| 摘要 |
The apparatus positively induces synchronism in at least two lifting jacks. It has an upwardly and downwardly movable carriage, on the lifting jack, a column, a lifting device extending along the column, a first control device to control the lifting device in the "lift" direction, a second control device to control the lifting device in the "lower" direction, a "lift" switch on the main lifting jack, a "lower" switch on the main lifting jack. For each lifting jack, a motor device acts on the lifting device. Along each column there is an equally spaced marking unit, the spacing corresponding to the maximum admissible lift difference between the lifting jacks. Each marking unit has an 'ON' zone and an 'OFF' zone. Rigidly fixed to each carriage is a tracer for scanning the marker units. Each tracer, is in an electrical switching device, and inhibits the motor device when the tracer is in the 'OFF' zone, until such time as the tracer of the carriage which is lagging most behind is also in the 'OFF' zone. After that, the switching device switches all motor devices on again.
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