Design of Non-overconstrained Energy-efficient Multi-axis Servo Presses for Deep-Drawing Applications * Francesco Meoni, Marco Carricato DIN-Department of Industrial Engineering University of Bologna, Bologna, Italy francesco.meoni2@unibo.it, marco.carricato@unibo.it Servo-actuated presses may provide maximum pressing force at any ram position in the same manner that hydraulic presses do, while offering several benefits in terms of preci- sion, energy-conversion efficiency and simplicity, due to their lack of hydraulic circuitry and oil. Several press builders have developed servo-actuated presses; however, issues re- lating to overconstrained multi-axis architecture have been neglected. The present study proposes an innovative method to avoid overconstrained architectures in multi-axis presses, by implementing a family of modular parallel mechanisms that connect multiple servo-axes to the press ram. Paral- lel mechanisms, which can be applied in several fields of robotics and industrial automation, exhibit important bene- fits for the application at hand, including high load capacity, stiffness and compactness. A biaxial industrial servo press prototype with a non-overconstrained and modular architec- ture was built and presented as a proof of concept. Each axis comprises a servomotor, a gearbox reducer and a ball- screw transmission. It is shown that such a press may be con- structed from commercially available components, achieving high energy efficiency and high press force with relatively simple construction. A direct comparison with an equivalent hydraulic-press model is carried out, thus highlighting the servo press energy efficiency. 1 Introduction Electronically-controlled servo drives are primarily used in industry as motors for the movement of manufacturing components or the actuation of tools. Recently, several press builders have developed next-generation pressing machines actuated by servo technology. This type of press maintains the flexibility of hydraulic presses while offering the unique benefits of a mechanical press: high speed and accuracy can be achieved without using hydraulic-oil, while, as with hy- draulic technology, maximum pressing force is available at any ram position and large strokes may be performed.These features, along with servo-drive digital control, allow the ex- ecution of a wide range of movements with improved ac- curacy, including those specific to the majority of high-load *A preliminary and partial version of this paper was presented at the 2014 ASME Manufacturing Science and Engineering Conference (MSEC 2014), June 9-13, 2014, Detroit, MI, USA pressing processes. The absence of hydraulic oil is a ben- efit from many points of view: it is more eco-sustainable, creates a cleaner working environment and eliminates the re- quirement for oil distribution circuits, thus avoiding issues related to piping and oil disposal, as well as removing the power consumption of auxiliary devices. Furthermore, there is no energy-conversion loss between mechanical and hy- draulic motion, thus yielding higher energy efficiency. The first applications of servomotors in pressing op- erations concerned standard mechanical press architecture, where a crank-lever mechanism was actuated by an electric motor along with a clutch and a flywheel. The flywheel al- lowed storage of kinetic energy while the motor was disen- gaged, subsequently being released during the pressing phase while relying on a crank-lever mechanism to generate peak force. In order to provide the necessary power, both (fixed- speed) induction motors and servomotors, appropriately cou- pled, were mounted together on the press, in the so-called hybrid architecture [1–7]. The induction motor provided the necessary energy to complete the process while the servomo- tor was responsible for precise regulation. Though this ap- proach saw integration of servomotors, maximum force was only available at specific positions, i.e. in the proximity of the dead centre of the linkage. To achieve complete machine flexibility, as with hy- draulic presses, maximum force must be available at any position over large strokes. To this end, electric presses equipped solely with servo-actuated axes have been devel- oped. The generic servo-actuated axis (also referred to as servo axis) is composed of a servomotor that provides rotat- ing motion, and a constant-speed-ratio mechanical transmis- sion that transforms the latter into linear movement for the press end-effector. Typically, ball or roller screw transmis- sions are preferred due to their high mechanical efficiency, back-drivability, backlash control, and precision. State-of- the-art servo presses of this type were presented in [8], with servomotors and related technologies analyzed in the context of major applications in sheet and bulk metal forming. How- ever, recirculating-body screws for severe dynamic loads are difficult to manufacture and very expensive. Accordingly, they are often the bottleneck of press design, posing techni- cal and economical limits to the admissible load that a sin- gle servo axis may sustain. Hence, to achieve greater press 1 Journal of Mechanical Design. Received February 17, 2015; Accepted manuscript posted March 22, 2016. doi:10.1115/1.4033085 Copyright (c) 2016 by ASME Accepted Manuscript Not Copyedited Downloaded From: http://mechanicaldesign.asmedigitalcollection.asme.org/ on 03/22/2016 Terms of Use: http://www.asme.org/about-asme/terms-of-use