Patient support apparatus with powered unloading dynamic weigh adjustment

A system for use in removably loading a patient transport apparatus into an emergency vehicle, the system comprising:

• a loading and unloading system for attaching to the emergency vehicle, the loading and unloading system including a receiver;
• and
• a patient transport apparatus configured for releasable attachment to the loading and unloading system, the patient transport apparatus including:
• a base supporting a wheel for engagement with a ground surface,
• a litter defining a patient support surface to support a patient,
• a lift mechanism to facilitate arranging the litter at different heights relative to the base with an actuator movable between a plurality of lift configurations including a fully-retracted configuration and a fully-extended configuration,
• a coupler operatively attached to the litter for releasably engaging the receiver of the loading and unloading system to secure the patient transport apparatus to the loading and unloading system,
• a first sensor configured to output a first signal indicative of a height of the litter relative to the base,
• a second sensor configured to output a second signal indicative of applied force occurring between the base and the litter, and
• a controller in communication with the actuator of the lift mechanism, the first sensor, and the second sensor, the controller being configured to determine a target lift configuration during unloading from the emergency vehicle as the actuator moves toward the fully-extended configuration, the target lift configuration being defined to inhibit compressing the patient transport apparatus between the wheel engaging the ground surface and the coupler engaging the receiver based on:
• a first value associated with at least one of the first signal and the second signal determined in response to contact of the wheel occurring with the ground surface;
• and
• a second value associated with at least one of the first signal and the second signal determined in response to the patient transport apparatus at least partially moving out of support from at least a portion of the loading and unloading system;
• and
• the controller being further configured to drive the actuator to the target lift configuration defined based on the first value and the second value to facilitate unloading the patient transport apparatus supported on the ground surface in an uncompressed state to limit relative movement between the patient transport apparatus and the loading and unloading system as the coupler and the receiver disengage to release the patient transport apparatus from the loading and unloading system.