Category — Products

A while ago, I did way too much mousing (setting up vision jobs with Cognex Insight) and ended up with significant shoulder strain.  I’ve been better since (but not back to normal), partly by watching how much mousing around I do.

Recently, I decided it was time for another approach, and bought a Kensington Orbit Trackball with Scroll Ring.  Overall, it’s working pretty well; I’ve been using it for less than a  week, and my arm and shoulder definitely feel better.  The scroll ring works pretty well (I’d say better than a typical mouse wheel).  The ball is pretty big (about 1.5″), and is very smooth.

I also went to a smaller keyboard; I think part of the problem may have been extending my arm too far to get to the mouse.  When I use the narrower keyboard, I don’t have to extend as far.  I was able to scrounge up an old PS/2 mini-keyboard with trackpad.  The keyboard is OK, with a usable layout, but the trackpad is pretty bad (it doesn’t feel good, and it takes a lot of motion to get across my monitor).  Also, I’ve been adjusting my chair height to find the best position.

I’ve used mini keyboards with trackballs in the past, and haven’t been happy with them, because they had mechanical mini-trackballs that took a lot of motion to get anywhere, picked up lint like crazy, and basically were a pain to use.  In the future, I might try a mini keyboard with trackpad if I can test it first (some trackpads are decent), the old Lenovo Thinkpad keyboard (with pointer stick and trackpad) or the new Lenovo Thinkpad keyboard (with pointer stick only, but more affordable price).

I looked at some Logitech trackballs; I went with the Kensington because the ball seemed substantially larger, I liked the the scroll ring, and I’ve tried some Logitech trackballs in the past and wasn’t impressed (I do like their mice).  I wouldn’t mind having a larger ball and more buttons, but I’m not willing to pay for a Kensington Ultimate (~$90) or CH Products with 2.25″ ball (~$230; I’ve used CH Products joysticks in the past — they are really nice).

Recently, I had what seemed like a simple task: select a DAC (digital to analog converter).  There are hundreds of models, so it should be easy, especially since most of my requirements were not demanding (1 channel, 12-bit or better, 1KHz output rate, 0-10V, low jitter output, and reasonable cost, hopefully <$500).   Even my low jitter requirement wasn’t demanding; I’d be happy with 100 microseconds of jitter; basically, any unit with a decent FIFO buffer and a hardware timed DAC update should work.

But finding candidates was a lot of work.  Early on, I concentrated on USB DAC models, because they have sufficient speed, are self-powered, tend to be reasonably priced, and don’t need a PCI or PCIe slot.

I’ve used Measurement Computing before, so they were one of my first stops.  It was really hard to find exactly which models have FIFO buffers and hardware paced outputs.  I had to do a lot of searching — and reading the full manuals.

The cheapest Measurement Computing model that met my requirements is the USB-1208HS-2AO, which is overkill ($599, high speed USB 2.0, 2 12-bit analog outputs at 1MHz, DAC has 4K FIFO buffer).  As far as I can tell, nothing cheaper has a FIFO buffer for the DAC.

Data Translation wasn’t much better; I had to dig through the detailed specs PDF to discover that the DT9812-10V meets my requirements, and has a 2K FIFO buffer.  It’s $375; DIN Rail mounting is an extra $60.

The final contestant is the Accesio USB-DA-12-8A, which has a 128K samples buffer.  It’s $525; DIN Rail mounting is an extra $19.

For my application, the Accesio looks the best fit; it more than meets all my requirements, I like the large buffer, andI like the DIN Rail mounting option.

Connectors can be very annoying.  Right now, I’m annoyed by Molex’s Micro-Fit 3.0mm connector family.

Here’s the scenario: some motors we use come with the feedback cable wired with a Micro-Fit receptacle.  We custom build a cable with a sub-D connector at one end and a Micro-Fit plug at the other (which connects to the feedback cable).  I was investigating building a simple PCB to test the cable, and therefore needed a PCB mount receptacle.

That part doesn’t exist.  All the standard Micro-Fit PCB headers are plugs.  You can get Micro-Fit PCB receptacle headers if you use the Micro-Fit BMI (Blind Mate) series, but according to Molex, BMI parts only mate to other BMI parts.

That’s another reason I like sub-D connectors: they’re available from multiple sources, in all kinds of variants.  And you can choose solder cup, crimp, or (for some sizes) IDC ribbon cable; Micro-Fit is only crimp.

It’s interesting to compare and contrast new micro PLCs from Siemens (S7-1200) and Panasonic (FP0-R).  Both are compelling upgrades from the previous series (Siemens S7-200, Panasonic FP0), but while Siemens adds Ethernet connectivity, Panasonic adds a USB port.

