WO2001074548A1

WO2001074548A1 - Lightweight reconfigurable robot arm for mobile robots

Info

Publication number: WO2001074548A1
Application number: PCT/SE2001/000692
Authority: WO
Inventors: Anani Vladimirov Ananiev; Peter Ivar Wide; Ivan Guentchev Kalaykov; Detelina Stoyanova Ignatova
Original assignee: Anani Vladimirov Ananiev; Peter Ivar Wide; Ivan Guentchev Kalaykov; Detelina Stoyanova Ignatova
Priority date: 2000-03-31
Filing date: 2001-03-29
Publication date: 2001-10-11
Also published as: AU2001244966A1; SE0001163L; SE0001163D0

Abstract

The present invention relates to a robot arm and especially to a lightweight reconfigurable robot arm for mobile robots comprising: a stationary base, supporting a rotation about a vertical axis of a swivel body; a first reconfigurable link, for fore-and-aft swiveling movements about a first horizontal axis; a second link, for swiveling movements about a second horizontal axis; a robot wrist; a pivoting link, which is parallel with the first reconfigurable link; three motors, for driving the robot wrist; three motors, for driving the first and second link and the rotation of the swivel body about the vertical axis.

Description

LIGHTWEIGHT RECONFIGURABLE ROBOT ARM FOR MOBILE ROBOTS

Technical field

The present invention relates to a lightweight reconfigurable robot arm that can passively change it configuration depending on the goals and tasks in a cooperative work with a wheeled or walking mobile robot.

Background considerations and prior art

The expansion of industrial robotic systems in manufacturing and assem- bly is well known and significant. It appears to be common that the robotic systems are preferred to be assembled from off-the-shelf components. Many of these components are massive and heavy and this implies a lot of unnecessary design constraints.

One example is when the robotic links are driven by electric motors with respective gear-boxes mounted directly at the link. Then the torque inertia becomes larger as the mass is concentrated at the far end of the link.

Alternatively, the electric motor can be mounted away from the joint and connected to the joint by a long rod er transmission mechanism.

These types of robots sustain a limited range of motion of the robot arm and configurations of such type have to be used in dedicated applications.

Such constraints might become exclusively severe in the case the robot arm is allocated on a mobile platform with small size of the fundament and limited payload, when an essential requirement is the need of lightweight of the entire construction and the power supply cannot provide high power to the motors for longer time of operation.

Several prior art configuration concepts that are used in the design of the constructions of robot arms are known.

Thus a prior art construction is disclosed and presented in the USA patent 5,145,312 (and Re. 35,584) where an industrial robot arm for spot welding is de- scribed.

The arm assembly includes a first link and a second link, each having a longitudinal axis. The first link is mounted at a lower end portion on a base for a swiveling movement in a substantially vertical plane about a substantially horizon- tal first axis. The second link is provided adjacent to an upper end portion of the first link to extend in a direction crossing the longitudinal axis of the first link.

A pivot means is provided between the first and second links for allowing swiveling movements of the second link with respect to the first link about a sec- ond axis, which is perpendicular to the longitudinal axis of the first link and a third axis which is in a plane containing the longitudinal axis of the first link. There is also a driving means for selectively effecting the swiveling movements of both links.

The drawbacks of this prior art is that the construction cannot be used for mobile platform as it has large own weight which can cause lower stability of the entire robotic system, the required power is far beyond the capacity of the mobile platforms usually driven by batteries, the robot has a very simplified wrist that cannot satisfy the general requirements for manipulating operations of mobile platforms. A further prior art that complements the above mentioned prior art in providing a wrist for robot manipulations is disclosed and presented in USA patent 5,178,032.

A wrist for articulated robot having an operative member which is rotatable about three mutually perpendicular axes and three motor units each of which can cause the operative member to rotate about only one of the three axes without causing any rotation about the other axes is described.

It includes a support structure, a first drive unit fixed to the support structure and a member driven by the first drive unit and supported by the support structure for rotation about a first axis. Then, the driven member supports a further wrist portion for rotation about a second axis perpendicular to the first axis and carries a second drive unit for rotating further wrist portion about the second axis.

