July 24, 2015
Okay, let's make this one simple...
Click HERE to answer a few brief questions about how your lab approaches instrument support.
All info is confidential We will publish results in an upcoming post.
Shortest darn blog all year...
July 23, 2013
In the last two installments, we talked about simple DC motors and stepper motors. To recap, a DC motor is basically the simplest (think 'Lloyd' from the movie 'Dumb and Dumber') motor you can find. Simply apply voltage with sufficient current and it spins. You can reverse the spin direction by reversing voltage polarity, and you can control the speed by applying varying voltage levels or by sending short pulses of voltage. Stepper motors are a...'step up' (I hate puns) insofar as intelligence goes (think 'Harry' from 'Dumb and Dumber'). By which I mean, you can send them specific (countable) pulses and the motor will rotate in very predictable increments (steps). Steppers are natively 'open loop' but are oftem fitted with rotary encoders to provide position feedback. However...that position feedback is often an 'after the fact' reconcilliation on the number of steps commanded vs the number of pulses counted. It is not a 'monitor on the fly' feedback loop and that is by definition what a servo motor brings to the table.
In the most basic sense, a servo motor is a brushess DC motor fitted with a feedback sensor. The output of the feedback sensor is used to determine the final position of the motor. These devices can be very small (like hobby RC servos) or larger. In general, with increased size comes larger windings which enable more current and greater torque. Depending on the device the motor is attached to, you can expect to see a series of drive reduction gears or pulleys for even greater torque. Unlike hobby servos which have both gear reduction and circuitry embedded within their housings and use potentiometers for feedback, most industrial servo motors require a separate driver or control board that provides motor voltage and also monitors the encoder in real time. The image to the left represents a simple hobby servo which nicely illustrates the feeback loop concept. Both the input signal and the output from the sensor (potentiometer, in this case) are feed into a comparator circuit. Because the gearing is built in and known relative to the gear ratios, the comparator can essentially decide when the motor needs to be stopped in order to achieve the commanded motion (so many pulses should equal so much resistance).
The pulses sent to the motor are generally all the same voltage but number of pulses sent over time is what determines speed. This is called Pulse Wideth Modulation (PWM).
Troubleshooting a servo motor is not easy. If the motor and encoder are separate units, you can apply the rated voltage to motor (disconnect any pulley/belt or linkages first!!!). Encoders are a bit trickier and we will cover them in a future tutorial. You can try some basics like checking wiring connectors or blowing air the encoder to remove dust, dirt or grease. Beyond that...you will need to crack open the case and hook up a scope to see what the pulse train coming from the encoders look like. Most encoders are off the shelf devices and you can Google specs to compare with what you have. This will at least help you zone in on the encoder or the controller/board it is plugged into.
July 15, 2013
If it moves...it probably has a motor. There are a number of different types of motors within lab instruments and while repair or diagnosis of many of them are beyond the expertise even the most savvy field service technician, it is helpful to know a bit about them and what makes them tick (or spin).
The most common motors are simple AC or DC motors. As their names imply, each uses a different current scheme to achieve basic rotation but a simple brushed DC motor has five parts:
- Armature or rotor
- Axle (shaft)
- Field magnet
In many motors, the outer metal housing contains at least two field magnets (North and South).
The armature, also called the rotor as it rotates about the axel, is an electromagnet made by coiling thin wire around two or more poles of a metal core.
The commutator is a pair of plates attached to the axle. These plates provide the two connections for the coil of the electromagnet.
The commutator and the brushes enable for the "flipping" of the electric field" part of the motor.
Brushed DC Motors have two coils of wire around a rotor in the middle. Surrounding the coil are two magnets, both facing in the same direction. When the coils are facing the magnets, electricity flows into them. When electricity flows into a coil, it creates a magnetic field, and this magnetic field pushes the coils away from their magnets. As the rotor turns, the current shuts off. When the rotor has turned 180 degrees, each rotor faces the opposite magnet. The coils turn on again, this time with the electricity flowing in the opposite direction. This creates another pulse, pushing the rotor around again. The rotor has electric contacts on it, and there are small metal brushes that bump against the contacts. The brushes send in electricity, turning the motor on and off at the right times.
