The Ball-on-Plate Balancing System is a system where the base is fixed to the ground, and the plate is connected to the base through a spherical joint and can rotate in two directions (X-axis roll rotation, Y-axis pitch rotation). Two rotational joints are located on the orthogonal coordinate line of the base, and these joints are connected to the operational links of a 4-bar linkage, creating rotation of the plate around the spherical joint. The goal of this system is to prevent a ball placed on the plate from rolling off and maintain it at the center of the plate. A 17-inch touch panel attached to the plate allows the orthogonal coordinates of a ball placed on the plate to be measured. A cross-shaped frame was designed to secure the touch panel, and a custom universal joint was centered in this frame. The Ball-on-Plate Balancing System was integrated into a cart table, and a horizontal maintenance system was designed to keep the table level. Experiments confirmed the ability of the table to maintain its horizontal position during movements on uneven surfaces and sudden starts or stops.

The magnetorheological material changes its characteristics according to the external magnetic field. Magnetorheological elastomer existing in the solid phase has micrometer-sized magnetically responsive particles inside. When a magnetic field is applied by a permanent magnet or electromagnet nearby, it can exhibit stiffness that changes according to the strength of the magnetic field. Many previous studies focused on verifying the variability of the material"s characteristics. However, this study newly proposed a variable stiffness joint for the suspension system of railway vehicles using a magnetorheological elastomer, as a basic study of magnetorheological elastomer for a mechanical component. Based on the characteristics test of the magnetorheological elastomer, the variable joint was designed to have the same structure as the conventional guide arm joint of a railway vehicle. Particularly, to overcome the low magnetic field strength, which may be a problem in the previous research, and to implement uniform magnetic field distribution, the electromagnet was designed to make direct contact with the magnetorheological elastomer. A mathematical model was established and a finite element method verified the model, resulting in an average magnetic flux density of 300 mT, which means 30% stiffness change at 15% shear strain.

Displacement estimation based on inertial sensor signals is usually performed in aid of global positioning systems or barometers. However, due to low accuracy estimation capabilities of such aiding sensors, inertial sensor-based displacement estimation is difficult to achieve high accuracy. This paper will show that it is possible to determine the vertical displacement of a link connected by a joint with higher accuracy while only using the inertial sensor. The proposed method utilizes a predetermined position vector from the joint center to the sensor and link orientation. By combining the joint constraint, accuracy of the orientation estimation is ensured even in highly dynamic conditions, and thus, the vertical displacement estimation with high accuracy can be achieved. Experimental results show that the proposed method outperformed the method by fusing inertial sensor and barometer signals as well as the method using inertial sensor signals only without constraint combination.