Then, the further wrist portion is carrying a third drive unit for driving an operative member of the robot about a third axis radial to the second axis. The disadvantage of this prior art is that the shaft of the second drive unit carries the rest of the wrist construction, namely the third drive unit and the respective portions of the wrist construction. This shifts the center of mass to the outer end of the robot link and increases the torque inertia. Also, the mentioned construction is complicated as it includes many wheels and transmissions.

All here mentioned prior art constructions have the disadvantage of being characterized by a large total weight and a rigid configuration of the first link of the robot arm, that restricts its application in the case of manipulating peripheral device of smaller mobile robot platforms.

With different grade of satisfaction, any of the referred existing constructions provides either accommodation of less heavy arm construction with the expense of using a rigid configuration of the link, or providing certain degree of flexi- bility in the construction of the link with the expense of larger total weight of the whole arm. Hence, the existing solutions so far involve limitations both in weight and flexibility to adapt the robot arm configuration to the specific application on a small mobile robot platform.

Summary of the present invention

Therefore, a need still exists in the designing art of robot arms for an improved construction having a very small weight and small sized links that provide eminent capabilities to serve and reach the widest possible working space from the mounting point on the mobile platform, in order to overcome the described limi- tations.

It is, therefore, an object of the present invention to provide a mechanical construction of a lightweight robot arm whereby the limitations, encountered by the prior art, for mounting on a small mobile robot platform with a small size of the fundament and a limited payload can be overcome. It is also, therefore, a further object of the present invention to provide a mechanical construction of a robot arm with a reconfigurable architecture that can be easily adapted to the particular construction of the mobile robot platform or to the specific need of the application task.

In accordance to the present invention, a lightweight reconfigurable robot arm is realized. It is based on the thought that a simplified arm scheme can be achieved by using of separate links each constructed by more than one parts with variable length and adjustable angle between the links.

In such case each link can obtain a dedicated profile of the construction just by rearranging few interconnecting components. In the preferred embodiment, the above-mentioned objects can be achieved by a lightweight reconfigurable robot arm for mobile robots comprising: a) a stationary base supporting a rotating about a vertical axis swivel body; b) a first reconfigurable link for fore-and-aft swiveling movements about a first horizontal axis; c) a second link for swiveling movements about a second horizontal axis; d) a robot wrist; e) a pivoting link which is parallel with the first reconfigurable link; f) three motors for driving the robot wrist; g) three motors for driving the first and second link and the rotation of the swivel body about the vertical axis.

Advantages

One special advantage of the present invention is that it provides a me- chanical construction of a robot arm with a reconfigurable architecture and sizes that can be easily adapted to the particular construction of the mobile robotic platform or to the specific need of the application task.

This arm holds a highly tractable structure and does not require special tools for adjustment to the concrete mobile platform. Therefore, it can be imple- mented/mounted on a diversity of mobile platforms from various manufacturers.

Another advantage of the present invention is that it provides a high manu- facturability and maintainability of the construction achieved by a small total number of components also by allocating of the motors which drive the wrist inside the body of the second link which avoids the necessity of any complicated mecha- nisms to transfer the movement from the motors to the wrist.

A further advantage of the present invention is that it provides a light weight of the entire construction by using light and cheap materials for components manufacturing. Hence, a lower relative price of this construction is achieved.

A still further advantage of the present invention is that the center of mass is allocated on a very low height, which ensures higher stability of the entire robotic system consisting of the mobile platform and the robot arm.

Still an additional and important advantage is that the present invention provides a construction that can be powered up by the batteries used to power the mobile platform, thus overcoming many of the known prior art constructions. These and other objects and advantages of the present invention show higher technical specifications compared to the prior art constructions that will become apparent from the detailed description below taken together with the drawings.

Brief description of the drawings

A preferred embodiment, exposing the significant features related to the present invention, will now be described more in detail with reference to the accompanying drawings, in which; Figure 1 depicts a side view of two postures of the lightweight reconfigurable robot arm for mobile robots according to the embodiment of the present invention, Figure 2 presents a plan view of a robot arm shown in fig. 1 and Figure 3 is a side view of two configurations of the first link of the robot arm shown on fig. 1.

