WO2002006018A1

WO2002006018A1 - An industrial robot with a balancing device in the form of a leaf spring

Info

Publication number: WO2002006018A1
Application number: PCT/SE2001/001465
Authority: WO
Inventors: Thomas Gunnarsson
Original assignee: Abb Ab
Priority date: 2000-07-05
Filing date: 2001-06-26
Publication date: 2002-01-24
Also published as: SE0002534D0; AU2001266516A1; SE515372C2; SE0002534L

Abstract

Industrial robot comprising a manipulator and a control system. The manipulator comprises a first arm part (4) and a second arm part (2) that are arranged to pivot in relation to one another. The first and second arm parts relative to one another during pivoting are balanced by a balancing device (7) that comprises a leaf spring (8). A first end (9) of the leaf spring is arranged to pivot in a first attachment (13) on the first arm. A second end (11) of the leaf spring is arranged designed with a longitudinal section (a) with a width (b) that decreases towards the second end. The second end is arranged to be displaceable in a second attachment (14) on the second arm.

Description

An industrial robot with a balancing device in the form of a leaf spring

TECHNICAL AREA

The present invention relates to an industrial robot with a balancing device in the form of a leaf spring, and a method for balancing.

BACKGROUND

Industrial robots that comprise at least two robot parts arranged to pivot in relation to one another need strong motors that require a lot of current to perform the pivoting. Strong motors that demand high currents are large, heavy and expensive, which leads to a need for alternative solutions. A common solution is to add to the robot a device that, during the pivoting of the robot, is itself active in the pivoting by taking up a torque during the pivoting from a resting/starting position, i.e. when the robot begins a cycle of work. The expression "pivoting from a resting/starting position" is here intended to mean a pivoting of the robot in a direction where the forces of gravity contribute to the pivoting. The device is of such a nature that the torque built up acts to return the robot to its resting/starting position and thereby helps/reduces the load on the driving motor in question during lifting/pivoting back. The expression "pivoting back to a resting/starting position" is thus intended to mean a pivoting that counteracts and thereby compensates for the forces of gravity, where such a pivoting is named "balancing" in the following. The device according to that above is thereby regarded as being a balancing device.

The balancing device helps the motor in question to balance the weight to be handled and also the actual own weight of the robot when pivoting takes place. The balancing device generally consists of balancing cylinders built up of coiled springs, bar springs and/or gas.

Document JP 10015875 shows an industrial robot with a balancing device. The robot is arranged with a lower arm arranged on a frame, where the arm swings around a horizontal pivoting axis. The arm is oriented vertically in the starting position. The robot has a balancing device for the lower arm in the form of a leaf spring. When the lower arm is in its vertical position, the leaf spring is also vertically oriented. When the arm pivots, the leaf spring, which is firmly attached to the frame at one end and freely displaceable at its other end between two guiding pins arranged on the arm, flexes outwards. The pivoting causes the length of the spring between the point of attachment and the guiding pins to shorten. It is stated in the document that the leaf spring can be layered. The aim of the device is to achieve a balancing device that returns to the starting position when the pivoting moment ceases. Advantages stated are that no expanding or contracting device that risks squeezing and damaging cables and similar is needed.

Industrial robots are usually arranged with a first arm that is pivotally joined to the frame of the robot by a joint. The arm is oriented vertically in its starting/resting position. When the robot moves, the first arm pivots in a vertical plan around the axis of rotation of the joint. The motor in question must be capable of both pivoting the robot arm and flexing out the leaf spring. Through the flexing out of the leaf spring, a moment of flexing is generated for the leaf spring that attempts to straighten up the leaf spring and thereby make it easier for the motor to pivot the arm back to its starting position.

Thus, the motor in question, when pivoting the arm, should be able to manage the remaining torque M that comprises the difference between the total loading moment of the robot and the flexing moment of the leaf spring. Torque M is small during small and during large pivoting (approaching 90 degrees). In between these, torque M passes a maximum value at about 45 degrees pivoting. In practice, it has been shown that it is during the pivoting range 25-50 degrees that the pivoting motor most needs its loading to be reduced. The balancing leaf spring should display its maximum flexing moment in this pivoting interval. There is thus a dependent relationship between the resistance to flexing of the leaf spring and the power of the pivoting motor in question.

Through arranging industrial robots with balancing devices that help and reduce the load on the driving motors, the robot manufacturer is not forced to install unnecessarily large and powerful motors in the robot.