Operationally, all you need to do is apply the proper DC voltage at the nominally rated current and the motor will spin. For simple devices this can be done via an on/off switch.
A brushless DC motor has a permanent magnet on the inside of the rotor, such that its north and south poles are perpendicular to the axle. Coils surround the rotor. These coils function similar to a brushed motor in that hey give out timed pulses to push the magnet, spinning the rotor. Because there are no brushes however, the motor cannot control itself. Instead, it is attached to a speed controller ciruit, which gives pulses of electricity at a certain speed to control the motor. The faster the coils pulse, the faster the motor will spin. This is called Pulse Width Modulation or PWM (more on that in Part 3).
On a final note, other than brushes, there reall isn't much that can be easily fixed on a DC motor. For older devices that are no longer supported, you can find rebuild services that can repair toasted armature (more common on larger motors). The most tempting way to test a DC motor is of course to apply power...but please, if you do this make sure to disconnect the motor from any mechanical drive components (pulleys, bests, chains, linkages...etc) first. As always, if you choose to ignore this advice, please do not send nasty emails, legal notices or graphic images of your physical injuries...
Next Up: Part 2 - Stepper Motors
June 28, 2013
Did you ever work with a field service engineer who was just plain awesome...someone who always went above and beyond to ensure your success? If so, you have probably asked yourself ''what would I do without them? ' Sadly, that hypothetical question, all too often, becomes reality.
For any number of reasons (some good, some not so good) people are transient. As the old saying goes, no one is truly irreplaceable, so the best protection vendors can provide for their customers is to ensure that more common procedures are documented. For example, irrespective of who is doing the work, a preventative maintenance procedure should always be the same. Each step, every tool, replacement part, lubrication or adjustment should be captured in a document that can be used to cross train FSE's so that your instruments always receive consistent maintenance.
Whether you are working with a new FSE to support a new install, or existing instrument don't hesitate to ask to see the procedure they will be following. Most vendors won't share all the details, but many will let you have a glance and most will provide checklist that highlights the work to be done.
If a vendor cannot produce documents for common procedures (like a PM). before they commence their work you should be concerned. I'm not saying that you are about to be mis-treated, however how can you be certain that the requisite work will be accomplished if there is no guideline? You wouldn't conduct an assay without a documented procedure and you shouldn't allow anyone to work on your instruments without one either.
If they can't show you 'the book', then throw the book at them!
May 21, 2013
Most labs have used floor mount or bench top centrifuges for separation based assays for decades. Whether spinning samples to remove air bubbles, spinning down cellular debris or isolating supernatent, there are numerous manual access centrifuges on the market, but when it comes to automation, the choices are limited.
For a number of years, Agilent (formerly Velocity11) has offered the compact VSpin. VSpin has a two position rotor with buckets for std microplates. It can spin up to 300o rpm/ 1000g and has an automated door that allows direct access to plates using an offset robot gripper. Units can be stacked on top of each other for increased use of vertical workspace. The Optional Access2 loader can also grab the plate and present it externally to a liquid handler gripper or top loading plate mover like Twister2 or KiNEDx.
Hettich also provides a larger unit called the Rotanta 460 which can accommodate 4 plates at speeds up to 6200prm, but is a bit more of a challenge to integrate as the robot gripper fingers need to reach into the unit from the top. I have seen this done with Mitsubishi and Staubli robots and Tecan actually integrates this unit under an EVO liquid handler accessible via an open locator in the deck.
Sias’s Ixion is a compact unit, similar in size to the VSpin, however plate access (total of two) is through the top just like the Rotanta and can spin up to 2000rpm. This unit integrates nicely with Sias’ Xantus liquid handlers.
