Punch line

Feb. 1, 2000
PC-based control simplified for metal fabrication

PC-based control simplified for metal fabrication.

ORANGE, TEX. – Need an easy way to bring PC control to CNCs? Recent field installations of the PC800 from PC Controls on turrent punch presses have yielded equipment productivity improvements up to 150%. Those installations have also benefited from lower direct labor costs and faster product throughput time. The PC-based control package is a retrofit for existing CNC turret punch presses and CNC press brakes.

The heart of the PC800 is the ACR2000 motion control card from Acroloop Motion Control Systems, Chaska, Minnesota. The card receives data from the user interface software and provides the real time communication links with the machine tool. PC Controls and Acroloop worked in partnership on the engineering and field testing of the product.

Alphabet soup

In case you didn't catch the full meaning the first time around, here are some definitions of words and phrases found in technology. You will undoubtedly find some of them unusual.

ATTRITION The wearing away of surface material from frictional contact; abrasion.

BAUD A data transmission unit corresponding to the signal speed or modulation rate, taken as the number of signal elements or events per second. Named after the French engineer Jean Maurice Emile Baudot.

CHORDAL ACTION As the links of a chain rotate around a sprocket, the rollers want to move through the centerline of the links (the chords), rather than moving through the arc of the sprocket pitch circle they are forced to follow. This sends ripples down the chain, causing transverse movement as well as output velocity fluctuation. This phenomenon is sometimes also called chordal effect.

DESMODROMIC CAM A formclosed cam in a car or motorcycle engine. Form-closed cams rely on geometry to keep the follower in contact with the cam (a follower riding in a track or groove is an example), whereas a forceclosed cam would rely on an external force element like a spring.

ENCODER A mechanical or electromechanical transducer that converts shaft rotation into output pulses that are used to determine shaft revolutions or shaft angle.

FRETTING When tightly mated surfaces experience minute relative motion, various adverse affects like discoloration, pitting, gross surface wear, and eventual fatigue cracking can occur. Fretting, or frettage corrosion, probably begins with a mere removal of surface film and escalates as surfaces "grind away" at each other and produce abrasive dust.

GALLING A severe case of surface wear caused by movement between microscopically rough surfaces that have adhered to each other. Weldable metals are susceptible to adhesive wear such as this.

HUNTING TOOTH In gears, a non-integer gear-to-pinion tooth ratio makes each pinion tooth mesh with a different gear tooth from one revolution to the next. By this design, pits and other flaws are prevented from impacting the same teeth cycle after cycle, which reduces wear.

INVERTER An electronic device that converts fixed frequency and fixed voltage to variable frequency and variable voltage. Often used to electrically vary the speed of ac motors.

JOURNAL The part of a shaft or axle that rides inside a bearing.

KINEMATICS A subdivision of mechanical physics concerned with the motion of objects and systems without regard to force.

LINEAR CIRCUIT Any circuit described by a set of linear constant-coefficient differential equations. Such circuits are relatively easy to analyze because they can be simplified using superposition and similar techniques.

MITER GEARS A set of equallytoothed bevel gears meshing at right angles.

NEEDLE BEARING A type of roller bearing having rollers of superlative slenderness. Among its properties are a high radial load capacity combined with a low radial space requirement. Sometimes the rollers are inserted side-byside, with no cage to separate them.

OVERHUNG LOAD A load acting on a shaft at a point outside of the support bearings, resulting in a cantilever beam arrangement.

PRECESSION Motion of the rotational axis of a spinning object. An example of precession is a simple gyroscope consisting of a wheel with an axle connecting to (and free to rotate around) a perpendicular shaft. As the wheel spins around its axis, the axis of the wheel rotates around the shaft.

QUALITY FACTOR (Q) In any resonant circuit, the sharpness of the response curve, as indicated by the Q factor, is proportional to the maximum amount of energy that can be stored divided by the total energy lost per response period.

RESOLVER A rotary electromechanical transformer that senses position in a servo-controlled system. It measures the phase angle difference between an ac excitation input and rotor coil output.

SERVOMECHANISM A feedbackbased motion system specifically designed to provide control over position and its time derivatives.

TOUGHNESS The area under the stress-strain curve of a material, indicating the amount of energy it absorbs before fracture. Toughness requires a fair amount of ductility, allowing the material to give as it withstands punishment, whereas extremely high-strength materials are often brittle and will merely snap after a point.

UNDERCUTTING When gears are shaped using generating cutters (rather than form cutters), the part of the tooth below the base circle that would cause meshing interference is cut away. Undercutting decreases interference but weakens the tooth. In cams, undercutting occurs when the radius of the cutting tool or follower is too large to trace the designated pitch curve; a cusp will be described as the follower or cutter attempts to trace tight convex curves on the cam profile.

VECTOR CONTROL A control technique for ac induction motors based on the magnitude and orientation of the ac excitation signal. By manipulating these variables, the controller establishes control over motor flux and torque.

WOW A slow pulsation in an acoustic playback due to uneven speed in the sound recording or reproduction instruments.

X ENGINE An engine with the cylinders arranged around the crankshaft in an X shape.

YAW Movement around a vertical axis. In an aircraft, for example, yaw can be initiated by the rudders, whereas roll is a function of the ailerons.

Z-DOMAIN A mathematical representation that simplifies the analysis of frequency-based signal content present in (digital) time-based sampled data. Because of it, engineers can apply such analytical tools as transfer functions, phase and gain diagrams, and Bode plots to digital (sampled) systems.

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