WO2004033161A1

WO2004033161A1 - Device for moving and orienting an object with at least two degrees of freedom

Info

Publication number: WO2004033161A1
Application number: PCT/IT2002/000623
Authority: WO
Inventors: Gianni De Paoli; Adriano Girotto
Original assignee: Evotech S.R.L.
Priority date: 2002-09-30
Filing date: 2002-09-30
Publication date: 2004-04-22
Also published as: AU2002347621A1

Abstract

Device for moving and orienting an object with at least two degrees of freedom, comprising a stationary plate (10), at least three rotary actuation units (29, 44, 46, 48) supported by said stationary plate (10), and a rotating chuck (70) that carries the means to pick up and release the object. The kinematic linkage of said rotary actuation units (29, 44, 46, 48) to the chuck (70) is ensured by rigid members (32, 81-86) provided with first Cardan joints (30, 71-76) and second Cardan joints (34, 91-96). All of said second Cardan joints (34, 91-96) are arranged directly on the chuck (70) and aligned along the axis (Z) of said chuck, wherein this axis remains constantly parallel to the axes of rotation (Zc, Z1, Z2, Z3) of said rotary actuation units (29, 44, 46, 48).

Description

Device for moving and orienting an object with at least two degrees of freedom

DESCRIPTION The present invention refers to a device by means of which an object is capable of being moved and oriented spatially with at least two degrees of freedom. Introduction

To move objects spatially, use is increasingly and widely made, in the most varied sectors of the manufacturing industry, of highly automated handling apparatuses that are commonly known under the designation of manipulators, as they are on the other hand referred to also in this specification. A first typical application of such manipulators is in their use in view of handling a workpiece, which may for instance be an electronic component to be mounted onto the board of a printed-circuit arrangement, or a mechanical part to be assembled onto or inserted into a piece of equipment, or again a bonbon to be placed on the machine for wrapping up. At each working cycle, these manipulators pick up a piece from a storage and/or feeding facility and transfer such a piece to a well-defined point in the space while imparting, if necessary, a pre-determined orientation to it. A second typical application of the above cited manipulators covers their use in view of imparting a desired disposition to a tool and, if required, moving such a tool along a pre-determined track or path during the machining operation whiph said tool is intended to perform. It will of course be appreciated that these manipulators can be used in a number of other applications throughout industry, in accordance with the particular needs of the field in which they are to be used.

In any case, a primary requirement that manipulators are required to meet is the accuracy with which the object being handled (i.e. workpiece or tool, as the case may be) must take the desired position, placing and orientation. In the first kind of application as cited above, equally important is the rate of the working cycles of the manipulators, that is the rapidity with which the following operations are capable of being sequencially performed : picking up a workpiece, giving it the desired orientation, moving it from the initial point to the final one, releasing it, performing a return stroke to pick up another workpiece, which may also be different from the previous one. In the case that the manipulators are on the contrary used to move a tool, the need arises for such a tool to be capable of maintaining the orientation that has been imparted to it throughout the machining operation which it is intended to perform, as well as to be capable of following the desired path, to a maximum extent of evenness and accuracy. State of the art

The state of the art that may be considered as being the most relevant one is the patent publication EP-A-0 250 470, which discloses a manipulator that is capable of moving and orienting an object with three degrees of freedom in parallel, or even with four degrees of freedom in parallel in the case that such a manipulator is associated to a tool that is driven rotatably about its own axis. This manipulators comprises a stationary or base element, at least a moving element that carries a working head associated to the object, and at least three actuators, each one of which has a fixed portion, firmly joined to the stationary base, and a moving portion. The moving portions of the actuators comprise three shafts having the axes thereof that are co-planar with and firmly joined to respective actuating levers which are connected to three pairs of parallel rods by means of first universal Cardan joints, or the like, that are arranged at an end portion of said levers. Accordingly, the moving portion of each actuator has just a single degree of freedom with respect to the fixed portion of the same actuator. The other end portions of said levers are provided with second Cardan joints that connect them to said moving element. The axes of these second universal Cardan joints are different for each pair of levers and perpendicular to the axis of the working head, since they practically are situated on the plane on which the moving element carrying said working head is actually lying. In this manner, the orientation of the last mentioned moving element remains spatially unvaried, regardless of which kind of motion the actuating levers being part of the actuators may also perform, even if the working head is able to rotate about its own axis along with the object being handled, i.e. carried by it.

