Posts Tagged ‘industrial automation’

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

Industrial Control Basics – Electric Relay Ladder Diagram

Sunday, January 22nd, 2012
     My daughter will be studying for her driver’s license exam soon, and I can already hear the questions starting.  “What does that sign mean?  Why does this sign mean construction is ahead?”  Symbols are an important part of our everyday lives, and in order to pass her test she’s going to become familiar with dozens of them that line our highways.

     Just as a triangle on the highway is a symbol for “caution,” industrial control systems employ a variety of symbols in their diagrams.  The pictures are shorthand for words.  They simplify the message, just as hieroglyphics did for our early ancestors who had not yet mastered the ability to write.  Ladder diagrams and the abstract symbols used in them are unique to industrial control systems, and they result in faster, clearer interpretations of how the system operates.  

     Last week we analyzed an electric circuit to see what happens when we put a relay to use within a basic industrial control system, as found in Figure 1.

Figure 1

     Now let’s see how it looks in an even simpler form, the three-rung ladder diagram shown in Figure 2.


Figure 2

     In industrial control terminology the electric relays shown in ladder diagrams are often called “control relays,” denoted as CR.  Since a ladder diagram can typically include many different control relays, they are numbered to avoid confusion.  The relay shown in Figure 2 has been named “CR1.” 

     Our ladder diagram contains a number of symbols.  The symbol on the top rung which looks like two parallel vertical lines with a diagonal line bridging the gap between them represents the N.C. contact.  This symbol’s vertical lines represent an air gap in the N.C. contact, the diagonal line is the relay armature which performs the function of bridging/closing the air gap.  This rung of the ladder diagram represents the contact when the relay is in its normal state.  

     In the middle ladder rung the N.O. contact symbol looks like two parallel vertical lines separated by a gap.  There is no diagonal line running through it since the relay armature doesn’t touch the N.O. contact when this particular relay is in its normal state.  The wire coil and steel core of this relay are represented by a circle on the bottom ladder rung.  The contact and coil symbols on all three rungs are labeled “CR1” to make it clear that they are part of the same control relay.

     Other symbols within Figure 2 represent the red and green bulbs we have become familiar with from our initial illustration.  They are depicted as circles, R for red and G for green, with symbolic light rays around them.  The pushbutton, PB1, is represented as we have discussed in previous articles on ladder diagrams.

     Just as road sign symbols are faster than sentences for drivers speeding down a highway to interpret, ladder diagrams are faster than customary illustrations for busy workers to interpret. 

     Next time we’ll expand on our electric relay by introducing latching components into the control system that will allow for a greater degree of automation.