Finally, BioNex offers the HiG centrifuge which can also spin two plates. The bright orange color makes this unit hard to ignore…and a closer look shows that this unit may be the best of the bunch. With an automated lid that retracts from the top, the HiG does not need a plate loader like the VSpin as plates can be accessed by just about any robot gripper. At 5000g, BioNex claims this unit to be the fastest robot accessible centrifuge available.
Maintenance requirements for each of these devices is similar. All include high-speed motors so proper ventilation is a must. Bearings must be greased, sensors cleaned and pneumatics (door opening, plate loaders) checked for leaks. Additionally, rotors and buckets should be checked for cracks or other signs of wear. As noted in previous blogs, rotational speeds can be verified using a digital tachometer but you may need to remove covers to gain access to the rotor (kids, don’t try this at home…call a professional). As always, if you ignore that last piece of advice, don’t come crying to me when your friends make fun of you because you have a mircrotitre plate permanently embedded in your cheek…
May 14, 2013
“A picture is worth a thousand words…so even at a reduced frame rate of 15FPS, one minute of video has to be worth 900,00 words.” – Me
For better or worse, advances in cellular communications aremaking the once seemly impossible, trivial. Specifically, I am referring to video communication. Just about everyone has a ‘smartphone’ these days and it is hard to find a new phone that does not include a camera. The resolution of these cameras is incredible (the Apple iPhone 5 = 8 MegaPixels) and product stunningly clear videos and images.
Video applications such as Apple’s FaceTime and Skype make face to face remote communications simple, fast and cheap. For service organizations, this has providedfield based techs with an incredible tool for diagnosing instrument failures. There are even iPhone apps that now allow users to perform thermal imaging (how cool is that…no pun intended)! Let’s face it, the pressure these on-site techs feel when faced with a failed instrument can be enormous. End user anxiety and a ticking clock only add to the stress. The ability to ‘phone a friend’, point the phone at the instrument and have a real-time conversation about such failures brings an added dimension to peer review.
On the wired side, I have visited many research labs that have added low-cost USB or Ethernet cameras to their automation systems that allow them to monitor status remotely (many times from home, over a weekend or at night). When combined with remote network access tools like PC Anywhere or LogMeIn, it is possible to deal with simple application errors and continue assays or applications that would otherwise had to wait for human to come into the lab and simple press a key. Remote observation in this fashion requires network access and must always include IT departments to prevent unauthorized access.
Still, many labs will not allow non-employee cameras or video use within their labs. Thisis short-sighted (IMO), and unfortunate. I understand the competitive nature of pharmaceutical or biotech research and the commercial implications of potentially providing competitors with a glimpse of a labs inner workings, but let’s face it…it would take a pretty savvy bunch of people to gleam something worthwhile from a phone camera. Instrument failures that render an instrument ‘down’ are generally easier to diagnose and repair, however it the aberrant or irregular failures that could benefit immensely from remote observation. Unless an instrument or system is under a service contract it can be very expensive to pay for a service tech to sit and watch for a reported failure (they always happen when the tech leaves, right?).
Most labs require non-disclosure agreements or safety training prior to granting non-employees access their labs and the time is well past to include the use of remote diagnostic tools, particularly cellular video in such protocols. Perhaps seeing is believing?
May 10, 2013
Having said that…I was a bit disappointed by a recent “Ask The Expert” interview by Tanuja Koppal, PhD. It was called “Optimizing Lab Services: Evaluating the Single-Vendor Option.” You can read the full article by clicking here.
Although there are some good insights there were some major pieces of informationmissing. For starters, it does not mention who the subject of the interview is. I will give Dr. Koppal the benefit of the doubt and assume the interviewee is not fictitious, but I have a hard time understanding why he/she would need to anonymized. Is there an MVS Mafia out there that requires a witness protection program? Secondly, all the MVS providers whom the user evaluated are also anonymized. I guess I could understand that given that many of these larger providers may have legal teams that would give any crime syndicate a scare.
In the spirit of peer review, I think it would be extremely helpful to both MVS providers and potential customers to know who this customer is and how they made the selection they did.
Who knows, using this feedback, maybe next time they need a contract, someone would be able to make them an offer they couldn’t refuse…