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Articles from 1998 In September

Linear motion system

Hepco SL2 stainless-steel slide system provides linear motion in arduous environments to those in a clean room. Aluminum carriage plates are treated with a corrosion-resistant coating certified by the FDA for food use. The SL2 system is available in slide widths including 12, 25, 35, 44, 50, 60, and 76 mm. Technical brochure provides data and dimensions on the SL2.

Bishop-Wisecarver Corp., (P) Box 1109, Pittsburg, CA 94565, FAX (925) 439-5931.


The DIH40 Series brushless dc motors are 4 inches in diameter and feature neo magnets, integral Hall-effect sensors, and a magnetics configuration that lends itself to variable speed operation. The units are available in three standard frame lengths of 2.2, 2.8, and 3.3 inches, providing continuous stall and peak torque ratings of 55, 110, and 175 oz-inches, respectively. Operating speeds are to 12,000 rpm. Other torques and operating speeds are also available.

BEI Sensors & Systems Co., Kimco Magnetics Div., 804-A Rancheros Dr., San Marcos, CA 92069, FAX (760) 744-8815.


UFM Series ac-to-dc converters for off-line switching power supplies measure 1.45 X 2.28 X 0.5 inches. They convert common ac line voltage to 300V dc inputs for most industry-standard dc-to-dc converters, accept inputs of 90 to 265V ac, and deliver up to 1,500W of output power. Technical bulletin offers a mechanical outline and includes a product description, a list of key features, and a chart of characteristics.

Powercube, (E) 9340 Owensmouth Ave., Chatsworth, CA 91311.


Escorene(reg) HD7845 high-density polyethylene resin features a density of 0.958g/cm(super 3) and a melt index of 0.45g/10 min. The molecular structure of HD7845 has been tailored to allow processing on conventional LLDPE extrusion equipment (pocket extrusion). HD7845 is compatible with a wide range of polyethylenes. High density of HD7845 provides increased stiffness with enhanced properties for thicker films, enabling heavy wall bag converters to downgauge either blends or multi-layer structures.

Exxon Chemical Co., Box 3272, Houston, TX 77253.

Design News for Design and mechanical engineers

September 21, 1998 Design News

Features Your guide to mid-range CAD
Shopping for a new CAD package can be confusing. Here, gathered in one forum, software companies explain. Edited by Paul Teague and Laurie Ann Peach

Open Sesame!
Designed to provide tight security and easy access, this unique hardware from around the world works almost by magic.  By Karen Auguston Field

Recipe for quick home cooking
Engineers wrestled with self-cleaning devices, heat transfer issues, size and power limitations in an effort to bring the JetDirect oven to the home. By Laurie Ann Peach

The 1999 Nominees for Engineer of the Year

Spherical roller bearing solves longevity problem
Eccentric locking collar offers greater shaft holding power. By Charles J. Murray

Motor/brake assembly takes aircraft seat comfort to new heights
Spur-gear drive is faster, stronger, and less expensive than worm-gear-driven designs. By John Lewis.

Variable-speed drive controls cart's feed rate
Adjustable drive enables users to change rates without dismantling chains and sprockets. By Charles J. Murray

Engineering News
Engineers lead the hunt for killer asteroids
Spindle design boosts appetite for aluminum
Hatch cover protects valuable rail cargo
Graphics accelerator targets Windows NT
ASI announces support of Engineering Education Foundation
Software integrates information-gathering tool to create new concepts
Lenses lighten spacecraft cost
Elastomer adds 'jazz' to hearing protector
Composites keep boats ice-free
Graphics benchmarks debut
My favorite all-around sports car
Free kit explains designing with microcontrollers.

Designer's Corner
Touchy, feely; closed-trough conveyor; and more

Tech Bulletin
Late developments that shape engineering

Standards Update
Technical news from around the world

New Products

How to think about.  By Paul E. Teague

Hot Products
Senior Editor Julie Anne Schofield reviews noteworthy workstations.

Instant Product Information

Guest Commentary
Plastics pace product development

Featured Product
Sealing system protects environment

Letters to the Editor
Readers state their views

Robot is pharmacy's 'little helper'

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Check out the recent winners of our Answer of the Month contest. The answer appears in the first issue of each month. Your job is to provide the question. Winners receive $100 gift certificate.

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Special supplement on Automotive Plastics and Elastomers

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Super Invar 32-5 alloy was made into sleeves 5.945 inches nominal diameter by 5.109 inches deep for use in Japan's Subaru telescope. The sleeves, which support the giant mirror, rest on an equivalent number of tapered balls made of chrome-nickel-moly steel. The surface of each ball is galvanized to protect the thin nickel coating on the sleeve.

Carpenter Technology Corp., Box 14662, Reading, PA 14662.

