US Patent 10150657 Crane

The crane includes a swing brake device installed between a hydraulic motor and a control valve and having a flow restrictor; a first backpressure detector detecting a motor backpressure between the flow restrictor and one of ports of the hydraulic motor; a second backpressure detector detecting a motor backpressure between the flow restrictor and the other port of the hydraulic motor; and a control device. The control device has an external-force direction estimation unit that estimates a swing direction of an upperstructure under an external force acting on the upperstructure on the basis of a motor backpressure detected by the first backpuressure detector and a motor backpressure detected by the second backpressure during an operating state of the swing brake device. The control device has a notification control unit that causes the notification device to provide notification of the estimated swing direction of the upperstructure.