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Posts from — January 2015

Robot Primer 13: Why Use Work Coordinates

Since Work coordinates are transformed into Base coordinates in the end, why bother?  Why not just use base coordinates?  Here are some possible reasons; I’m sure creative programmers have come up with others.

  • Using Work coordinates can be more natural.
  • Using Work coordinates can save re-teaching points.
  • Palletizing
  • Using dynamically updated Work coordinate makes complex situations such as picking and placing from a moving conveyor easy.

Next I’ll look at some examples in more detail

Using Work Coordinates To Save Re-Teaching

If we use base coordinates and the robot’s base coordinates change, then all the points have to be re-taught.  However, if we’ve used world coordinates, all we have to do is to add the offset between the old and new base coordinates, and we’re done.

Some reasons why the robot’s base coordinates could change:

  • Robot needs to be re-calibrated
  • Robot needs to be replaced by another robot of the same or possibly different type
  • Moving the whole base plate to a different robot cell
  • If base plate fabrication is precise enough, to allow easier production

Let’s look at a simple example using a simple assembly robot.

Simple Assembly Cell

Robot Primer World Coord 1

This imaginery work cell uses a robot to:

  1. Pick up the circular yellow bases from the top left pallet (defined by points P1 to P4)
  2. Place the base in the assembly fixture (P13) and add glue
  3. Pick up the blue part from the bottom left pallet (defined by P5 to P8) and place it onto the base.
  4. Move the completed part to the inspection fixture (P14)
  5. Finally move the inspected part to the output pallet (defined by P9 to P12).

The base plate is big blue rectangle, and the base coordinates are represented by the even larger gold rectangle, with the coordinates for P1 shown (54.5mm and 85.0 mm).

My example is simple and easy, there’s no need for additional complications such as work coordinates, right?

Work Coordinates to the Rescue

But now suppose the robot breaks down and is replaced by a new robot, with slightly different base coordinates (represented by the bold red rectangle).

Robot Primer World Coord 2

As you can see, the position of P1 has shifted quite considerably on the base plate.  So we will need to re-teach all 14 points.

No big deal, right?  But now suppose the pallets and fixtures and interchangeable so we can assembly 10 different types of parts.  Now we have to re-teach 140 positions: ouch!

Unless, of course, we used work coordinates – then all we have to do is change the offset so that the work coordinates for the robot matches the work coordinates for the old robot.  Now a little bit of extra work pays off: we only have to teach 1 work coordinate instead of 140 positions.

Personal Note

I actually saw this situation; a robotic system I serviced had its robot re-calibrated, and the program used base coordinates, so all the points had to be re-taught.


January 24, 2015   1 Comment

Daiso Adventures

Over the past few months, I’ve had fun checking out the Daiso Japan store near Mitsuwa marketplace in San Jose.  The good side is that most items are $1.50, so when I see something new and cool, it’s hard to resist the temptation to add it to the basket to try it out.

Recent temptations have included

Daiso B5 Grid Notebook

Daiso B5 Grid Notebook

Daiso Grid Notebook - Inside

Daiso Grid Notebook – Inside

This red notebook has paper with a grid design.  I’ve never seen a grid notebook at retail, but I’ve been curious to find out if I’d like it, so I couldn’t resist the temptation of a mere $1.50 for 80 sheets of B5-sized grid goodness (the grid’s dots are at 5mm intervals).  My initial impression is, yes, I like it a lot.


This graph notebook with a translucent blue plastic cover was a no-brainer, also at $1.50 for 60 sheets of A4-sized paper.


My kids love these funky pencils with cute designs and a bunch of tips.  They’re a bargain at $1.00 for a pack of 8.

Daiso A4 Copy Paper

Daiso A4 Copy Paper

A4 paper comes and goes at Daiso, so I jumped at the chance at grabbing several 110-sheet packs for a miserly $1.50 each (A4 paper is double that price at Staples or Amazon, and is stratospherically priced at Kinokuniya/Maido).  Since it’s copy paper, I’ll have to see how does in my inkjet printer.


I might prefer LED light bulbs, but at $0.50 for these 32W, 2100 lumen CFL bulbs, I couldn’t resist picking up a bunch.

The Downside of Daiso

I’ve seen lots of cute and neat things at Daiso over the years (such as brush pens, cute stationery, cute sketchbooks, affordable handy storage boxes, made in Japan dishes, unique egg timers, and more), but it’s kind of like Costco because:

  1. It’s so tempting to add “just one more bargain” that you get surprised at check out time.
  2. Many items are here today, gone tomorrow.  Just of the items I’ve shown, last time the blue notebooks were gone, and the cute pencils have been replaced by boring pencils.  A4 paper has always been hit or miss (sometimes nothing, sometimes only colored paper, sometimes great selection, and so on).
  3. It’s not always a bargain.  Some items aren’t worth a $1.50.  Some items are sold in such small quantities (such as the wire frame storage) that when you add up all the $1.50 items you need, it’s not so cheap.
  4. Inventory can vary a lot store to store.  Daiso has a wide of items, but many of the stores are pretty small, so they get a different assortment of what’s available at the moment.

January 17, 2015   No Comments