As far as this prior-art manipulator construction is concerned, at least the following drawbacks can be noticed to exist : a) the interposition of said moving element between the rods and the working head, further to constituting a constructional complication, makes it difficult for the desired accuracy to be obtained in the orientation of the object being handled, owing to the pairs of rods moving on continuously variable planes during the operation of the actuators; b) the rigid connection between the pairs of levers and the actuators, which is provided by the moving portions of the same actuators, causes said moving portions themselves to undergo flexural stresses during the operation of the actuators, as well as torsional stresses that are brought about by the opposite reaction of the working head carried by the moving element. Object of the invention and short description of the drawings

It therefore is a main object of the present invention to provide a manipulator construction that is capable of moving and orienting spatially an object with two or more degrees of freedom, which is free of the above cited kind of drawbacks, and which, further to ensuring excellent performance capabilities as far as the working accuracy and rapidity are concerned, is also constructively robust, simple, reliable and low-cost. According to the present invention, this and further objects are reached in a manipulator featuring the characteristics as recited and defined in the appended claims, the advantages of which will be more readily and better understood from the description given below of a preferred, although not sole embodiment with reference to the accompanying drawings, in which: - Figure 1 is a three-dimensional bottom view of a manipulator according to the present invention, which is capable of moving and orienting an object with four degrees of freedom;

- Figure 2 is a bottom plan view of the same manipulator;

- Figure 3 is a further bottom plan view of the manipulator in a different configuration with respect to the ones illustrated in Figures 1 and 2, so as to also show some parts that, when the manipulator is installed and operating, are generally not to be seen;

- Figure 4 is a view of the manipulator along the vertical-section line A-A of Figure 3;

- Figure 5 is an enlarged-scale view of the manipulator along the vertical-section line B-B. Preferred Embodiment of the Invention

As this has been already explained earlier in this description, a manipulator is used to spatially move and orientate an object by means of a rotating chuck 70 associated to workpiece-holding (or tool carrying) means provided to pick up and release the same object. All these parts of the manipulator are anyway well-known in the art, so that there is no need for them to be either described more in detail in this specification or shown in the accompanying drawings, even if they may differ from case to case depending on the nature of the object (e.g. a workpiece to be processed and/or a part to be assembled onto a more complex equipment, or a working tool).

The manipulator according to the present invention comprises a support portion 10, which is in the form of a box-like structure having the shape of a prism whose bases consist of equilateral triangles with markedly rounded-off corners. The height of this prism, i.e. the distance of said bases from each other (wherein said bases are closed by a first cover 17 and a second cover 18 to protective purposes) is shorter than the sides thereof : owing exactly to this reason, the support portion 10 will be simply referred to as plate in this specification. For the purposes of the present invention, the plate 10 is to be considered as being stationary owing to the fact that, during the operations which the manipulator is intended to perform, the lying plane thereof has to remain absolutely unvaried, e.g. horizontal. On the other hand, during set-up of the manipulator and similar operations, said lying plane of the plate 10 may be varied by correspondingly adjusting the blocks 11 , 12 and 13 that are provided along the three sides 14, 15 and 16 and by means of which the plate 10 can be fixed on pillars, columns or the like (not shown in the Figures for reasons of greater simplicity) - see in particular Figures 1 and 3. A circular aperture 20 extends at the centre of the plate 10 and is provided with a guard 23 having a decreasing section starting from the base corresponding to the first cover 17, which is only shown in Figures 1 and 2, up to thje one corresponding to the second cover 18. A rotating actuator (namely a motor or a gerodotor) is mounted with the aid of an appropriate support 21 on the plate 10 in correspondence of the aperture 20. A shaft 29, the axis Z_G of which is orthogonal to the lying plane of the plate 10, extends beyond the base of said guard 23 and transmits the motion it receives from the actuator 28 on to a first Cardan joint 30 which is provided at an end portion of a telescopic rod 32. A second Cardan joint 34 is provided at the other end portion of said rod 32 for the connection to the end portion of the chuck 70 lying on the opposite side of the end portion of the afore cited workpiece-holding (or tool carrying) means - see in particular Figures 1 and 4. Accordingly, the shaft 29 constitutes an actuating unit that rotates about said axis Z_c and that, when the actuator 28 is operating, causes the chuck 70 to rotate about its own axis Z via the kinematic linkage established by the rod 32 and the Cardan joints 30 and 34. As a result, the object (which is not shown in the accompanying drawings) being handled is oriented with one degree of freedom. The actual sizing of the telescopic rod 32 and the Cardan joints 30 and 34, including the selection of the materials of which said parts arjs made, shall itself take into due account the kind of application in connection with which the manipulator is going to be used. In particular, in the case that the manipulator is due to operate with high-frequency working cycles, such as they are for instance needed to handle an order of magnitude of, say, 120 pieces per minute, it is appropriate for these parts of the manipulator to be made of ultra-light materials in view of minimizing inertia and, as a result, the power absorbed by the actuator 28.

