Difference between revisions of "Power Scissors 2 - The Better Power Scissors"

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(Rendered Scotch Yoke)
(Rendered Scotch Yoke)
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[[Image:yokeback.jpg|thumb|250px|left|Figure 3. Rendered Scotch Yoke (Back)]]
[[Image:yokeback.jpg|thumb|250px|left|Figure 3. Rendered Scotch Yoke (Back)]]
[[Image:yokeanim.gif|thumb|150px|right|Scotch Yoke Animation]]
[[Image:yokeanim.gif|thumb|150px|right|Scotch Yoke Animation]]

Revision as of 15:19, 7 February 2008

Black and Decker Power Scissors



Mike Morena

Eric Miller

Brian Peters


The Powered Scissors are designed to cut dozens of materials in the workshop and around the house in an easy fashion. The scissors contain a battery that is charged by plugging the power cord into an outlet. A trigger is pulled to activate the motor inside the scissors. The motor rotates the input linkage. The Scotch Yoke translates the motor's rotational movement into translational movement. This translational movement is used to move one of the scissor blades back and forth which provides the cutting force. The other scissor blade is held stationary in the scissor housing. A spring, which holds both blades in place, is also in the housing.


Cuts a Variety of Materials - Can cut wrapping paper, plastic, fabric, cardboard and paper.

Cordless Power - Fast and easy cutting without limitation of a power cord.

Long Lasting Battery - 70 minutes of continuous use. A long lasting battery makes it a practical tool.

Durable - Strong tool that will last for a long time.

Lightweight - Scissors are easier to handle with lighter weight

Dull Edges - In case of an accident, the edges are dull so it doesn't hurt customers.

Low vibration - It would be uncomfortable for the user to hold scissors if they had high vibration.

Comfortable Grip - User comfort, especially for long use.

Small in Size - Easy to store and easy to handle.

Attractive Color - Black and red are typical colors for this type of tool.

Engineering Specifications

Table 1: Customer Requirements and Engineering Specifications
Number Customer Requirements Engineering Specifications
1 Battery Life Hours of use (h)
2 Strong Cutting Blade Force produced by blade (N)
3 Blade that retains sharpness Rockwell hardness
4 Lack of vibration (Dampening) Weight required to dampen vibration (g)
5 Material Removal Rate Cutting speed (rpm)
6 Reasonable Size Volume (cm^3)
7 Ergonomic Grip Diameter of handle (cm)
8 Light Weight (Easy to hold) Weight (g)


The table belows lists the components for the Black and Decker Power Scissors:

Table 2: Power Scissors Component List
Part # Part Name Category Function Material Picture
1 Scissor Blades Output Shears material Aluminum *
2 Scotch Yoke Motion Coversion Converts motion from rotation to translation Plastic
3 Scissor Housing and Spring Structural Component Provides support to blades. Holds them together tightly. Plastic and Aluminum
4 Input Linkage Motion Coversion\Transmission Also converts motion from rotation to translation. Aluminum
5 Electric Motor Transmission Takes energy from battery and drives rotating shaft. Copper, Alumnium, Plastic
6 Power Source - Battery Input Provides energy for electric motor operation. Nickel Cadmium/Lithium Ion
7 External Housing Structural Component Holds all parts in place and creates a easy surface to grip Plastic/Rubber
8 Plastic Trigger/Spring Input Provides a way for user to easily turn the device on or off. Plastic/Aluminum
9 Trigger Switch Input Allows battery power to flow to the electric motor. Plastic/Aluminum
10 Power Switch Input Turns the device on or off. Disables trigger switch when off. Plastic/Aluminum
12 Power Input/Charger Input Provides method to charge internal battery Plastic/Aluminum
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13 Wires/Resistor Other Allows for passage of energy through switches, battery, and motor. Plastic/Copper
13 Power Supply/Charger Input Charges internal battery. Plastic/Copper

Rendered Motor

Figure 1. Rendered Electric Motor

Question Answer
What decisions were made in the design of this component/module?
  • Power requirements and battery usage had to be considered
    • Ideal RPMs and Watt/s had to be calculated
  • It was required that the input linkage meshed smoothly with the scotch yoke.
    • Dimensional accuracy and lubricant
  • The ability to maintain speed without vibration
    • Weighting of the input linkage and motor
What are the critical features and dimensions?
  • Length of the Axle - meet up with scotch hoke
  • Width of input linkage
  • Offset distance for input linkage/scotch yoke insert
  • Diameter of the motor - must fit within handle
What kind of loading do we expect to be on the component?
  • Cyclical Loading - sinusoidal
  • Depending on the material being cut - a range of loads
What measures can we use to evaluate performance?
  • Time the tool is in use before motor fails
  • Maximum load the motor can power the scissors to cut
  • The linear force the motor translates to the scotch yoke
  • Vibration created

Rendered Scotch Yoke

Figure 2. Rendered Scotch Yoke (Front)
Figure 3. Rendered Scotch Yoke (Back)
Scotch Yoke Animation

Question Answer
What decisions were made in the design of this component/module?
  • Functionality- a scotch yoke converts rotational motion in to translational motion, serves as the linkage between the electric motor and scissor blades
  • Geometric compatibility- the scotch yoke must have proper dimensions to produce needed displacements as well as mate to the motor input and scissor output linkages
  • Material selection- the scotch yoke is made of high strength plastic, the plastic will undergo harsh cyclical loading and therefore must resist failure due to fatigue
What are the critical features and dimensions?
  • Vertical slider – mates to the motor input linkage, creates the horizontal displacement by sliding up and down while motor rotates (green component in Figure 3.)
  • Horizontal translation guides – allow the yoke to translate freely while guiding its motion in one direction; create stability for system; have precise tolerance to allow free motion while reducing friction (red components in Figure 2.)
  • Yoke – holds vertical slider inside of it, floats in between horizontal translation guides, translate horizontally, contains the scissor mating linkage (oval-like protrusion in Figure 2.), contains slots for lubrication (orange component in Figure 2.)
What kind of loading do we expect to be on the component?
  • Linear load
  • Depending on the material being cut - a range of loads
What measures can we use to evaluate performance?
  • Time the tool is in use before scotch yoke fails
  • Maximum load before scotch yoke fails
  • Amount of force the scotch yoke translates to the scissors
  • Strength of plastic

Rendered Blades

Figure 4. Rendered Blades

Question Answer
What decisions were made in the design of this component/module?
  • Functionality- The scissor blades use the translational motion from the scotch yoke to cut the material
  • Geometric compatibility- The scissor blades must be sharp enough to cut numerous materials. The blades must have enough material for strength. They also have to be long enough to ensure they do not cut in small pieces
  • Material selection- The scissor blades are made out of a strong metal. The metal will undergo loads from various materials so they must resist failure due to fatigue and dullness
What are the critical features and dimensions?
  • Stationary Blade – Sharp blade which is stationary in the blade housing. The blade does not have to move because the other blade does all of work (red component in Figure 4.)
  • Moving blade – Sharp blade which translates to provide the cutting force of the scissors. The moving blade is mated tightly to the stationary blade (green components in Figure 4.)
What kind of loading do we expect to be on the component?
  • Linear load on a slight angle
  • Load decreases after the initial incision is made
What measures can we use to evaluate performance?
  • Sharpness of blade
  • Max load the scissors can cut
  • Amount scissors can cut before failure(scissors break or get to dull to cut)

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