IROS2019国际学术会议论文集 0226

WLR II a Hose less Hydraulic Wheel legged Robot Xu Li Student Member IEEE Haitao Zhou Songyuan Zhang Haibo Feng and Yili Fu Abstract The performance of traditional hydraulic robots is often limited by their hoses across moving joints or connecting hydraulic drive units which would reduce their mobility and impede their ability to operate in complex environment In response to this defi ciency this paper introduces the WLR II the second generation of wheel legged robot a novel hydraulic wheel legged robot developed by using hose less design approach which is focused on improving the reliability of the hydraulic system and perfecting the appearance of the robot As its notable features seven Hydraulic Hose less Joints HHJ that include a pair of high and also low pressure oilpipesbasedonrotaryseal Cylinder Valve Skeleton CVS integration thighs and arms which are produced by subtractive manufacturing as well as oscillating cylinders driven by gear rack transmission are included In addition to a description of its design experimental characterizations of rough pavement adaptability and payload capability together with the achievement of the reliability of hydraulic system are also demonstrated As a result we confi rmed effectiveness of the hose less design by moving on the rugged ground climbing slope squatting with load dragging and picking up a heavy load To the authors best knowledge this is the fi rst time that the design of a hose less hydraulic wheel legged robot has been presented I INTRODUCTION For quite some time legged robots have been supposed as a promising solution to the movement problem on rough ter rain where traditional wheeled or tracked vehicles could not traverse effectively 1 Whereas wheeled and tracked robots have great maneuverability in an environment where the terrain is smooth and with well structured surfaces Wheel legged hybrid robots aim at combining the effi ciency of wheeled robots with the versatility of legged robots By adding wheels to the end of legs they can act like wheeled robots on simple terrains and adapt their posture to the shape of uneven ground Quite a bit of wheel legged robots 2 9 were proposed to obtain better adaptability for complex ter rain and maintain high mobility on fl at ground Among these robots Handle developed by Boston dynamics is a biped robot but with wheels instead of feet which combines the rough terrain capability of legs with the effi ciency of wheels 6 Wheels can be fast and effi cient on fl at surfaces while legs can go almost everywhere By combining wheels ResearchsupportedbytheFoundationforInnovativeResearch Groups of the National Natural Science Foundation of China Grant No 51521003 corresponding author Yili Fu and Haibo Feng Xu Li Haitao Zhou Songyuan Zhang Haibo Feng and Yili Fu iswithStateKeyLaboratoryofRoboticsandSystem Harbin InstituteofTechnology Harbin HeilongjiangProvince 150001 China fax 86 0451 86414422 hitlx htzhouhit zhangsy haibo feng meylfu and legs Handle is a sophisticated wheel legged robot with extraordinary rough terrain mobility The design of WLR II is highly inspired from Handle Nevertheless so far there have been no published papers concerning Boston Dynamics locomotion framework hardware hydraulics and detailed designs of Handle Fig 1 The WLR II a novel hose less hydraulic wheel legged robot for both rough and fl at terrain The robot has the potential to be applied in the following applications including search and rescue polar exploration and other occasions Therefore the power density of the driv ing system is becoming increasingly demanded for robots and the defects of traditional motor drive are gradually high lighted 1 The power of the motor is relatively insuffi cient 2 The working region is not ideal with repeatedly start and stop 3 Inadequate loading capacity is not conducive to fi eld operations Overall hydraulic drive has many properties that make it an ideal choice for highly dynamic articulated robot applications Firstly hydraulic actuation has been proven to be a suitable actuation technology due to its high power density robustness against impacts and high stiffness for high bandwidth control 10 Secondly mechanical robustness cylinders are slim and they well fi t a humanoid body shape if linkages are designed properly Thirdly it will be easier to obtain explosive force for jumping Furthermore the hydraulic fl uid can also serve as the lubricant and coolant of actuators The fl ow characteristics of