Modelling and Control of a Hydraulic Large Range Robot

Abstract

Large range robots are of increasing importance for various difficult applications at building sites or in hazardous areas. In collaboration with industrial partners the KfK has developed such extended multi joint robot (EMIR) which is driven by hydraulic actuators. The position control of EMIR is a tough problem due to the extreme nonlinearities of the kinematics and hydraulic actuators as well as the remarkable elasticities of the mechanics and hydraulics. In the first part of this paper a realistic physically transparent model of the robot will be presented. In the second part different suitable control concepts based on the model will be discussed.Keywords: Hydraulic large range robot, automatic control, modelling of nonlinearities and elasticity, model-based control concepts MOTIVATIONThere are various important out-door applications in the fields of civil engineering, environmental technoloy or catastrophy management which require necessarily the introduction of a large range robot. Complying with the existing and expected demands of these important future-oriented markets in collaboration with different industrial partners KfK has developed the EMIR robot (Extended Multi Joint Robot) [1]. It is a six-joint machine powered by hydraulic servo drives. The mechanics of the EMIR is characterized by one vertical and five kinematically redundant horizontal joints which provide the robot with an amazing dexterity for complex manipulation tasks. At the TCP (Tool Center Point) the EMIR can carry payloads of up to 1500 kg within a working range of up to 22,5 m. The hydraulic servo drives are cylinders for the five horizontal joints and one rotary actuator for the vertical base joint. The hydraulic oil flow of each actuator will be controlled by means of electro-magnetic (solenoid) servo valves. A safety logic valve between each hydraulic drive and servo valve checks permanetly the fluid pressure within the cylinder in order to prevent uncontrolled hazardous robot motions in the case of any hydraulic malfunctions (cf. Fig. 1). The control hardware is implemented on a conventional AT-386 computer including a signal processor board extension.The static and dynamic system behaviour of the uncontrolled robot is characterized by several difficulties. Mainly due to the kinematics of the joints and the behaviour of the hydraulic actuators the response of the servo system is extremely nonlinear. The nonlinearity depends both on the actual joint position and the velocity. Especially the integrated safety logic block of the actuators seriously disturbs the system dynamics mainly in the case of lowering the TCP. An additional source of trouble for the control design is the spatially distributed elasticity of the slim and huge robot mechanics which is unfortunately superimposed by the elasticity of the hydraulic fluid within the actuators. Because of the highly nonlinear and elastic system behaviour of hydraulic actuators and robot mechanics for the closed-loop position control of the robot joints sophisticated model-bas...

Concept of a Flexible Microprocessor System of Controlling Electro-Hydraulic Drives of Building Machines

“…Electro-hydraulic systems use in building machines are exceptionally complicated nonlinear [1] dynamic systems with distributed parameters . So, an attempt to linearize the dynamic model of a concrete pump extension arm [1] leads after reduction to an 8-th order system in vicinity of the operating point .…”

“…So, an attempt to linearize the dynamic model of a concrete pump extension arm [1] leads after reduction to an 8-th order system in vicinity of the operating point . Non-stationary status of the object caused by rheology, change of model descriptions caused by changes in order , strong nonlinearity effects , such as stick-slip , make automation of objects of this type particularly complicated .…”