According to a basic feature of the present invention, the chuck 70 is kinematically linked in the following manner to three further rotary actuation units. These units comprise three cylindrical rings 44, 46 and 48, which are mounted by means of corresponding rolling bearings 45, 47 and 49 in three apertures 24, 26 and 28 and extend with a constant circular section between the two bases 17 and 18 of the stationary plate 10. The axes Zι, Z₂, Z₃ of said three cylindrical rings 44, 46 and 48 are parallel to the axis Z_c of the central aperture 20, namely orthogonal to the lying plane of the plate 10 (see Figures 4 and 5), too, and their points of intersection with said lying plane form the apices of an equilateral triangle, as this can be best noticed in Figure 3. Each one of the three above mentioned rotary actuation units, i.e. each one of the above mentioned rings 44, 46 and 48, the outer surface of which has to this purpose a toothed portion, receives the motion from a corresponding rotary actuator or motor 54, 56 and 58 via a cogged belt 53, 55 and 57 - see Figures 3 and 5. In a per se known manner, both the actuators 54, 56 and 58 and the afore described actuator 28 are operatively connected to a programmable control and governing unit (not shown) which in a preferable manner is a part of the manipulator, too.

In order to ensure the kinematic linkage of the rings 44, 46 and 48 with the chuck 70, there are provided three pairs of parallel rods 81 and 82, 83 and 84, 85 and 86, at the end portions of which there are provided first Cardan joints 71 and 72, 73 and 74, 75 and 76 and second Cardan joints 91 and 92, 93 and 94, 95 and 96, respectively. Through said first Cardan joints each pair of said rods is connected to a corresponding hub 65, 67 and 69 that is firmly secured to a radial appendix 64, 66 and 68 extending outwardly of the plate 10 from the free base of the rings 44, 46 and 48, as this can be best noticed in Figures 1 , 4 and 5. According to another feature of the present invention, the axes Yι, Y2, Y3 of the hubs 65, 67 and 69 are parallel to the axes of rotation Z1, Z₂, Z3 of the rings 44, 46 and 48, so that they are orthogonal to the lying plane of the stationary plate 10, too, and their points of intersection with said lying plane form the apices of another equilateral triangle.

According to the main feature of the present invention, the said second Cardan joints 91 and 92, 93 and 94, 95 and 96, owing to them being aligned along the axis Z of the chuck 70, do connect each pair of said rods directly with the latter- see Figures 1 and 4. In this way, the manipulator according to the present invention is capable of moving the chuck 70, and therefore the object being carried by the latter, with three degrees of freedom. Altogether, the object can be moved and oriented by the manipulator with four degrees of freedom.

Following features and advantages of the present invention are therefore clearly apparent from the above description: a) owing to such an arrangement of the second Cardan joints 91-96, which is moreover effective in reducing the overall number of parts that are kinematically connected with each other, an advantage is derived in that this manipulator is capable of operating with a better accuracy than the afore described prior-art manipulator; b) such an accuracy is further improved by the stability ensured by the relatively large diameter (corresponding to the one of the apertures 24, 26 and 28) of the bearings 45, 47 and 49 provided to enable the rings 44, 46 and 48 to be duly supported by the stationary plate 10; c) the provision - at both end portions of the three pairs of rods 81-86 - of Cardan joints 71-76 and 91-96, which are mounted in an idle manner both on the hubs 65, 67 and 69 associated to the rotary actuation units, ie. the rings 44, 46 and 48, and on the chuck 70, is effective in ensuring that the sole stresses, which the rods 81-86 are actually subject to, are tensile and compressive stresses. It is in this way possible for said rods to be made with an extremely lightweight, simple and low-cost construction, as well as for a reduced power absorbed by the three rotary actuation units, while enabling the manipulator to operate at a high reliability and accuracy level even in the case of high- frequency working cycles; d) all actuators 28, 54, 56 and 58 are provided to operate in a fully autonomous, i.e. independent manner with respect to each other, so that they can be controlled and driven with a maximum extent of freedom. Further embodiments and variants of the invention

As this has already been made clear, it will be appreciated that, while the above description refers to a particular embodiment of the present invention providing for an object to be capable of being moved and oriented with four degrees of freedom, a number of different embodiments and variants thereof may be developed without departing from the scope of the present invention as defined by the appended claims. So, for example,

- when the application in which the manipulator is used just requires three degrees of freedom, the first of said rotary actuation units, i.e. the one receiving the motion from the actuator 28, will be omitted as well as all corresponding means used to establish its kinematic linkage to the chuck 70;

- when the application in which the manipulator is used requires the object to be just moved on a plane, but not to be oriented, i.e. to be moved with just two degrees of freedom, the three rotary actuation units associated to the pairs of rods 81-86 will receive the motion in the following manner: one of these units, e.g. ring 44, will receive its motion from the actuator 54 via the cogged belt 53, while the remaining two units, i.e. rings 46 and 48, will receive their motion from another actuator 48 and a single cogged belt 55; - the three rotary actuation units associated to the pairs of rods 81-86 may also be solely constituted by the hubs 65, 67 and 69 (on which there are provided the first Cardan joints 71-76) as supported directly by the stationary plate 10, while of course maintaining the due parallelism between the axes thereof and the axis of the chuck 70;

- the transmission of the motion to the three rotary actuation units associated to the pairs of rods 81-86 by the respective actuators may be implemented through the use of means differing from the above cited cogged belts, such as for example via gear means.

