a universal joint including Cardan joint, Persian joint or any type of joint that can transfer the shaft torque over the angle between the upper arm and the lower arm.
  6. The parallel mechanism according to claim 1 wherein a plurality of rotary actuators are connected to the plurality of joints 12 and 13.
  7. The parallel mechanism according to claim 1 wherein at least six rotary actuators are connected to the plurality of the revolute joints 12 and 13.
  8. The parallel mechanism according to claim 6 wherein the plurality of rotary actuators are connected to plurality of joints 12 and 13 by means of any kind of transmission mechanism including gears or belts.
  9. The parallel mechanism according to claim 7 wherein the plurality of rotary actuators are connected to plurality of joints 12 and 13 by means of any kind of transmission mechanism including gears or belts.
PCT/IB2016/051066 2016-02-26 2016-02-26 Six degrees of freedom parallel mechanism WO2017144954A1 (en)

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Citations (4)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US5301566A (en) * 1992-07-20 1994-04-12 The United States Of America As Represented By The Administrator Of The National Aeronautics & Space Administration Simplified and symmetrical five-bar linkage driver for manipulating a Six-Degree-of-Freedom Parallel "minimanipulator" with three inextensible limbs
CA2633395A1 (en) * 2007-06-01 2008-12-01 Socovar, Societe En Commandite Parallel manipulator
US9044271B2 (en) * 2009-03-10 2015-06-02 Stryker Trauma Sa External fixation system
CN103144106B (en) * 2013-03-13 2015-11-18 燕山大学 There is the asymmetric parallel institution of two turn of one shift three degrees of freedom

Patent Citations (4)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US5301566A (en) * 1992-07-20 1994-04-12 The United States Of America As Represented By The Administrator Of The National Aeronautics & Space Administration Simplified and symmetrical five-bar linkage driver for manipulating a Six-Degree-of-Freedom Parallel "minimanipulator" with three inextensible limbs
CA2633395A1 (en) * 2007-06-01 2008-12-01 Socovar, Societe En Commandite Parallel manipulator
US9044271B2 (en) * 2009-03-10 2015-06-02 Stryker Trauma Sa External fixation system
CN103144106B (en) * 2013-03-13 2015-11-18 燕山大学 There is the asymmetric parallel institution of two turn of one shift three degrees of freedom

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