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This study presents a well‐defined design paradigm for multi‐segment constant‐force compliant mechanisms (CFCMs). These CFCMs are capable of achieving dual‐stage zero‐stiffness characteristics via innovative stiffness hybridization. To tackle the critical limitation of conventional single‐range constant‐force mechanisms, we put forward two distinct configurations: a discrete two‐state CFCM equipped with reconfigurable stiffness modules, and a continuous dual‐stage architecture that employs cascaded negative stiffness elements. The core innovation is centered on the synergistic integration of positive‐stiffness structures with hierarchical negative‐stiffness mechanisms, namely bistable beams and their compensated derivatives, to establish overlapping zero‐stiffness regimes. By means of analytical modeling using elliptic integrals and pseudo‐rigid‐body approximations, combined with finite element validation, we illustrate that the mechanisms can sustain constant forces of 4 N (1.2–5.6 mm) and 20 N (12.2–15.1 mm) within continuous motion trajectories. Experimental characterization of 3D‐printed prototypes confirms that the force variation is less than 5% across the designated displacement ranges, and it attains an extension of the operational range in comparison with single‐stage counterparts. This stiffness engineering framework offers multi‐phase force regulation capabilities for applications that demand adaptive interaction forces, spanning from precision microassembly to bio‐compatible robotic manipulation. This work presents a novel design for two‐segment constant‐force compliant mechanisms that achieve dual‐stage zero‐stiffness via stiffness‐matched parallel integration. Experimental results demonstrate constant forces of 4 N and 20 N with less than 5% variation, enabling extended operational ranges for precision applications such as robotic manipulation and micro‐assembly. The discrete CFCM employs a single linear PSM that is mechanically switched between two matched NSMs (NSM‐1 and NSM‐2) to generate two non‐overlapping zero‐stiffness regions. In State I, the PSM parallels NSM‐1, achieving stiffness cancellation and the first constant‐force plateau. In State II, a deterministic mechanical switch (e.g., cam‐actuated latch) reconfigures the load path to engage the PSM exclusively with NSM‐2—identical in negative stiffness magnitude but activated at higher displacement—yielding a second plateau. The switching mechanism ensures repeatable, hysteresis‐free state transitions. This architecture provides robust dual‐segment constant‐force output without requiring continuous tuning or external actuation.

The development of handling technology for microscopic biological samples such as cells and spheroids has been required for the advancement of regenerative medicine and tissue engineering. In this study, we developed micro-tweezers with a compliant mechanism to manipulate organoids. The proposed method combines high-resolution microstereolithography that uses a blue laser and topology optimization for shape optimization of micro-tweezers. An actuation system was constructed using a linear motor stage with a force control system to operate the micro-tweezers. The deformation of the topology-optimized micro-tweezers was examined analytically and experimentally. The results verified that the displacement of the tweezer tip was proportional to the applied load; furthermore, the displacement was sufficient to grasp biological samples with an approximate diameter of several hundred micrometers. We experimentally demonstrated the manipulation of an organoid with a diameter of approximately 360 µm using the proposed micro-tweezers. Thus, combining microstereolithography and topology optimization to fabricate micro-tweezers can be potentially used in modifying tools capable of handling various biological samples.

In this study, a three-dimensional (3D) micromanipulator mounted on a glass capillary is developed for handling biological samples, such as multicellular spheroids and embryos. To fabricate the micromanipulator, we developed an additive manufacturing system based on high-resolution microstereolithography using a 405-nm blue laser. The fabrication system makes it possible to fabricate 3D microstructures on a glass capillary with 2.5 µm lateral resolution and 25 µm layer thickness. We also demonstrated the capture and release of a spheroid with the micromanipulator fabricated using our additive manufacturing system. We showed that spheroids can be easily handled by a simple operation with minimal damage using a cage-like multiple finger structure. Additive manufacturing of tailor-made micromanipulators mounted on a glass capillary will be useful in biological and tissue engineering research.

Compliant mechanisms are widely used for instrumentation and measuring devices for their precision and high bandwidth. In this paper, the mechatronic model of a compliant 3PRS parallel manipulator is developed, integrating the inverse and direct kinematics, the inverse dynamic problem of the manipulator and the dynamics of the actuators and the control. The kinematic problem is solved, assuming a pseudo-rigid model for the deflection in the compliant revolute and spherical joints. The inverse dynamic problem is solved, using the Principle of Energy Equivalence. The mechatronic model allows the prediction of the bandwidth of the manipulator motion in the 3 degrees of freedom for a given control and set of actuators, helping in the design of the optimum solution. A prototype is built and validated, comparing experimental signals with the ones from the model.

