Large optical mirrors for space applications require accurate surface evaluation between successive corrective machining steps. Without proper compensation for self-weight, gravitational deformation can affect the measured surface figure and thereby reduce the reliability of the machining process. In this study, an air-cylinder-based gravity compensation device was developed to maintain the target support loads for large optical mirrors. A proportional–integral–derivative (PID) controller with load-cell feedback was implemented, and the initial gains obtained using the Ziegler–Nichols method were retuned on the basis of the measured system response. Single-axis experiments showed that the retuned controller met the specified performance requirements for overshoot, settling time, and steady-state error, even when applied to air cylinders with different spring reaction forces. The validated control method was then applied, via a sequential multi-channel control scheme, to a five-axis gravity compensation system to assess its applicability to multi-point gravity compensation. The experimental results confirmed stable convergence to the target support loads and effective load regulation at steady state, demonstrating that the proposed system is suitable for the multi-point gravity compensation of large optical mirrors.

This study introduces a wire-spring based planar gravity compensation mechanism and evaluates its performance through both analysis and experiments. The mechanism features three pulleys, one spring, and one wire, all arranged in a planar configuration for compact installation within a robotic arm. A linear approximation of the target gravitational torque was derived using the least-squares method, allowing for the determination of spring stiffness and initial tension. Experimental results indicated that the proposed mechanism reduced the maximum torque by approximately 63%. However, the measured slope was gentler than the theoretical model due to friction losses. Additional tests that varied spring stiffness (k) and initial wire tension (A) confirmed that k primarily influences the slope of the compensation torque, while A affects its intercept. This finding suggests that compensation performance can be tailored to specific requirements by adjusting these parameters. The study successfully demonstrates a compact and lightweight mechanism and experimentally validates its tunability through design adjustments. Future research will focus on reducing friction, extending the mechanism to multi-degree-of-freedom systems, and validating performance under dynamic conditions for applications in collaborative and medical robots.

In the field of construction automation, significant research efforts continue to focus on replacing human labor; however, the varied and dynamic nature of construction sites still requires human intervention. The high task intensity in construction sites, particularly in lifting heavy materials, frequently results in musculoskeletal disorders among workers. To address this issue, this paper proposes a lifting device to replace manual material transportation through an opening between floors. The lift is designed with a gear-constrained double parallelogram mechanism to enable straight vertical movement. Moreover, a crank-rocker mechanism is incorporated to improve efficiency in repetitive tasks, reduce the required driving torque, and simplify control complexity. Additionally, this study introduces a passive gravity compensation mechanism that employs springs and cables, tailored to the lifting process, to enhance payload capacity and stabilize actuation. Through the integration of these mechanisms, the necessary motor capacity and control costs are significantly reduced. The effectiveness of the device is validated by actuation experiments with a fabricated prototype.