hydraulic oil can transfer local heat to the whole body of the robot which is 2019 IEEE RSJ International Conference on Intelligent Robots and Systems IROS Macau China November 4 8 2019 978 1 7281 4003 2 19 31 00 2019 IEEE4339 benefi cial to the distributed heat dissipation of the robot This paper presents the development of WLR II Fig 1 which aims to operate in a variety of indoor and outdoor missions with high mobility All joints of WLR II besides wheels are driven by hydraulic pressure which is also adopted by HYQ 11 HYDRO D 12 and the robots from Boston Dynamics BigDog 13 and ATLAS 14 In result WLR II has the potential to carry a higher payload when compared to electric driven robots Hydraulic biped robots like CB 15 ATLAS TaeMu 16 and HIT biped 17 all adopted the rubber hose to connect the hydraulic drive units with the hydraulic power unit Although it is simple and effective the hose across moving joints may have negative effects on the dynamics of robots and cause unpredictable disturbances The hose is harder than the cable and the bending radius is large In order to protect the hydraulic hose from the wearing and tearing of robot joints a long margin will be reserved in the design of the hose which leads to the robot s hydraulic hose looking long and complicated What s more the exposed hoses which consist of rubber pipe and steel hydraulic inlets increase the weight and complexity of the robot ATLAS is a hydraulically actuated humanoid robot with a very careful hose arrangement but it still retains hoses at the joints Therefore this paper tries to implement hose less design on WLR II which can improve the reliability of the hydraulic system and perfect the appearance of the robot This paper gives an overview of the design and hydraulic system of WLR II We will focus on the hose less design of the novel hydraulic wheel legged robot and present the results of its payload and obstacle avoidance ability The rest of this paper is organized as follows Section II introduces the related works and explains the hose less conceptual design as well as discusses the pros and cons of hose less design Section III presents an overview of the WLR II system Section IV details the implementation of hose less design of the WLR II Section V introduces the preliminary experimental process and results Finally Section VI gives the conclusions and future works II RELATEDWORKS Open challenges in the fi eld of hydraulic legged robots are primarily the energy effi ciency of the hydraulic actuation system the hose routing and the large size of commercially available components 18 A neat routing of hoses across moving joints is complicated especially if the joint range of motion is large To the authors best knowledge hose less fl uid routing is presented by Boston Dynamics fi rstly However they have only published the concept design which adopted 3D printing technology to set the hydraulic pipe routing inside the leg In addition there is no paper or phys ical evidence to prove the feasibility of the design Designing hydraulic circuits in a robot s rotating joints will circumvent many problems posed by hoses and Boston Dynamics s conceptual design inspired us Claudio Semini presented that direct metal laser sintering DMLS can produce highly integrated hydraulic components with reduced weight and higher complexity when compared to traditionally manufac tured manifolds 19 and this technology was successfully applied on HyQ2Max 20 which reduces the number of hoses that connect hydraulic pumps and servo valves What s more Moog in collaboration with IIT presents the hydraulic additive manufactured Integrated Smart Actuator ISA 21 which prints the fl ow path between servo valve and cylinder cavity in the cylinder shell In this way the number of exposed hoses was reduced In our previous research work on the design of WLR 7 we adopted the selective laser melting SLM technology to print two thighs and a pelvis which integrated the hydraulic pipes between the servo valve and the cylinder into the mechanical structure to achieve the goal of both reducing the number of exposed hoses and improving the reliability of hydraulic system a The rotary Glyd Ring for holes and installation diagram b The rotary Glyd Ring for shafts and installation diagram Fig 2 The rotary Glyd Ring and installation diagram DNH9 and dNh9 represent the diameter of the hole and shaft and its available range is about 6mm 130mm d1h9 and D1H9 represents groove diameter d1 DN 4 9mm D1 dN 4 