This study presents an optimal design procedure, including topology and geometry optimization methods to design a compliant constant-force mechanism, which can generate a nearly constant output force over a range of input displacements. The proposed constant-force mechanism is a passive force regulation device that can be used in various applications such as precision manipulation and overload protection. The numerical optimization problem is treated as an error minimization problem between output and objective forces. Both material and geometric nonlinearities are considered in topology and geometry optimization steps. Although the element stiffness for void and gray elements after topology optimization are quite small comparing with solid elements, their existence also contributes to the output force characteristic of the synthesized mechanisms. As these low-stiffness elements are not easy to manufacture in physical prototype, a helical compression spring is introduced in the topology optimized constant-force mechanism to account for the effect of low-stiffness elements, and an additional geometry optimization step is utilized to identify the spring constant as well as to fine-tune the geometric parameters. The optimized constant-force mechanism is prototyped by three-dimensional printing using flexible thermoplastic elastomer. The experimental results show that the proposed design can generate a nearly constant output force in the input displacement range of 3–6 mm. The developed constant-force mechanism is installed on an electric gripper drive mounted on a robot arm for robotic picking and placing application. Test results show the constant-force gripper can be used in handling of size-varied fragile objects.

中文翻译：

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顺应恒力机构的优化设计，可在一定范围的输入位移上提供近乎恒定的输出力

本研究提出了一种优化设计程序，包括拓扑和几何优化方法来设计一种柔顺的恒力机构，该机构可以在一定范围的输入位移上产生几乎恒定的输出力。所提出的恒力机构是一种被动力调节装置，可用于各种应用，例如精密操纵和过载保护。数值优化问题被视为输出和目标力之间的误差最小化问题。在拓扑和几何优化步骤中考虑了材料和几何非线性。尽管与实体单元相比，拓扑优化后的空单元和灰色单元的单元刚度很小，但它们的存在也有助于合成机构的输出力特性。由于这些低刚度元件在物理原型中不易制造，因此在拓扑优化恒力机构中引入了螺旋压缩弹簧，以解决低刚度元件的影响，并利用额外的几何优化步骤来识别弹簧常数以及微调几何参数。使用柔性热塑性弹性体通过三维打印对优化的恒力机构进行原型设计。实验结果表明，所提出的设计可以在 3-6 mm 的输入位移范围内产生几乎恒定的输出力。开发的恒力机构安装在安装在机器人手臂上的电动夹具驱动器上，用于机器人拾取和放置应用。