Mentaca: Universal Mobile Jamming Gripper - Hardware Summary

Harold-Rodrigo Valenzuela-Coloma(*), Yi-sheng Lau-Cortes, Ricardo-Enrique Fuentes-Romero, Ricardo-FrancoMendoza-Garcia

Escuela Universitaria de Ingenieria MecanicaCampus Saucache, Universidad de Tarapaca

18 de Septiembre 2222, PO BOX 1010069Arica, Chile

Abstract

Versatile robotic grasping is a complicated task that an universal jamming gripper simplifies to a big extent due to itsability of picking up objects of different shapes with little effort. This technology, however, has yet to be mounted ina mobile platform, so an universal mobile device capable of transporting objects of arbitrary shapes is still missing.This work replicates an universal jamming gripper, explores materials and granularity levels to make the gripper moretransportable, mounts the device on a custom-made mobile base loaded with a 3-DOFs robot arm, and thus providesan universal mobile grasping platform. Important design trade-offs relating hardness and granularity of the jammingmaterial with grasping and pushing force of the robot arm are found. Applications include robotic competitions andeducational platforms, among others.

Keywords: Jamming Gripper, Mobile Robot, Robot Arm

1. Introduction

Robotics competitions generally consist in graspingand transporting objects of different shapes and colorsfrom one place to another according to some rules [1].Identifying this pattern may save considerable develop-ment time as robots may not need to be prototyped fromscratch for each competition instance.

Versatile robotic grasping can be achieved with anuniversal jamming gripper [2], an actuator with the abil-ity of picking up objects of different shapes by extract-ing air from a balloon to harden the granular materialinside, as shown in Fig. 1. This technology, however,has yet to be mounted in a mobile platform, so an uni-versal mobile device capable of transporting objects ofarbitrary shapes is still missing.

This work replicates an universal jamming gripper,explores materials and granularity levels to make thegripper more transportable, mounts the device on acustom-made mobile base loaded with a three DOFsrobot arm, and thus provides an universal mobile grasp-ing platform.

∗Corresponding author. Tel.: +56 58 2205091; fax: +56 582205281. Email: harold.valenzuela.coloma@gmail.com

Figure 1: Working principles of an universal gripper.

Important design trade-offs relating hardness andgranularity of the jamming material with grasping andpushing force of the robot arm are found. Applicationsinclude robotic competitions as well as a testbed forstudies of new technologies and programming method-ologies.

2. Design

In order to design the different parts of the robot,two CAD softwares were used: OpenSCAD1 and Solid-

1http://www.openscad.org

Preprint submitted to X IEEE Latin-American Summer School on Computational Intelligence November 25, 2014

(a) Simulation of the mobile platform. (b) Connexion diagram of the mobile platform.

Figure 2: Mechanical and electronics designs of the mobile platform.

Works2. OpenSCAD was used at the beginning of theproject to model the mobile platform with motors andwheels (see Fig. 2a), and SolidWorks was used later onto draw more complex parts, such as the robot arm linksand the jamming gripper components (see Fig. 3). Thematerials used to build the prototypes were acrylic andABSplus. Acrylic (or PMMA) is used to build 2D-partsbecause it has high resistance to impact and is easy tomanufacture when using a laser cut. 2D-parts are 3mmthick. ABSplus is used to build 3D-parts because it isthe material consumed by the available 3D-printer.

2.1. Mobile Platform

The mobile platform holds all the electronics control-ling all the components of the robot, and some of thesecomponents too. Among the electronics one can findan Arduino DUE board and two H-bridges, and amongthe components, four DC-motors and a AIRPO D2018B12V vacuum pump (see Fig. 2b).