When developing industrial robots, there is a need for, among other things, fast and compact robots with a low weight. The arm parts of the robot can be designed in material with a low density. However, it is not as easy to reduce the weight of the driving motor of the robot. One pathway of development is thus to reduce the need for large and powerful driving motors. In this case, the robots have been equipped with balancing devices to help and reduce the loads on the driving motors. To further decrease the weight and radius, leaf springs have been arranged as balancing devices. The next step in the development towards faster and more compact robots with a low weight is thus to arrange the leaf springs so that the leaf springs themselves allow a reduction in the size and strength of the driving motors.

The development of industrial robots according to that above, with balancing devices in the form of leaf springs, aims to limit the pivoting angles of the robot arm to that approaching 90 degrees. It has been shown that the most frequent working area of a robot is equivalent to a pivoting of 25-50 degrees.

Herein arises the need to arrange a leaf spring as a balancing device in a robot according to that above having the maximum possible flexing moment at every pivoting position.

For a minor pivoting of the arm from the resting position, the leaf spring should thus have a relatively low resistance to flexing. For a pivoting of the arm in the interval 25-50 degrees, the leaf spring should have a larger resistance to flexing, to then acquire an even greater resistance to flexing when the arm approaches the horizontal.

According to the Japanese document, the leaf spring is firmly attached to the frame at one of its ends. This means that the part of the leaf spring nearest the point of attachment remains rigid and inactive during the balancing process. At the other end, the leaf spring is inserted between two guiding pins. This allows an axial displacement of the leaf spring without giving any significant flexing of the leaf spring before very large loads are applied. A minor pivoting of the arm from the resting position results in a flexing out of the leaf spring that is active only in a shorter section of the leaf spring between and at a distance from the points of attachment of the leaf spring. The leaf spring displays too much stiffness and the pivoting takes place with a too large radius/a too small acceptable flexing out, which for the robot means that the desired pivoting angle is not achieved and the working area is not fulfilled.

When the Japanese robot pivots its arm in the interval 25-50 degrees, flexing out takes place only in a limited section of the leaf spring between and at a distance from its points of attachment. The ends of the leaf spring at their respective attachment points are thus still inactive during the flexing out. The leaf spring has a large flexing resistance. It is first when the arm pivots relatively much that the leaf spring acquires a comparatively proper flexing out thereby giving a torque required by the robot. When the Japanese robot pivots from a vertical position, the motor in question is required to bend out the leaf spring plus balance in part the added manipulation weight and in part the current own weight of the robot. This therefore places big demands on the size and strength of the pivoting motor in question.

The attachment of the leaf spring is therefore a factor that affects most significantly the flexing out of the leaf spring under loading. When the robot according to the Japanese patent works, the flexing out of the leaf spring is comparatively small and the leaf spring is therefore not an optimal balancing device. The leaf spring in the Japanese patent can thus not fulfil the need to be able to reduce the size and strength of the pivoting motor in question.

That the leaf spring in the Japanese patent is inserted between two guiding pins but is otherwise free at its end brings about a risk of getting caught in other parts of the robot. In addition, there is a risk for getting stuck between the guiding pins so that the axial displacement and thereby the shortening/extension of the leaf spring being disrupted. This leads to a balancing device for the robot that is less reliable in its operation.

The leaf spring shown in the Japanese patent is firmly constricted at one of its ends. This means that wear of the leaf spring occurs and increases at one specific section of the leaf spring. This reduces significantly the life length of the leaf spring, especially for layered or multi-leaved leaf springs.

When manufacturing industrial robots of the type stated above, there thus arises a need for a balancing device in the form of a leaf spring that is arranged so that it can utilise its maximum flexing moment during flexing. In addition, the leaf spring should have a variable resistance to flexing; a comparatively low resistance to flexing during a minor pivoting from the starting/resting position that successively increases with the pivoting. With otherwise unchanged conditions, the pivoting motor in question can be chosen to be comparatively small both in size and strength. The leaf spring should also be easy to fit/replace. Furthermore, the leaf spring should not have any freely moveable end. The leaf spring should be arranged so that the wear is distributed over a comparatively longer section of the leaf spring. The points of attachment of the leaf spring should give a secure and gentle guiding of both end sections of the leaf spring.

