Antoine Guivarch
Taesik Lee
Carissa Tudryn
guivarch@mit.edu
tslee@mit.edu
tudi@mit.edu
2.875
Mechanical Assembly and its Role
in Product Development
Dr. Daniel Whitney
Project Assignment #2
Quartz Analog Alarm Clock
DFC Analysis of the Bell
Subassembly
PICTURES
October 2001
Guivarch, Lee, Tudryn
Mechanical Assembly and its role
in Product Development
October 2001
BILL OF MATERIALS
5 subsystems, 32 parts
FRONT CASING SUBSYSTEM FC
10 parts
BELL SUBSYSTEM BSS
6 parts
Front casing
Clock paper
Battery + contact
Battery – contact
LED
Transparent clock cover
Alarm hand
Hour hand
Minute hand
Second hand
Support
Motor
Ring holder
Rings (2x, no difference)
Bell
Capacitor
FC1
FC2
FC3
FC4
FC5
FC6
FC7
FC8
FC9
FC10
GEAR BOX GB
4 parts
Gear box
Gear box switch
Printed Circuit Board
Flex cable
SPRING SLIDE SS
7 parts
Base
SS1
Slide
SS2
Spring
SS3
Electric contact holder
SS4
Electric contact bumper
SS5
Metal contacts SS6 (comes with SS5)
& SS7
BSS1
BSS2
BSS3
BSS4
BSS5
BSS6
GB1
GB2
GB3
GB4
BACK CASING SUBSYSTEM BC
5 parts
Back casing
Battery cover
Alarm button
On / off switch
Knob setter
BC1
BC2
BC3
BC4
BC5
Not counted: wires
screws
Guivarch, Lee, Tudryn
Mechanical Assembly and its role
in Product Development
October 2001
CAD Models of Parts Involved in DFC
Bell
Guivarch, Lee, Tudryn
Mechanical Assembly and its role
in Product Development
October 2001
Support
Guivarch, Lee, Tudryn
Mechanical Assembly and its role
in Product Development
October 2001
Ring Holder
Guivarch, Lee, Tudryn
Mechanical Assembly and its role
in Product Development
October 2001
Ring
Guivarch, Lee, Tudryn
Mechanical Assembly and its role
in Product Development
October 2001
Motor
Guivarch, Lee, Tudryn
Mechanical Assembly and its role
in Product Development
October 2001
Bell Subassembly Exploded
Guivarch, Lee, Tudryn
Mechanical Assembly and its role
in Product Development
October 2001
Bell Subassembly Assembled
Guivarch, Lee, Tudryn
Mechanical Assembly and its role
in Product Development
October 2001
LIAISON DIAGRAM
FC6
Transparent
Front cover
FC5
L.E.D.
FC10
Second Hand
FC8
Hour hand
FC7
Alarm Hand
FC3
Battery +
contact
FC9
Minute Hand
FC1
Front Casing
FC4
Battery contact
GB4
Flex
Cable
FC2
Clock Paper
GB1
Gear Box
BSS1
Bell Support
BSS6
Capacitor
GB3
Printed
Circuit
Board
BSS5
Bell
BSS2
Motor
GB2
Gear Box
Switch
BSS3
Ring Holder
BSS4
Ring
BSS4
Ring
BC5
Knob
SS4
Elec. Contact
holder
SS1
Spring Slide Base
BC4
On/Off Switch
SS2
Slide
SS6
Metal
Contact
SS3
Spring
SS7
Metal
Contact
BC3
Alarm Button
SS5
Elec. Contact
Bumper
Guivarch,
BC1
Back Casing
Lee, Tudryn
Mechanical Assembly and its role
in Product Development
BC2
Battery Cover
October 2001
1. Liaison Diagram of the alarm clock:
Our goal in this liaison diagram was to describe relationships between parts (not only
physical, simply interdependencies). This explains that the liaison diagram involves
links that the DFC would not include. For example, the clock paper (FC2) is related to
the Gear Box (GB1) on the liaison diagram because it has a hole specially made for
the Gear Box for the hands support to reach the front of the clock. But there is no
mating or even physical relationship between those two parts.
Other similar cases are the GB1 – BC5 – BC1 and BSS1 – BSS2 – BSS3 triangles.