Stepper motors

The PF Series of canned stack stepper motors are for medical, information, HVAC, and instrumentation and range in diameter from 25 to 55 mm, with step angles of 15, 7.5, and 3.75 degrees. The motors can be modified to fit specific applications with mechanical variations, winding changes, and connector options. Application engineering support and product documentation are available on all products.

Nippon Pulse Motor Co. Ltd., No. 16-13, 2-chome, Hongo, Bunkyo-ku, Tokyo 113, Japan, FAX +81 3 3813 2940.

Break Time 9-21-98

September 21, 1998 Design News


Robot is pharmacy's 'little helper'

Stacy Orr, Manager of Engineering Ron Leonard, Manager of S/N ScriptoPro LLC Mission, KS

The ScriptPro (SP) 200, a four-axis robot, is the first fully automated prescription dispensing machine for retail pharmacies. Running unattended from start to finish, this technological marvel receives fill requests into its queue from existing pharmacy computer systems via a serial or network interface. It processes each request automatically by selecting a vial of the proper size and filling it directly from its universal medication dispensing cells.

Getting to here from there was not without its challenges, however. Our major hurdle was to make the system "fit" in terms of affordability, size, and functionality. Reliability was also a major concern. We felt the product had to withstand a 1.5-million-cycle life test--the equivalent of roughly 10 years of continuous use in a high-volume retail pharmacy.

To meet this goal, ScriptPro went to the aircraft industry for leads on quality components, such as reliable brushless dc motors and highly flexible cabling. We selected Windows NT as the operating system, but prior to that decision our software engineers thoroughly tested it out.

We spent a fair amount of time in the research and evaluation of motion control boards, which are the critical link between hardware and software in a robotics system. The board would need to work within the NT multitasking environment and provide sufficient I/O to control all of the SP 200 functions. Ultimately, we selected an Acroloop MCB, working closely with the company's engineers to develop the interface.

The universal dispensing cell is a feat of engineering and design simplicity. Basically, it is an assembly of six inexpensive polycarbonate, acetal, and low-density polyethylene components. To test the cell prototypes, we needed access to a wide spectrum of pharmaceutical products, which we obtained through a special research license from the Kansas State Board of Pharmacy. Thousands of man-hours were spent perfecting the control surfaces, which cause pills of varying sizes and shapes to flow in a single file pattern past the optical counting sensor.

Our design incorporates cross-over conveyors to align all vials, regardless of size, in front of a triangulated mechanical ram and roller assembly. The ram, which is dampened by a linear decelerator, presses the vial into position, while an industrial quality thermal transfer printer applies the label. The computer uses sensors, timers, and buffer procedures to control the process, ensuring that the correct label is applied to each prescription vial. The unit runs on a standard 100V circuit and does not require compressed air.

A comprehensive control procedure involving extensive use of bar codes and graphics ensures dispensing accuracy. Each cell is labeled with an identifying bar code and the system database records the current drug assigned to each cell. When a cell is refilled, the system requires scanning of the stock bottle as well as scanning of the corresponding cell. Pills will not be dispensed from the cell without a successful match.

A scanner mounted on the robotic arm also verifies that the cell is in its proper position before dispensing. When the operator removes the labeled prescription from the system, a bar-code label is scanned. In response, the system displays prescription information, including a color picture of the drug.

Were we successful? Our customers think so. "The SP 200 makes it fun to be a pharmacist," notes Dr. Elizabeth Allan-Flynn of the Auburn University School of Pharmacy.

Solve an engineering challenge you'd like to share with Design News? E-mail Karen Field at [email protected] 

Design Objective:

Develop an automated prescription dispensing system to meet cost, size, accuracy, and reliability goals.

Design Challenges:

Produce a dispensing system to:

Operate completely automatically

  • Withstand a 1.5-million-cycle life test

  • Accommodate a broad range of vial and pill sizes

  • Ensure dispensing accuracy

Recipe for quick home cooking

Mmmmmm, roast pork. Mmmmmmmmmm, apple pie. No longer will you have to eat out or spend hours in the kitchen for a great meal. Engineers at Enersyst Development Center (Dallas, TX), in collaboration with those from appliance manufacturer Thermador (Huntington Beach, CA), are bringing fast, high-quality, cooking into your kitchen.

Look at these cooking times of the new JetDirect(TM) oven compared with a conventional convection oven:

JetDirect Regular

Pork & potatoes 30 mins. 60 mins.

Vegetable medley 7:30 25

Bundt cake 20 40

The JetDirect combines the best of two worlds--the speed of a microwave with the browning capability of Enersyst's air impingement oven. This technology is not new. Restaurants, such as Pizza Hut, Dominos and Red Lobster have been using Enersyst's impingement ovens for the last 20 years. But the combination of impingement and microwave has not been available for home use.

