Design and Realization of a Full-Sized Anthropometrically Correct Humanoid Robot

ORIGINAL RESEARCH published: 25 June 2015 doi: 10.3389/frobt.2015.00014 Herbert: design and realization of a full-sized anthropometrically correct humanoid robot Brennand Pierce* and Gordon Cheng Institute for Cognitive Systems, Technische Universität München, Munich, Germany In this paper, we present the development of a new full-sized anthropometrically correct humanoid robot Herbert. Herbert has 33 DOFs: (1) 29 active DOFs (2 × 4 in the legs, 2 × 7 in the arms, 4 in the waist and 3 in the head) and (2) 4 passive DOFs (2 × 2 in the ankles). We present the objectives of the design and the development of our system, the hardware (mechanical, electronics) as well as the supporting software architecture that encompasses the realization of the complete humanoid system. Several key elements, that have to be taken into account in our approach to keep the costs low while ensuring high performance, will be presented. In realizing Herbert we applied a modular design for the overall mechanical structure. Two core mechanical module types make up the Edited by: Lorenzo Natale, main structural elements of Herbert: (1) small compact mechanical drive modules and (2) Istituto Italiano di Tecnologia, Italy compliant mechanical drive modules. The electronic system of Herbert, which is based Reviewed by: on two different types of motor control boards and an FPGA module with a central Giovanni Stellin, Telerobot Labs Srl, Italy controller, is discussed. The software architecture is based on ROS with a number of Kensuke Harada, sub-nodes used for the controller. All these supporting components have been important National Institute of Advanced in the development of the complete system. Finally, we present results showing our Industrial Science and Technology, Japan robot’s performances: demonstrating the behavior of the compliant modules, the ability of *Correspondence: tracking a desired position/velocity as well as a simple torque controller. We also evaluate Brennand Pierce, our custom communication system. Additionally, we demonstrate Herbert balancing and Institute for Cognitive Systems, Technische Universität München, squatting to show its performance. Moreover, we also show the simplicity of the higher Karlstrasse 45/II, Munich 80333, level supporting software framework in realizing new behaviors. All in all, we show that Germany our system is compact and able to achieve comparable human performances and has [email protected] human proportions while being low cost. Specialty section: Keywords: humanoid robot, compliant control, anthropometrically correct humanoid robot, human performance, This article was submitted to torque controllable Humanoid Robotics, a section of the journal Frontiers in Robotics and AI Received: 16 December 2014 Introduction Accepted: 19 May 2015 Published: 25 June 2015 Over the past two decades, a number of full-sized humanoid robots have been designed and realized: Citation: Hubo (Park et al., 2005), Honda P2/P3 (Hirai et al., 1998), HRP-series (Kaneko et al., 2008), CB Pierce B and Cheng G (2015) (Cheng et al., 2007), LOLA (Lohmeier et al., 2009), TORO iteOtt2010 and ARMAR-4 (Asfour et al., Herbert: design and realization of a 2013), just to name a few. All these humanoid robots are commonly human in size and achieve full-sized anthropometrically correct humanoid robot. similar or greater human performance. However, all of these humanoid robots suffer from one Front. Robot. AI 2:14. common drawback: their high costs, which are all in the hundreds of thousands of Euros (ranging doi: 10.3389/frobt.2015.00014 from AC200 K to AC1 M). This being one of the main reasons holding back humanoid robots from Frontiers in Robotics and AI | www.frontiersin.org 1 June 2015 | Volume 2 | Article 14 Pierce and Cheng Herbert: design and realisation leaving the high-end laboratories and becoming more widely dealing with impact or safety. Some examples of these humanoid used, and even 1 day being part of everyday life. The popularity robots are MACCEPA (Vanderborght et al., 2009), Blue (Enoch of the humanoid robot NAO (Gouaillier et al., 2009), which is et al., 2012a), and MABEL (Grizzle et al., 2009). The problem small at 0.57 m, weighs 4.5 kg, and is low cost, has shown that with adjustable compliances is that the mechanical complexity an inexpensive platform can help to make humanoid research still needs to be solved. Furthermore, two coupled motors, which more widely accessible to a larger audience from universities to are used to control the joint position and the stiffness of a sin- high schools. Thus, we have been designing a full-sized humanoid gle joint, add extra weight, space, and costs. This means that robot that has similar physical specifications as current full- the humanoid robot will require at least twice as many motors sized humanoid robots, but with the main objective of making it and controllers than normal. Currently no full-sized