Design and fabrication of a novel quick-change system

Technical Note

Design and fabrication of a novel quick-change system

Ali Meghdari*, Farshad Barazandeh

Advanced Manufacturing Research Center (AMRC), Sharif University of Technology, Tehran, Iran

11365-9567

Received 9 February 1999; accepted 23 February 1999

Abstract

In robotics, the quick-change system is a device that when attached to the wrist of arobot, increases its ability to automatically change the grippers/end-e�ectors whennecessary. As a result, this will increase the robot's ¯exibility in handling various shaped

objects and tools.This paper presents an overview of the design features and the fabrication results of a

novel quick-change system for robotics applications. Upon fabrication, the AMRC quick-change system was tested satisfactorily with a series of di�erent robotic grippers; namely

the magnetic, vacuum, in¯atable and ®nger-like grippers. 7 2000 Published by ElsevierScience Ltd.

1. Introduction

A major enhancement to any light industrial assembly robot manipulators is to

allow it to change its tools and grippers without assistance from an operator [1].

The key goal here is to mimic capabilities of a human assembly person. An

important area of human versatility, which is of primary interest, is the ability to

use several tools at a workstation, which might have vastly di�erent operating

0957-4158/00/$ - see front matter 7 2000 Published by Elsevier Science Ltd.

PII: S0957 -4158 (99)00041 -0

Mechatronics 10 (2000) 809±818

* Corresponding author. Visiting Research Professor, Division of Engineering, Colorado School of

Mines, Golden, CO 80401, USA. Fax: (303) 384-2212.

E-mail address: [email protected] (A. Meghdari).

characteristics. One approach to achieve this ¯exibility is to fabricatemultifunctional end-e�ectors, while the other is to allow the robot to change end-e�ectors when necessary [2]. While both approaches have their advantages, thispaper will concentrate on the latter case. This is due to the fact that this system isfound to be more applicable if robotics is to move into the factory of the future.

The end-e�ector attach/detach mechanism known as the quick-change systemdescribed in this paper was developed for a medium load (6 kg) assembly robot,namely the Unimation-Staubli RX-90 robot manipulator [1]. Although manyquick-change systems may be available in the market today, but this mechanism isfound to have the advantage of simplicity in design and fabrication processes,being very reliable and fail-safe. The AMRC quick-change system allows therobotic arm to detach an end-e�ector into a tool table, select another, and attachit automatically without outside assistance. The overall operating system describedhere has a large degree of ¯exibility and expandability.

2. Design objectives and functional speci®cations

Several factors were considered important for the successful design andimplementation of the gripper exchange mechanism called the AMRC quick-change system. A list of these items identi®ed and used as our design objectivesare given as follows:

1. Light weight; to preserve the e�ective payload of the robot arm.2. Axial, longitudinal and rotational repeatability; to allow the robot function

within its absolute world coordinate system.3. Reliability and fail-safe design for locking mechanism; for securing attachments

in the case of a power failure.4. Coupling and torque sti�ness capacity; must be adequate to prevent the need for

excess de¯ection correction by the overall robotic system.5. Connection and full rotation capabilities of pneumatic and electrical lines; to

allow the most advantageous mix of power transmission, control ¯exibility, andfuture expansion capabilities for adding sensors, ®ber optic lines, vision etc.

6. Adaptability to a variety of robotic con®gurations; in order to cover a widerange of applications.

7. Repeatability of mating; mating is considered to be su�ciently repeatable tomeet the misalignments under maximum payload.

Figure 1 shows the schematics of the wrist of a robotic arm equipped with aquick-change system as well as the attached gripper/end-e�ector.

3. Description of the AMRC quick-change system

As shown in Fig. 2, the overall mechanical design of a quick change mechanismis composed of an adapter/interface plate; attached to the end-e�ector/gripper, a

A. Meghdari, F. Barazandeh /Mechatronics 10 (2000) 809±818810

Fig. 1. Gripper attachment by a quick-change system.

Fig. 2. Various parts of a quick-change mechanism.

master plate; housing the pneumatic and electrical lines as well as the bearing

mechanism, a tool plate; providing the ring for locking mechanism, and an

interface/adapter plate; mounted on the robot wrist's ¯ange [2,3,4].

The AMRC quick-change system is capable of handling objects/tools weighting

2±3 kg, at a maximum distance of about 25 cm from the robot wrist. A total of

four pneumatic lines with a minimum diameter of 3.5 mm, and nine electrical

Fig. 3. The overall schematics of the AMRC quick-change mechanism.

Fig. 4. The sealing methods in the quick-change mechanism.


Fig. 5. Detailed drawings of the AMRC quick-change mechanism±(a).

