US Patent 11572260 Electric well service rig with speed limiter

A method for limiting the speed of a hoist mounted to a mobile well service rig involves determining a safe speed limit that ensures the hoist's capable stopping time is less than the maximum allowed time for stopping. In some examples, the maximum allowed time for stopping is based on the wellstring's modulus of elasticity and independent of the hoist's braking characteristics. The capable stopping time, however, is independent of the wellstring's modulus of elasticity and dependent on the hoist's braking characteristics.