From DDL Wiki

(Difference between revisions)

Revision as of 20:02, 8 February 2007

Purpose

The purpose of this information page is to analyze in entirety all manufacturing and working aspects of a paper shredder. Following the analysis, what is deemed the most crucial of all possible modifications will be prototyped. Our analysis will take into account Design for manufacturing and assembly as well as user considerations.

Product Study and Dissection

Conventional and Unconventional Purposes:

Shreds paper or credit cards placed correctly into feeder

Increase security - not able to easily retrieve information from shredded items
Facilitate disposal - reduce volume of garbage
Substitute for a recycling bin - provide a seperate container for paper wastes
Produce confetti - save money on party decorations

Inputs/Outputs:

Material Inputs: Paper, Staples, Credit Cards (no ties)
Information Inputs: Direction of motor rotation
Energy Inputs: 120V AC
Material Outputs: Shredded material inputs
Information Outputs: Operation status
Energy Outputs: Heat, Noise, Light

Stake Holders:

Possible outsourced companies (computer chips, bulbs, motor)
Raw materials suppliers
Retail stores
Transportation workers
Stock holders

Operation Procedures:

If stored without power cord plugged into electrical wall outlet
- Position basket in desired place (making sure it is close to an outlet)
- Place shredder assembly on top of basket
- Confirm the off/auto/reverse switch is in the off position
- Plug power cord from shredder assembly into the wall outlet
If stored in the off position or continuing from un-powered storage
- Set off/auto/reverse switch to auto
Identify the items for shredding, confirming acceptable destruction
- Documents(s)
- Credit Card
Confirm dimensions of items to be shredded
- There is not more than a thickness of 8 pieces of paper
- There is not more than one credit card
Orient items for better control when feeding them into the shredder
- Align documents
- Fold/unfold documents
- Orient credit card to be fed long-ways
Confirm that the “ready light” is illuminated
Feed item into proper opening
- Position document(s) in proper groove
- Position credit card in proper slot
Action following feeding
- Let go of document(s) once feeder has caught them, allowing them to be pulled through automatically
- Continue pressing credit card downwards until no longer possible
If finished shredding, return to desired storage conditions
- If placing in desired storage area
  - Turn off shredder
  - Unplug power cord from wall outlet
  - Pick up shredder assembly or shredder assembly and basket, placing it where desired
- If leaving in desired spot
  - Can leave in auto position, off position, or off position with power cord unplugged from wall outlet

Specific User Considerations:

Certain tasks difficult for people with a neural disorder and/or coordination difficulty
- Feeding tasks
- Switch control
Bending over to feed items difficult for individuals with orthopedic (e.g. back) and/or balance problems
Inconvenient and inefficient for large corporate tasks
Main shredder assembly is heavy and possibly difficult to lift for weaker individuals
- Main shredder assembly must be lifted when emptying basket and setting up
- Main shredder assembly may often be moved depending on storage preference

Functional Operation:

There are three switches in the electrical circuit that must be activated to begin shredding. First, the shredder must be properly resting on the waste bin to toggle the safety switch, and then the off/auto/reverse switch that allows power to go to the shredder must be moved to "auto". Finally, the paper being put into the shredder compresses an air damper which trips the third switch and sends power to the AC motor. The damper slowly depresses and when it is fully extended the switch is released, terminating the shredding process. The AC motor drives a gear train that reduces the speed of the shaft rotation and increases the torque. The first two gears are helical gears in order to reduce noise. At the end of the gear train, two spur gears are meshed and attached to individual shafts with cross-hatching blades. The blades are in a wave shape that cuts paper into the desired diamond shaped shreds. The blades spin in opposite directions and the paper is fed in between the spinning blades. The shredded paper falls into basket.

Media:

For videos of user-trials and general operation, please visit the following: http://www.youtube.com/view_play_list?p=501153C70A89F93B

Components:

