HP card reader drive coupling

[GreyUser]

I don’t want to hijack the OP’s thread so I’m starting this one to continue discussion. With respect to Geoff’s comment over in the HP-25 keyboard thread:

(09-26-2021 10:41 PM)Geoff Quickfall Wrote:  As GreyUser accurately points out, the ‘pores’ are vias. I just didn’t want to assume everyone here including me is an electronics engineer ;-)

Just as the card reader does not have a clutch but rather a ‘dampening couple’ used to prevent vibration from the motor transferring to the card as it is read.

Cheers, Geoff

Well, it’s certainly not a clutch but practically speaking, it does not pass muster as a vibration dampener. It’s just a coupling. There is no dampening going on there.

If we want to call it vibration dampener, what vibration does the arrangement dampen? More importantly, how does it dampen vibration? The end of the lead screw fits directly onto the tip of the motor shaft, the urethane inside the aluminum sleeve is there to add friction and to help center the screw on the motor shaft. The lead screw was cemented onto the motor shaft, likely an with cyanoacrylate adhesive or similar.

If the designers were concerned about vibration, it would not be hard coupled, it would float in some way. Have you ever seen a true vibration dampening coupling? They are also known as flexible couplings. They are typically three pieces. Two shaft hubs with something in between to transmit the torque through the medium. Soft plastics are used in low torque applications, flexible metal grids are used on motors into the megawatt range.

Vibration is created from misalignment between a motor and the shaft it is driving. A vibration dampening coupling allows for that misalignment. But, that’s not what we have in a card reader. It’s hard coupled.

I suppose if you wanted to torture the verbiage, one could say it is a vibration dampener - because it centers the driven shaft on the driving shaft, thereby reducing vibration. I’m not sure but that sounds like recursive thinking to me.

It took years to dispense with the notion it was a clutch. Perhaps it will take a few more to bury the vibration dampener canard. That is of course if you agree with me. If I’m just being pedantic, feel free to tell what you think. If not, let’s call this thing by its proper name. It’s a coupling.