Instrument with strengthened hollow handle

An elongated bail handle for an electronic instrument housing with opposed ends providing handle mounts. The handle has an elongated intermediate portion extending the width of the instrument, and a pair terminal arm portions each connected to the intermediate portion and having a free end for connection to a respective end surface of the housing. The intermediate portion defines an elongated bore, and a reinforcing bar laterally spans the bore to connect opposed walls of the intermediate portion. The arm and bore may have an oblong cross section, with the bar spanning the short span. The bar may define a passage, and an overmolded handle grip encompassing the reinforcing bar may have material filling the passage to secure it to the handle.

FIELD OF THE INVENTION 
The invention relates to portable instruments, and more particularly to 
handles for such instruments. 
BACKGROUND AND SUMMARY OF THE INVENTION 
Portable electronic instruments such as oscilloscopes are often required to 
be portable for testing devices at various locations. Accordingly, they 
are typically provided with carrying handles. The handle is typically a 
bail handle pivotally mounted to opposite side panels at positions near 
the front panel. The handle has arms that extend parallel to the side 
panels, with a cross member connecting the handle ends. 
A lightweight handle provides improved portability, and a slim handle 
provides a compact profile and an aesthetic appearance. Having a broad 
cross section provides a large surface for comfortable carrying. However, 
these desired qualities are typically contrary to the desire that the 
handle be stiff. Stiffness provides a quality feel by preventing sagging 
under load, and allows the handle to be used as a support leg. Moreover, a 
stiff handle resists unwanted torsional flexing in which the arms are 
pivoted to different angles twists, which can potentially lead to the arms 
locking in a different angular positions. Essentially, a closed or tubular 
cross section provides good stiffness, although it is not readily moldable 
by conventional techniques. 
Tubular members with circular cross sections have been effective to provide 
relatively lightweight and stiff handles and to resist collapse under 
limited lateral compressive loads, such as occur during secondary molding 
operations when a conformal elastomeric grip is molded about a rigid 
plastic handle. Handles with non-circular cross sections are susceptible 
to collapse under these substantial loads. While a thin wall design may be 
acceptable for the limited forces faced during normal use, it may fail 
during secondary molding. Thus, even designers using advanced plastic 
molding techniques to create hollow handles of wide diverse shapes are 
limited in the cross sectional aspect ratio they may employ. There remains 
a need for a readily moldable instrument handle with good torsional 
strength, and particularly for a handle with a non-circular cross section. 
The embodiments disclosed herein overcome these limitations by providing an 
elongated bail handle for an electronic instrument housing with opposed 
ends providing handle mounts. The handle has an elongated intermediate 
portion extending the width of the instrument, and a pair terminal arm 
portions each connected to the intermediate portion and having a free end 
for connection to a respective end surface of the housing. The 
intermediate portion defines an elongated bore, and a reinforcing bar 
laterally spans the bore to connect opposed walls of the intermediate 
portion. The arm and bore may have an oblong cross section, with the bar 
spanning the short span. The bar may define a passage, and an overmolded 
handle grip encompassing the reinforcing bar may have material filling the 
passage to secure it to the handle.

