Antoine Guivarch

Taesik Lee

Carissa Tudryn

PICTURES

October 2001
BILL OF MATERIALS

5 subsystems, 32 parts

Guivarch, Lee, Tudryn Mechanical Assembly and its role October 2001

in Product Development

Front Casing Subsystem FC

10 parts

Front casing FC1

Clock paper FC2

Battery + contact FC3

Battery – contact FC4

LED FC5

Transparent clock cover FC6

Alarm hand FC7

Hour hand FC8

Minute hand FC9

Second hand FC10

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

BELL SUBSYSTEM BSS

6 parts

Support BSS1

Motor BSS2

Ring holder BSS3

Rings (2x, no difference) BSS4

Bell BSS5

Capacitor BSS6

GEAR BOX GB

4 parts

Gear box GB1

Gear box switch GB2

Printed Circuit Board GB3

Flex cable GB4

BACK CASING SUBSYSTEM BC

5 parts

Back casing BC1

Battery cover BC2

Alarm button BC3

On / off switch BC4

Knob setter BC5

Not counted: wires

screws

Guivarch, Lee, Tudryn Mechanical Assembly and its role October 2001

in Product Development


CAD Models of Parts Involved in DFC

Bell

Support

Ring Holder

Ring

Motor

Bell Subassembly Exploded

Bell Subassembly Assembled


LIAISON DIAGRAM

  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.

  1. The bell subassembly is significant in the operation of the alarm clock. Its function is to ring the bell.
  1. 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.
  1. 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.
  1. The root for the DFC is the support BSS1 because it locates every other part in the subassembly.
  1. Datum Flow Chain delivering the key characteristics (see next page)

7. Important Features and Key Characteristics for each Part.

Part / Features / Important KC
BSS1 / ·  square peg
·  x-y plane to prevent z-translation
·  | , | Two clippers (effectors)
·  motor hole / ·  Center of the motor support to the center of the peg
·  Height: distance from flat bell support to motor support surface
BSS5 / ·  Bell center hole / ·  Center of motor support surface to end of bell wall
·  Height: bottom of bell to top of bell
BSS2 / ·  Cylinder housing
·  Two small holes on surface for support
·  Shaft / ·  Cylinder: height of shaft
·  Shaft being perpendicular to motor
·  Radius
·  Center: location of shaft
BSS3 / ·  Two pins
·  Center hole
·  | | Two clippers (effectors) / ·  Distance between pin and center-hole
·  Diameter of center-hole
·  Height of clippers
·  Height of pins
BSS4 / ·  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 / Constraint
BSS1 to BSS5 / Properly constrained
BSS1 to BSS2 / Properly constrained
BSS2 to BSS3 / Purposely Under constrained
BSS3 to BSS4 / Purposely Under constrained

DFC
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 October 2001

in Product Development