Detailed description of the preferred embodiment according to the present invention —

The present invention provides a lightweight reconfigurable robotic arm for mobile robotic platforms. It is created on the base of the essential concept presented below.

As viewed in fig.1 , fig. 2 and fig.3, the lightweight reconfigurable robotic arm includes means for a rotation about a vertical axis, supported by a stationary base 1 and driven by the first motor 2. The stationary base 1 supports a swivel body 3 for swiveling movements about a horizontal axis 4. On the swivel body 2 an upward reconfigurable first link 5 consisting of three bodies 5a, 5b and 5c for fore-and-aft swinging movements about a horizontal axis 4 is extended.

The first body 5a is swiveling about the axis 4. The second body 5b is hinged to the outer end of the first body 5a in such a way that the angle between both bodies 5a and 5b can be fixed. The third body 5c is hinged to the upper end of the second body 5b such that the angle between both bodies 5c and 5b can also be fixed. Hence, the entire first link can be reconfigured according to the necessities of the concrete robot arm application and desired working space of the robot arm. The motor 6, viewed on fig. 2, is driving the swiveling movements of the entire first link 5 about the axis 4 by a pair of wheels and a teeth-belt. A rearward link 8a is extended from the swivel body 3.

The motor 7 viewed on fig. 2 is driving the swiveling movements of the rearward link 8a about the axis 4 by a pair of wheels and a teeth-belt.

A bushing 10 is mounted to the upper end of the third body 5c of the first link 5 such that the front end of the bushing 10 and the third body 5c hinge at a horizontal axis 9, which is parallel to axis 4.

A second link 1 1 is extended both for swiveling movements about the horizontal axis 9 and rotational movements about the longitudinal axis of the wrist 26 that is perpendicular to the axis 9. The bushing 10 is swiveling about the horizontal axis 9 and transferring the same swiveling movement to the second link 11. The second link 11 carries the whole wrist 26 and its driving components.

A pivoting link 8 is extended in parallel to the entire first link 5 from the rearward link 8a and is hinged to the rear end of the bushing 10. The pivoting link 8 is also hinged to the rearward link-8a. The movements of the pivoting link 8 and the rearward link 8a are in a plain that is parallel to the plain of the movements of the first link 5 and the second link 11.

The pivoting link 8 has a telescopic construction such that its length can be adjusted depending on the total length of the entire first link 5.

The wrist 26 having three degrees of freedom is mounted to the front end of the second link 11 and is driven in three mutually perpendicular axes by motors with integrated gear-boxes which are placed inside the second link 11.

The first wrist motor 13 performs the rotation of the wrist 26.

As shown on fig.1 and fig. 3, the body of the first wrist motor 13 is fixed to the body of the second link 11 and the shaft of this motor 13 is fixed to the rear end of the bushing 10. When the motor 13 rotates, the body of the second link 11 hold by two pairs of bearings 12 also rotates inside the bushing 10.

The body of the second wrist motor 14 is fixed to the body of the second link 1 1 and a conic teeth-wheel 15 is fixed on its shaft. Teeth-wheel 15 is coupled to another teeth wheel 15a fixed to a first shaft 16 that transfers the rotation to a teeth-belt wheel 17 also fixed to the shaft 16.

The body of the third wrist motor 18 is fixed to front end of the body of the second link 11. A conic teeth-wheel 19 is fixed to the shaft of motor 18. Teeth-wheel 19 is coupled to another conic teeth-wheel 20 placed and freely rotating on a second shaft 21 on which a second teeth-belt wheel 22 is fixed to receive the rotational movement from the first teeth-belt wheel 15 by means of a teeth-belt 24.

Teeth-wheel 20 is also coupled to another conic teeth-wheel 23 that is connected to rotate the gripper 25 of the wrist 26.

According to the invention, the advantages of the lightweight reconfigurable robotic arm consist of a first link 5, composed by three bodies the relative angle between which can be adjusted and fixed, so that the arm can be reshaped depending on the allocation where it is mounted in order to optimize the working space of the entire arm.

