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THK KR20 Rail adaption

 
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mawyatt



Joined: 22 Aug 2013
Posts: 1626
Location: Clearwater

PostPosted: Tue Aug 08, 2017 9:03 am    Post subject: THK KR20 Rail adaption Reply with quote

For those folks interested in the precision THK surplus rails for use as a focus rail I have adapted a KR20 model with a inexpensive (<$10) eBay 150mm long ARCA mount. These mounts are intended for long telephoto lens with the long mating clamp on a tripod. Thus mounting the camera/lens combo by the lens base rather than the camera base which gives better balance and less stress on the camera 1/4-20 mount.

Adding 4 drilled and tapped holes (M3-0.5) in the ARCA mount, the mount fits under the KR20 rail base. The standard ARCA clamps are 38mm wide which fits prefectally under the KR20 40mm base, and looks like it was part of the original rail design. 4 Allen head M3 0.5 bolts fit within the recessed KR20 base (inside) and secure the rail to ARCA clamp.

Now you can mount the rail to a long ARCA clamp which is attached to your optical test bench base, and have a quick release of the focus rail and camera/lens assembly which is very sturdy when clamped down.

I've used this setup with the WeMacro Vertical Stand. The KR20 rails can use a standard NEMA 17 stepper motor. Peter at MJKZZ has a nice adapter kit for the THK rails that includes the motor and various mounting adapters. BTW the KR20 rails work beautifully with the Stackshot controller and Zerene. This is an extremely good stacking system for precision work, as the Stackshot controller has lots of builtin flexibility and utility, and Zerene provides a friendly user interface. Also, the WeMacro focus rail controller works with the KR20 setup. You just need to build a custom cable for each controller, either the Stackshot or WeMacro.

Anyway, hope this helps some folks looking into these precision THK surplus rails.

Best,

Mike


Last edited by mawyatt on Wed Aug 09, 2017 5:56 pm; edited 1 time in total
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ray_parkhurst



Joined: 20 Nov 2010
Posts: 1700
Location: Santa Clara, CA, USA

PostPosted: Tue Aug 08, 2017 5:26 pm    Post subject: Reply with quote

I've been looking at various THK rails and I am finding them to be fabulous for PM work. I ended up integrating a KR2602A into a vertical setup, and it has now replaced my Trinamic based system. I built it using the conversion kit from mjkzz, though I ended up fabricating my own supports and carriage hardware since I wanted something a bit "different".

This system works down into sub-micron steps, though I am not really trusting anything below 1.25um. In any event, it's small enough that I can be confident in accuracy in the 5-10um range that I usually work.

This is using a 400-step (0.9deg) NEMA17 motor, which when combined with the 2mm pitch gives 5um full steps and 1.25um quarter steps.

I am now working with a KR2001A and an SKR2001A. SKR has caged balls, so is built for more lifetime and less noise in operation since the balls never touch each other. These both have 1mm pitch, so the full steps are 2.5um with 400-step motor.

One thing to be aware of is that smaller step size means slower movement. If you need to move the stage for focusing or composition, which I do with my vertical setup, it can take quite a while to go from one end to the other!

For those not familiar with the THK numbering system:

KR is the rail type, linear rail with screw actuator
20 is the height of the rail in mm
01 is the screw pitch
A means single carriage. B means dual carriage, for higher load capacity

I just recently ran across some KR1502 as well, which came with NEMA08 motors. these things are so very small!

I'm having a lot of fun learning how to configure these THK rails, and in what are the important BKMs for building a vertical stand with them. My configurations are probably different from others in that I am moving the stage, not the camera. I found early on that with continuous light, making everything as rock solid stable as possible (meaning tight coupling between camera and stage) is critical for sharp shots. These THK rails are about as rigid as it gets, so fit well with this philosophy.
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mawyatt



Joined: 22 Aug 2013
Posts: 1626
Location: Clearwater

PostPosted: Wed Aug 09, 2017 9:50 am    Post subject: Reply with quote

Ray,

One of the many nice things with the Stackshot controller and Zerene interface is the ability to set the rail speed and acceleration rates. This makes traveling to the extremes of the rail fairly quick, and accurate.