The FP0-R series looks like a direct replacement for the FP0, but with more: more memory, faster instructions, faster counters, and faster pulse outputs.  The biggest upgrade is a USB port, which is very nice: no custom programming cable required!  Or save some money: I like to use PLCs with two comm ports, one for communicating with the PC, and one for debug.  With the added USB port, I can use a PLC with one serial port, saving about $30, and use the USB port for debug.

I hope Panasonic has improved the USB port speed; I’ve heard that the FPX series uses an internal serial/USB bridge, so the USB port is limited to a wimpy 115,200 bps.

The FP0-R still isn’t as capable as the FPG (FP Sigma) series, but since it’s the same price as the FP0, I’m already looking at changing over from the FP0 to the FP0-R.

The Siemens S7-1200 models appear similar to the previous S7-200 models, but with more: more memory, more analog (even the base models have analog inputs), faster instructions, faster counters, more expansion (using signal boards) and faster pulse outputs.

What’s wonderful?  Siemens added an Ethernet port with Profinet and standard TCP/IP capabilities.  Networked devices are so much more convenient and useful than PC-connected USB devices.  For example, Profinet should make it simple and inexpensive to create a peer to peer PLC network, in addition to high speed communications to HMIs.  You have to add expensive networking modules to create a Panasonic PLC network.

The S7-1200 CPUs include other goodies, such as room for extra boards on the base CPU (for extra comm ports or wimpy (2DI/2DO or 1AO) I/O boards), 1M flash memory for extra (non-program) storage, and a proprietary memory slot.

Unfortunately, Siemen’s STEP7 Basic software currently only includes Relay Ladder Logic and Function Block programming; Panasonic’s FPWinPro supports all five IEC61131 languages, including my favorite: Structured Text.

Like the previous S7-200 series, base models have limited expansion: no signal modules for the 1211, 2 for the 1212, and 7 for the 1214.

The Panasonic FP0-R PLCs are much smaller; the transistor output models use high density box header connectors , while Siemens provides screw terminals.  I much prefer the box headers, since I can easily make a cable to a custom PCB breakout board.  It’s hard to wire directly with screw terminals without additional terminal blocks (for extra power and ground, etc).

The Panasonic FPX series are more like the S7-1200, since they also use screw terminals and provide room for plug in modules.

Excluding communications (USB vs Ethernet), the S7-1200, FP0-R, and FP-X are all similar in capabilities and price (IIRC, S7-1214 DC/DC/DC, FP0R-C32CT, and FPX-C30TD are all about $280, while the FP0R-C32T is about $245).

Which will I use?  I’d love to try out the S7-1200, but for my current projects the FP0-R and FPG are a better fit, since they support Structured Text and use box header connectors.

The S7-1200 is pretty close to a no-brainer if you need Ethernet:  Panasonic’s Ethernet module (FPWeb2; ~$430) alone costs more than a S7-1214 CPU; Automation Direct’s Ethernet modules start at $175, and you still have to add the PLC CPU.

I plan to write about this in more detail: I think micro PLCs are a great alternative to PC I/O options such as PCI boards from Advantech or USB modules from Measurement Computing.  The PLC’s cost the same or less for 24V I/Os, and have the advantage of being programmable — it’s nice to have the PLC handle some I/O, while the PC handles the rest via serial, USB, or Ethernet communications to the PLC.

Final notes:

• Panasonic has gone backwards by not listing prices and requiring registration to download PDFs.
• If you’re interested in the S7-1200, talk to your local distributor to see if they have a package deal.  For example, in Silicon Valley, E&M periodically offers 1 day introductions with a nice deal on the S7-1211.

Recently, I had to select a servo motor.  We had already chosen to use a NEMA 23 mount with a 0.25″ shaft, and had other requirements such as maximum length, torque, speed, and voltage.

I was amazed at the different shaft diameters and lengths supposedly standard NEMA 23 motors have — I recall 0.25″, 8mm, and 0.375″ diameters, and can’t remember all the lengths.  It was even worse when I had to select a NEMA 17 motor a while ago– at least one manufacturer’s supposedly NEMA 17 mount wasn’t the same as everyone else.

Then of course there are all the non-standard mount motors – but I only use those as a last resort, since I’ve already had motors go out of production twice; at least with a standard mount, there’s a possibility of finding a suitable replacement.

Maybe there are other standards: maybe the various European and Japanese 40mm, 60mm, and larger motors really do follow a standard, but I don’t have time to analyze them all.

Connectors are even worse.  I can understand why manufacturers use different kinds of connectors, and I know there are no connector standards.  A motor intended for harsh environments needs a tough but expensive connector, while a light duty motor is much better off with a cheap connector (such as Molex or Tyco/AMP crimp connectors) or flying leads.  But, just like industrial Ethernet, it’s easy to think: do we really need all those choices?  Couldn’t we have just three or four?

I personally like sub-D connectors a lot, since you can get high power (Combo-D), can use crimp pins or solder cups, and choose from a wide range of backshells (including straight, right angle, and 45 degree in metal, metalized plastic, and plastic) and manufacturers.

