3.2 Test Setup
The buttons on this reference design were designed with the same parameters but due to mechanical tolerances
there can be slight differences in performance. Since the design is meant to be 3D printed, different printers
or printing technologies will have different accuracies and tolerances. Additionally, if a different material is used
for the 3D printing, then deflection of the button surface will change and can require more force for a press
event to trigger a button output. Even though the buttons on a single print will all have the same printer and
material, there can still be variation in force required for a button, especially if the design is hand assembled.
The tape used to keep the mechanical tolerance can have an impact on the button if it is not uniform or differs
between units. To showcase this, an analog force gauge is used to apply a force to the button surface. The
force required for each button threshold to trigger is then recorded as well as the raw data response for varying
forces. Additionally, testing is performed on two different material types with different 3D printing processes while
keeping the same mechanical design.
3.3 Test Results
The required force for each button press shows the difference in mechanical structure that can occur when using
materials that are not completely uniform or have design tolerances large enough to impact the performance.
Additionally, testing with two different materials shows the differences between them as well.
Table 3-1. Button Press Force Required
Button Position
ABS Left
(Newtons)
ABS Right
(Newtons)
Nylon Left
(Newtons)
Nylon Right
(Newtons)
1
7
5
2
3.75
2
20
3.5
3
0.75
3
16
1.5
1
1.5
4
3
1
3
1
3.3.1 ABS Force Response
The differences shown between the buttons is due to more than just the material difference. Because these
test units were hand assembled, there is variation in the mechanical alignment and the adhesion that creates
the mechanical isolation. This difference can cause some of the buttons to have a worse response and can be
alleviated by having a controlled and repeatable assembly process. The different force responses can be offset
by applying a different gain factor to each button so they all end with a button output at the same force. To better
showcase this, the raw data is collected for each button with varying forces. The force response for the ABS
button surface is shown in
Sample
Chang
e
in Data Code
0
500 1000 1500 2000 2500 3000 3500 4000 4500 5000
-2500
0
2500
5000
7500
10000
12500
15000
17500
2N
4N
6N
8N
10N
Ch 0
Ch 1
Ch 2
Ch 3
(a) Left Side
(b) Right Side
Figure 3-3. ABS Force Response
Hardware, Software, Testing Requirements, and Test Results
Inductive Touch and Magnetic Dial Contactless User Interface Reference
Design
13
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