2.2. Robot Arm

The robot arm is made of 3D-printed links and threeHitec HSR-5498SG servomotors, as shown in Fig. 3.Hence, the robot arm has three DOFs. A Denavit-Hartenberg approach [3] was used to deduce the forwardkinematics, as follows:

px = cos(q1)[l∗1 + l3 cos(q2 + q3) + l2 cos(q2)] (1a)py = sin(q1)[l∗1 + l3 cos(q2 + q3) + l2 cos(q2)] (1b)pz = l1 + l3 sin(q2 + q3) + l2 sin(q2) (1c)

, where px, py and pz are referenced to the world co-ordinate frame shown in Fig. 3a. Also, a geometricalapproach [3] was used to deduce the inverse kinematics

2http://www.solidworks.com

and so to control the movements of the arm following astraight line, as follows:

q1 = arctg(

Py

Px

)(2a)

q2 = arctg

Pz − l1√P2

x + P2y − l∗1

− arctg(

l3 sen(q3)l2 + l3 cos(q3)

)(2b)

q3 = arctg±

√1 − cos2(q3)cos(q3)

(2c)

, where q1, q2 and q3 angles correspond to those shownin Figs. 3b and 3c. Simple way-points extrapolationis programmed to join origin and destiny targets in theCartesian space.

2.3. Jamming GripperThe first replication of the jamming gripper used cof-

fee as the granular material enclosed within the balloon,as proposed by Amend et. al. in [2] . However, the con-sistency of this gripper required considerable strength atthe robot arm to achieve successful grasping. Since therobot arm under development was a small, transportableone, another materials and levels of granularity were ex-plored3. The most convenient combination found –forthis particular robot arm– was 1-to-1.5mm diameterstyrofoam balls as shown in Fig. 5.

3. Results

The robot is currently commanded from a PC thor-ough a serial interface, USB or Bluetooth, that sendscommands such as SET 3D-point arm target, TURN

3These findings will be soon reported on [4].

2

(a) Robot arm. (b) Overhead view. (c) Side view.

Figure 3: (a) Robot arm with the world coordinate frame and lengths of fixed links. (b) Overhead view of the robotarm showing the q1 parameter. (c) Side view of the robot arm showing the q2 and q3 parameters.

(a) Lateral view of the robot. (b) Overhead view of the robot.

Figure 4: (a) lateral view of the robot including itswheels, and (b) overhead view of the robot includingits workspace.

ON/OFF vacuum pump, and SET base speed and direc-tion, among others. Due to its omni-directional wheels(see Fig. 4a), the robot moves forward, backward, side-to-side, diagonally and rotates. The robot arm positionsthe gripper at any point within its workspace, as par-tially shown in Fig. 4b. The jamming gripper graspsobject of diverse shapes, such as LEDs, cubes, and ballbearings; as shown in Fig. 5.

4. Discussions

Due to the lack of encoders at the wheels, speedcontrol is not optimal. This issue is specially notori-ous when moving diagonally at low speed. The grip-per works correctly as long as the grasped objects arelighter than 100gr. Heavier objects needs a larger con-tact surface with the balloon. This issue can be ad-dressed with a larger balloon or a heavier base to pushstronger. Currently, when the servos apply their maxi-mal force against an object, the base is lifted.

(a) Grasping a LED. (b) Grasping a cube. (c) Grasping bearing.

Figure 5: Jamming gripper holding diverse objects.

5. Conclusions

A mobile universal gripper with potential to solvetypical challenges of robot competitions was built. Animportant relation between the hardness and granularityof the jamming material with the pushing force requiredfor successful grasping was found. At future, the robotwill be improved with encoders at the wheels, a largerballoon, a camera such as CMUcam4 for color detec-tion, and algorithms to solve competition challenges.

References

[1] B. Munske, J. Kotlarski, T. Ortmaier, The robotchallenge - a re-search inspired practical lecture, in: Intelligent Robots and Sys-tems (IROS), 2012 IEEE/RSJ International Conference on, 2012,pp. 1072–1077. doi:10.1109/IROS.2012.6385496.

[2] J. Amend, E. Brown, N. Rodenberg, H. Jaeger, H. Lipson, A pos-itive pressure universal gripper based on the jamming of granularmaterial, Robotics, IEEE Transactions on 28 (2) (2012) 341 –350.doi:10.1109/TRO.2011.2171093.

[3] R. J. Schilling, Fundamentals of Robotics: Analysis and Control,1st Edition, Prentice Hall, 1990.

[4] H.-R. Valenzuela-Coloma, Y.-s. Lau-Cortes, R.-E. Fuentes-Romero, R.-F. Mendoza-Garcia, Mentaca: Universal mobile jam-ming gripper, Mechatronics, The Science of Intelligent Machines(2015) to be submitted.

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