Part #	Part name	QTY	Function	Materials	Dimensions	Manufacturing Process	Picture
001	Top Cover	1	Protect the user from moving parts Aesthetics Support the shredder on basket Houses the on/off switch Informs the user of acceptable inputs Houses item entrance for shredding	Plastic	12" x 5" x 1"	Injection Molding
002	Switch Housing	1	Sets desired functionality Houses child safety button	Plastic	3" x 1" x 1"	Injection Molding
003	Base	1	Houses main components Lightbulb Motor Gear train Blades Operation safety switch Dispense of shredded paper	Plastic	12" x 5" x 3"	Injection Molding
004	Feeder Lip Top	1	Guides paper Protects user	Plastic	8" x 2" x 1"	Injection Molding
005	Feeder Lip Bottom	1	Guides paper Protects user	Plastic	8" x 2" x 1"	Injection Molding
006	Child Safety	1	Prevents unintentional use	Plastic	2" x 1" x 1"	Injection Molding
007	Electrical & Motor Sub-assembly	1	Drives gear train (motor) Automatic safety switch (must be sitting on basket properly) Shredding cutoff time-delay Ready LED Off/auto/reverse switch Light bulb Provides electrical power to the system	N/A	N/A	Purchased
008	Helical Gear	1	Component of gear train Conects to motor Quieter than spur gears	Plastic	1" x 1"	Injection Molding
009	Large Spur Gear	1	Component of gear train Reduce Speed/Increas Torque	Plastic	3" x 1"	Injection Molding
010	Small Spur Gear	1	Component of gear train Reduce Speed/Increas Torque	Plastic	1" x 1"	Injection Molding
011	Output Spur Gear	1	Drive shaft	Plastic	1" x 1"	Injection Molding
012	Light Bulb Reflector	1	Increases intensity of light	Plastic+Aluminum	.5" x .5" x 1"	Injection Molding and Sheet Foil
013	Delay Trigger Housing	1	Houses the shredding cutoff time-delay	Plastic	3" x 1" x 1"	Injection Molding
014	Cutoff Switch Time-Delay Trigger	1	Triggers cutoff switch time-delay	Plastic	1" x 1" x .5"	Injection Molding
015	Spring for Child Safety Switch	1	Hold the safety switch in position	Spring Steel	1/8" x .5"	Winding
016	Bow-Tie Washer	1	Attaches auotmatic safety switch to the base cover	Plastic	1" x 1" x 1/8"	Injection Molding
017	Main Shaft Base Plate	1	Hold axes aligned	Plastic	3" x 3" x 1/4"	Injection Molding
018	Cover Plate for Shaft Alignment	1	Hold axes aligned	Plastic	2" x 2" x 1/4"	Injection Molding
019	Gear Train Housing Base Plate	1	Holds gears Holds axes aligned	Metal	4" x 2" x 1/4"	Stamped
020	Gear Train Housing Top Plate	1	Holds gears Holds axes aligned	Metal	3" x 1" x 1/4"	Stamped
021	Attachment Aligner for Motor Base Plate	1	Holds motor to gear train housing top plate	Plastic	1" x 1" x 1/4"	Injection Molding
022	Screws	31	Fastening	Steel	#10-20	Machined	In the background
023	Helical Blade	104	Cut paper in diamond shape Feeds paper	Steel	.5" x 1\32"	Stamped
024	Flat Blade	8	Feeds paper	Steel	.5" x 1\32"	Stamped
025	Paper Aligners	54	Ensures proper feeding of paper	Plastic	1/2" x 1/4" x 1"	Injection Molding
026	"Paper Aligner" Aligning Rod	2	Aligns aligners	Metal	1\4" x 8"	Extrusion	Gold rod
027	Long Main Shaft	1	Driven by gear train Turns blades Aligns blades	Steel	10" x 1/4"	Machined	Center rod
028	Short Main Shaft	1	Driven by gear train Turns blades Aligns blades	Steel	9" x 1/4"	Machined	Center rod
029	Basket	1	Collect shredded waste Houses tab Shredder assembly rests on top of basket Keeps shredder assembly aligned	Steel	12" x 12" x 5"	Stamp
030	Tab	1	Press safety switch	Steel	1/2" x 1/2" x 1/2"	Stamped	On the basket

FMEA: Failure Mode and Effects Analysis

Item & Function	Failure Mode	Effects of Failure	S	Causes of Failure	O	Design Controls	D	RPN	Recmd Actions	Responsibility & Deadline	Actions Taken	S	O	D	RPN
Motor Drives gear train/blades	Electrical failure	Product ceases to function reliably. Shredding no longer possible.	8	Intense heat and/or vibrations loosen connections, resulting in itermittant operation	4	Run under extreme working conditions	3	96	Add solder to strengthen connections. Add dampening to decrease effect of vibrations	Motor manufacturer prior to purchase	-	8	3	3	72
Motor Drives gear train/blades	Mechanical Failure		8	Gear train shears helical gear. Thermal deformation from heat generation. Shredding unapproved items	3	Test at high rpm with strain gage and thermocouple	5	120	Treat motor axis to add strength	Motor manufacturer prior to purchase	-	8	2	5	80
Main shafts	Mechainical Failures. Shearing. Torsion. Thermal	Depending on degree of failure, blades may begin to clash or will function at a reduced capacity	7	Heat. Applied load from gear train. Shredding unapproved items	2	Feed solid items. Run under extreme conditions	6	84	Treat rod to increase strength. Increase diameter	Machinist(s) prior to installation	-	7	1	6	42
Helical gear	Mechainical Failures. Shearing. Torsion. Thermal. Elastic deformation to out of spec	Under complete mechanical failure, gear train will not be connected to the motor. Under partial failure, will have possible slippage which will result in inefficient operation and noise	7	Heat from motor. Vibrations. Forces from gear train.	4	Drive gear at high rpm and/or under intense working conditions	3	84	Thicker injection mold to make gear larger. Use stronger plastic.	Injection molder(s) prior to installation	-	7	2	3	42
Shredding cutoff time-delay Turns motor on and keeps motor temporarily turning after paper has passed through to ensure complete shredding	Electrical failure	Product ceases to function reliably. Shredding no longer possible.	8	Intense heat and/or vibrations loosen connections, resulting in itermittant operation	4	Run under extreme working conditions	3	96	Add solder to strengthen connections. Add dampening to decrease effect of vibrations	Switch manufacturer prior to purchase	-	8	3	3	72
	Mechanical Failure		8	Flat metal spring fatigues leading to fracture. Thermal deformation from heat generation. Plastic deformation from shredding unapproved items	4	Compress and expand spring repeatedly and under extreme conditions	3	96	Treat metal to strengthen. Increase thickness of spring.	Switch manufacturer prior to purchase	-	8	2	3	48

