Evaluation of Human Safety in the DLR Robotic Motion Simulator Using a Crash Test Dummy
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2013 IEEE International Conference on Robotics and Automation (ICRA) Karlsruhe, Germany, May 6-10, 2013 View metadata, citation and similar papers at core.ac.uk brought to you by CORE provided by Institute of Transport Research:Publications Evaluation of Human Safety in the DLR Robotic Motion Simulator using a Crash Test Dummy Karan Sharma, Sami Haddadin, Sebastian Minning, Johann Heindl, Tobias Bellmann, Sven Parusel, Tim Rokahr and Alin Albu-Schaeffer Abstract— The DLR Robot Motion Simulator is a serial kinematics based platform that employs an industrial robot (as opposed to the conventional ’Hexapod’) to impart motion cues to the attached simulator cell. This simulation platform is the culmination of ongoing research on motion simulation at the Robotics and Mechatronics Center, German Aerospace Center (DLR). Safety tests were undertaken to ascertain the effects of critical motions and subsequent emergency stop procedures on the prospective human passengers of the simulator cell. To this end, an Anthropomorphic Test Device (ATD) aka ’crash test dummy’ was used as a human surrogate for these tests. Several severity indices were evaluated for the head-neck region, which was found to be more susceptible to injuries compared to the rest of the body. The results of this study are discussed in this paper. I. INTRODUCTION Motion simulation systems enjoy widespread applications Fig. 1. DLR Robotic Motion Simulator (DLR-RMS) in fields ranging from entertainment industry to defense research. In the domain of flight simulation, motion sim- ulators have been in use since decades for pilot-training this version includes a completely overhauled simulator cell and research. The majority of these simulators employ vari- that offers a better Audio/Video experience. This version has ants of the six cylinder Stewart platform aka Hexapods to also been adapted for active (online) motion simulation and generate the necessary motion cues. This platform has a the underlying research has been addressed in [6], [7]. parallel kinematic configuration that allows motion in six The latest iteration is known as the DLR Robotic Motion degrees of freedom [1]. While these parallel kinematics based Simulator (DLR-RMS) [8]. The design and setup of this simulators can handle large loads e.g. complete cars [2] and simulator was formulated based on experiences gained from hence provide for enhanced realism during simulations, they earlier iterations of this simulation platform. Major modifi- are expensive to deploy and offer a limited range of motion. cations include a linear axis at the base of the manipulator, In recent years, KUKA robotics has introduced several which extends the workspace of the simulator and a com- heavy duty serial kinematics based industrial manipulators pletely overhauled simulator cell design (Fig. 1 & Fig. 2). such as the KR-500, KR-1000 ’Titan’ etc. which have pay- This cell is inherently modular and allows usage of various loads of 500kg and 1000kg, respectively. It was envisioned instrument consoles as per the requirements of different sim- that, since the workspace of a KR-500 is larger and its ulation scenarios. This version has been primarily designed also cheaper than a Stewart platform based simulator, it for active (passenger controlled) simulation and is capable of could be used as a motion simulation platform. The KUKA- 1 simulating land vehicles [7], airplanes [9] etc. Besides this, Robocoaster was the first manifestation of this idea. It is a it also includes 3-D projection capabilities, several safety passive (i.e. preprogrammed) motion simulator that can sit features, new seating setup etc. up to two passengers and is primarily used as a amusement The passenger seating setup of the RoboSim 4-D simu- ride at several theme parks [3]. Since then, the partnership lator was designed for passive simulation scenarios, so it between DLR and KUKA has led to several iterations of the featured top closing roller-coaster type seats. These seats are Robocoaster, e.g. KUKA RoboSim 4-D simulator [4]. It is constricting and therefore not suitable for active simulation a passive motion simulator that has been developed at DLR scenarios. Hence, the seating arrangement in the DLR-RMS [5]. Besides the usual features offered by the Robocoaster, was modified to make it more suitable for active simulation *This work is supported by KUKA Roboter GmbH scenarios. The passenger can freely move his hands and has The authors are with the Robotics and Mechatronics Center, German an unconstrained view of the instrument console. Aerospace Center (DLR), 82234 Oberpfaffenhofen-Wessling, Germany [email protected] Passenger safety is of paramount importance in every 1Copyright: KUKA Roboter GmbH motion simulator. Initial attempts to determine the safety- 978-1-4673-5642-8/13/$31.00 ©2013 IEEE 205 motion profile etc. are widely varied to facilitate for a more comprehensive analysis from a diversified set of data. For the tests presented in the following sections (refer