This paper presents an efficient and compact Matlab code to solve three-dimensional topology optimization problems. The 169 lines comprising this code include finite element analysis, sensitivity analysis, density filter, optimality criterion optimizer, and display of results. The basic code solves minimum compliance problems. A systematic approach is presented to easily modify the definition of supports and external loads. The paper also includes instructions to define multiple load cases, active and passive elements, continuation strategy, synthesis of compliant mechanisms, and heat conduction problems, as well as the theoretical and numerical elements to implement general non-linear programming strategies such as SQP and MMA. The code is intended for students and newcomers in the topology optimization. The complete code is provided in Appendix C and it can be downloaded from http://top3dapp.com .

This study presents an optimal design procedure including topology optimization and size–shape optimization methods to maximize mechanical advantage (which is defined as the ratio of output force to input force) of the synthesized compliant mechanism. The formulation of the topology optimization method to design compliant mechanisms with multiple output ports is presented. The topology-optimized result is used as the initial design domain for subsequent size–shape optimization process. The proposed optimal design procedure is used to synthesize an adaptive compliant gripper with high mechanical advantage. The proposed gripper is a monolithic two-finger design and is prototyped using silicon rubber. Experimental studies including mechanical advantage test, object grasping test, and payload test are carried out to evaluate the design. The results show that the proposed adaptive complaint gripper assembly can effectively grasp irregular objects up to 2.7 kg.

Controlling the contact force on workpieces is a challenging task for industrial deburring operations. To solve this issue, a novel constant force mechanism (CFM) based on the combination of positive and negative stiffness mechanism is proposed by using folding beam and bi-stable beam mechanisms. Without using any additional sensors and control algorithms, the proposed CFM can produce a travel range in constant force manner. In this paper, the design concepts, analytical model, finite element analysis (FEA) simulation and experimental studies are presented and discussed. Firstly, a novel spatial CFM is proposed and the pseudo rigid body (PRB) method is used to establish the mathematical model of the whole mechanism. Then, the FEA simulation is performed to validate the correctness of theoretical analysis. In addition, to eliminate the force variation, particle swarm optimization (PSO) method is utilized to find optimal architectural parameters solutions of the CFM. Finally, the experimental tests are performed to verify the performance of the designed CFM. The configuration design and parameter optimization proposed in this paper can be further applied to the design of other types of CFM mechanisms for polishing operations as well.

This paper presents the design, fabrication and testing of a shape memory alloy (SMA)-actuated monolithic compliant gripping mechanism that enables translational motion of the gripper tips for grasping operation suitable for micromanipulation and microassembly. The design is validated using a finite element analysis (FEA), and a prototype is created for experimental testing. The reported gripping structure is simple and easy to build and design. The gripper is demonstrated to have a displacement amplification gain of 3.7 that allows maximum tip displacement up to 1.2 cm to possess good handling range and geometric advantage which cannot be accomplished by conventional grippers. The position of the gripper tip is predicted from the variation in the electrical resistance of the SMA wire based on the self-sensing phenomena. Self-sensing actuation of the SMA allows the design of a compact and lightweight structure; moreover, it supports the control loop/scheme to use the same SMA element both as an actuator and sensor for position control. The geometrical dimensions of the SMA wire-actuated monolithic compliant gripper is 0.09 m × 0.04 m and can be operated to handle objects with a maximum size of 0.012 m weighing up to 35 g.

To meet the increasing demands for large stroke and low cross-axis coupling in precision instruments such as atomic force microscopy (AFM), a low-coupling parallel piezoelectric nanopositioning stage based on a pseudo-symmetric guiding mechanism is proposed. By integrating a compact flexure-based lever amplification mechanism with a parallel pseudo-symmetric guiding structure, the design achieves effective suppression of cross-axis coupling while maintaining a relatively large motion range. A static model is established based on Castigliano’s second theorem, and electromechanical coupled finite element analysis is performed to evaluate the output characteristics and dynamic behavior. A prototype is fabricated and experimentally validated. The results demonstrate that the stage achieves a travel range of 121 μm × 122 μm, a cross-axis coupling error ratio of 1.1%, resolutions of 7 nm and 5 nm along the X- and Y-axes, respectively, and a first natural frequency of 476 Hz. The proposed design provides a feasible approach for achieving a balance among large stroke, low coupling, and high dynamic performance in piezoelectric nanopositioning systems.