Hi super10018,
Sheet A: When I designed my first pivoting tangentially tracking tone arm, I realized that its pivot had to be movable. The shortest possible distance is achieved when the two locations of the pivot lie on a straight line which runs through the center of the turn table. At the time I knew nothing of the Thales principle. The length of the track upon which the tone arm pivot travels, is 1.6056” with an effective tone arm length of 7.950”
I stopped working on the project for many years because CDs came on the market.
Sheet B: In 2017 I discovered that I can reduce the length of the track to .8412”, which is a reduction of almost 50%! if I offset the head-shell by ~15.17°. However, that introduced the dreaded “inward force”.
Sheet C: Also in 2017 I discovered that, if I arranged the head-shell to be floating, the inward force no longer affected the head-shell/cantilever/stylus assembly. In order for that idea to work, I developed variable electronic anti skating, GOVERNED by the instantaneous position of the floating head-shell with respect to the tone arm.
Figure 4: In order to make the tone arm a tangentially tracking one, the tone arms location has to be precisely controlled throughout its travel across the LP. I did that with cams 4a, 4b and cam followers 9 (2).
Figure 5: This drawing shows in detail how the cam and cam followers control the position of tone arm 12. tone arm 12 pivots where it meets with swing arm 5. The angular relationship between tone arm 12 and the cam followers 9 is fixed!
Figure 6: This drawing shows the approximate mid position of the tone arm and its cam followers.
Figure 7: This drawing shows the end position of the tone arm and its cam followers.
My original drawing that you reposted, does not show the cam and cam follower arrangement.
There was no way you could have known how that works.
The tone arm’s path is not circular but is a curve generated by the above described cam and cam followers.
The offset head-shell in my design absolutely is the cause of the inward force. If that was not so, the tone arm would not work.
In 2020 I applied for a Us Patent on the offset, floating head-shell and the fact that the offset causes the tone arm to be self propelled. The patent examiner agreed with my claims and allowed the Patent to be issued. That was late last year and the patent should issue some time this spring.
Sincerely,
Ralf
"The offset head-shell in my design absolutely is the cause of the inward force. If that was not so, the tone arm would not work."
Since the stylus assembly moves freely in the headshell, the headshell cannot be a source of inward force.
Your use of the term skating force is ambiguous. A servo driven arm is moved by the servo, so it cannot be pressed inwards by the skating force.
Since the stylus assembly moves freely in the headshell, the headshell cannot be a source of inward force.
Your use of the term skating force is ambiguous. A servo driven arm is moved by the servo, so it cannot be pressed inwards by the skating force.
For me, it's not that complicated. If the headshell is 4" wide with a straight path in line with the radius that covers the playing area, we wouldn't have all these speculations. Then it would resemble a passive parallel tracker. All these terms like skating force or inward force are moot. But the headshell is only about an inch wide so the servo is simply there to extend this path, it is not correcting any angle. This could've been a completely passive linear tracker, except now we have to deal with a 4" wide headshell whose effective mass might be too high. The arm assembly is there to deal with vertical movement and tracking force. The quasi-pivot arm look makes for easier mounting and more aesthetically pleasing. This is not a Birch style arm and does not rely on the Thales principle, similar to the Schroder LT because the tail end does not move in an arc but a curve or cam. It's a servo arm with a base that moves on a cam and not based on linkages a la Birch. Although using a Birch geometry can make the base construction much simpler, if you are willing to accept a tiny bit of tracking error.
Ralf,
If the arm's path is not circular, it is possible to reach zero tracking errors as long as the stylus is perpendicular to the center of the spindle. So, your arm is not a variant of Birch-style arms.
Offset is only structural property. It doesn't generate any force. The only source of the driving force is generated by the interaction of stylus and groove.
Jim
Parts marked with 2, 5, 9, 4a, 4b are part of the servo mechanism, so their "efficiency" is not a problem.
But they might be a problem if they generate noise that is coupled into the tonearm.
If I understand it correctly, the servo for Ralf's arm is not a driving mechanism. The servo generates a force against the inward force so the linear rail is always in the correct position.
I think that is incorrect. No lateral force is exerted on the cartridge by the tonearm or visa versa. The servo keeps the carrier for the "floating" headshell in the right position so that the cartridge can track tangentially. The tonearm is providing a 'race', 'track' or 'rail' perpendicular to the tangent so the headshell carrier can move towards or away from the spindle whilst remaining essentially perpendicular.
