Machinedesign 1466 Synchronous Carrier 0 0

Ensure compatibility with CAD software

April 1, 2000
When it comes to designing machinery and controlelements for automationsystgems, machine builders rely on CAD to optimize designs and achieve compatibility with requirements

Computer-aided-design (CAD) has become an essential tool for machinery builders, even small ones, for designing various machine elements including PT drive components. Many of their customers are driving the use of CAD — demanding not only that suppliers furnish CAD drawings, but, that these drawings are compatible with the customer’s CAD system. Usually, the supplier that doesn’t comply becomes a nonsupplier!

Machines for car makers

The automated equipment in large manufacturing and assembly plants often originates at small, specialized design firms. Take R.P. Gatta Inc., machinery supplier for the automobile manufacturing giants. Located in Twinsburg, Ohio, this company designs and assembles equipment primarily for automotive assembly lines.

Three designers crank out the machine drawings on IBM-compatible personal computers (PCs) with 286, 386, or 486 microprocessors. The company bought three PCs, each one faster and with more memory than the last. The newest model sports a 120-MB hard drive and a 486 microprocessor that operates at 50 MHz.

Limitations of the older 286 machine, which is only 3 years old, are already evident — it slows down as a drawing grows because of the file space required. To speed things up, the designer divides a large drawing into several smaller drawings that take up less space. The newer PCs are more productive because of higher speeds and larger memory.

Mouse-operated tablets are used to speed the selection of macros — miniprograms that perform special functions — rather than going through a series of menus.

The company uses CADKEY design software from Cadkey Inc., Windsor, Conn. This program offers 3D design, drafting, and solid modeling capabilities.

Though 80% of their machines are custom designed, says Raymond P. Gatta, owner, some require only small modifications from a previous design. Thus, a big advantage of CAD is the ease in making design changes. Also, it is easier to perform multiple iterations, thereby achieving a better final design.

A valuable asset for large, complex drawings is the ability to enlarge part of a CAD drawing on screen to view details. Another useful feature is the automatic insertion of dimensions when the user selects the dimension lines.

Though it is difficult to quantify the benefits of CAD, Mr. Gatta estimates that it increases design productivity about 10% compared to traditional drafting methods. For detail drawing, time savings are likely to be greater, perhaps 25 to 30%. The biggest savings come with pneumatic system drawings because many standard components, such as valves, can be automatically generated on a drawing after being imported from a manufacturer’s catalog disk.

Electrical systems also have many standard components and symbols that can be generated from disk libraries. Further, machine subassemblies, such as a motor-gearbox combination, can be drawn once and saved, then duplicated in multiple locations.

Thorns among roses. CAD isn’t without drawbacks, though. One is the need to translate drawing files into a format compatible with the customer’s CAD system. This requires, for example, that a designer translate a CADKEY file, using a generic translator program such as DXF or IGES, to an AutoCAD file before sending it on disk to the customer. This translating step, which typically takes several minutes per drawing, becomes a tedious process when large numbers of drawings are involved.

Also, when software is upgraded, it takes up to a day to incorporate the upgrade and get back in operation.

CAD training begins with a two-day introductory session conducted by a local hardware and software supplier. But the key, says Ray Gatta, is to learn by using the system. The designers recognize that CAD helps the company remain competitive, thereby building job security. Therefore, they have been very receptive to learning the system. Generally, it takes the designers only about 1 mo to become reasonably proficient in CAD.

Stuck on cars

Much of the equipment designed by Gatta is used on automotive assembly lines. For example, three different machines are used in applying side molding strips to cars. These machines latch on to the production line so they move at the same speed. The first machine cleans the car body to provide a good adhesive surface. The second applies the side moldings to within 60.5 mm, using a pneumatic drive. A third machine rolls down the strip to ensure that it firmly adheres to the car body. Then, the machines are repositioned for the next car by a rack-and-pinion assembly driven by an air-motor.

Another machine, called a synchronous carrier, holds parts and tools needed by the production-line operator. Sometimes, it carries the operator as well. The carrier keeps pace with the production line so the parts and tools are readily available when the operator needs them. At the end of a cycle, a chain drive returns the carrier to its original position. Some carriers are electric-motor driven and PLC-controlled. Others use air motors and air logic controls.

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Printed circuit boards

At least a half-dozen different software packages are used to design printed circuit boards for control-system applications at J. Nelson Graphics Inc., Beachwood, Ohio. Why so many programs, you ask? There are two basic reasons:
• File format. Customers send circuitboard requirements in either IBM or Macintosh files that must be converted to a format capable of creating film or manufacturing files. Having two formats doubles the number of software conversion packages required.

The main software programs used for layout are AutoCAD, from Autodesk Inc., Sausalito, Calif., and Douglas CAD/CAM System, from Douglas Electronics Inc., San Leandro, Calif.
• Program function. Generally, one CAD program is used to prepare a detailed circuit layout. Then, operators convert this layout to a film image that is used in manufacturing the circuit boards.

Another program establishes the location and size of holes to be drilled in the circuit board. These holes, numbering 100s or 1,000s per board, permit inserting, anchoring, and connecting circuit components, mostly wire leads. The hole data is converted to drilling instructions on punched paper tape or floppy disk, which, in turn, controls the machine that drills the holes.

Other software programs either convert files stored on magnetic tape to floppy disk, or convert files to a format that allows the layout to be reproduced on a plotter.