The simplified construction of the first link 5 and the second link 11 gives the possibility to reduce significantly the robot's own weight. It also makes possible that the center of mass of the lightweight robotic arm can be allocated very low that increases the stability of the mobile robotic platform. In addition the wrist 26 provides all three degrees of freedom by a simplified construction, also reducing the overall own weight of the robot arm.

It has been demonstrated that the present invention is very effective and simplified as:

• the total number of components is relatively low and they have all a simple con- struction;

• the configuration of the robot arm can be simply adjusted to the needs of each application and the particular construction of the mobile platform;

• there is no need to use expensive materials to implement the components of the robot arm. As this invention may be concretized in several forms without deviating from the spirit of indispensable characteristics thereof the present embodiment is therefore illustrative in showing one aspect of the present invention and shall not be considered restrictive, since the scope of the invention is defined by the appended claims rather than by the description preceding them, and all changes that fall within the metes and bounds of the claims, or equivalence of such metes and bounds thereof are therefore intended to be embraced by the claims.

Claims

1. A lightweight reconfigurable robot arm comprising in combination:

• a swivel body, rotative about a vertical axis, and mounted on a stationary base for swiveling movements about a first horizontal axis;

• a first driving motor, mounted on said base, for rotational movement of said swivel body;

• a first link, for fore-and-aft swinging movements about said first horizontal axis mounted on said swivel body; • a second motor, mounted on said swivel body for driving the swiveling movements of said first link about said first horizontal axis;

• a rearward link, which is extended from said swivel body for swiveling movements about said first horizontal axis;

• a third motor, mounted on said swivel body for driving the swiveling movement of said rearward link about said first horizontal axis;

• a bushing, whereby the front end of which is hinged to the upper end of said first link for swiveling movements about a second horizontal axis which is parallel to said first horizontal axis;

• a second link, whereby the backward side of which is hold by the bearings of said bushing in such way that it swivels about said second horizontal axis together with said bushing and rotates inside said bushing about a longitudinal axis that is perpendicular to said second horizontal axis;

• a pivoting link, the lower end of which is hinged to the end of said rearward link and the upper end of which is hinged to the backward end of said bushing; • a wrist, with three degree of freedom the body of which is mounted at the front end of said second link.

2. A lightweight reconfigurable robot arm according to claim 1 in which said first link is characterized by: • a first body, swiveling about said first horizontal axis;

• a second body, hinged to the outer end of said first body in such way that the angle between said first body and second body can be fixed; • a third body, hinged to the outer end of said second body in such way that the angle between said second body and third body can be fixed.

3. A lightweight reconfigurable robot arm according to claim 1 , in which said pivoting link is characterized by a telescopic construction such that its length can be adjusted and fixed depending on the total length of said first link.

4. A lightweight reconfigurable robot arm according to claim 1 , characterized by that said pivoting link is moving in a plain that is parallel to the plain of move- ment of both said first link and said second link.

5. A lightweight reconfigurable robot arm according to claim 1 , whereby said wrist link is characterized by a wrist motor, the body of which is fixed to the body of said second link and the shaft of which is fixed to said bushing to provide the ro- tational movement of said wrist about said longitudinal axis a second wrist motor mounted inside said second link on the shaft of which a first conic teeth-wheel is fixed, a second conic teeth-wheel fixed to a first shaft, which has an axis that is perpendicular to the said longitudinal axis, in such way that it is coupled to said first conic teeth-wheel, a first teeth-belt wheel fixed to said first shaft such that both said second conic teeth-wheel and said first teeth-belt wheel rotate in parallel, a third wrist motor mounted inside said second link on the shaft of which a third conic teeth-wheel is fixed, a fourth conic teeth-wheel freely rotating on a second shaft in such way that it is coupled to said third conic teeth-wheel, a second teeth- belt wheel fixed to said second shaft for receiving the rotational movement from said first teeth-belt wheel by means of a teeth belt, a wrist body mounted on said second shaft and fixed to said second shaft such that both said wrist body and said second teeth-belt wheel rotate in parallel about the axis of said second shaft, a fifth conic teeth-wheel fixed to a third shaft supporting a gripper with an axis that is perpendicular to said second shaft. 1/3