Posts Tagged ‘circuit boards’

Systems Engineering In Medical Device Design – Production, Part 3

Sunday, March 10th, 2013
     When I was a kid I had a toy robot that captured my attention like no other toy.  I thought it was so cool to have something animated that looked both humanoid and machine-like at the same time.  It couldn’t do much, just walk in a stiff, jerky way and move its arms up and down, but that was enough to keep me fascinated.

     Today’s generation of robots do not often take on the humanoid form, but they’re capable of so much more.  Robots on assembly lines perform a variety of tasks like welding and placing electronic components on circuit boards, and they do it much more quickly and accurately than any human could, so they’re often employed in manufacturing.

     We’ve been discussing the Production stage of the systems engineering approach to medical device design.  We learned that within the manufacturing process there are often opportunities for cost reduction, and today we’ll see how robots can be used to reach those goals.

     Last week we presented a sample scenario involving the manufacture of a percussion therapy device.  In their quest to reduce manufacturing costs, engineers identified bottlenecks along the assembly line which led to idle worker time and the inability to keep up with orders.

     In addition to these production woes, it was discovered that the tedious, repetitive manual labor that occurred at each bottleneck created opportunities for assembly mistakes.  As many as 30 devices per day were being rejected by quality control inspectors due to issues such as faulty wiring and improper parts usage.  This led to expensive rework to correct mistakes.

     After further evaluation, design engineers determine that bottlenecks can be eliminated by installing automated assembly equipment in the three distinct assembly stages represented on the line, those involving wiring harnesses, printed circuit boards, and the motor drive mechanism.

     The potential for human error is high during many facets of manufacturing, and this can be minimized or eliminated through the use of robots, that is to say, mechanized equipment capable of automatically performing a complex series of specific tasks.  These robots never tire of performing tedious, repetitive work, and their efficiency is unparalleled.  Their introduction at key junctures on the assembly line has benefits across the manufacturing process, enabling workers to keep continuously busy and reducing the incidence of human error.

     The introduction of robotics is known as industrial automation.  Robots efficiently increase manufacturing speed, and along with it profits, so their introduction more than compensates for the investment costs associated with purchasing them.

     Next time we’ll continue our look at the Production stage to discover another way that systems engineering can simplifying the assembly process, by eliminating some functions altogether.


Medical Device Manufacturing

Systems Engineering In Medical Device Design – Preproduction, Part I

Monday, February 4th, 2013
     If you’ve been following along with our blog discussion on the systems engineering approach to medical device design, you should by now be convinced that instructions are important.  In fact, the meticulous instructions produced during the manufacturing, operating, and maintenance  phases of the Development stage are also crucial to later stages, that of Production  and Utilization.  Let’s finish up our discussion on the Development stage by taking a look at its final aspect, Preproduction.

     The Preproduction aspect is instrumental to nipping potential problems in the bud before the medical devices go into actual production.  In the initial Preproduction stages, systems engineers coordinate with the manufacturing and purchasing departments within the company as well as outside suppliers.  The goal is to acquire all parts and equipment necessary to build a limited number of medical devices on the assembly line.  Subjects such as preference in molded plastic components, motors, gears, pumps, springs, electronic components, circuit boards, wire, and tubing are discussed and agreed upon.  Vendors are assessed with regard to their ability to produce parts when they are needed and that meet design specifications, satisfy quality requirements, and have costs that fall within budgetary constraints.

     The assembly of Preproduction devices provides an opportunity for systems engineers to validate manufacturing and quality control instructions and assess the device design with regard to manufacturability, meaning, the extent to which devices can be manufactured with relative ease, at minimal cost, while maintaining maximum reliability.  Devices manufactured during this aspect of the Development stage serve as a test.  Are instructions clearly written?  Do the device parts fit together as they should?  Are parts strong enough to withstand the assembly process?  Can the devices be assembled as quickly and easily as expected?

     If the answer is “no” to any of these questions, then the device design and instructions must be returned to the design engineers and technical writers.  Heads come together to rehash things and work out the bugs.

     Next time we’ll continue with the Preproduction aspect of the Development stage to see how laboratory and field testing enables systems engineers to shake out any more bugs from the medical device design, operating instructions, and maintenance instructions.


Medical Device Design

Transistors – Voltage Regulation Part XIV

Monday, October 22nd, 2012

     As we’ve come to know through this series of blogs, all electronic components pose some degree of internal resistance to the electric current flowing through them.  This resistance results in electrical energy being converted into heat energy, heat which poses potential problems to sensitive components like electronic circuit boards.  If things get hot enough, components fail and fires may ignite. 

     To address these issues engineers design circuits with resistors whose job it is to limit the current flowing to electrical components.  In this article we’ll see how a limiting resistor protects a Zener diode from this fate, allowing it to continue doing its job of regulating voltage.    

     In our last blog we applied Ohm’s Law to our regulated power supply circuit, which makes use of a Zener diode.  See Figure 1.power supply

Figure 1


     Ohm’s Law gave us the following equation to determine the amount of current, IPS, flowing from the unregulated power supply portion, through the current limiting resistor RLimiting, and making its way into the rest of the circuit:

IPS = (VUnregulatedVZener) ÷ RLimiting

     We learned last week that for the circuit to work, the voltage of the unregulated power supply portion of the circuit, VUnregulated, must be greater than the Zener voltage, VZener.

     Looking at the equation above, we see that the voltage difference is divided by RLimiting, the value of the limiting resistor in the circuit.  This limiting resistor is there to constrain the current flowing to the Zener diode, allowing the diode to keep things under control within the circuit. 

     Basic mathematical principles hold that if a smaller number is divided by a bigger number, the resulting answer is an even smaller number.  Applying this principle to the equation above, if RLimiting is a big number, then IPS must be a smaller number.  On the other hand the smaller RLimiting gets, the bigger IPS becomes. 

     So what does it take for our circuit to fail?  Remove the limiting resistor as shown in Figure 2 and the value for RLimiting disappears.  In other words, RLimiting becomes zero.

zener diode with no limiting resistor

Figure 2


     In this case our Ohm’s Law equation becomes:

IPS = (VUnregulatedVZener) ÷ 0 =

     The resulting answer is said to go to infinity, or , as it is represented mathematically.  In other words, without a limiting resistor being employed within our circuit, IPS will become so large it will overwhelm the diode’s current handling capacity and lead to circuit failure. 

     Next time we’ll go over some advantages and disadvantages of this Zener diode voltage regulating circuit, and why the disadvantages outweigh the advantages for many applications.