adjustable affordable. compliant humanoid robot has been realized with similar capa- The cost of the actuation mechanism is one of the most costly bility than the more classical approach. As the extra cost of the components on any humanoid robot. For instance, in hydraulic motors and mechanical structures goes against our primary goal humanoid robots (Cheng et al., 2007; Alfayad et al., 2011), the of a low-cost humanoid robot we discounted variable compliance high costs are created by the servo valves and the high machin- actuation in our design. ing tolerances associated with the pistons; whereas in electric Most traditional humanoid robots control strategies rely on humanoid robots, the main costs are in the motors, gearboxes, very accurate knowledge about the robot’s dynamics (i.e., kine- and motor controllers. In our current approach, we have elected to matics and inertia properties) and its environment, and work with focus on electric actuated humanoid robots, as we believe that this high-gain joint position control. Since the major breakthrough approach provides us with the best opportunity of making a full- in walking control being the introduction of the “zero moment sized humanoid robot at the lowest price while at the same time point” (ZMP) (Vukobratović and Borovac, 2004), ZMP was used keeping the same physical performance that other robots possess. in the design and control of a number of high performance biped Looking over the classic design practice of some of the current robots (Hirai et al., 1998; Park et al., 2005; Kaneko et al., 2008). generation of humanoid robots, we can identify key aspects that The main principle of ZMP is that its moment of inertia should can be improved. Firstly, we set out to replace the Harmonic drives be kept in its support polygon, which is normally the supporting that are used in most high-performance electric humanoid robots, foot. Robots like the HRP-series, Hubo, or LOLA are classed as such as HUBO (Oh et al., 2006), HRP-series (Kaneko et al., 2008), stiffed fully actuated robots, where the structure and actuation TORO (Ott et al., 2010), iCub (Parmiggiani et al., 2012), and system are rigid with the only compliant element in the sole of ARMAR-4 (Asfour et al., 2013). Secondly, we need to examine the the foot. These robots all require very accurate control of the power and control electronics followed by the mechanical design joint angles and velocities. Hence, torque-controlled robots have with the aim to reduce the costs and simplify the design of the become more attractive in recent years because of the key features overall system. of safe interaction with the environment and humans (Haddadin Compliant joints have shown to be beneficial in humanoid et al., 2013), compliant behavior, and the ability to directly control robots (Tsagarakis et al., 2011; Enoch et al., 2012b), therefore the forces within the controller. CB (Cheng et al., 2007) and TORO we set out to examine the use of compliant joints in a selected (Ott et al., 2010) are two examples of full-sized humanoids robots, number of joints, primarily for the legs. The reason we believe which are both fully force-controllable. mechanical compliance is important for the humanoid’s legs is the There has been three humanoid robots that have the pri- foot placement, which is essential for absorbing the impact forces marily design goal of being anthropometrically correct. The first for actions like walking and jumping (Hurst, 2011). Controlled humanoid is HRP-4C (Kaneko et al., 2009) which is based on an compliance was also considered but that would not provide us average young Japanese female. This humanoid was designed for with the performance we needed as the latency from the sensors the entertainment industry such as a fashion model or the master detecting the impact force to the time of the joint moving would of ceremony. So the hands and head of the robot were designed to be too long (Pratt and Williamson, 1995). Typically, compliance be as life like as possible with realistic skin. The second humanoid is added to the joint using “Series Elastic Actuators” (SEA), as is WABIAN-2 (Aikawa et al., 2006). This humanoid was designed introduced by (Pratt and Williamson, 1995) where a spring is to help researchers study rehabilitation and welfare instruments. placed in-between the motor and the output. This has two advan- The WABIAN-2 researchers had three reasons that they felt an tages: (1) first, it makes measuring forces easier as the measured anthropometrically correct humanoid is beneficiary. First, they spring displacement corresponds to the force (2) second, it allows hypothesized that measuring the angle and torques at the joints, absorption of impact forces and could also be used to store energy. when the robot used a device, could be measured more easily SEA has been successfully implemented in a number of robots compared to the corresponding values from a human subject.

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