Claims

CLAIMS 1. Device for moving and orienting an object with at least two degrees of freedom, comprising: - a stationary plate (10),

- at least three rotary actuation units (29, 44, 46, 48) supported by said stationary plate (10) and operatively associated to a programmable control and governing unit that is preferably a part of the device, too,

- a rotating chuck (70) that carries means to pick up and release the object and is kinematically linked to said rotary actuation units (29, 44, 46, 48),

- means adapted to ensure said kinematic linkage, which comprise rigid linkage members (32, 81-86) provided with first Cardan joints (30, 71-76) in correspondence of said rotary actuation units

(29, 44, 46, 48), as well as second Cardan joints (34, 91-96), characterized in that all of said second Cardan joints (34, 91-96) are arranged directly on the chuck (70) and aligned along the axis (Z) of said chuck, wherein this axis remains constantly parallel to the axes of rotation (Z_c, Zi, Z2, Z3) of said rotary actuation units (29, 44, 46, 48).

2. Device according to claim 1 , characterized in that the axes of rotation (Z_c, Z1, Z₂, Z3) of said rotary actuation units (29, 44, 46, 48) are orthogonal to the lying plane of said stationary plate (10).

3. Device according to claim 1 or 2, characterized in that said rigid linkage members include, as a part thereof, three pairs of parallel rods (81 , 82; 83, 84; 85, 86) which are provided with the task of moving the chuck with at least two degrees of freedom, so that the corresponding second Cardan joints (91-96) are provided idle on said chuck (70), and in that the corresponding rotary actuation units comprise rings (44, 46, 48) that are accommodated in through-apertures (24, 26, 28) of said stationary plate (10) and are supported by the latter by means of rolling bearings (45, 47, 49), and wherein said rings (44, 46, 48) receive their motion from motors (54, 56, 58) via motion-transmitting means (53, 55, 57) and are firmly joined to hubs (65, 66, 67), or the like, which are supported by the stationary plate (10), too, where there are provided said first Cardan joints (71 , 72; 73, 74; 75, 76) of said pairs of parallel rods (81 , 82; 83, 84; 85, 86) in a two-by-two arrangement.

4. Device according to claim 3, characterized in that the points of intersection of the axes of rotation (Z1, Z₂, Z3) of said rings (44, 46, 48) with the lying plane of said stationary plate (10), as well as the points of intersection with the same lying plane of the axes of rotation (Y-i, Y₂, Y3) of said hubs or the like (65, 66, 67), where said first Cardan joints (71 , 72; 73, 74; 75, 76) are provided, form the apices of two equilateral triangles.

5. Device according to claim 3 or 4, characterized in that each one of said rings (44, 46, 48) receives its motion from a separate motor (54, 56, 58) via a motion-transmitting means of its own.

6. Device according to claim 5, characterized in that said motion-transmitting means consists of a cogged belt (53, 55, 57) engaging a portion of the outer surface of a ring (44, 46, 48).

7. Device according to claim 5, characterized in that said motion-transmitting means is in the form of gears.

8. Device according to claim 3 or 4, characterized in that a first ring (44) receives its motion from a first motor (54) via a first motion-transmitting means, wherein both of the other rings (46, 48) receive their motion from a second motor (56) via a second motion-transmitting means (55) that is common to both of them.

9. Device according to claim 8, characterized in that said first and said second motion- transmitting means consist of two cogged belts (53, 55) engaging a portion of the outer surface of said rings (44, 46, 48).

10. Device according to any of the preceding claims, characterized in that said rigid connection members include, as a part thereof, a telescopic rod (30) performing the task of rotating said chuck (70) about its own axis (Z), so that the corresponding second Cardan joint (34) is firmly joined to the chuck (70), and in that the corresponding rotary actuation unit consists of a shaft (29) that receives its motion from a motor (28) of its own and extends through an aperture (21) provided at the centre of said stationary plate (10).

11. Device according to any of the preceding claims, characterized in that said rigid connection members (32, 81-86), which are in the form of rods, and said Cardan joints (30, 34; 71-76, 91-96), which are provided at the end portions thereof, are made of ultralight materials.