To help tailor their technology for residential use, Enersyst partnered with Thermador in 1997. "The JetDirect oven for us is a continuation of something we introduced to the market 25 years ago--combination cooking," says Alan Leukhardt, vice president of Thermador.

Engineers from both companies worked together to overcome challenges such as:

- Air flow

- Size constraints

- Heat Transfer

- Power limitations

- Materials

- Combining technologies.

Impingement System: The principle of cooking lies in the heat transfer rate, the "h" factor--or the speed that heat moves from one point to another. The air impingement process heats the surface of food through extremely hot, directed jets of air. The 450F degree blasts speed the rate of surface heat transfer by 60% over that of a conventional oven. Air impingement sweeps away the cooling stagnant layers of air created as water evaporates from the food.

Food cooks evenly in this type of oven when moved through the "jet stream" on either a turntable or conveyor belt. "If you take a piece of bread, place it in an impingement oven and keep it stationary, you would see toasted spots in the bread where the jets of air hit," says Michael Dobie, vice president of engineering for Enersyst. But because of size constraints, designers can't put conveyor belts in residential units. And market surveys show that people don't like turntables in their "conventional" ovens. "They want to be able to use their standard cooking utensils such as rectangular, metal cooking pans for their cookies and cakes," he points out.

Since they couldn't move the food, engineers moved the air. Jay Dougherty, project engineer, designed a "stirrer" that literally mixes both the microwave field and the jet air stream.

"We tried several iterations before we got the design right," says Dobie. Because of space constraints, Enersyst engineers had to design one stirrer that moved both the microwave field as well as the hot air. "If a stirrer affected the microwaves, it did nothing for the hot air and visa versa."

Finally, Dougherty, designed a patented rotating, tapered stirrer that met performance objectives. Dougherty drew on his prior knowledge of air vectoring and mathematical modeling and developed his 3D model using Vellum Solids from Ashlar (Santa Clara, CA).

Another requirement for home use was that no moving parts could be exposed. "When I thought about this for home use, I knew I couldn't have any exposed blades, motors, and blowers, so a child could stick his or her hands inside and not get hurt," Dougherty says.

But moving columns of air without seeing the parts became a materials problem: the stirrer, motor, and blowers had to be hidden, while the microwaves and the hot air generated had to reach the food at specified angles. Dougherty and team decided on a ceramic material to form the jets of air. Not only can ceramics handle high temperatures, but this particular ceramic allows microwaves to pass through to the food.

Size considerations. To accommodate home cooking needs, individual jets had to be re-engineered for a 30-inch cavity. The Enersyst restaurant ovens had a cooking chamber of no more than 8 inches in height. "Ninety percent of the foods we eat are cooked within a 4- to 8-inch range," says Dobie. "However, for the occasional Thanksgiving turkey, people like to have the option of having more room."

Expansion of the oven cavity meant redistributing the columns of air and microwaves without affecting performance, says Thermador's Leukhardt. "We had to project air streams further to reach the food," he continued. Because impingement ovens have air jets above and below the oven rack, engineers found adjusting the spacing and the size of the top air holes did the trick. The bottom jets, on the other hand, weren't a problem. Everything at home is typically cooked in a pan, which automatically distributes the heat. Bottom jets could therefore be less powerful than the top, with smaller air holes, and a tighter pattern.

While the cooking chamber had to be larger than commercial units, the oven's outside dimensions had to be downsized. "Squeezing all the equipment from a commercial model in to a compact residential model was tough," says Dobie.

This required rearranging components and cutting the size of the blower. Instead of one large device, Enersyst used two smaller blowers stacked on top of each other. These steps produced the added benefit of reducing duct work.

A smaller size required better insulating materials as well. "Because we didn't have as much room for insulation, we had to use a better quality insulator," says Dobie. Their choice: ceramics.

Self Cleaning/Materials. Enersyst's original proof-of-concept oven did not have a prototype self-cleaning mode. Thermador required this feature because of the high demand in the consumer market. "This was probably our biggest challenge," says Dobie. 'We relied on Thermador for its self-cleaning and mass production know-how.'

The first change was in the material used to line the oven cavity. Enersyst's commercial models are made of stainless steel. But stainless steel darkens after repeated self-cleaning cycles. The new models are made from low-carbon-cold rolled steel with porcelain coating.

Fixing one problem led to another challenge. The cavity walls of Enersyst's commercial ovens have sharp edges. In order to use porcelain coating, "we couldn't have any sharp corners," says Dobie. "Essentially, you are melting glass directly on the cavity and we couldn't have it warp." So they used curved corners instead.

Nor could they use any low temperature bearings. Traditionally, Teflon was used for restaurant commercial ovens where temperatures only reach 550F. Now materials had to withstand temperatures of 900F for a two- to four-hour period. They used high temperature grease between ball bearings and interior driven parts.

Certain components had to be respecified to withstand the higher temperatures. For example, the blower wheel would deform at high speeds, so a stronger blower was used, although the blower motor was acceptable, says Leukhardt.