The balancing device according to the Japanese patent named above cannot fulfil these needs. DESCRIPTION OF THE INVENTION

An industrial robot, comprising a manipulator with a control system, has a first and a second arm part that are arranged to pivot in relation to one another. A balancing device in the form of a leaf spring is arranged at the arm parts to balance the positions of the arm parts relative to one another during pivoting. One end of the leaf spring is arranged on the first arm part in a first attachment and the other end of the leaf spring is arranged on the second arm part at a second attachment.

The aim of the invention is to arrange a leaf spring as a balancing device on a robot according to that above and to flex out the leaf spring along its entire active length when the first and second arms of the robot pivot in relation to one another. The active length of the leaf spring relates here to the entire length of the leaf spring between the attachment points named above, and this active length varies with the pivoting of the robot. The flexing of the leaf spring relates here to flexing in the plane of the leaf spring. The aim of the invention is also that the relative flexing out of the leaf spring increases during a certain pivoting so that the leaf spring acquires a comparatively greater flexing moment.

A further aim of the invention is to design the actual leaf spring so that the resistance to flexing of the leaf spring varies with the pivoting of the robot. In this way, the pivoting motors in question can have their loads further reduced. With a leaf spring of variable resistance to flexing, the pivoting motors in question can be chosen to be smaller and weaker. It is part of the concept of the invention that the pivoting motor in question and the leaf spring should be able to balance the movements of a robot even when the robot is run empty, i.e. without added manipulation weights.

The solution according to the invention is characterised by the industrial robot specified in claim 1 with a leaf spring arranged so that it displays a successively increasing/decreasing resistance to flexing. By means of a first attachment in the form of a joint, the first end of the leaf spring is arranged to pivot on the first arm part. By having its second end arranged in a second attachment, the leaf spring is axially displaceable in an elongated attachment device arranged on the second arm part. The second attachment comprises the actual opening of the attachment device. The leaf spring is guided in a displaceable manner in the attachment device and mounted with its long sides with the width (b) between two opposing roller beds. When manufacturing the industrial robot according to the invention, the balancing device is installed in accordance with the independent method claim.

When the robot pivots, the arm parts pivot in relation to one another and the active sprung length of the leaf spring comprises the entire length of the spring between the attachments in accordance with the independent method claim. The mounting allows a rolling so that the resistance to flexing of the spring increases and its active length decreases during pivoting of the arm from a vertical position in accordance with the subordinate claims.

The invention is thus built up in that the leaf spring is displaced into an attachment device and that it in this way takes account of the shortening/extension of the active sprung length of the leaf spring that is necessary to balance the pivoting between the arm parts. The active sprung length is thereby a critical variable in the balancing procedure. As the first end of the leaf spring can pivot continuously in the joint, it adapts its orientation to the loading and to the second end of the leaf spring. The active sprung length here comprises the entire length of the leaf spring between the attachments. During pivoting, the invention gives a longer active sprung length, which gives a comparatively greater flexing out. The invention thus gives a maximum possible flexing for a given loading. It even gives a more effective balancing and the driving motor in question can be chosen to be smaller and more energy efficient.

The leaf spring according to the invention is designed so that it gives a relatively low resistance to flexing when the arm parts are located in their starting/resting position. The resistance to flexing increases when the pivoting between the arm parts increases. The increased resistance to flexing is obtained by designing the leaf spring with a longitudinal section a with a successively increasing/decreasing width b (Fig. 2).

The force of the spring can be expressed in a simplified way as:

F = 3 E I δ / (L³), where l = b h³/ 12

E = the module of elasticity,

I = the moment of resistance to flexing, δ = the downwards flexing of the leaf spring,

L = the active length of the spring, b = the width of the leaf spring, h = the thickness of the leaf spring.

This means that:

For an active spring length L1<L0, an increasing spring force F with otherwise retained values is obtained (Fig. 2). For the width of the leaf spring bl>b0, an increasing spring force F with otherwise retained values is obtained. A certain width of leaf spring gives a certain moment of flexing at a certain flexing of the spring. A reduction in the width of the leaf spring gives a reduced moment of flexing for the same flexing of the spring since a narrower width gives less stiffness in flexing.

