Doctoral thesis, 2020

The manufacturing industries have been using flexible production technologies to meet the demand for customisation. As a part of production, fixtures have remained limited to dedicated technologies, even though numerous flexible fixtures have been studied and proposed by both academia and industry. The integration of flexible fixtures has shown that such efforts did not yield the anticipated performance and resulted in inefficiencies of cost and time. The fundamental formulation of this thesis addresses this issue and aims to increase the efficiency of flexible fixtures.

To realise this aim, the research in this thesis poses three research questions. The first research question investigates the efficiency description of flexible fixtures in terms of the criteria. Relative to this, the second research question investigates the use of efficiency metrics to integrate efficiency criteria into a design procedure. Once the efficiency and design aspects have been established, the third research question investigates the active control of flexible fixtures to increase their efficiency.

The results of this thesis derive from the outcome of seven studies investigating the automotive and aerospace industries. The results that answer the first research question use five criteria to establish the efficiency of flexible fixtures. These are: fundamental, flexibility, cost, time and quality. By incorporating design characteristics in respect of production system paradigms, each criterion is elaborated upon using relevant sub-criteria and metrics. Moreover, a comparative design procedure is presented for the second research question and comprising four stages (including mechanical, control and software aspects). Initially, the design procedure proposes conceptual design and verification stages to determine the most promising flexible fixture for a target production system. By executing detailed design and verification, the design procedure enables a fixture designer to finalise the flexible fixture and determine its efficiency. Furthermore, a novel parallel kinematics machine is presented to demonstrate the applicability of the design procedure’s analytical steps and illustrate how appropriate kinematic structures can facilitate the efficiency-orientated design of flexible fixtures.

Based on the correlation established by the controller software’s design procedure, the active control of flexible fixtures directly affects the quality criterion of flexible fixture efficiency. This provides the answer to the third research question, on general control strategies for active control of flexible fixtures. The introduction of a system model and manipulator dynamics proposes force and position control strategies. It is shown that any flexible fixture using a kinematic class can be controlled, to regulate the force and position of a workpiece and ensure that process nominals are preserved. Moreover, using both direct and indirect force control strategies, a flexible fixture’s role in active control can be expanded into a system of actively controlled fixtures that are useful in various processes. Finally, a position controller is presented which has the capacity to regulate both periodic and non-periodic signals. This controller uses an additional feedforward scheme (based on the Hilbert transform) in parallel with a feedback mechanism. Thus, the position controller enables flexible fixtures to regulate the position of a workpiece in respect of any kind of disturbance.









Virtual Development Laboratory, Chalmers
Opponent: Professor Anders Robertsson, Department of Automatic Control,Lund University


Ilker Erdem

Chalmers, Industrial and Materials Science, Production Systems

Feedforward control for oscillatory signal tracking using Hilbert transform

European Journal of Control,; Vol. 50(2019)p. 41-50

Journal article

A novel comparative design procedure for reconfigurable assembly fixtures

CIRP Journal of Manufacturing Science and Technology,; Vol. 19(2017)p. 93-105

Journal article

Development of Automated Flexible Tooling as Enabler in Wing Box Assembly

Procedia CIRP. 6th CIRP Conference on Assembly Technologies and Systems, CATS 2016; Gothenburg; Sweden; 16 May 2016 through 18 May 2016,; Vol. 44(2016)p. 233-238

Paper in proceeding

Automated Flexible Tooling for Wing Box Assembly: Hexapod Development Study

SAE Technical Papers,; Vol. 2016-October(2016)

Journal article

Development of Affordable Reconfigurable Tooling in Car Manufacturing Cells – A Case Study

23rd International Conference for Production Research, ICPR 2015, Manila, Philippines, 2-6 August 2015,; (2015)

Paper in proceeding

Erdem, I, Asbjörnsson, G, Kihlman, H. Workpiece Force and Position Control for Active and Flexible Fixtures

Erdem, I, Abadikhah, H. n-PRPR: Kinematics Analysis of a Novel Translational Parallel Kinematics Machine

Miljöanpassade flygmotordemonstratorer för ökad konkurrenskraft (SWE DEMO MOTOR)

VINNOVA (2015-06047), 2016-01-01 -- 2016-08-31.

AProC - Automated Process Controll BIW

VINNOVA (2013-04706), 2014-01-01 -- 2015-12-31.


VINNOVA (2016-01973), 2016-04-01 -- 2016-12-31.

LOw COst Manufacturing and Assembly of Composite and Hybrid Structures (LOCOMACHS)

European Commission (EC) (EC/FP7/314003), 2012-09-01 -- 2016-02-29.

Subject Categories

Production Engineering, Human Work Science and Ergonomics

Areas of Advance




Doktorsavhandlingar vid Chalmers tekniska högskola. Ny serie: 4791



Virtual Development Laboratory, Chalmers


Opponent: Professor Anders Robertsson, Department of Automatic Control,Lund University

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