Sec. V), the watchdog application is not used. This application is currently under further development and is not very robust. By not employing this application for these experiments, one can account for scenarios where this application could fail to detect a critical situation. This allows for a more rigorous evaluation of the general safety setup. The field of serial kinematics based motion simulation is currently in its initial stage. In the past years, the range of simulation scenarios has expanded from passive to active Fig. 2. Simulator Cell and some of its safety features and new simulation scenarios are being actively pursued [13]. However, in the knowledge of the authors, the issue of passenger safety has not yet been thoroughly addressed. This worthiness of serial kinematics based motion simulators were work aims to bridge this gap by undertaking a comprehensive made using the RoboSim 4-D simulator [8]. Typical testing safety analysis for such a simulator. Through this evaluation, scenario involved driving the robot axes at high velocities we hope to identify and subsequently address any critical and subsequently triggering an emergency stop (e-stop) to scenarios that affect human safety. Thereby also addressing generate decelerations of the simulator cell. An inertial issues that could impede the further development of this field. measurement unit (IMU), mounted near the usual head In the following section, the critical scenarios that a position inside the cell was used to measure the resulting passenger could face during a simulation are introduced. This decelerations. The peak value of e-stop deceleration during is followed by an introduction to different injuries and their one of the tests was 3g (including gravity). This is within the evaluation indices. Then the experimental setup is described 5g (harmless acceleration) limit for whiplash related injuries and finally a discussion of the results is presented. defined by a German jurisdiction [10]. Further investigation of the results revealed that these tests are not truly represen- II. CRITICAL SCENARIOS tative of the accelerations that would’ve been experienced by the passenger, as the sensor was mounted on the cell’s As established earlier, the DLR-RMS employs a manip- enclosure. This way, the effects that would’ve been induced ulator to produce the motion cues during simulation. The by the motion of head relative to the cervical spine and the safety setup of these manipulators is designed for industrial torso, are not observed. Secondly, injury assessment criterion settings, where the aim of this setup is to immediately stop used in this investigation is not universally applicable to all the manipulator and prevent its axes from colliding with types of high deceleration scenarios. It is supposed to serve each other. To achieve this, they are equipped with brakes as rough assessment criterion for disorders resulting from and several e-stop procedures (refer Sec. IV). But, what rear impacts (explained in section II). happens when a human is seated at the Tool Center Point Based on the results of these initial tests, several software (TCP) of such a manipulator and one of these e-stops is based safety measures (together referred to as ’watchdog executed? To analyze these scenarios, first the classification application’) were developed and integrated into the control of accelerations that are critical to humans is presented as architecture to provide an extra layer of security [11]. This follows: watchdog application continuously observes the state and • Impact accelerations: acceleration pulses of up to motion profile of the manipulator to predict and prevent an 200ms are classified as impacts e.g. high decelerations impending high deceleration scenario (such as a software due to car crashes, resulting accelerations when slapping triggered e-stop). To analyze the accelerations experienced in someones back etc. the head-neck region, an anthropomorphic test device (ATD) • Sustained accelerations: accelerations lasting longer popularly known as ’crash test dummy’ [12] was used for the than 200ms are classified as sustained accelerations e.g. subsequent safety evaluation mentioned in [11]. This work in roller-coasters, fighter planes etc. These accelerations was an important step in the safety analysis of the DLR- (in a range of few g) can lead to G-Induced Loss RMS, but was limited by type and number of sensor data of Consciousness (G-LOC) e.g. an acceleration with (only accelerations) available for evaluation. an onset rate of 0.5g/s in the +Gz direction (upwards In this paper, a more detailed and thorough analysis of acceleration, that pushes the body back into its seat) can passenger safety in the simulator is presented. The usage lead to G-LOC within 6s [14]. of multiple types of sensors in the ATD e.g. acceleration, The manipulator used for the simulator is constrained by its force/torque as opposed to only acceleration sensors in the joint limits and hence, is not capable of producing sustained earlier analyses, allows for a broad range of data from which accelerations in one direction that could lead to G-LOC.