Folding attic stair assembly

Abstract

A folding attic stair assembly comprises a rectangular outer mounting frame. An inner stairway carrying frame is mounted by a hinge at one end of the outer mounting frame for movement between a raised stored position on the outer mounting frame and a lowered position extending downwardly from the mounting frame. An extendable attic stair is mounted on the inner frame. A pair of folding support arms extend between the outer mounting frame and the inner stairway carrying frame. A cable connects between each folding support arm and an associated reel mounted on a drive shaft which is connected to a drive motor. This drive motor is operable to wind and unwind the cables on the reels to raise and lower the attic stair in a controlled manner.

1 . A folding attic stair assembly, comprising:
 a mounting frame,   a collapsible attic stair,   the attic stair mounted on the mounting frame for movement between a raised stored position and a lowered position extending downwardly from the mounting frame,   an actuator for controlled movement of the attic stair between the raised position and the lowered position,   said actuator comprising a cable having an inner end connected to a reel and an outer end connected to the attic stair,   reel drive means operable to wind and unwind the cable on the reel to raise and lower the attic stair,   the reel drive means comprising an electric motor operatively connected to an associated controller,   a position detector for detecting the position of the attic stair relative to the mounting frame,   the controller being operable to regulate operation of the motor in response to the sensed position of the attic stair.   
   
   
       2 . The folding attic stair assembly as claimed in  claim 1  wherein the position detector is a current sensor for detecting the current drawn by the motor when the motor is operating, the controller being operable to switch off the motor when a preset motor operating current is sensed by the current sensor. 
   
   
       3 . The folding attic stair assembly as claimed in  claim 1 , wherein each reel is mounted on a one-way bearing which is mounted on a driveshaft driveably connected to the motor. 
   
   
       4 . The folding attic stair assembly as claimed in  claim 3  wherein the controller is operable to continue to drive the motor for a preset period after the cable has been unwound from the reel. 
   
   
       5 . The folding attic stair as claimed in  claim 1 , wherein the position detector includes a sensor for sensing the number of turns of the motor output shaft when the motor is running, the sensor being connected to a calculator in the controller for calculating the position of the attic stair relative to the mounting frame in response to the sensed turns of the motor output shaft. 
   
   
       6 . The folding attic stair as claimed in  claim 5 , wherein the sensor is operable for measuring the ripple current in the motor, the calculator being operable to calculate the motor turns as a function of the frequency of the ripple current. 
   
   
       7 . The folding attic stair as claimed in  claim 5 , where the sensor comprises an optical sensor, a hall sensor or a magnetic pickup in the motor. 
   
   
       8 . The folding attic stair assembly as claimed in  claim 1  wherein the attic stair is hinged at one end of the ceiling opening and the reel is mounted at the opposite end of the opening. 
   
   
       9 . The folding attic stair assembly as claimed in  claim 1  wherein a pair of spaced-apart actuating cables and associated reels are provided, the cables being connected to opposite sides of the attic stair. 
   
   
       10 . The folding attic stair assembly as claimed in  claim 9  wherein each reel is mounted on a drive shaft connected to the drive motor for rotation of the reels. 
   
   
       11 . The folding attic stair assembly as claimed in  claim 1  wherein there is provided a hood assembly for the folding attic stair, the hood assembly comprising:
 a support frame defining an access opening for the folding attic stair,   a cover hingedly mounted on the support frame and moveable between an open position and a closed position, and   sealing means engagable between the cover and the support frame when the cover is in a closed position to seal the access opening.   
   
   
       12 . The folding attic stair assembly as claimed in  claim 11  wherein the cover incorporates a layer of insulating material. 
   
   
       13 . The folding attic stair assembly as claimed in  claim 11  wherein a gas strut is mounted between the cover and the support frame, said gas strut being operable to urge the cover towards the open position. 
   
   
       14 . The folding attic stair assembly as claimed in  claim 11  wherein a releasable latch is provided on the cover for engagement with the base frame to retain the cover in the closed position. 
   
   
       15 . The folding attic stair assembly as claimed in  claim 11  wherein the collapsible attic stair is hingedly mounted at an opposite end of the support frame to the cover.