Electrically driven hand tool e.g. chain saw - has two handles with associated switches in series for safe operation and self-braking action

摘要

The electrically driven hedge trimmer has a main hand grip (13) and a secondary grip (11) both having a pressure-activated switch. The switch (4) in the main handle (13) has a trigger (18) for closing it, and the second switch (5), which is contained in the motor housing, is closed by a lever action when the trimmer is gripped by the operator. To supply current to the drive motor (12), both switches (4,5) have to be closed, necessitating the operator holding and gripping both handles of the trimmer at the same time. An internal relay is connected via the switches so that in the 'off' position, the motor field winding and armature are in parallel. This gives a braking effect as the motor runs down, due to the generator configuration. When both switches are closed, the relay connects the armature and field in series and the motor runs normally. It is not possible to use the hedge trimmer without gripping both handles, thus avoiding accidents to fingers or hands.