| 摘要 |
<p>A sensor unit (19) detects any length variation in the chain (8). The sensor unit is mechanical or optical. It has optical components comprising a light source (21) and photocell (22). The sensor unit also includes a switch for emergency operation, and/or during the stationary state. There are two or more chains. A transmitter signals a maximum variation in length. One chain (8) is loaded by the load carrier (30) and/or counterweight (40). Another chain (8) is not. Alternatively there are two chains which are loaded, and another two which are not. The chains (loaded and non-loaded) are arranged on a common drive shaft (6). A spring is provided between chain and load carrier and/or between chain and counterweight. The sensor unit measures force or its variation, acting on the chain.</p> |