The fan in the cooling system also had to be redesigned. This promotes flow of air through the door. Hot-air exhaust with cool air is forced through the bottom of the unit. Engineers used a reverse-flow cooling system, says Leukhardt. "This keeps warm air out of users' faces and away from services that people would touch."

The self-cleaning requirement created a problem for the microwave as well. A traditional microwave is manufactured to tight tolerances, he says, and those tolerances must be maintained before and after self-cleaning.

The temperature requirement limited the materials that could be used. Forget low-temperature plastics and Teflon. Instead, engineers used high-temperature plastics and resins. They also replaced metal surfaces with dielectric materials.

Controls. The electronics controls developed by Thermador in conjunction with Digital Appliance Controls (Elgin, IL) specified the user interface.

The panel had to reflect how the end user would interact with the oven in terms of audio and visual tactile performance, as well as manage the power control for the oven. Physical requirements of control include such items as dimensions, color, layout, graphic design, mechanical size, and power relay boards that relay heat to the oven.

These had to be easy for consumers to use and understand, "which was about as tough as making it cook quickly,' jokes Dobie.

The oven cooks food so quickly that engineers needed a control that was user-friendly, says Leukhardt. Thermador engineers developed a controller, Cook-Smart(TM), with pre-programmed modes to optimize performance for the user. It defines various food groups that have common cooking temperatures and microwave power levels. The controller converts radiant cooking time to the equivalent time for a jet oven.

For example, the user selects the Cook-Smart mode for cookies and inputs the normal cooking time of 12 minutes. The new oven automatically converts to JetDirect times.

Two at once. The JetDirect will be part of a two-oven unit, with a standard convection oven as the lower half. As Enersyst took the lead on the JetDirect, Thermador simultaneously developed its convection platform. This meant an integration of both ovens from a mechanical and structural standpoint. "We needed to fasten parts together. We need to integrate the two cooling systems, the insulation systems, and the electronic controls including wiring," says Leukhardt.

This required constant communication between the two companies. In addition to weekly conference calls to discuss plans, and informal calls in between, Thermador employed a new EDM/PDM/CAD system: Pro/ENGINEER from Parametric Technologies (Waltham, MA). "We set Enersyst up with the same system," says Leukhardt, "and provided them with a design station of Pro/ENGINEER. Through electronic transfer of files, we sent them our basic design information and they sent us back integration data. We had daily updates."

"It's amazing what you can do with Pro/ENGINEER," says Dobie. "If it fits on the screen, it'll fit in real life."

Look for the JetDirect ovens expected on the market by January 1999.

For more information

To speak with a company representative, call 1-800-828-6344, x 011 and key in the specific Product Code below

Pro/ENGINEER from PTC (C): Product Code 4439

Sens-A-Touch(TM) from TouchSensor Technology (E): Product Code 4440

Digital Appliance Controls (E): Product Code 4441

Pilkington Seraphic (E): Product Code 4442

Time Line:

January 1995: Decided to develop a microwave/air impingement oven for the home

March 1995: Began designing a 24-inch prototype

February 1997: Entered into agreement with Thermador

February 1997 to August 1997: Tested proof-of-concept oven

June 1997: Developed specifications for JetDirect oven

June 97 to August 97: Initial design

July 1997: Began design in Pro/ENGINEER.

September 1997: Began construction on prototype

December 1997: Intermediate design review, discussed hardware

January 1998: First prototype; began tooling for long lead time items

February 1998: Tested UL needed laboratory approval

March 1998: Prototypes #2,3,4 were built. These are presently being used for agency approval.

April 1998: Debuted at the Kitchen and Bath show (Chicago)

December 1998: Target production startup

Partners in design

- TouchSensor Technologies, LLC Component worked on: patented, proprietary, Sens-A-Touch(TM) electronic glass touch system.

- Digital Appliance Controls Component worked on: electronic clock and oven control system including display head, power relay control boards and microwave triac power control board.

- Pilkington Seraphic Component worked on: curved, tempered glass control panels and door panels.

Design considerations:

- Food behavior

- Impingement system:

--Air management

--No moving parts

--Heat transfer management

- Size Constraints

--Larger cavity

--Smaller footprint

- Self-cleaning

--High temperature allowances

- Smart energy utilization

- Power management

Pneumatic hoses

Chainflex Air(reg) pneumatic hoses are for use in cable carriers and resist high abrasion, oil, and coolant; are flexible; and are abrasion-proof. Chainflex Air have been tested for more than 10 million cycles at 10 times OD inside and Energy Chain. The pneumatic hose can be used anywhere a flexible cable carrier is needed. It is constructed from durable polyurethane and is available in blue.

igus inc., Box 14349, East Providence, RI 02914, FAX (401) 438-7270.