September 6, 2017
CRASH!!!! Your 8-channel liquid handling robot arm just raked across the deck and one of the z-axis rods looks bent. No problem, just call the manufacturer and have them come fix it, after all, it is still under warranty...right? Well, maybe...
Most instrument warranties cover parts and labor but, that usually comes with the expectation that the failure is due to normal wear and tear, not abuse or unintended usage. Using the liquid handler failure above as an example, the 8-channel arm likely got damaged because it failed to move to a safe Z-travel height before moving in X or Y. But, was that because the arm failed to execute that command or because the programmer failed to instruct the arm to do so? While a failure such as this might not occur in assays that have been running successfully for some period of time, they are more common when the user is still developing the assay or debugging it. This type of failure could also occur because an operator forgot to retract the arm after some assay interruption or error condition.
Many OEM's (Original Equipment Manufacturer) will work with you to get the instrument back online and some may even be tolerant of such failures to the point of covering the associated costs under their warranty..but, you will most likely find there is a limit to their understanding. If an instrument fails under normal usage, OEM's should and will cover repair costs but if an instrument fails again, or frequently due to operator error the OEM could and should charge for parts and labor and travel, even though the unit is under warranty. Although such a stance would be unpopular for end-users, it is really no different than what you might experience in other areas of your life. If you use your SUV to haul a boat that exceeds the vehicles gross towing rate you will probably damage your transmission or rear axle. Should you expect Ford or GM pay for that? The honest answer is, no.
Whether you bought the instrument new and are under the original warranty, or if you have purchased an extended warranty, make sure you understand just what kinds of failures are covered. Ask up front. Even if you purchase refurbished instruments, there is a limit to they nature of the failures that are covered (BTW - you should always insist on a minimum of a 6 month warranty on refurbished equipment). New or used, a warranty is a quality statement by the provider. Buying instruments "AS IS" or with a "Money Back Guarantee" should set off alarm bells that the low price option that looks so attractive today, could prove to be a costly investment in the future. Caveat Emptor...
What options should you consider when the warranty expires? That will be the subject of our next blog...
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.
January 31, 2013
Budget time…you know the drill. Salaries, supplies, new equipment and oh yeah, ongoing maintenance support. Has there ever been a more sexy and attention riveting topic than maintenance budgeting? Your options are pretty straight forward;
- Annual Service Contracts (typically 10-15% of purchase price, per year )
- Break/Fix Repair As You Go (cross your fingers, ready the checkbook)
- Basic Periodic Maintenance (pay for basic upkeep, then Repair As You Go)
If a particular instrument is critical to your labs mission you cannot afford downtime. And, while we are on the subject, exactly what types ofinstruments are mission critical? Of course, the answer to that question will be different for every lab and largely depends upon their focus area. For instance, if you have are in a cell biology group and have a high content imaging system such as a GE IN Cell, it might be wise to put that unit under a service contract with the manufacturer. This is advisable for any instrument that can be considered unique or expensive but could even be extended to relatively new technology such as microfluidic based analyzers. Caliper (now Perkin Elmer) provide a line of such analyzers for enzymatic assays as well as nucleic acids and protein analysis. The first and second generation instruments are still out there and they require a great deal of TLC and in depth operation and support knowledge. Newer versions of these refrigerator sized devices are much more compact and a lot less support intensive, eliminating complex laser alignments and environmental controls. Still, while the instruments themselves may be easier to service, the actual “microfluidic chips” that perform sampling and separation cost several thousand dollars each and users may run the risk of voiding the chip warranty if they don’t use the OEM to maintain the instrument. Stick with the OEM service contract.
Okay, so what instruments that are less specialized…do you really need to spend your precious budget dollars on annual service contracts? Let’s take a look at the staple of many labs, liquid handlers. There are literally thousands of such units from companies like Beckman Coulter, Tecan, Hamilton, Agilent and Perkin Elmer. These XYZ robots offer great pipetting repeatability and walkaway automation of mixing, filtration, incubation and other critical assay steps. A liquid handler that cost $100-150K ten years ago can still command a $10-15K+ price tag for an annual maintenance contract. That’s a lot, but is it really necessary? Liquid handlers, at least the good one’s from mainstream companies like those listed above have proven to beremarkably reliable. With even basic annual maintenance, these instruments can run trouble free for the foreseeable future. In fact, most OEM periodic or preventative maintenance (PM) procedures are just that, minimal approaches that clean, inspect and lubricate. One exception would be Tecan, whose EVO PM procedure calls for replacing all fluid path components making their PM (and subsequently their annual maintenance agreements) costs some of the most expensive. Is that necessary? Probably not, but one could argue that such a thorough approach is akin to performing a ‘field refurb.’ If your lab has GxP requirements, this would certainly be advisable, but otherwise you might think about doing this every other year. If you own a Beckman FX /NX, or PE Janus you might want to follow the Tecan lead, and get that ‘field refurb,’ especially if you have never had this level of service after several years of use.
Be wary of annual contracts for integrated robotic systems. A system with an industrial robot in a safety enclosure might tend to many additional instruments such as plate washers, readers, centrifuges, incubators and so on. If you apply the 10-15% of sales price logic to the purchase price of the system, you will find your coverage costs being inflated by things that could never fail like the extruded aluminum tables, the safety enclosure or even the design and build labor that was factored into the original system price tag. Better to look as the individual instruments in that system and determine their support costs piece by piece, not in the aggregate.
(In Part II of this post, we will look at the service requirements of thermal cyclers, plate readers and centrifuges).