# Button Test - Tactility Criteria

#### johnnybegood

##### Involved In Discussions
Button Test - Tactility

There is this button test that we are performing on a radio. Recently we received customer complaint that while the radio is functional when depressing the button there is no tactility feel. Tactility is consider good if we can feel the 'spring effect' but we are not able to quantify this criteria as it's too human depended. Different operator may exert different finger force on the button. As such to some operator the radio button test is accept but to other is a reject.
How do I go about quantifying the tactility criteria?

M

#### M Greenaway

If it is a straightforward depressing of a button against a spring you could measure the force required to depress the spring, or if you know the stiffness of the spring do a simple calculation to determine the force required to depress it.

#### johnnybegood

##### Involved In Discussions
The test is currently done by finger pressing the button. Beside tactility at the same time we are testing the functionalty of the radio. How can I control the force if it's done by using the first finger. I personally dont think the engineering can come out with a fixture.

G

#### Graeme

Borrow energy's fish scale ...

How's this for one back-of-the-envelope minimal-cost suggestion?

• Obtain a spring scale marked in the units of your choice (grams, ounces). I am thinking of the type where the top is held by a hand or fixture, and the mass to be weighed is suspended from the bottom. Ensure that the scale will work acceptably when held in a horizontal position.
• Fasten the bottom of the scale (the load attachment point) to a fixed object.
• Attach a plunger of a convenient size to the top of the scale. It could be arranged so that one end can be pushed by the finger and the other end contacts the radio button, and the spring scale is attached somewhere between. Details depend on the physical configuration.
• Support the scale and plunger so they are horizontal and able to move freely. Place the radio so that the plunger is just barely touching the button when at rest. (The scale reads zero.)
• Apply gradually increasing pressure to the plunger with the finger, so as to operate the radio button. Read the scale value when the radio changes state.
• If a standard value and tolerance have been established then compare the result. Otherwise, experiment to determine optimum values.

I am sure the mechanical engineers can adapt this to read to several more significant figures and a cost of several more kilobucks ...

Graeme

M

#### M Greenaway

Johnny

It dont take rocket science to determine how much force is 'good' force, and then select a suitable spring to achieve this, then you would not even have to do the so called tactility test !!

#### Mike S.

##### Happy to be Alive
Trusted Information Resource
It may not be a simple matter of force, but force + a certain "feel" that the customer wants. Very hard to quantify and measure I'd think -- maybe one of things that you can't describe but you know it when you feel it. For example, I think of the trigger pull on a firearm. Two different guns may have the same trigger pull from the standpoint of the number of pounds of pull force required to make the firing pin drop, but the feel may be much different. One may release "crisply and cleanly" while the other may have lots of "creep". Maybe you find a button the customer likes, then just build future models in the same way with the same parts.

M

#### M Greenaway

Mike

I take your point, but we arent talking about gun triggers. It appears that we are talking about a straight forward push in/out button. If you want a click on the button again that can be achieved through design, and should not need testing.

Maybe I am wrong, but I am picturing a small button that is depressed straight in by the tip of an index finger. If you want feel on this button all you can be talking about is the force exerted back on the finger tip, which is a straightforward selection of a suitable spring. If you need friction on the button tip then use a suitable polymer for the button material. If you want it to click design some mechanical click system at the end of the button stroke.

You cannot operate any SPC on an unquantifiable subjective attribute such as tactility - i strongly suggest you understand what tactility is better in the design of your button, and design in the tactility required !

#### Mike S.

##### Happy to be Alive
Trusted Information Resource
Martin,

I'm picturing the same kind of button as you.

But... Who said there must be SPC on this attribute? SPC, is a really great tool, but it isn't for everything.

You said "If you want feel on this button all you can be talking about is the force exerted back on the finger tip..." I disagree. I think they are thinking about not just force, but rather force OVER TIME/DISTANCE. Thus my trigger analogy.

Maybe Johnny could mount several types of available buttons on a board, have the customer pick one they like, and just use that button from now on -- hopefully something that is a standard part from a switch maker who can probably do all the tactility testing required and who understand it much better.

M

#### M Greenaway

Mike

The thread was posted in the 'Statistics' section so I jumped to an assumption - sorry.

Johnny are we helping any ?

#### johnnybegood

##### Involved In Discussions
I check with our engineering folks. The button consist a keypad and inside the button there is switch where a plunger pushes against a metal piece dome. And this result in the spring effect. The tactile feel is very subjective.

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