Best,

Mike
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ray_parkhurst



Joined: 20 Nov 2010
Posts: 1700
Location: Santa Clara, CA, USA

PostPosted: Wed Aug 09, 2017 10:40 am    Post subject: Reply with quote

The mjkzz system has controls for rail speed and motor currents as well.

What is the max RPM you can get from a Stackshot/Zerene combo with a 400-step motor?
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Lou Jost



Joined: 04 Sep 2015
Posts: 2765
Location: Ecuador

PostPosted: Wed Aug 09, 2017 11:53 am    Post subject: Reply with quote

Ray, my Stackshot carriage goes from one end to the other in 20 seconds. Total distance moved = 100mm.

WeMacro rail is similar, and does 1 micron step size.
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ray_parkhurst



Joined: 20 Nov 2010
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Location: Santa Clara, CA, USA

PostPosted: Wed Aug 09, 2017 12:45 pm    Post subject: Reply with quote

Lou Jost wrote:
Ray, my Stackshot carriage goes from one end to the other in 20 seconds. Total distance moved = 100mm.

WeMacro rail is similar, and does 1 micron step size.


Are you using a 200 or 400 step motor? And what is the pitch of the lead screw on the Stackshot?
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Lou Jost



Joined: 04 Sep 2015
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PostPosted: Wed Aug 09, 2017 12:49 pm    Post subject: Reply with quote

Sorry, I don't know those details. It is just the standard Stackshot.
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ray_parkhurst



Joined: 20 Nov 2010
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Location: Santa Clara, CA, USA

PostPosted: Wed Aug 09, 2017 1:07 pm    Post subject: Reply with quote

No worries, I was just hoping to translate to my parameters. My KR26 rail has 2mm pitch, 220mm total travel, and I'm using a 400-step motor. It travels end-end in 90-sec. So if I scale for 2.2x longer travel, I get 41sec to travel 100mm. I assume the standard Stackshot uses a 200-step motor, so factoring that in I get to the same 20sec. So perhaps the Stackshot has 2mm pitch screw as well, and pulses the motor at the same max speed as the mjkzz controller.
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Lou Jost



Joined: 04 Sep 2015
Posts: 2765
Location: Ecuador

PostPosted: Wed Aug 09, 2017 1:19 pm    Post subject: Reply with quote

That's a nice set of deductions!
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mawyatt



Joined: 22 Aug 2013
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Location: Clearwater

PostPosted: Wed Aug 09, 2017 2:16 pm    Post subject: Reply with quote

The standard Stackshot rail has a ~1.59mm pitch (1/16") and 200 step motor. You can set the thread pitch, microsteps/rotation, rail speed, acceleration ramp time, high precision threshold, backlash distance , rerun distance, and a number of other rail related timing parameters in the controller.


Very flexible rail controller.
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ray_parkhurst



Joined: 20 Nov 2010
Posts: 1700
Location: Santa Clara, CA, USA

PostPosted: Wed Aug 09, 2017 2:28 pm    Post subject: Reply with quote

mawyatt wrote:
The standard Stackshot rail has a ~1.59mm pitch (1/16") and 200 step motor. You can set the thread pitch, microsteps/rotation, rail speed, acceleration ramp time, high precision threshold, backlash distance , rerun distance, and a number of other rail related timing parameters in the controller.


Very flexible rail controller.


The mjkzz controller has many of the same functions, though perhaps with different ways of approaching them. I'm not sure what some of the Stackshot settings mean:

acceleration ramp time
high precision threshold
rerun distance

Is there an explanation for these in the Stackshot docs?
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mawyatt



Joined: 22 Aug 2013
Posts: 1626
Location: Clearwater

PostPosted: Wed Aug 09, 2017 4:31 pm    Post subject: Reply with quote

ray_parkhurst wrote:
mawyatt wrote:
The standard Stackshot rail has a ~1.59mm pitch (1/16") and 200 step motor. You can set the thread pitch, microsteps/rotation, rail speed, acceleration ramp time, high precision threshold, backlash distance , rerun distance, and a number of other rail related timing parameters in the controller.


Very flexible rail controller.


