Development of a cordless electric impact driver with Li-ion capacitor pack as an energy storage device

摘要

In this study, the authors developed an electric cordless impact driver with an Li-ion capacitor (LIC) pack as an energy storage device. At first, an equivalent circuit of the LIC was established. The equivalent circuit comprised a single resistance, single capacitor, and single resister-capacitor parallel circuit. It was found that the established equivalent circuit was useful for simulation, as has been conducted in the development of some products using LICs as energy storage equipment. Before starting the development of the electric cordless impact driver with its LIC pack, the topology of the LIC pack was determined. Next, a design simulation of a rapid charger for the LIC pack installed on the cordless electric impact driver was carried out, by using the equivalent circuit. From this simulation, the operational behavior of the rapid charger designed in this study could be confirmed, and the authors were able to build upon the development base of the rapid charger. Based on the experience, the rapid charger was assembled for the LIC pack. Using the rapid charger, a test of rapid charging of the LIC pack was carried out. From the test, it was confirmed that the development of the rapid charger for the LIC pack had been successfully achieved, since the charging operation performed during the test was as shown in the simulation. Subsequently, demonstration tests of screw tightening were executed, using the cordless electric impact driver with the LIC pack. Throughout the tests, it was evident that the cordless electric impact driver with the LIC pack can be used to tighten screws with lengths of 75 mm and 90 mm. In addition, the cordless electric impact driver with the LIC pack offers enhanced comfort to users, due to the reduced net weight of the energy storage device. These results reveal that the impact driver is a suitable candidate for applications in, which the LIC is integrated as an energy storage device. Therefore, the findings of this study may contribute to an expansion of applications that use an LIC and promote the further development of electric tools with novel energy storage systems.