9mm The groove width is 2 2mm The diameter of the O ring section is 1 8mm S is the maximum radial clearance which can reach 0 15mm at 32Mpa None of the above solutions for reducing the number of hoses has completely removed the hoses of hydraulic robots Compared to relatively non moving parts it is very diffi cult for hoses cross moving joints to be embedded in a mechanical structure In industrial applications hydraulic rotary inlets are widely used when liquid or gas is imported from a fi xed part to a rotating part However the standard rotary inlets still need hoses to connect It is not practical to integrate them directly with hydraulic robot s moving joints Unlike the linear Glyd Ring used in hydraulic cylinders for linear motion seals the rotary Glyd Ring is specifi cally used to seal rods shafts pins rotating joints etc with rotating or swinging motion It is a kind of rotating sealing ring which can be subjected to two way action of pressure on both sides or alternating pressure The rotary Glyd Ring is composed of 4340 an elastic rubber O ring and a polytetrafl uoroethylene PTFE ring The O ring is applied to squeeze the PTFE ring through elastic deformation which increases the contact stress be tween the PTFE ring and sealing surface to prevent leakage The rotary Glyd Ring has the characteristics of minimal start up and movement friction no creeping phenomenon good abrasion and high pressure chemical corrosion and temperature resistance What s more the rotary Glyd Ring which needs simple groove structure has good sealing effect on dynamic and static sealing It can be used for the holes and for the shafts The rotary Glyd Ring for holes Fig 2 a is fi tted on the shaft with grooves which is very convenient for groove processing However the assembly of the rotary Glyd Ring requires custom tooling which leads to assembly diffi culties and increased costs but if the rotary Glyd Ring for shafts Fig 2 b is fi tted on the holes with grooves it is easy to assemble the real ring But it is diffi cult to process and monitor the grooves especially in deep holes In summary in order to facilitate assembly and improve the strength of the joint shaft we chose the Glyd Ring for shafts as the joint rotary seal scheme In this paper for the purpose of verifying the reliability of the rotary Glyd Ring for shafts conveniently a joint with two fl ow paths Fig 3 was developed The joint passed the half hour pressure test with 21Mpa and the friction measured by experience did not increase obviously under high pressure Fig 3 The section of joint with two fl ow paths left and physical object right Integrated cylinder and servo valve using additive man ufacturing or subtractive manufacturing can save the hoses between servo valve and hydraulic cylinder It is necessary to realize the hose less design of hydraulic robot by embedding the oil path inside joints There are many advantages of hose less design for hydraulic robots Firstly the mechanical structure embedding all hydraulic pipes of the robot is lighter and more compact Secondly the robot is more beautiful and safer without exposed hoses which are complex and rigid to impede robot movement Thirdly it is benefi cial for robot to establish accurate dynamic model without hoses crossing moving joints Last but not the least hydraulic oil similar to human blood provides energy for the drive units and also spreads heat throughout the robot which has better cooling effect compared with the rubber hoses Correspondingly there are some disadvantages of hose less design On the one hand at least 2 Glyd Rings at the joints increase friction which would slow down the joint force position control response On the other hand inserting the fl ow path into the joints increases the diffi culty of robot design assembly and maintenance Fortunately we succeeded in overcoming these problems This paper presents the concepts of hose less design and also shows the outline of our latest results about WLR II which is the succeeding version of our previous robot WLR III WLR II OVERVIEW In this section the humanlike appearance with high mobil ity and actuator performances for load capacity are discussed Firstly the confi guration of the each actuator was optimized and integrated with the structure for maximizing the mobile abilities as well as reducing the weight Secondly the load capacity was ensured with the high power density hydraulic drive units A Mechanical Structure Overview Fig 4 Overall structural dimension mm and