Mechanical design of the HP 4980 Network Advisor - protocol analyzer - Technical

Hewlett-Packard Journal, Oct, 1992 by Kenneth R. Krebs

Bottom Feet. Along the bottom of the pod housing are molded two long rails that "join" the front and rear bottom feet molded into the bottom chassis. These rails are 0.5 mm shorter in height than the chassis bottom feet. This ensures that while the bottom feet are always the ones to bear the weight of the instrument, they do not catch the back of a user's leg when the instrument is carried by its padded, flexible side handle.

Rear Panel. The molded rear panel mounts the line filter/fuse module, the fan, and the external PC ports printed circuit board, which provides two serial ports, one parallel port, and one video port (see Fig. 8). The area behind which the PC ports board mounts is formed usmg mold inserts to allow easy changes in the number and configuration of connectors (e.g., adding HP-IB or SCSI). A fan grill and cage are molded into the panel so that the fan can be snapped into the panel without the use of fasteners. A molded-in feature acts to capture the RAM backup battery in the bottom chassis when the rear panel is installed. All text and graphics (connector labels, line information, safety warnings) are molded-in on mold inserts to make them easy to change or repair. Also, text is indented in the plastic (raised on the inserts) and molded into shallow recesses to accept labels to cover the text if it becomes necessary (e.g., labels for different language versions). A long label was added to accept new warning and regulatory messages as they become necessary.

Tooling and Molding

HP's Palo Alto Fabrication Center (PAFC) molds most of the Network Advisor's plastic parts. Mobay's Bayblend FR1441 polycarbonate/ABS blend was chosen as the basic material for its combination of strength, moldability, appearance, and price. Two parts, the display cover lid and the display housing rear cover (both large, thin parts), required FR1439, which has a higher percentage of ABS, for increased moldability to prevent warping and to reduce blush. Two small parts (molded by a second vendor), the snap-on side feet and the snap-on rear mounting screw covers, use GE's Lexan 920 straight polycarbonate. While we feared a noticeable gloss difference between the blended and straight materials, our fears were not realized and the match has been good. The snap-on display lid latches also use this material for strength reasons. They have a molded-in cantilever spring that provides the force to return them to their home positions after unlatching. Straight polycarbonate with its higher allowable strain rates and creep resistance was needed for these springs. The friction clutch arm bears the brunt of the display housing support and torque when moving the display. For this reason, it is molded in a 40% glass fiber filled polycarbonate for strength and stiffness. The keycaps are molded in polyester to allow sublimation printing of the three keycap legend colors.

All external cosmetic surfaces are textured using an HP frosted grain III specified as 0.001 inch deep on typically 2.5* draft.* Some surfaces, however, were designed with only 1.5* draft. On these surfaces, the texture is specified as 0.0005 inch deep to avoid possible ejection problems.