**Design, Setup, and Evaluation of a Compensation System for the Light Deflection Effect Occurring When Measuring Wrought-Hot Objects Using Optical Triangulation Methods**

#### **Lorenz Quentin \*, Carl Reinke, Rüdiger Beermann and Markus Kästner and Eduard Reithmeier**

Institute for Measurement and Automatic Control, Leibniz University Hannover, Nienburger Strasse 17, 30167 Hannover, Germany; reinke@imr.uni-hannover.de (C.R.); beermann@imr.uni-hannover.de (R.B.); kaestner@imr.uni-hannover.de (M.K.); sekretariat@imr.uni-hannover.de (E.R.)

**\*** Correspondence: lorenz.quentin@imr.uni-hannover.de or quentin@imr.uni-hannover.de

Received: 10 June 2020; Accepted: 3 July 2020; Published: 7 July 2020

**Abstract:** In this paper, we present a system to compensate for the light deflection effect during the optical geometry measurement of a wrought-hot object. The acquired 3D data can be used to analyze the formed geometry of a component directly after a hot forging process without waiting for the needed cooling time to room temperature. This may be used to parameterize the process and to detect defect components early in the production process, among others. The light deflection as the deviation from the linear path of the light is caused by an inhomogeneous refractive index field surrounding the hot object. We present the design and setup for a nozzle-based forced air flow actuator, which suppresses the light deflection effect. The design process includes a simulation of the developing field, as well as of the interaction of the field with an external forced air flow. The cooling effect of the air flow is evaluated, and conclusions are drawn from the conflicting interests of good measurement conditions against the forced cooling of the hot object. The findings are then implemented in the physical setup of the suppression system. The system is evaluated using a previously established method based on optical triangulation and fringe projection. Other occurring effects and their influence on the evaluation are considered and discussed.

**Keywords:** tailored forming; bulk metal forming; geometry measurement; wrought-hot objects
