Operation:

     The Auto Shelf uses a commercially available manual pull down shelf, modified by installing a linear actuator to automate the raising and lowering travel of the shelf.  The position of the shelf is monitored by a control unit(CU) consisting of an Arduino Uno R3 microcontroller utilizing input from a set of switches that relay whether the shelf is fully retracted in cabinet, fully extended, or neither indicating that it is in motion.  

     User input is communicated to the CU from a 315MHz wireless push button keyfob RF transmitter and corresponding receiver.  The CU uses the input signals from the position switches, RF receiver, and last known direction of the shelf to logically determine which direction to next operate the shelf.

     The Arduino can only provide a maximum of 40mA at any of it’s I/O connections, so to provide power to the actuator, which typically draws .5 to 1.5 amps, the CU uses an external 12VDC power supply passed directly through the Arduino which it switches on and off by biasing a NPN power transistor through a predetermined I/O connection.

     Once direction is determined by the CU, a 5VDC relay is used to change the polarity of the power supplied to the actuator to either raise or lower the shelf.  Positive polarity will retract the actuator effectively raising the shelf and negative polarity will extend the actuator effectively lowering the shelf.  Due to the relay’s operating current of 80 to 100 mA, the current limitations of the Arduino’s I/O connections mentioned above require that the 5VDC relay supply is directly passed through the Arduino, which is again switched on and off by biasing a NPN power transistor through a predetermined I/O connection.

     The ability to detect obstacles below the shelf before a collision occurred was determined to be an important safety feature to implement in the design of the shelf.  This is achieved through the use of an array of ultrasonic sensors mounted under the bottom shelf to determine the distance to any objects underneath it.  The sensors have a minimum detection range of 2cm(1in) and a maximum detection range of 400cm(13ft) and a resolution of .3cm.  To avoid interference from it’s own or other sensor “pings”, the first sensor in the array will ping every 250ms, the second 35ms after the first, and third 35ms after the second.  This results in a complete array distance sampling rate of approximately 3 per second( 1000ms/[250ms+35ms+35ms] = 3.125).  To avoid a collision any object detected less than an upper threshold of 6″ from the base of shelf will halt the shelf’s motion until the object is removed.  Since the base of the containing cabinet will likely be within the 6″ threshold of the sensors, a lower threshold has been established allowing the sensors to ignore anything detected less than 5″ from shelf base.  This will eliminate the “false detection” of the cabinet itself.  We feel this is acceptable as it is highly unlikely that an object, other than the cabinet base itself, will suddenly appear under the 5″ threshold.

Potential Consumers:

     The Auto Shelf was conceived after receiving feedback from a number of residents at the Cerebral Palsy Research Foundation pertaining to the difficulty of accessing upper kitchen cabinets and pantry shelves, thus it was initially designed with the disabled community, especially those who are wheelchair bound, in mind.  Conceivably, though, anyone could benefit from installing these units in tall kitchen cabinets, pantries, closets, garage, workshop, etc.  Presumably the exact design could be used in any of these situations without modification from the original. 

Comparison to Alternatives:

     Benefits:

  • While manual pull down shelves are commercially available, automated versions are extremely limited and none were found to be mass produced.
  • Has the advantage of using a pre-manufactured manual shelf as the basis of the unit.  Simple modifications make it fully automated economically, while still retaining the easy installation procedures of the manual shelf in pre-existing cabinets.  Of the few alternatives found, all were custom designed shelves, and in some cases the entire cabinet had to be custom built, dramatically increasing the up front cost and difficulty of installation.
  • Easily and economically mass produced control unit.
  • Wireless user interface.  No others have this feature.
  • Collision detection.  Others do not appear to have this capability. 
  • Much more useful to disabled individuals than a manual pull down, which for some may be no better than just a standard cabinet.     

     Disadvantages:

  • Use of a premanufactured shelf might introduce patent infringement issues with the shelf manufacturer.  This would need to be further explored and remedied before the Auto Shelf is made commercially available.
  •  Added complication of mechanical and electrical components over a manual shelf.
  • Loss of wireless transmitter or power would leave shelf inoperable and possibly stuck in a position outside of cabinet, although by resetting the power to the control unit it will return to a fully up position in cabinet.  Manual shelves would not suffer from this limitation. 

Flow Chart