Traveling motor door operator

Claim 1

A POWER ACTUATOR OF THE CHARACTER DESCRIBED HAVING, IN COMBINATION, A CARRIAGE MOUNTED FOR BACK AND FORTH MOVEMENT ALONG A PREDETERMINED PATH BETWEEN SPACED LIMIT POSITIONS, A REVERSIBLE ELECTRIC MOTOR HAVING A TUBULAR SHAFT FIXED TO SAID CARRIAGE WITH ITS AXIS EXTENDING ALONG SAID PATH, MEANS COUPLING SAID CARRIAGE AND MOTOR TO A PART TO BE RECIPROCATED, AN ELONGATED SCREW EXTENDING THROUGH SAID HOLLOW SHAFT ALONG SAID PATH, TWO BODIES OF RESILIENTLY YIELDABLE MATERIAL ENCLOSING AND SECURED TO OPPOSITE ENDS OF SAID SCREW, STATIONARY MEANS SUPPORTING SAID BODIES TO PERMIT SOME DEGREE OF AXIAL YIELDING OF SAID SCREW WHEN SAID ACTUATED PART ENCOUNTERS AN OBSTRUCTION, SWITCH MECHANISM CONTROLLING THE OPERATION OF SAID MOTOR IN OPPOSITE DIRECTIONS TO MOVE SAID MOTOR AND CARRIAGE BACK AND FORTH ALONG SAID SCREW AND STOP THE MOTOR WITH THE ACTUATED PART IN THE RESPECTIVE LIMIT POSITIONS, SELECTIVELY OPERABLE MEANS TO INITIATE SUCCESSIVE CYCLES OF SAID MOTOR TO MOVE THE ACTUATED PART TOWARD SAID LIMIT POSITIONS, AND MEANS RESPONSIVE TO ENDWISE SHIFTING OF SAID SCREW WHEN AN OBSTRUCTION IS ENCOUNTERED BY SAID ACTUATED PART IN TRAVELING IN ONE DIRECTION AND OPERABLE THROUGH SAID SWITCH MECHANISM TO REVERSE SAID MOTOR AND TRANSFER THE CONTROL THEREOF TO SAID SWITCH MECHANISM FOR CONTINUING OPERATION OF THE MOTOR IN SUCH REVERSE DIRECTION UNTIL SAID PART REACHES ONE OF SAID LIMIT POSITIONS.