Mechanical & Materials Engineering, Department of


First Advisor

Dr. Benjamin S. Terry

Second Advisor

Dr. Arthur Zygielbaum

Date of this Version

Summer 8-1-2017

Document Type



Salafian, I. (2017). Development of the End-Effector of a Cable-Driven Parallel Manipulator for Automated Crop Sensing (Master's thesis).


A THESIS Presented to the Faculty of The Graduate College at the University of Nebraska In Partial Fulfillment of Requirements For the Degree of Master of Science, Major: Mechanical Engineering and Applied Mechanics, Under the Supervision of Professor Benjamin Terry. Lincoln, Nebraska: August, 2017

Copyright © 2017 Iman Salafian


A four cable-driven parallel manipulator (4CDPM), consisting of sophisticated spectrometers and imagers, is under development for use in acquiring phenotypic and environmental data over an acre-sized maize field. This thesis presents the design, controls, and testing of two sub-systems in a 4CDPM: a Center of Mass Balance System (CMBS) and a Drop-Down System (DDS).

One of the factors that influences stability is the center of mass (COM) position of the end effector. An offset in COM can cause a pendulum effect or an undesired tilt angle. A center of mass balancing system is presented in this thesis to minimize the vibration and enhance the stability, accuracy, and quality of acquired data from the instruments.

The current design of the 4CDPM enables the sensing of the canopy at normal as well as oblique angles, but the end-effector itself must remain above the canopy; otherwise, the four support cables (and the end-effector itself) may impinge upon the crops surrounding those being imaged. Thus, a supplementary drop-down system is needed for positioning a small sensor package inside the canopy, which enables the researchers to analyze the low-height crops and take images of the side views of the maize canopy.

For the CMBS, the results demonstrate that this system improves the stability of the end-effector by decreasing vibrations and static tilt angle. The results for the DDS show that this system needs an additional stabilization system to damp oscillations.This thesis is divided into two parts, exploring both devices. Part one focuses on developing a system and method for the CMBS, while part two focuses on the feasibility of the DDS. In each part, the motivation behind each of the devices is described, and the design of the respective device and the reasons behind some of the design choices are presented. Several experiments are designed and executed for both projects, and the results are given for each.

Finally, the conclusion section describes the future work associated with the devices as well as the accomplishments achieved through the design of each device.

Advisor: Benjamin S. Terry