By designing the leaf spring according to the invention with one of its ends with a longitudinal section a having a successively increasing width b when viewed from that end, the resistance to flexing can be changed/steered and the leaf spring will leave its linear behaviour. When the robot arm is located in its vertical / starting position, the leaf spring according to the invention is inserted in an attachment device, the active length of the spring is L0 and its width is BO (Fig. 2). When pivoting the arm from the vertical position, position 0, to position 1, the leaf spring is displaced into the attachment device, whereby the active length of the leaf spring decreases to LI and the width of the spring increases to Bl. The leaf spring thus displays a relatively low resistance to flexing during a minor pivoting from the vertical position, which makes things easier for the pivoting motor in question. After that, the resistance to flexing increases with continued pivoting as the width of the leaf spring in the second attachment named above, the opening of the attachment device, increases. During pivoting back to the starting position, the leaf spring has a comparatively greater pivoting moment that acts against the forces of gravity and thus lightens the load of the driving motor in question. In this way, the invention allows the driving motor in question to be smaller and consume less energy.

By designing and attaching the leaf spring according to the invention, the whole of the leaf spring between the points of attachment can be utilised. The leaf spring receives a more evenly distributed outwards flexing along its whole active length. In addition, the leaf spring, in contrast to the leaf spring in the Japanese invention, receives a more even flexing tension along the spring, which gives a more even flexing out. This leads to reduced wear on the leaf spring.

According to one advantageous embodiment of the invention, the leaf spring is designed with a width that successively varies/increases along the whole of its length.

According to other advantageous embodiments of the invention, the leaf spring is designed with several layers of the same length, of different length or of different thickness. The leaf spring can be arranged in a direction that deviates from the vertical. The concept of the invention also includes embodiments where the attachments of the leaf spring exchange places.

The concept of the invention also includes not only designing the leaf spring with sections with increased/decreased width, but also influencing the resistance to flexing through the choice of material. The leaf spring is manufactured of composite material actively chosen to affect/steer the resistance to flexing of the leaf spring.

This description should not be seen as a limitation of the invention but only as a guide to a full understanding of the invention. Adaptation to robots that include other active parts plus the replacement of parts and details that are obvious for a person skilled in the art can naturally be made within the concept of the invention.

DESCRIPTION OF THE FIGURES

The invention will be described in more detail through the description of an embodiment with reference to the attached drawings where

Fig. 1 shows an industrial robot with a balancing device in the form of a leaf spring arranged according to the present invention where the leaf spring is viewed from its short side. Fig. 2 shows the design of the leaf spring at the tapered longitudinal section.

DESCRIPTION OF AN EMBODIMENT

An industrial robot 1 (Fig. 1) comprises a frame 2, a lower arm 4 connected to the frame 2 through a joint 3 and an upper arm 6 connected to the lower arm 4 through a joint 5. The pivoting axles 3a and 5a in the two joints are horizontally oriented. A balancing device 7 in the form of a leaf spring 8 is arranged on the robot. Leaf spring 8 is arranged to pivot on the lower arm 4 around its first end 9 by means of a joint pin 10. At its other end 11, leaf spring 8 is arranged to be axially displaceable in an elongated attachment device 12 that is firmly attached to the frame 2. Joint pin 10 and the attachment device 12 are firmly arranged and vertically displaced in opposite directions from the pivoting axis 3a of the lower arm 4 in joint 3 and constitute the two attachment points 13 and 14 of the leaf spring. When the robot 1 is in its resting position/position 0, both the lower arm and the non-loaded leaf spring 8 take up a vertical position.

The leaf spring is designed with long sides 15 with a width b and short sides 16 with a thickness/depth h (Fig. 2). Leaf spring 8 is displaceably guided into the attachment device 12 with its second end 11. When the leaf spring is displaced, the long sides 15 move/are guided and supported between two opposing vertically oriented roller beds 17 and 18 that are firmly arranged on the frame 2. At the same time, the attachment device 12 comprises support/guidance for the short sides 16. The opening 19 of the attachment device 12 that faces joint 3 constitutes the attachment 14 of the leaf spring.

When the lower arm 4 is pivoted in relation to the frame 2, the leaf spring 8 is subjected to loading so that it is flexed out of its own plan. In this case, the first end 9 of the leaf spring pivots around joint pin 10 on the lower arm 4 where the joint pin 10 constitutes the attachment 13 of the leaf spring. The other end 11 of the leaf spring is displaced axially between the roller beds 17, 18 during pivoting (see the directional arrow in Fig. 1). Since the leaf spring 8 and the attachments 13 and 14 are the whole time (except for the resting position) positioned at a distance from and on the same side as the axis of rotation 3a of the lower arm, the active sprung length L of the leaf spring 8 will be shortened during pivoting away from the resting position, position 0 in Fig. 1.

