TECHNICAL DESCRIPTION OF NASA SCREWGUN

MAY 25th, 1989

DEVELOPED BY ROBERT L. FULLERTON

INTRODUCTION:

The purpose of this technical description is to provide an explanation of the workings of the NASA SCREW-GUN developed by Mr. Robert L Fullerton.    The reader is referred to illustration number one (AUTOMATIC NUT GUN) attached to this technical description.    Mr. Fullerton is also the inventor of the Fullerton ZipNut®; a device showing great promise for the NASA Space Shuttle Program.     On STS 29, NASA has already used the ZipNut® as a "S.H.A.R.E. stop-removal-tool".

HISTORY:

In 1981, Mr. Robert L. Fullerton invented the ZipNut®.    The patented ZipNut® allows a bolt to be freely slid straight into the nut without turning the bolt or the nut.     When the bolt is inserted, the desired depth a short quarter to one-half turn tightens the bolt and nut in the same manner as a conventional fastener.     An added feature of the ZipNut® is that it does not require that the bolt and nut be perfectly aligned (on a longitudinal axis) before the fasteners can be threaded or securely tightened.     This feature is very important for robotic applications where precision alignment is a problem.     With the invention of the ZipNut®, it was only a matter of time until the evolutionary design needs of outer space prompted the need for a "Screw-Gun" to place the ZipNut®s and bolts into position.     It is this expressed need for which we proposing to address with the NASA SCREW-GUN.

The functional design objective for the NASA SCREW-GUN is to provide the astronauts with an efficient, single-handed means of attaching nuts and bolts while, in a near weightless environment.

The design problem emanates from the following criteria:

  1.     The astronauts time, while in outer space, is valued at $50,000 to $90,000 per hour.    Therefore, time consuming manual operations, complex hand maneuvers, and simple routine activities must be reduced.
  2.     The astronauts must have a means of generating small amounts of torque and applying that torque to a series of fasteners without the torque counter-reacting upon the astronaut and thereby rotating the astronaut.
  3.     The astronauts require a means of attaching and tightening fasteners in such a manner as to eliminate, or severely reduce, the fatigue factor for the astronaut.
  4.     The NASA SCREW-GUN must be operable with one hand only and must be reversible to serve as a tightening and loosening device for the fasteners.
  5.     Materials utilized in the construction of the NASA SCREW-GUN and its components must be compatible with a space environment.
  6.     The NASA SCREW-GUN must be able to store the nuts and bolts as it is removing them, or tightening them, in an effort to avoid the loose fasteners from floating away.    The astronaut should not have to remove them from the gun until the storage cavity is filled.
  7.     The NASA SCREW-GUN must be designed as a modular system to change from one size of fasteners to another size in a convenient manner.     Additionally the NASA SCREW-GUN shall be designed as a modular system to change from bolts to nuts and back in a simple manner.
  8. It is necessary for the NASA SCREW-GUN to be able to reach behind, or around, a strut or fastened component and "grasp" the nut at the same time inserting, or unthreading, the bolt.    This feature will allow astronaut to assemble/disassemble bolts and nuts.    The nut must not be allowed to "escape" or float away.
  9.     The weight of the NASA SCREW-GUN must be as light as possible; in order to reduce motion fatigue of the astronaut and because of the high costs associated with lifting each, and every, pound of weight into outer space.

DIMENTIONS/WEIGHT

The NASA SCREW-GUN will be approximately 12 to 14 inches long, approximately 6 inches high and approximately 3 inches wide.    It will weigh less than three pounds (unloaded).

OPERATION:

Bolts and nuts, within the NASA SCREW-GUN, are adhesively bonded together in a straight-line with an adhesive, or plastic, designed to "break-away".    This line of adhesively bonded bolts becomes a clip that is inserted into the NASA SCREW-GUN much like a magazine of cartridges that is inserted into the conventional semi-automatic rifle.

The "breach-block" secures a bolt, separates the bolt from the other bolts, and lowers the bolt into the "chamber" of the barrel and then drops below the barrel.    The barrel is rifled with straight hexagonal internal cross-section; much like a conventional socket wrench.    The barrel receives the bolt and secures the bolt by the head of the bolt riding in the internal socket shaped barrel.    The chamber (breech) of the barrel is chamfered from a round internal shape to that of the hexagonal internal shape to provide a smooth transition for the bolt head.

The barrel is rotated by means of an electric (rechargeable) battery powered motor located in the handle of the NASA SCREW-GUN.    This rotary motion provides the torque necessary to turn the bolt, or nut, thereby tightening the fasteners.    Counter-rotation of the NASA SCREW-GUN is provided by "fore-arm hook" which rests perpendicularly to the forearm of the astronaut; and is specifically designed to counter act the torque of the rotating barrel and fastener.    Activation of the NASA SCREW-GUN is provided by pulling a "trigger" type switch that controls a rheostat electrical circuit.

The more the trigger is pulled, the more torque is applied to the bolt or nut.    At maximum torque, a clutch mechanism restrains the NASA SCREW-GUN from applying any more torque.

Reversing the rotation of the NASA SCREW-GUN is accomplished by flipping a lever on the side of the gun with the thumb of the hand used to pull the trigger; thus maintaining a single hand operation characteristics while tightening or removing bolts or nuts.

A "backing-arm" is used to reach around behind a fastened component or strut.    This "backing-arm will be firmly attached (though easily removable) to the front of the NASA SCREW-GUN.    The "backing-arm" will be utilized to grasp the nut in such a manner that the screw-gun can insert the bolt and tighten it in place.    This feature allows the astronaut to assemble/disassemble nuts and bolts using one hand.

The top of the NASA SCREW-GUN is hinged to allow for insertion/removal of the bolt "cartridge" clips, nut "cartridge" clips, changing the barrel-breech block assembly, or for removing accumulated nuts/bolts (when disassembling fasteners).    This feature allows easier maintenance, modular changeovers, and cleaning.

A printable PDF document of the Technical description of the NASA SCREW GUN.

MATERIALS:

It is envisioned that the "NASA SCREW-GUN" will be fabricated out of the following materials:

    Handle/fore-grip/forearm hook - - - - - - Engineered plastic

    Barrel/breach block/bolt guides - - - - - -Stainless Steel

    Motor - - - - - - - - - - - - - - - - - - - - - - - - Copper, Steel

    Trigger mechanism/Backing arm - - - - - - Stainless Steel

    Battery pack - - - - - - - - - - - - liquid gel battery pack*

    *(Manufacturer unknown).

Prototypes of the NASA SCREW-GUN will be fabricated of aluminum and/or stainless steel.