Edit: I say 'essentially perpendicular' because the important bit that needs to be perpendicular is not the cartridge body, except for spherical styli the important bit is the plane of the cut line of the stylus. In an ideal world this would translate to the cantilever being perpendicular, but only if the stylus is correctly positioned on the cantilever which in my experience is frequently not the case. The latter requires an adjustment of the yaw of the cartridge body.
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I did a search. Here is the link to Ralf's patent if anyone is interested. The patent was published only last year.
https://www.patentguru.com/assignee/dieckmann-ralf-eckehart
https://www.patentguru.com/assignee/dieckmann-ralf-eckehart
Hello alighiszem,
My tone arm is not 'servo driven". It is driven purely by the frictional force between the vinyl LP and the stylus. It is beyond me why anyone would tell me how my own tone arm works. Read my various posts!
Sincerely,
Ralf
Hi Jim,
Today was shopping day, where we always come home after dark. Too late to respond. Tomorrow I'll make another CAD drawing, illustrating why I and others think that an offset head-shell is the cause of the dreaded inward force.
Sincerely,
Ralf
"
I think I understand now.
If we would perform the string test, the cradle would remain in place, but the headshell would move inwards. So the friction between the record and the stylus moves the headshell.
The servo just exerts a CCW torque (the variable antiskating Ralf wrote about) to avoid the collision of the cradle with the headshell.
carlo,
What I meant was to eliminate all the side forces generated by the structure of the arm itself. The perfect condition for a tonearm is like my 6B or a passive linear arm. Once the arm sits on a blank disc, it doesn't move sideways. The only driving force comes from the groove, i.e., stylus drag. I hope we use the term, stylus drag, with the same meaning.
Jim
Hi Jim, clearly i wasn't not talking about pivoted linear TA. which use both the tracking forces in a complex and variable way (from outer to inner grooves).
I'm talking about the usual Linear trackers that can use only the Side Force (= cart friction) to advance, since they dissipate the SD (orthogonal to the rail) completely on constrains.
Therefore to affirm that:
What I meant was to eliminate all the side forces generated by the structure of the arm itself.
seems strange for a constructor of - excellent and sophisticated - linear TAs.
Imo Ralf's arm makes a very clever use of the Stylus Drag with the minimum needed offset, and controlling its variability actively.
Personally, following Percy Wilson old attempt, I chase the dream of doing the same on a pivoted one passively, struggling very far from a solution. It will remain a dream, I believe
ciao carlo
The blank disc test has very little to deal with real tracking forces, for many people - me included.
I'm talking about the usual Linear trackers that can use only the Side Force (= cart friction) to advance, since they dissipate the SD (orthogonal to the rail) completely on constrains.
Therefore to affirm that:
What I meant was to eliminate all the side forces generated by the structure of the arm itself.
seems strange for a constructor of - excellent and sophisticated - linear TAs.
Imo Ralf's arm makes a very clever use of the Stylus Drag with the minimum needed offset, and controlling its variability actively.
Personally, following Percy Wilson old attempt, I chase the dream of doing the same on a pivoted one passively, struggling very far from a solution. It will remain a dream, I believe
ciao carlo
The blank disc test has very little to deal with real tracking forces, for many people - me included.
carlo,
Ralf added inward force or skating force, to propel the arm inward. Do we really need such force to propel the arm? All pivot arms are self-propelled arms, but with negative effects on playing back because they all have skating force. Furthermore, all passive arms will be driven by the friction between the stylus and the groove except some of the arms such as my 6B and linear arms with no skating force. Why do we need additional force to drive the arm? How about the negative effects of adding additional external force because such external force will have negative effects on the cantilever? This is why I said I rather let the friction between the stylus and the groove drive the arm only without any other external force. Adding external force may make things worse.
The beauty of a blank disc test is to separate the skating force from the side force generated by the groove wall.
Jim
Ralf added inward force or skating force, to propel the arm inward. Do we really need such force to propel the arm? All pivot arms are self-propelled arms, but with negative effects on playing back because they all have skating force. Furthermore, all passive arms will be driven by the friction between the stylus and the groove except some of the arms such as my 6B and linear arms with no skating force. Why do we need additional force to drive the arm? How about the negative effects of adding additional external force because such external force will have negative effects on the cantilever? This is why I said I rather let the friction between the stylus and the groove drive the arm only without any other external force. Adding external force may make things worse.
The beauty of a blank disc test is to separate the skating force from the side force generated by the groove wall.
Jim
Keep chasing the dream! Your pursuit of nonpivoting vertical movement in your Corkscrew design is awesome and your single-minded focus is the sign of a true inventor and admirable.