The present invention relates to a cordless screwdriver.
Cordless screwdrivers in the output class between 2.4V and 3.6V are already known, e.g. from EP 1 066 930. For the most part, they have several NiCd cells as energy storage devices, an on/off switch with a short contact button and without stepless speed control, a switch for changing between clockwise and counterclockwise rotation, a transmission that reduces the motor speed, in particular a sun-and-planet gear, and a motor with a standard diameter of 27.5 mm. There are rod-shaped and pistol-shaped designs and there are designs that have a handle with an adjustable inclination angle. These devices are either recharged by being connected to the charging unit by means of a plug —similar to a mobile phone or shaver—or are recharged by means of a cradle with contacts into which the device is placed. The cradles can be attached to a wall, for example, in order to facilitate recharging.
To this end, the charging mode must first be initiated for the charging unit and the electrical connection, but this does not occur automatically after each use. As a result, the device is often not ready for use right when it is needed, in addition to the disadvantageous impact of the known memory effect. After a certain amount of time without outputting power, NiCd cells become discharged and even when they are not used, cordless drills are partially discharged after a short period of time. If they are recharged when they are only partially discharged, then the memory effect causes them to have only the difference of the new charge quantity after the recharging process—consequently leaving them with only a reduced amount of available power.
Another disadvantage of the known cordless screwdriver is its voluminous size due to its large components, e.g. the transmission, the switch system, and the rechargeable battery comprised of NiCd cells whose size “4/5 Sub-C” when they are situated in the handle interferes with both ergonomics and usability because narrow, angled screw locations cannot be reached.
USPTO Backgrounds
USPTO Backgrounds