The active sprung length L of leaf spring 8 relates to the part of the leaf spring that allows itself to be flexed during loading. The leaf spring according to the invention thus has an active length L that constitutes the whole length of the leaf spring between attachment points 13 and 14.

Leaf spring 8 has a longitudinal section with a continuously increasing width b when seen in the direction from its second end 11 (Fig. 2). In the resting position (position 0 in Fig. 1), the leaf spring 8 is not subjected to loading and is arranged with its second end 11 and only a part of the said longitudinal section a inserted between the roller beds 17 and 18 of the attachment device 12. Position 0 is equivalent to an active sprung length LO and a sprung width bO (Fig. 2 is not drawn to scale). During pivoting of the lower arm 4 from resting position/position 0 to an arbitrary position (position 1 in Fig. 1), the active sprung length LO has decreased to LI at the same time as the width of the spring bO has increased to bl .

Pivoting of the lower arm 4 from resting position thus means that the second end 11 of the leaf spring and the longitudinal section a are successively displaced axially into the attachment device 12 through the opening 19, whereby the width of the leaf spring in the opening 19 increases continuously up to full width. This means that the active length of the leaf spring 8 decreases at the same time as a desired increase of the resistance to flexing is obtained. The design of the leaf spring thus means that the resistance to flexing is guided to vary with the balancing.

During a pivoting of the lower arm 4 back towards the starting position L0, the pivoting moment of the leaf spring opposes the forces of gravity, the flexing out of the leaf spring 8 decreases and the leaf spring 8 is displaced axially upwards from the opening 19 of the attachment device 12. In this case, the leaf spring 8 is displaced so that the width b of the spring at the attachment 14/opening 19 decreases at the same time as the active length L of the leaf spring increases. The second end 11 of the leaf spring remains inserted in the attachment device 12 for all working positions of the robot.

Claims

1. Industrial robot (1) comprising a manipulator and a control system where the manipulator comprises a first arm part (4) and a second arm part (2) that are arranged to pivot in relation to one another where the positions of the first (4) and second (2) arm parts relative to one another during pivoting are balanced by a balancing device

(7) that comprises a leaf spring (8) characterised in that a first end (9) of the leaf spring is arranged to pivot in a first attachment (13) on the first arm part (4) and that a second end (11) of the leaf spring (8) is arranged designed with a longitudinal section (a) with a width (b) that decreases towards the second end (11) where the second end (11) is arranged to be displaceable in a second attachment (14) on the second arm part (2).

2. Industrial robot according to claim 1 characterised in that the leaf spring is arranged with an active length (L) that is constituted by the whole length of the leaf spring (8) between the attachments (13) and (14).

3. Industrial robot according to any of claims 1-2 characterised in that the first attachment point (13) comprises a joint pin (10).

4. Industrial robot according to any of claims 1-3 characterised in that the second attachment point (14) is constituted by an opening (18) on an elongated attachment device (12).

5. Industrial robot according to claim 4characterised in that the attachment device (12) comprises two opposite roller beds (16) and (17).

6. Method when manufacturing an industrial robot (1) comprising a manipulator and a control system where the manipulator comprises a first arm part (4) and a second arm part (2) fhat are arranged to pivot in relation to one another where the positions of the first (4) and second (2) arm parts relative to one another during pivoting are balanced by a balancing device (7) that comprises a leaf spring (8) characterised in t h a t a first end (9) of the leaf spring (8) is brought to pivot in a first attachment (13) on the first arm part (4) and that a second end (11) of the leaf spring is brought to include a longitudinal section (a) with a width (b) that decreases towards the second end (11) where the second end (11) is brought to be displaceable in a second attachment (14) on the second arm part (2).

7. Method for an industrial robot (1) comprising a manipulator and a control system where the manipulator comprises a first arm part (4) and a second arm part (2) that are arranged to pivot in relation to one another where the positions of the first (4) and second (2) arm parts relative to one another during pivotmg are balanced by a balancing device (7) that comprises a leaf spring (8) characterised in that during pivoting, a first end (9) of the leaf spring (8) pivots in a first attachment (13) on the first arm part (4) and that a second end (11) of the leaf spring is arranged designed with a longitudinal section (a) with a width (b) that decreases towards the second end (11) where the second end (11) is displaced in a second attachment (14) on the second arm part (2).

8. Method according to claim 7characterised in that the leaf spring (8) is brought to balance the arm parts during pivoting by flexing out along its whole length between the attachments (13) and (14).