CALCULATIONS

DISCUSSION

CONCLUSION

MISTAKE PROOFING

Several elements of this screwdriver were designed for mistake-proofing.

 

The following features exemplify methods to eliminate assembly error and prevent misalignment or misconnection of critical parts.

1. Exterior Casing

Part of the assembly requires putting and locking the two halves of the exterior casing (orange) together to encapsulate the gearbox and connect them to the handle. To prevent the pieces from being attached on the wrong side of the handle, there is a gear like groove engraved in the handle that must match that of the case piece to be attached. See the right Figure for a visualization of this.

Comparison of the two pieces
Comparison of the two pieces

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Correct alignment
Correct alignment

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Correct fit and orientation
Correct fit and orientation

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Comparison of the two pieces
Comparison of the two pieces

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Single Groove+Protrusion
Single Groove+Protrusion

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Double Groove+Protrusion
Double Groove+Protrusion

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Click above for full image
Click above for full image

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Single Groove+Protrusion
Single Groove+Protrusion

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2. Motor and Gear Train Connection

The upper body of the screwdriver contains two parts: one that hold the motor and one that holds the epicyclic gear train. To ensure proper assembly of these two parts and prevent misconnection, the plastic adjacent to the ring of the gear train contains a pattern of grooves. Two major grooves dictate how the motor should be attached; 1, a wide single groove should match the wide single protrusion on the motor casing and 2, two grooves parallel and adjacent to each other should match the two parallel protrusions on the motor casing. These features are highlighted in red in the left images.

3. U-Pin Insertion

To ensure that the motor and gear train parts (discussed above) are properly connected and stay connected, a U-pin must be inserted. However, there are two pairs of holes on opposite sides of the gear train case through which this pin can be inserted. One of the pairs, however, contains a groove between the holes that allows the pin to fit into after insertion. This way, the pin will mold itself into the cylindrical shape of the case and allow proper encapsulation of the exterior casing around it. If the pin was inserted in the other pair, which doesn't contain the groove, part of the pin will stick out and its protrusion will interfere with the assembly of the exterior casing.

See the set of figures to the right for visualization.

Correct Insertion of U-Pin
Correct Insertion of U-Pin

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Incorrect Insertion of U-Pin
Incorrect Insertion of U-Pin

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Correct Insertion of U-Pin
Correct Insertion of U-Pin

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MECHANICAL ELEMENTS

1. Tool Handle Pivot Lock

The handle and upper body (motor and gearbox) of the screwdriver are connected by a pivot lock where the user can adjust the angle between the two parts. To keep the desired position in place and prevent sliding of the upper body, a pin runs through the pivot hole. One end of this pin has a gear like segment with 9 teeth, one of which is wider and has an upside-down U shape to it, which will be called the major tooth. These teeth fit through the gear shape of the exterior casing (depicted and explained above). During the adjustment of the screwdriver orientation, the pin gear slides above the casing gear and is "unlocked". When an orientation is set in place, the major tooth slides onto one of the teeth of the casing gear rending it "locked".

IMG_0503_edited.jpg

The image above depicts (from left to right):

1) how the pin looks from the bottom of its cylindrical shape to the gear segment, emphasizing the difference between the major tooth from the other teeth of the gear

2) how the gear segment pin looks relative to​ that of the exterior casing in the 'unlocked' position and

3) how the gear segment pin fits into that of the exterior casing in the 'locked' position

2. Forward/Reverse Switch

Depending on the position of the power switch, the screwdriver can operate in either clockwise (CW) or counter-clockwise (CCW) rotation. (Note that this CW/CCW rotations are observed when looking directly at the chuck). This switch piece has a center protrusion that the user can push and adjust the switch position either to the left or right. When the piece is pushed to the left and the right-hand triangle pointing down is shown, the screwdriver will operate clockwise. When the piece is pushed to the right and the left-hand triangle pointing up is shown, the screwdriver will operate counter-clockwise.

IMG-0505_edited.jpg

The image above depicts how the chuck operates according to the position of the power switch. Note that squiggle lines are break lines that exclude a sketch of the upper body to emphasize the relation between the chuck and power switch. 

The mechanism described above is depicted as an electric circuit image below

IMG_0504_edited_edited.jpg

3. Power/Manual Option

A handy and practical feature of this screwdriver is a toggling option between power/automatic mode and manual mode. This can be done by rotating the top piece of the upper body. Mechanically, the different modes changes the position of a base gear. When the screwdriver is set to power/auto mode, the base gear is lowered and separated from the first planetary carrier of the gear train. This allows the gear train to rotate continuously with its speed  controlled by the power of the motor. When the screwdriver is set to manual mode, the base gear is lifted to surround and fit around the first planetary carrier. The outer part of the base gear has teeth that fit into the ring so when the power switch is turned on, the base gear locks the planetary carrier in place and blocks rotation.

IMG_0502_edited.jpg

The image above depicts the base gear position relative to the first planetary carrier of the gear train depending on the mode set. Note that the shading denotes the interior of the upper body.