Design,Modeling And Performance Analysis Of Constant-force Stage With Zero Stiffness

Constant-force mechanisms are widely applied in vibration protection,vibration isolation,static balance,gravity compensation and other fields.In order to meet the demand of constant force in the precision engineering field,and apply it to micro-operation,micro-positioning and other precision engineering fields.To avoid excessive contact force causing damage to some tiny parts,especially vulnerable ones,a constant force micro-motion platform with zero stiffness based on compliant mechanism has important theoretical and practical significance.In this paper,three kinds of one-dimensional constant force platforms and a two-dimensional constant force platform are designed using the principle of combination of positive and negative stiffness.The performance optimization and structural improvement of one-dimensional constant force platform are performed.The main contents are listed as follows:Aiming at the problems such as the clearance of motion,assembly error,and friction and wear of the traditional constant-force mechanism,a constant-force micro-motion platform based on the compliant mechanism was designed by using the positive and negative stiffness combination principle.The platform achieves its zero-stiffness properties by utilizing the positive stiffness of straight beam and the buckling behavior of a bistable beam to create a negative stiffness.The platform is composed of a symmetrical straight beam,a bistable beam,and a rigid connecting block.The straight beam and the bistable beam are connected in parallel through the connecting block.A theoretical model reflecting the mechanical properties of constant-force platform was established by combined pseudo-rigid body method with elliptical integral method Compared with the results of finite element analysis,the analysis results indicate that the established model can accurately reflect the mechanical properties of the constant force micro-motion platform.Based on the established mechanical model,an optimized design method is proposed to improve the range and load capacity of the constant force platform.The prototype was fabricated to test the mechanical properties of the platform.The experimental results show that the platform can maintain a constant force of approximately 48 N within the output displacement range of [0.6-1.7] mm,illustrating the accuracy of the model and effectiveness of the proposed performance optimization method.In order to solve the problem of matching the positive and negative stiffness of the zero-stiffness constant force micro-motion platform,a design idea of using a positive-negative stiffness structure with a linear mechanical relationship to form a zero-stiffness constant force platform is proposed.In order to form a zero-stiffness structure,Z-shaped and trapezoidal positive-stiffness structures with linear force-displacement relationships are designed.Combining the designed two kinds of positive stiffness structures with the bistable beam structures with linear negative stiffness mechanical properties,two new types of constant force micro-motion platforms were designed.The pseudo-rigid body method is used to establish the mechanical model of the positive stiffness structure.Based on this model,the linear positive and negative stiffness matching principle is used to determine the structural parameters of the platform.The prototype was fabricated and compared with the normal stiffness structure platform with nonlinear mechanical relations.The theoretical and experimental results show that the designed platform has a constant force range of 2.4 mm,which is 1.3 mm larger than that of the non-linear structure,which shows the feasibility of the constant-force platform.The proposed method provides a simpler design idea for design of constant force micro-motion platform.In order to solve the problem of a single constant-force stroke during the movement of the constant-force platform and to make it suitable for applications that require different constant force ranges.Three kinds of constant-force micro-motion platforms with two constant force ranges are designed.An un-adjustable platform with two constant force ranges is obtained by combining the same linear positive stiffness structure with two different negative stiffness structures respectively.A constant force adjustable platform with two constant force ranges was designed by combining two positive stiffness structures and two negative stiffness structures.A continuous two-stroke constant force platform with two constant force ranges is obtained by using a linear positive stiffness structure and a two-level negative stiffness structure with two negative stiffness regions in parallel.A design idea of multi-stroke constant force platform based on multi-level negative stiffness structure is proposed.The finite element analysis was performed and the analysis results showed the feasibility of the proposed design method of two-stroke constant force platform.A platform prototype was fabricated to test the mechanical properties of the platform.The experimental results show that the platform has constant force performance in the range of [1.3-4.8] mm and [6.7-9.5] mm respectively,which validates the effectiveness of the design method of the proposed two-stroke constant force platform.And a way of thinking for the design of a multi-stroke constant force mechanism was provided.Aiming at the problem that the one-dimensional constant force micro-motion platform has limited dimensions and is difficult to apply to multi-dimensional motion situations,a parallel two-dimensional constant-force micro-motion platform is designed.The platform is composed of symmetrical positive stiffness structure,negative stiffness structure,guiding structure and decoupling structure.In a single direction,a bistable beam negative stiffness structure and three composite beam positive stiffness structures are connected in parallel to form a zero stiffness to achieve constant force behavior.The finite element analysis and theoretical results show that the platform can achieve constant motion in both directions and has a good coupling performance.The prototype of the platform was fabricated and the mechanical properties of the platform were tested.The experimental results show that the two-dimensional constant force micro-motion platform has constant force performance in the range of [1.6-4.0] mm,which shows that the design ideas of the two-dimensional constant force platform are effective.