In recent years, there has been an increase in the number of elderly and lower limb disabled persons. This is due to the growth of the elderly population from year to year and also due to advances in medical technology. Many of them need a walking aid such as a cane or a wheelchair to support their walking or transportation in their daily life. Even though the cane is quite common and widely used it has the disadvantage of putting a large load on the upper limbs. In this study, we aim to develop an assistive tool to support walking in the form of a robotic assisted cane. We propose a novel actuator for the walking cane with a force retention mechanism by integrating MR (Magneto-rheological) fluid and a spring (MR Spring). MR fluid is a functional fluid, and its rheological characteristics change according to the applied magnetic field.

We propose a specially designed spring that is used as the assistive mechanism for the walking cane. MR fluid, which is the functional fluid was used to the force retention mechanism. MR fluid can have its state changed by changing its viscosity through a magnetic field. For an instance, when an electrical current is applied to a conducting coil placed near the MR fluid, the increase
in magnetic field strength causes an increase in the MR fluid viscosity, and there by the frictional force due to viscosity. By carefully selecting the dimensions and the electromagnetic field strength, it is possible to keep the spring under the loading condition as long as it is required, even after the crutch is recessed from the ground. Furthermore, by reducing the electrical current energy applied to the spring, the stored mechanical energy can be used to do an effective work at a later desired time.

We conducted some preliminary experiments to analyze walking with crutches and the load on the crutch for different walking patterns. This experiment yielded the result that the weight on the arm and palm is great and it is necessary to generate a great measure of power to assist the walking. And, we confirmed the effectiveness of the spring in the walking using the crutch. We developed the MR Spring to support walking in the form of a robotic assisted crutch. By using a prototype model of the proposed MR Spring, several experiments were conducted to analyze the effectiveness and the capacity of the MR Spring. The experiment of the magnetic field confirms that the largest flux density occur near the piston cylinder gap of the MR Spring. And, retention force of the MR Spring increases with the coil current and can be easily controlled.