For the bell subsystem example, which is the purpose of this report, there is no mating
relationship between the Ring Holder BSS3 and the Bell Support BSS1, but the motor
shaft (BSS2) goes through the bell support to mate with the ring holder.
We added those relationships because the liaison diagram could have been
misleading. For example, one can decide on the basis of the liaison diagram to
assemble the Bell subassembly first by cutting the BSS1-FC1 link. If we had not
included a link between BSS1 and BSS3, one could have thought that it was possible
to cut the link between BSS1 and BSS2 and make the BSS2 – BSS3 – BSS4
subassembly independently from BSS1, which is not possible.
Datum Flow Chain Analysis of the Bell Subassembly of the Alarm Clock
From this point, we did not include the capacitor in the analysis because of its special and
accessory role in the subassembly.
2. The bell subassembly is significant in the operation of the alarm clock. Its function is
to ring the bell.
3. The motor (BSS2) is driven to spin the ring holder (BSS3). The rings (BSS4) are
attached to the ring holder (BSS3) and make contact to the bell.
4. The key characteristics are the clearances between the rings to the bell.
The bell ringing is a dynamic process in which rings are pushed away from the ring
holder center because of the centrifuge force induced by the rotation of the motor
shaft. In order for the ring on the side of the bell to ring it, the clearance between the
bell edge and the “outer wall” of the ring has to be negative (see below). After the ring
hits the bell, the shock pushes the ring back and contact stops in order for the sound to
last. The clearance has then to be positive. There are thus two key characteristics that
relate to two different states of the system. This picture shows the negative clearance
first because the ring hits the bell before it retracts. The distance from the pin to the
center of the bell is labeled d. The ring holder rotates around the motor shaft in respect
to the rotating arrow labeled w.
Guivarch, Lee, Tudryn
Mechanical Assembly and its role
in Product Development
October 2001
5. The root for the DFC is the support BSS1 because it locates every other part in the
subassembly.
6. Datum Flow Chain delivering the key characteristics (see next page)
7. Important Features and Key Characteristics for each Part.
Part
BSS1
BSS5
BSS2
BSS3
Features
 square peg
 x-y plane to prevent z-translation
 | , | Two clippers (effectors)
 motor hole
 Bell center hole
 Cylinder housing
 Two small holes on surface for
support
 Shaft
 Two pins
 Center hole
 | | Two clippers (effectors)
BSS4
Important KC
 Center of the motor support to the
center of the peg
 Height: distance from flat bell
support to motor support surface
 Center of motor support surface to
end of bell wall
 Height: bottom of bell to top of bell
 Cylinder: height of shaft
 Shaft being perpendicular to motor
 Radius
 Center: location of shaft
 Distance between pin and center-hole
 Diameter of center-hole
 Height of clippers
 Height of pins
 Diameter of inner and outer of ring
8. There are no over-constraints or any risk of them. Each assembled part is either
properly-constrained or purposely under-constrained for assembly or requirement of the
mated parts.
Assembled Parts
BSS1 to BSS5
BSS1 to BSS2
BSS2 to BSS3
BSS3 to BSS4
Guivarch, Lee, Tudryn
Constraint
Properly constrained
Properly constrained
Purposely Under constrained
Purposely Under constrained
Mechanical Assembly and its role
in Product Development
October 2001
DFC
BSS1:
support
Center hole
(Large clearance)
Flat surface 1
X, Y, X, Y
Flat surface 2
Square peg
Cylindrical Wall
Pins
Z
Z, X, Y
5
X, Y, X, Y
Top cylinder
wall
Z
Top Surface
Cylinder housing
Bottom
X, Y, X, Y
Center Hole
Pin hole
BSS5:
Bell
BSS2:
motor
X, Y, X, Y
(Z, Z by friction)
KC1:
clearance < 0
Edge
KC2:
clearance > 0
Center hole
Post
BSS3: Ring
holder
Floor
X, Y range only
Inner wall
Bottom Surface
Z, X, Y
Clipper
Z (max)
Guivarch, Lee, Tudryn
Outer wall
Top Surface
Mechanical Assembly and its role
in Product Development
BSS4: Ring
October 2001
9. Suggestions for redesign of parts that improve constraint or KC delivery
We did not find any special improvements for this subassembly, it looks properly
designed for the Key Characteristic.
Guivarch, Lee, Tudryn
Mechanical Assembly and its role
in Product Development
October 2001