DETAILED DESCRIPTION OF A PREFERRED EMBODIMENT 
FIG. 1 shows a compact portable oscilloscope 10 having a housing 12 and a 
movable bail handle 14. The housing has a generally orthogonal box-like 
shape, with a front surface 16, a rear surface 20, top surface 22, bottom 
surface 24, and left and right side or end surfaces 26 and 30. A display 
screen 32 and interface panel 34 having numerous controls and lead 
connectors occupy the front panel. The side panels each have a central 
pivot boss 36 to support the handle 14. 
The display screen 32 is a flat panel display having minimal intrusion into 
the chamber defined by the housing, permitting the housing to have a 
limited depth less than or comparable to the housing's height, and 
substantially less than the width of the housing. In the preferred 
embodiment, the housing has a width of 13", a depth of 6", and a height of 
7". The generally box-like shape provides the bottom panel with a front 
edge 40 where it intersects the front panel 16, and a rear edge 42 where 
it intersects the rear panel 20. In the carrying position shown, with the 
bottom panel horizontal, and the handle in a vertically upward extending 
position, the front and rear edges provide some stability when the bottom 
panel rests directly on a flat surface. 
The handle 14 is a hollow, rigid plastic elongated member having an oval 
cross section for torsional rigidity. In alternative embodiments, the 
handle may have any oblong cross section, or may have other tubular 
shapes. The handle has an elongated cross member or intermediate portion 
44 extending the width of the housing and having a centrally located hand 
grip 46. The grip 46 has a resilient elastomeric surface that resists 
sliding on smooth surfaces when used as a support leg, and has an 
elongated central portion terminated by a pair of enlarged lobes 48 that 
are widely spaced apart by at least about one third the length of the 
handle. 
A pair of arms 50, 52 extends perpendicularly from each end of the cross 
member to provide a bail shape. A pivot mechanism 54 is connected to the 
free end of each arm. Each pivot mechanism is connected to a respective 
boss 36 on the housing, and includes a limiter that prevents the handle 
from pivoting beyond a selected range of motion. The pivot mechanism also 
includes a stop, lock or detent mechanism, so that the handle is made 
stable in several selected different angular positions, to the rear and 
below the instrument, providing a support for different viewing angles. In 
each of the stable positions, the handle resists movement in response to a 
limited force below a selected threshold, so that the weight of the 
instrument or forces associated with operation do not move the handle. A 
deliberate force, such as to unlock a stop, or to overcome a resistance 
are required to move the handle. The pivot, limit, and stop mechanisms may 
include components mounted on the arm and on the housing to operate in 
concert. The handle pivots through a range of several alternative handle 
positions. With spring biased detent mechanisms in each of the pivot hubs, 
the handle may be moved by applying force to the grip portion of the 
handle. 
FIGS. 2 and 3 show the handle 14 in cross sectional detail. Except for the 
circular pivot ends 54, the handle is a hollow tube defining a bore 56 
extending the length of the intermediate portion 44 and the arm portions. 
The bore is entirely enclosed to define a single chamber. Depending on the 
manufacturing process, minimal apertures not affecting structural 
characteristics may open into the bore from the exterior. The majority of 
the handle has an approximately constant wall thickness, with the bore 
having an oblong or oval cross section concentric with the exterior 
profile. As shown in FIG. 3, the handle has broad, gently curved upper and 
lower walls 60, 62, and more sharply radiused edge walls 64, 66. 
The grip 46 conformally encompasses a central portion 70 of the handle, in 
which several support columns or bars 72 are formed. Each support bar 
spans between the upper wall 60 and lower wall 62, centrally positioned 
between the handle edges 64, 66. The bar essentially functions as a column 
bearing compressive forces between a floor and a ceiling. The bar is 
integrally formed with the handle, and is chamfered or filleted where it 
meets the interior surface of the bore to reduce stress concentrations. As 
shown, the bar separates the bore into two parts that pass laterally on 
opposite sides of the bar, and rejoin past the bar. 
Although many advantages may be obtained with a solid bar, in the preferred 
embodiment the bar defines a central passage 74 extending axially through 
the bar, perpendicular to the length of the handle portion. The central 
passage does not communicate with the bore 56. The grip is cast or molded 
conformally about the handle, so that some of the grip material fills each 
of the passages, melding with grip material entering the passage from the 
opposite end to form a rope 76 of grip material integral with the grip and 
securing it to the handle against slippage. Although the preferred grip 
material is Desmopan thermoplastic elastomer by Bayer, which has a 
thermoplastic matrix that chemically bonds to the polycarbonate handle, 
the rope of grip material is particularly important when using grip 
materials that do not provide such a bond, but provide only a mechanical 
connection. 
In the preferred embodiment, the handle is molded of polycarbonate with a 
20% glass fiber fill for strength reinforcement. The grip is formed of 
thermoplastic polyurethane, which chemically bonds to the handle. The 
handle cross section has a typical height of 0.410 inch, and depth of 
1.125 inch, with a wall thickness of about 0.10 inch. The bars are about 
0.30 inch in diameter at their midsections, and the passages are 0.10 inch 
in diameter. With a grip length of about 6 inches, the bars are positioned 
at about 1-3/8 and 2-5/8 inches on each side of the central gate 80 
The handle is preferably manufactured by gas assisted injection molding. In 
this process, a tool is created with a cavity shaped to form the exterior 
of the handle, and with cylindrical pins passing through the cavity 
defined by the mold at positions corresponding to the bar passages 74. A 
central gate positioned at the midpoint of the handle along an edge 64 or 
66 provides for injection of liquid thermoplastic into the mold. Using gas 
assisted molding, a volume of liquid thermoplastic is injected into the 
cavity. The plastic volume is less than the volume of the cavity, so that 
it does not initially reach the free ends of the handle arms. 
Then, a volume of nitrogen or other inert gas is injected into the gate to 
form a bubble that propels some of the plastic to fill the remainder of 
the cavity. Because the injected plastic that contacts the cooler tool 
surfaces or pins "freezes" rapidly, only the central core of material 
remains liquid or molten at the time of gas injection. Thus, the gas 
bubble does not displace this shell of material, but merely displaces the 
central liquid core to form the eventual bore, and to fill the remaining 
mold cavity. This process inherently creates thicker walls at corners and 
vertexes to generate chamfers. The bore surface is slightly rough and 
irregular, and may narrow adjacent the ends of the arms, providing added 
material for strength where needed. 
The pins are withdrawn, the tool separated, and the handle ejected. Then, 
the handle is placed in another tool with a cavity that closely receives 
the handle, except in the central portion 70, where the tool cavity is 
spaced apart from the handle surface to accommodate the thickness and 
contour of the grip 46. In this press, liquid thermoplastic polyurethane 
in injected at approximately 6000 to 15,000 pounds per square inch. Thus, 
the approximately inch-wide and six-inch-long central portion of the 
handle is subject to about 36,000 to 90,000 pounds of force. This force 
would likely be sufficient to excessively flatten the handle, but 
deformation is prevented by the support of the four reinforcement bars. 
Deformation would be unacceptable for the additional reason that flexing 
of the handle would allow injected grip material to escape where the mold 
would normally be sealed against the handle. A secondary benefit of the 
molding process is that reinforcing bar is loaded in compression during 
the overmolding process, so that it enjoys the inherent principle that 
thermoplastics are stronger in compression than in flexure. 
While the disclosure is made in terms of a preferred embodiment, the 
invention is not intended to be so limited.