Automation of an Educational Gantry Crane

Andrea Pino-Ramos(∗), Yi-Sheng Lau-Cortes, Ricardo Fuentes-Romero

and Ricardo Mendoza-Garcia

School of Mechanical EngineeringUniversity of Tarapaca

Arica-Chile(∗) Corresponding author: andrea.pino.ramos@gmail.com

I Introduction

In order to motivate the learning of basic subjects of Mechanical Engineer-ing, students of an introductory course build a small, manually-operated gantrycrane using low-cost materials, such as aluminum foil and silicone [1]. After-wards, in order to put in practice their theoretical knowledge, students of amore advanced course of Mechatronics Engineering automate the same craneusing an Arduino UNO card [2], software PID controllers, bidirectional 360o

servomotors, ultra-sonic sensors, and 3D-printed parts.

(a) Manually-operated gantry crane. (b) Automated gantry crane.

Figure 1: Educational gantry crane “before” and “after” automation.

The hook of the crane can then perform semi-smooth trajectories in theCartesian space although the whole structure struggles to support the addedweight of servomotors, sensors, pulleys and other parts. The resulting bendingof the structure makes it difficult to implement a precise control scheme for axesdisplacement. At future, stronger material could be used at the introductoryproject, such as wood or acrylic, which are still cheap, and quick and easy tolaser cut [3].

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II Conception of the crane - Methods

A Welcome! Build it from paper

Students of an introductory course to Mechanical Engineering face a project tobuild a small structure with restrictions in construction time and composingmaterials. Projects include a drawbridge, a crane, and a gantry crane, butthis work documents only the last one. All constructions must be operatedmanually; and teams are limited to five members, construction time to 3.5hr,and composing materials to aluminum foil (Fig. 2a), glue, and sewing thread.

B Advanced? Make it wise!

At a more advanced course of Mechatronics Engineering, students are askedto automate the gantry crane. To this end, teachers provide an Arduino UNOcard (Fig. 2b), bidirectional 360o servomotors (Fig. 2c), and ultrasonic “PING”sensors (Fig. 2d). In addition to that, students are asked to control the dis-placements in the X, Y, and Z axes by using PID software controllers, and theyare given access to LEGO pieces and a Dimension 1200es 3D printer.

(a) Aluminum foil. (b) Arduino “UNO”. (c) 360o servomotor. (d) Ultrasonic sensor.

Figure 2: Hardware available for building the gantry crane.

III Birth of the crane - Results

A From soft to hard

In response to the requirements of Sec. IIA, the basic structure of the gantrycrane was made of matches, aluminum foil, thermal silicone and sewing thread.Actuation was made of cotton strings, glue was applied at discrete points, androlling elements, such as wheels for displacement across axes, were provided bytoys. The final structure is shown in Fig. 1a.

B From manual to automated

The first consideration was to design pulleys, transmissions, and holders forsensors and actuators, and to print them out in the 3D printer in ABSplus ther-moplastic. Then, the servomotors were engaged to the pulleys, and a support

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for the Z-axis was built with LEGO pieces. Finally, the PID software controllerwere implemented in the Arduino UNO card with a proportional plus integral(PI) term controlling the absolute displacement provided by the ultrasonic sen-sors. The 3D-printed and LEGO pieces are shown in Fig. 3.

(a) X-axis pulley. (b) 90o force transmission. (c) Sensor holder. (d) Z pulley.

Figure 3: 3D-printed pulleys, transmissions, and holders for sensors/actuators.

C Performance

Before automation, the structure was able to lift a load of approx. 0.7Kg at aheight of 30cm over the floor, and to move it –in the (X, Y) plane– a distance of40cm from the initial point. After automation, as the total weight of the addedcomponents was of 0.85Kg, the crane was basically left without capability oflifting and the Y-axis was curved. The servos of the X and Y axes moved at4 cm

s and the ones of the Z-axis at 8 cms .

IV Discussions

The weight of added components to the Y-axis produced a stress greater thanthe yield strength that resulted in a plastic deformation, as shown in Fig. 1b,which also caused problems with the PID controllers as axes were not able toroll smoothly anymore. At future introductory projects, wood or acrylic couldbe good replacements to aluminum foil because they allow elastic deformationand still are cheap and easy to laser cut.

V Conclusions and Future Work

We showed the automation of a entry-level mechanics project and concludedthat stronger, less bendable materials should be used in the initial project.Interaction between novel and advanced student was reciprocally motivating.At future, an Universal Jamming Gripper [4] could be added to the hook andcombined with a CMUcam (http://www.cmucam.org/) to provide versatile, au-tonomous grasping of objects. We also want to use optical fiber as pulleysstrings to mix mechanical transmission with communication and so to decreasethe final count on cables.

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References

[1] R. Fuentes-Romero, “Experiences on creativity and design challenges atearly stages of Engineering studies,” in Chilean Conference on MechanicalEngineering. Pucon, Chile: University of ”La Frontera”, November 2010.

[2] M. Banzi, Getting Started with Arduino, 1st ed. O’Reilly Media / Make,October 2008.

[3] M. Torrico-Claure and H. Valenzuela-Coloma, “We shouted, we got it: aMechatronics and Robotics Research Laboratory for Northern Chile,” in VLatin American Summer School on Robotics. Santiago, Chile: Universityof Chile, December 2011.

[4] J. Amend, E. Brown, N. Rodenberg, H. Jaeger, and H. Lipson, “A posi-tive pressure universal gripper based on the jamming of granular material,”Robotics, IEEE Transactions on, vol. 28, no. 2, pp. 341 –350, April 2012.

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