DFX: Design for 'X'

DFE: Design for Environment

Possible Environmental Problems:

Power usage
Harmful products of manufacturing processes
- Pollution from production
- Leftover materials
- Odd shapes make it difficult to transport product
Heat production
Noise production

Possible Environmental Improvements:

Use alternative energy sources (solar power)
Use less power if possible
Use recyclable/recycled materials
Reduce amount of material used
Add heat sink and bigger fan
Add noise dampening materials to inside of shredder
Make parts shaped such that as many stamped parts as possible can be stamped on one sheet
Make stackable parts
Use leftover materials for other parts

DFMA: Design for Manufacturing and Assembly

What is DFMA? DFM - The design for ease of manufacture of the collection of parts that will form the product after assembly.*

DFA - The the design of the product for ease of assembly.*

Why DFMA? - reduce cost and increase quality

DFM - The means of manufacture of the individual components is listed above in the components table. All of the plastic pieces are injection molded and most are simple pieces with little space for improvement. A few pieces like the cover are larger and have complicated webs which could possibly be redisigned or eliminated as neccesary.

All of the metal parts excluding shafts and electrical subassemblies are stamped. These pieces are nd there are few opportunities for improvement.

Shafts are extruded and then machined. Again opportunities for improvement are limited.

DFA - Since we do not have any official document describing the assembly process we can only guess at the way the product is put together. We assume the assembly process is largelly automated or mixed with some automation and some manual assembly.

The product breaks down into a number of sub-assemblies, namelly: plastic housing, motor and electrical assembly, geartrain/cutter assembly. The plastic housing is fastened together using screws and snap fit in some parts. The motor and electrical assembly is purchased so we don't care about the way it is put together. The assembly with the most opportunities for improvement is the geartrain and cutter assembly. The cutter is made from a number round cutting blades and dividers slipped onto a pair of shafts. The blades are alligned on the shaft through a key-groove interface. During disassebmly we found that sliding the blades onto the shaft is difficult. Its is hard to align the keys to the grooves and the blades often get stuck along the way. There are about 50 blades on each shaft and their assembly must take considrable time. We assume this process can be improved.

From "Product Design for Manufacture and Assembly, Boothroyd," Dewhurst, Knight.

Design for Maintainability

Design for Reliability

Design for Safety

The on/off/reverse switch is "child-proof."
- The user must press a button and slide the switch in order to move it.
There is a protective cover over the blades so that fingers cannot fit inside the paper slot but paper and credit cards can.
Electrical components are housed inside of the shredder.
Shredder has a safety switch that does not allow shredding to occur unless the shredder is on basket.
When shredder is on for a prolonged period of time, it shuts off auotomatically for a fixed amount of time for motor to cool.

Design for Usability / ergonomics

Shredder mounts easily on top of basket
On/off/reverse switch is on top of shredder for easy access
Shredder has convenient slot for paper and convenient slot for credit cards
Basket height is such that it can hold alot of paper but still fit under the user's desk
Lightweight and portable

Design for Variety (product families)

Modification:

Areas of Possible Improvement:

Improved shredding capability for added security
- Rotary blade in which confetti is funneled into
- Pulp making apparatus
  - Water jet (maybe acetone)
  - Stirrer

Decrease heat generation (when shredder overheats, safety mechanism kills motor till it has cooled significantly)
- Fan and vents

Way to empty basin without taking off top

Wall-mounting capabilities

Weight issues of shredder assembly which affect portability, sotrage, and emptying waste basket
- Use a lighter material than machined steel for main rods
  - Titanium
  - Plastic
  - Composite
- Smaller motor
- Lighter blades
  - Composite
  - Titanium

Decrease noise pollution of system
- Line shredder with sound-dampening material
  - Foam

Improved feeding capabilities
- Large queue where can position multiple sheets that will automatically feed
- Examine a printer and fax feeder

Prototype:

Mass Production:

Current Bulk Manufacturing Strengths

Areas for Improvement

@@ Line 360: / Line 360: @@
 ==Design for Usability / ergonomics==
 * Shredder mounts easily on top of basket
-* Switch is on top of shredder for easy access
+* On/off/reverse switch is on top of shredder for easy access
 * Shredder has convenient slot for paper and convenient slot for credit cards
 * Basket height is such that it can hold alot of paper but still fit under the user's desk

Paper shredder