The mjkzz controller has many of the same functions, though perhaps with different ways of approaching them. I'm not sure what some of the Stackshot settings mean:

acceleration ramp time
high precision threshold
rerun distance

Is there an explanation for these in the Stackshot docs?


There's probably an explanation on Rik's site, maybe he can assist.

My understanding is as follows.

1) Acceleration Ramp time is the time to go from zero to the specified rail rate, or from specified rail rate to zero.
2) High Precision Threshold is the distance where the rail enters a precision positioning mode as approaching a specified rail point, thus going down to a high accuracy mode as it approaches a point.
3) Rerun Distance is the distance the rail will bypass the point and return to allow approaching a point from only one direction. This effectively removes any backlash for accurate positioning.

BTW I can't use Peter's software because I don't have an available PC, I use only Macs. I'm looking for a Windows laptop, but confess haven't been looking hard. William at WeMacro fortunately supports PCs and well as Macs, so I can utilize his rail controller.
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mawyatt



Joined: 22 Aug 2013
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PostPosted: Wed Aug 09, 2017 4:56 pm    Post subject: Reply with quote

Zerene with the Stackshot system & controller is a really well thought out and developed rail, controller and interface. It allows the user to focus (pun intended) on the stacking details rather than the rail, software, user interface quirks. Very intuitive behavior that follows ones thinking and work habits. This system is exceptionally good from a performance and user standpoint, a tribute to the Cognisys folks and Rik. Things that you want and need to do for stacking setup, image capturing, and preparation have already been well thought out and implemented in this system. However, the Stackshot rail is fine for most work but can be improved upon for high precision needs. The modified THK rails are really a work of art for stacking rails IMO, and combining them with the Stackshot controller and Zerene interface is about as good a stacking rail system as one could expect. These rails are very expensive as you might suspect, but a number of them (surplus) have shown up on eBay at fair prices. Peter at MKJZZ has a nice kit for the THK rails that includes the motor and mounting bracket, some specific for the T board system. My original post was about an ARCA clamp method to mount the THK rail, which is some ways more flexible than the T board method, and only adds about $10 if you drill and tap the holes yourself.

Best,

Mike
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elf



Joined: 18 Nov 2007
Posts: 1356

PostPosted: Wed Aug 09, 2017 5:57 pm    Post subject: Reply with quote

Speed will depend on how many steps/microsteps per second the processor can handle. My Teensy 3.2 board with it's 32 bit processor can easily do 60,000 steps/second. If my calculations are correct that would translate to about 30mm/second (ignoring acceleration time) with a 200 step motor. How many steps/second can a Stackshot do?
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rjlittlefield
Site Admin


Joined: 01 Aug 2006
Posts: 19330
Location: Richland, Washington State, USA

PostPosted: Wed Aug 09, 2017 7:44 pm    Post subject: Reply with quote

mawyatt wrote:
ray_parkhurst wrote:
acceleration ramp time
high precision threshold
rerun distance

Is there an explanation for these in the Stackshot docs?

There's probably an explanation on Rik's site, maybe he can assist.

I don't find two of those exact names mentioned anywhere, but here's my guess.

acceleration ramp time: I assume this is what the StackShot and Zerene Stacker documents call just "ramp time". Those are the time needed to accelerate from stopped to max, or vice versa. I assume the acceleration is linear, but I've never checked that.

high precision threshold: In Zerene Stacker, this parameter is a threshold based on step size. For step size smaller than the threshold, the rail runs all the time in StackShot's "High Precision" mode. That means it maintains a much higher holding torque that overcomes most of the non-linearity of microstepping in the basic StackShot controller. See HERE for details.

rerun distance: Zerene Stacker has a "prerun distance" (with a leading "p"). That is described HERE like this:
Quote:
"Prerun distance" allows you to specify a distance that the rail should "back off" before moving to the start position to begin shooting a stack. It will also back off before positioning in response to the "Go to Start" and "Go to End" buttons. The purpose of prerun is to guarantee that all types of mechanical slack have been removed before the designated position is reached. The main type of slack is backlash along the rail axis, but usually there is also a small amount of rotational backlash that can be important at higher magnifications.

--Rik
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