Fig. 6. Detailed drawings of the AMRC quick-change mechanism±(b).

connections are incorporated in this mechanism. The locking system is composedof six ball bearings with 4 mm in diameter. The whole mechanism is a cylindricalpackage which is roughly 60 mm in diameter by 35 mm long when both plates areattached together. The mechanism is composed of two plates, where the main(master) plate is mounted on the robot wrist, and the tool plate is attached to thecorresponding gripper. The whole mechanism weighs about 420 g. Figure 3 showsthe overall schematics of the AMRC quick-change mechanism. The lockingmechanism is operated by the air (shop air is about 6 bar 3 90 psi), and is verysecure in the case of an air cut-o�. For locking to occur, the air pressure moves

Fig. 7. Detailed drawings of the AMRC quick-change mechanism±(c).


the piston forward, causing the ball bearings to be placed behind the lock ring,and as a result creating a secure grasp within both plates. To separate the plates,the air direction is reversed, causing the piston to move backward thus freeing thebearings as shown in Fig. 3. The locking/unlocking mechanism safely meets thedemand requirements. It is robust enough to withstand power line back pressures,and therefore maintains exceptional reliability.

One of the main issues considered in our design was to put so much attentionin reducing the amount of force required for a successful attachment/detachmentprocess. This issue not only a�ects on the performance of the robot, but alsoin¯uences the size of our mechanism. To achieve this objective, sealing mechanismplays an important role here. In general two methods are used in sealing thepressured pneumatic lines: one being the dynamic seal in which the sealing partsmove relative to each other, and the next is the static seal in which the sealingparts are ®xed. In any case, combination seal, U-packing, O-ring, wiper seal etc.may be used. The simplest, smallest and the least expensive seal is the O-ring,which can also undergo a shape change in the presence of an applied pressure.Figure 4 shows three methods of sealing by O-rings. In our mechanism, the ®rstmethod was selected for this purpose. In this method, the air pressure itself alsocontributes to the sealing process. The other two methods either necessitate aprecision manufacturing and high surface ®nishing, or the air pressure does nothelp the sealing process thus requiring a stronger locking mechanism [2].

Figures 5±7 clearly show the detailed Autocad drawings of the fabricated quick-

Fig. 8. Picture of the prototype AMRC quick-change system.

A. Meghdari, F. Barazandeh /Mechatronics 10 (2000) 809±818 815

Fig. 9. Computer animated pictures of the AMRC quick-change system. (a) The master plate: mounted

on the robot wrist. (b) The tool plate: attached to the end-e�ector.


change mechanism. Figure 8 shows the picture of the quick-change systemfabricated, attached and tested successfully on the Staubli RX-90 robot. Figure 9shows the animated pictures of the AMRC quick-change system composed of themaster and the tool plates. Prior to fabrication, the whole mechanism, the robotand the grippers were modeled and animated using the 3D-Studio software on aPentium computer. Figure 10 shows a picture of the AMRC quick-change systemin operation with the ®ve di�erent grippers placed on a tool table. The wholesystem was run repeatedly, and successfully tested over 200 times performing aspeci®c task. The performance results were observed to be excellent [2].

4. Conclusions

The AMRC prototype robotics quick-change system with its novel lockingmechanism has been brie¯y described. This description included remarks oncharacteristics and capabilities of the system. The novel locking mechanismfeatures a bearing embedded mechanical system, which permits a small cylinder/piston actuator powered by shop air to secure and release the robot end-e�ectorreliably.

In order to take maximum advantage of the quick-change system and to test itscapabilities in full, several grippers with various features were designed andfabricated following a modular or building block approach. This allows the user

Fig. 10. Picture of the RX-90 Staubli robot equipped with the AMRC quick-change system at the

presence of a series of grippers.

A. Meghdari, F. Barazandeh /Mechatronics 10 (2000) 809±818 817

to con®gure a tool as simply as possible at the start and add complexity as neededto perform the desired task.

References

[1] Meghdari A, Barazandeh F. In: Proc. of the 1st Annual Seminar on Automation, Robotics &

Control, May 20±21, Tabriz, Iran, 1998. p. 207±23 (in Persian).

[2] Barazandeh F. Design and fabrication of a series of modular robotic grippers equipped with a

quick-change system. M.Sc. thesis, School of Mechanical Engineering, Sharif University of

Technology, October 1997, Tehran, Iran.

[3] Pham DT, Heginbotham WB. Robot grippers. Springer-Verlag, 1986.

[4] Craig JJ. Introduction to robotics: mechanics & control. 2nd ed. John Wiley & Sons, 1989

(Authorized translation into Persian; By: Ali Meghdari, SUT press, 1st print 1995, 2nd print 1998).


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Design and fabrication of a novel quick-change system