The software runs on either an IBM PC or Macintosh computer. IBM-types include an IBM XT, plus several PCs with 286, 386, or 486 microprocessors. The old machine is used to drive pen plotters and send or receive data by modem. The 286 through 486 machines handle drawing files that range in size from 10,000 to 10 million bytes. Macintosh units include two Mac Pluses.

Easy way. According to John Nelson, owner of the company, laying out circuits with CAD is easier and less expensive than on a drawing board. In fact, he says CAD is the only way to design circuit boards in volume. Estimated time savings are 10 to 30%.

Though difficult to quantify, CAD benefits also include increased productivity and expanded capabilities. For example, designers previously created ink drawings from which tapes, then circuits, were produced. Some circuits now require traces only 0.005 to 0.015-in. wide; these thin traces are difficult or impossible to draw by hand. With CAD, the lines are drawn thicker, then converted to the correct size by a line-thickness code.

Another feature, called step and repeat, makes it easy to draw the same line repeatedly and at precisely the same distance between lines. Thus, a 16-pin integrated circuit, consisting of two rows of eight pins each, can be configured in seconds by drawing one line, then stepping over the necessary distance and repeating the line. Other benefits include automatic dimensioning and simplified drawing changes.

One problem in working with a computer screen is that large drawings, such as those of a large GE lamp-making machine, are difficult to examine — they must be scanned a portion at a time.

CAD has gotten steadily better in recent years. However, the growing number of bells and whistles in these programs cause training needs to go up as well. Also, frequent upgrades, typically every 6 mo, make it difficult to keep up. Some users would prefer limiting upgrades to once every two years.

The three CAD operators — two engineers and one technician — took about 6 mo to become proficient with CAD. Additional training needs are generally met by holding classes inhouse on Saturdays.

The company performs about 90% of their design and drafting on CAD. Hand layouts on the drawing board are still used for jobs involving repair of old equipment. Here, the designer typically puts film on top of an old beat-up drawing submitted by the customer and makes the changes manually.

Fast turnaround

Based on customer requirements, the company makes and sends negative film images and drill tapes to nearby circuitboard manufacturers. Typical turnaround time for the negatives is 24 hr. One image is required for each layer of the circuit board — ranging up to 18 layers. Sizes for these boards generally range from 1/2 x 1 in. to 20 x 26 in.

End uses of the circuit boards vary, with about 80% industrial, 15% commercial, and 5% other. Some examples are electric motor controls, Magnetic Resonance Scanner (X-ray) tables, testing and monitoring equipment, and radiation monitors. Others include electric bingo displays and shipboard monitors for humidity and temperature.

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Other machinery

A Cincinnati-based engineering firm, Belcan Engineering Services, provides a variety of engineering services related to processes, products, and equipment for industrial applications. For example, its Specialty Equipment Engineering Div., Solon, Ohio, designs assembly and process machines for electronic consumer products, plus pharmaceutical, medical diagnostic, and automotive applications.

This division has over 50 PC-based CAD stations, mostly IBM-compatible PCs with 386 or 486 microprocessors. Peripheral equipment includes both a mouse and a digitizing tablet at each station. The company opted for large (17 and 19-in.) color monitors for those workstations that are in constant use. The reason is twofold: First, the large screens have better resolution, which is easier on the eyes and avoids fatigue. Second, color makes it easy to distinguish different sections of a complex machine or system.

A Novell server links the PCs, enabling them to share drawings, libraries of commonly used parts, and output devices (plotters and printers). The PC link also enables access to more software at the Cincinnati headquarters.

Software includes design, drafting, and analysis packages. Operators perform most of the mechanical design with AutoCAD and most electrical design with PRO-CADD, a general-purpose program from Infinite Graphics Inc., Minneapolis. Other programs perform modeling and analysis. ANSYS (Swanson Analysis Systems Inc., Houston, Pa.), for example, is used for FEM analysis.

New capabilities. According to Ben Spidalieri, general manager, CAD enables them to do things that are difficult to do otherwise. For example, older drawings can easily be modified to create new designs. And, drawings of manufacturer’s parts can be inserted from parts libraries. Moreover, designers can explore more options by performing “what if” simulations — a process that leads to better designs.

CAD operators include engineers and design draftsmen with technical backgrounds or associate degrees. Initially, we had to push those people without experience into learning CAD, says Ben Spidalieri. But now, they recognize the advantages and are anxious to learn the new method. Training is conducted either by a local training firm or within the company.

Software upgrades and macros that are written by Belcan require periodic training and hardware upgrades. These macros are mini-programs that define commonly used components (a special linkage, for example). The company has customized the digitizing tablet menus so that commonly used mechanical and electrical symbols can easily be selected and generated as many times as needed on the drawing.

The company performs 100% of its electrical design on CAD. Mechanical design is at a lower level — about 65% — but the percentage is growing every year. Some mechanical work is performed on drafting machines because it is easier to work with an existing drawing rather than convert to a CAD format.

Customer is always right

AutoCAD, a widely-used design and drafting program that offers 3D wireframe and solid-modeling capabilities, performs the lion’s share of the work, mainly because customers require Auto- CAD drawings that can be imported into their own systems. Other Belcan divisions use different CAD systems, such as Intergraph, Calma, and Computervision, as well as AutoCAD, to meet customer requirements.

A design project may include a single machine or a system containing several machines. Most jobs require designing special components such as cams and shafts, plus sizing and specifying standard components such as motors. n

For more information on software programs

Douglas CAD/CAM

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