main components overview of the WLR II The weight of WLR II is 70 kg without on board hydraulic pump as shown in Fig 4 and the maximum height is 1 8m WLR II has two legs but wheels instead of feet MR damper and spring systems 22 23 in the calf to absorb shock and recycle energy while jumping or rolling on the uneven surface two arms with a pair of fi xed grippers for carrying load What s more the IMU sensor attached in the pelvis provides the posture information for further motion control WLR II is a wheel legged robotic platform which can be used to study motion balance object operation as well as dynamic motion control for complex terrain To obtain the fl exibility for accomplishing different tasks WLR II is designed with fl exible mechanical properties and adequate controllers Mobility operability and structural strength to gether with actuation performance strength power speed range of motion were considered to meet the requirements of high maneuver during emergent scenarios The main specifi cations of WLR II are presented in Table I One of the hardware design requirements is to improve the robot s performance while reducing the total weight The frameworks of WLR are mainly fabricated from aluminum alloy titanium alloy and quenched tempered steel in order to realize high stiffness as well as lightweight Most of 4341 TABLE I MAINSPECIFICATIONS OFWLR II Mass Wheel 5 1kg x 2 Leg 8 6kg x 2 Pelvis 4kg Torso 28 6kg Arm 5kg x 2 SizeHeight 1800mm Width 520mm DOFLeg 3 x 2 Waist 1 Arm 3 x 2 ActuationHydraulic cylinder Power supply 7 5kW hydraulic power unit External Pressure 12MPa normal 21MPa max 96V battery 30Ah Controllers 32 bit QNX on PCI 104 onboard IntelR AtomTMD525 1 8GHz Dual core Actuator sensorLVDT Load cell Pressure Perception sensorsIMU LIDAR Stereo camera Sampling rateTask level 200 Hz Servo level 1 kHz the mechanical components cylinder skeleton and link structures are machined from aluminum alloy type 7075 T6 while heavily stressed units such as joint shafts gear rack and piston rods were produced from quenched tempered steel 45 which gives an excellent combination of oxidation and corrosion resistance together with high strength What s more the core of the connecting drive parts used to transfer cylinder force like two force bar and slider connectors were made by titaniumalloy TC4 to improve stiffness strength and low weight to critical central structure while the body covers were made of photosensitive resin B Actuators Specifi cations and DoF Confi guration Fig 5 Confi guration and Integration Design of the Actuator WLR II is a highly integrated and articulated robot with 13 actuated degrees of freedoms DOF packaged into a humanoid form Each leg has 3 DOF one at the hip one at the knee level and one at the ankle For the torso there is 1 DOF at the waist Each arm has 3 DOF two at the shoulder and one at the elbow level Among them 11DOF of the arm leg and torso joints adopt hydraulic driven units HDU which consist of a low friction linear hydraulic cylinder a fl ow servo valve Star 200 a force sensor Interface WMC and a displacement sensor LVDT while the remaining 2 DOF for wheels are driven by DC torque motor Kollmor gen TBM 7615 with reduction gearbox PSR70SHA 19 The integrated actuation units can provide position torque feedback as well as output high speed and torque The joint degrees of freedom DOF and actuators confi guration are confi gured as shown in Fig 5 TABLE II WLR II MAXANGULARVELOCITY RAD S JOINTSRANGE DEG ANDDRIVINGTORQUE NM Joint Max Angular Velocity rad s 21MPa supply ROM Peak Driving Torque Nm 21MPa supply Wheel2236055 Knee11 3 40 180400 Hip10 5 15 90350 Waist10 8 25 65240 Shoulder Pitch10 8 25 90240 Shoulder Roll100 90250 Elbow10 7 40 180300 Joint specifi cations are presented in Table II In detailed for fast rolling the wheels should meet the speed index 10Km h For keeping balance on rough terrains high angular acceleration and fast torque response must be guar anteed for knee and hip joints and the high driving torque of joints should meet the payload requirements Large range of motion with adequate torque and velocity should also be considered during the joint design for operation IV IMPLEMENTATIONSCHEME OFHOSE LESSDESIGN This section will discuss the implementation scheme of hose less design in detail The hoses are mainly distributed in two aspects between the pump and the HDUs and between the servo valve and the cylinder The problem that the fl ow path passes through the joints can be sol