Grasping Force Analysis And Structural Design Of The Compliant Manipulator Driven By Dual Motors

Though China is a traditional agricultural country,and the food industry takes a great part in output value in China,the picking,sorting and storage of agricultural products like fruits,greens and eggs is still operated manually.One important cause is that the processing,transportation and packaging work of food raw materials,semi-finished products and finished products in enterprises need operation of grasping which couldn't be done automatically due to the complexity of object to be gripped.In this case,the complicated object could be(1)irregular shapes and large differences in size objects;(2)deformable soft objects;(3)fragile brittle objects;(4)abnormal shapes,disordered position and difficult to straighten out objects;(5)electronic distribution,secondary transport packaging process of various shapes and materials of internal packaging goods.Variation of shape and size,soft and easily damaged material,easy deformation,hard,brittle and fragile material,abnormal shape and disordered position are the three characteristics of complex objects.Manipulator,as the executive component of the interaction between robot and operated object,is the key link to realize the automation of grasping operation.Its performance directly affects the execution effect and work efficiency of the operation task.In order to meet the requirements of complex object grasping with complex shapes and various physical properties,and to improve labor efficiency,it is urgent to flexible manipulator driven by two motors which could grasp the complex object.Firstly,the character of soft-robot and under-actuated manipulator are summarized.On the basis of emphatically analyzing the flexible finger manipulator and aiming at controlling the rotation angle of the finger root,a design idea of adding a motor driving is proposed.Through the cooperative control of two motors,the grasping range of the manipulator can be enlarged and the position and magnitude of the grasping contact force can be accurately controlled.It can not only achieve the pinching method,but also grasp the envelope to ensure the reliability of grasping.Secondly,the mechanism principle analysis and the structure design of the compliant manipulator driven by two motors are carried out.Through the mechanism of leadscrew with self-locking function,one motor drives the turntable of the finger root and controls the rotation of the finger root.The other motor drives the turntable of the finger root and drives the finger tip directly.The two mandrels of the finger are equipped with different torsion springs,which have compliant structure and cushioning property,and the fingertip contacts the grasped object at first and drives the grasped object to the palm of the hand during enveloping grasping,thus overcoming the defect that the grasped object moving by the finger root,the middle of the finger,fingertip of underactuated mechanical finger gradually contacting.The two fingers can be manually adjusted to grasp both circular objects and square objects,and the coordinate origin of the manipulator remains unchanged when grasping circular and square objects.Then,the kinematics of the manipulator is analyzed,and the formula of the position of the driving turntable-the position of the finger root knuckle and the formula of the stroke of the driving rod-the position of the finger are established.Taking manipulator pinching operation as an example,the static analysis of manipulator is carried out.The mechanical equilibrium equations of manipulator under static loading and hovering loading are established.Aiming at the specific grasping object,on the premise of adjusting the angle of the knuckle,and aiming at satisfying the reliable grasping,the structure size of the manipulator and the parameters of two torsion springs are determined.After,for the above-mentioned specific grasping object,the multi-variable nonlinear equations obtained by kinematics analysis and static analysis are calculated,which gives the torsion angle of the torsion spring of the manipulator in the no-load state and the contact force of the grasped object in the static state which is changed when the manipulator is driven and loaded and the grasped object in the static state,the change of contact force when the manipulator is driven and loaded in hovering condition.And then,The manipulator model is imported into ADAMS to do static analysis of the grasping process,and the contact force change rule of the flexible finger under the static state of the grasped object is verified when the manipulator is driven and loaded.Thereafter,the control system of the compliant manipulator is designed,and the corresponding control program is compiled.The PC application interface can be used for grasping control,with manual and automatic mode.Which enable the simple control of dual motors and the grasping action of the manipulator.Finally,the prototype of the manipulator was made,and the control system platform of the manipulator was built to verify the static model of the manipulator when it is unloaded.At the same time,the adaptability of the manipulator to a variety of grasping objects is verified.The result shows that the curves of torsion spring with the stroke of the push rod are basically consistent with the theoretical results of the static model.The manipulator has better adaptability to grasping objects with different sizes and shapes and different materials..