Motorized latch retraction with return boost

An electronic actuator assembly configured for use with a pushbar assembly having a drive assembly operable to retract a latchbolt, the electronic actuator assembly comprising:

• a link mounted for reciprocal movement along a longitudinal axis in a proximal direction and an opposite distal direction between an extended position and a retracted position, wherein the link is configured for connection to the drive assembly such that movement of the link in the distal direction is operable to cause retraction of the latchbolt;
• an input shaft connected to the link via a lost motion connection, wherein the input shaft is mounted for reciprocal movement in the proximal direction and the distal direction, the input shaft having a proximal position, a distal position, and an intermediate position between the proximal position and the distal position;
• a housing, wherein each of the link and the input shaft is slidably coupled to the housing such that the housing prevents rotation of the link and the input shaft;
• an electronic actuator operable to drive the input shaft between the proximal position and the distal position;
• an overtravel spring connected between the link and the input shaft, wherein the overtravel spring is configured to drive the link from the extended position to the retracted position in response to movement of the input shaft from the proximal position to the intermediate position, and to deform in response to movement of the input shaft from the intermediate position to the distal position such that the link remains in the retracted position during movement of the input shaft from the intermediate position to the distal position, thereby altering a relative position of the link and the input shaft;
• and
• a boost spring exerting a boost force urging the input shaft in the proximal direction, wherein the boost force is independent of the relative position of the link and the input shaft.

An exit device, comprising:

• a pushbar assembly comprising:
• a mounting assembly;
• a drive assembly movably mounted to the mounting assembly, the drive assembly having a deactuated state and an actuated state;
• and
• a biasing assembly urging the drive assembly toward the deactuated state;
• and
• an electronic actuator assembly comprising:
• a motor mounted to the mounting assembly;
• an input shaft engaged with the motor such that the motor is operable to linearly drive the input shaft between a proximal position and a distal position, wherein the input shaft is connected with the drive assembly such that the biasing assembly exerts a biasing force on the input shaft, the biasing force urging the input shaft toward the proximal position;
• a boost assembly comprising a boost spring, the boost assembly exerting a boost force on the input shaft, the boost force urging the input shaft toward the proximal position;
• and
• a controller in communication with the motor, wherein the controller is configured to selectively operate the motor in each of a retracting state, a holding state, and a releasing state;
• wherein with the motor operating in the retracting state, the motor drives the input shaft from the proximal position to the distal position;
• wherein with the motor operating in the holding state, the motor exerts a holding force on the input shaft to retain the input shaft in the distal position against a combined force including the biasing force and the boost force;
• wherein with the motor operating in the releasing state, the motor exerts a residual force resisting movement of the input shaft in the proximal direction, and the combined force overcomes the residual force to drive the input shaft to the proximal position;
• and
• wherein the biasing force alone is insufficient to overcome the residual force to drive the input shaft to the proximal position.