Of course, pin-outs are even more varied.  For example, on the controller side, Galil (DMC-21×3/AMP205x0 combo), AMC (DX30, DX60, etc), and Copley (ADP series) all use HD15 connectors for feedback, but each one uses a different pin-out.

Oh, well, at least commutation and incremental encoder signals are pretty standard: three signals, either RS-422 differential or single ended (TTL or open collector) –  except if you use some Japanese motors (e.g. Panasonic).  And I’d better leave absolute encoders for another time…I’m not even sure how many “standards” there are for them.

In an article in Control Engineering, Steve Feketa of Rockwell claims that magnetic linear encoders are available for $200 for a 1 meter encoder, while optical linear encoders can cost up to $2000 for a 1 meter encoder.

If you’re paying $2000 for an optical linear encoder, you’re either getting a very high resolution encoder, a very rugged encoder, or some golf at the country club for the encoder manufacturer’s sales team.  I can buy a nice optical linear encoder with a 1 meter scale for substantially less than $1000.

But I can’t find any information on inexpensive magnetic (or magnetorestrictive) linear encoders.  I do know of inexpensive optical linear encoders from US Digital and Avago that are under $200 for 34″, but they are hard to mount and the resolution is only 12.7µm.  I found that Heidenhain, Renishaw, Netzer, and Temposonics (magnetorestrictive) all make magnetic linear encoders.   I couldn’t find any pricing, and I’m not going to spend a lot of time trying to get quotations when I’m not ready to buy one.  I suspect that Netzer is the only one that might be close to $200 for a 1 meter length.  OK, New Scale Technology’s Tracker is probably under $200, but its length is only 8mm.

Why am I interested in low cost linear encoders?  Because the current cost of linear restricts their use to when I really need them (I’ve used linear encoders twice in > 10 years of machine building).  Even a low resolution linear encoder is helpful to minimize problems from backlash, and to provide feedback for linear motors.

For the hobbyist, eBay is one solution.  I recently bought two MicroE M2000 linear encoder read heads + electronics on eBay for a very reasonable price.  True, I don’t have the scales, but I’m not sure where I’ll use them, so that’s OK.

I was having weird problems trying to run CoCreate PE on my Thinkpad: sometimes CoCreate would complain that the display resolution had changed, the model would disappear all the time (just from moving the mouse around), and such.

My Thinkpad has an Intel GMA X3100 integrated graphics chip (also known as the Mobile Intel 965 Express Chipset).  It’s not the greatest mobile chipset, but I was more interested in a small laptop with long battery life, and the laptops with mobile Quadros (e.g. Lenovo W700) are large, heavy, and have short (OK, normal) battery life.

Anyway, I found a tip via the CoCreate Users forum: turn off hardware graphics acceleration by setting the SDPIXELFORMAT environment variable to SOFTWARE; detailed instructions are here.  So far after making this change, CoCreate has been stable, and speed is still fine.

Inspired by this post at Evolving Excellence, I decided to try a stand up desk at home.  I can’t afford the fancy $1,000+ motorized desks, so instead I bought an Ikea Fredrik desk and a Summera keyboard shelf at a total cost of $160.

So far I like it, although I’m not sure I would want to stand all day at work.  Ikea specifies a maximum desk height of 38.625″, but I have the desk at the next notch up (about 41″), and it still works.   I do wish the desk was more adjustable — since it isn’t very adjustable, an adjustable height monitor would be a plus.  But so far the current heights seem OK for me (but not so great for my wife, who is significantly shorter).

Also, the desk does wiggle a little bit.   My guess is that some of that is from the carpet, and some of it from the construction (it’s not the world’s most solid desk).  I’ll have to experiment with wedging the feet and such to see if I can make it a little more solid.

Update 2/17/09 — an additional advantage for those of us with small children: little kids find it harder to reach the keyboard and mouse on the stand up desk, which makes using the computer at home much more enjoyable.

Ikea Fredrik Desk used as a stand-up desk

Stepnet with PacSci Stepper Motor

I’ve decided to document all the motor/drive connections that I make using my CANOpen drives.  I hope that others will find this information useful.  The first two are up on my trac site:

• Emoteq (Hathaway) BH02300E06HE BH series NEMA23 brushless DC servo motor to Copley ACP servo drive.
• Pacific Scientific N31HRHJ-LNK-NS-00 NEMA34 stepper motor to Copley Stepnet drive.

It was a lot easier to connect the stepper motor, but the servo motor is more fun.  It maxes out at 7,500 RPM using my Logosol power supply.

Copley RJ11 to DB9F serial cables

I have a new page here on my trac site describing how to make a RJ11 to DB9F serial cable for Copley Accelnet and Stepnet CANOpen drives.