PSN-L Email List Message

Subject: Re: Lengthening a vertical period with pulley
From: "Mark Robinson" mark.robinson@...............
Date: Fri, 2 May 2003 11:10:20 +1200

Hi John and all,

My most recent project has been refurbishing a weighing and packaging machine which included a mechanical movement amplifier
arrangement which may be applicable to your suggestion below.

The basic arrangement of the weigh head was a parallelogram with leaf springs making up the top and bottom sides, the world in
general the left hand side, and the moving mass the right. beyond this there was an arm in the middle of the parallelogram actuated
by the moving mass, and pivoted on crossed shims (the low friction pulley).

I've made a rough conceptual diagram of it which is at

These weigh heads also included rather nifty dashpot dampers which could be adjusted by simply turning one half which was mounted on
a screw until critical damping was achieved.



----- Original Message -----
From: John D Nelson
To: PSN-L@..............
Sent: Friday, May 02, 2003 8:25 AM
Subject: Lengthening a vertical period with pulley

Has anybody ever thought of lengthening the period of a vertical with a pulley arrangement like a compound bow.  Seems to me that If
you took the basic LaCoste arrangement and fixed the spring where the weight would ordinarily be, placed a multiple pulley from the
spring to the top point and then hung the weight on the cable to the pully, the period would lengthen times the amount of the
mechanical advantage.  Ideally the best medium instead of rope would be flat metal tape.  The only problem I see is friction in the
bearings of the pulleys lowering the sensitivity of the instrument.  Has this ever been done?

John Nelson


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