| 摘要 |
A power tool, eg a cordless electric screwdriver, includes a tool carrier (not shown) which may be rotated and driven via a gearing, which is preferably in the form of planetary gearing 10, by a drive motor (not shown), a clutch half 36 within the gearing 10 cooperating with a clutch (not shown) which operates when an adjustable torque is exceeded. The power tool also includes switching means (not shown) which disconnects the drive motor upon a rotation of the clutch half 36 relative to the gear housing 12, detection of the relative movement of the clutch half 36 being effected in a contactless manner, using a sensor 44 connected to an electronic device 48 to send a signal to the switching means. The sensor 44 is preferably fixed in the gear housing 12, and detects the relative rotation of the clutch half 36, the clutch half 36 including a primary detector 52. The sensor 44 may be a Hall-effect sensor, an induction coil or a magnetoresistive sensor, the primary detector 52 in these cases being a permanent magnet (see figure 2). Alternatively, the sensor 44 may comprise a source and a sink of electromagnetic radiation (64,66; figure 3), the primary detector 52 in this case being a series of reflective surfaces (60; figure 3) punctuated by a non-reflective material. Altematively, the sensor 44 may be an induction coil (72; figure 4), the primary detector 52 in this case being at least one reluctance element (68; figure 4). In addition to these alternatives above, the sensor 44 may also be a piezoelectric, capacitative or inductive element, or a dry-reed switch. |
