Printing element with shock absorber feature

A marking element assembly including a yoke which is driven by an arm. The arm is connected to a slider block which transfers motion to the yoke. The yoke has an interior channel for slider block free motion, with drag, after a marking element connected to the yoke stops yoke motion. The slider block moves against interior walls of the yoke dissipating arm motion and providing shock absorption for the marking element.

BACKGROUND OF THE INVENTION 
1. Field of the Invention 
The invention relates to printing and marking elements and in particular, 
to a printing and marking element having a shock absorption mechanism. 
2. Prior Art 
In some printing and marking systems, the objects which are printed upon 
are fragile and subject to damage by the printing system. While methods 
for printing on paper are well known, methods for printing on other 
materials, such as onto goods, are not well known. The reasons for 
printing directly onto goods vary, but may include the necessity to apply 
model designations, trademarks, copyright notices, serial numbers, 
warnings, cleaning or maintenance instructions, country of origin 
designation or the like. The alternative to printing directly onto goods 
is to print labels and affix labels to the goods. However, labels are 
often not permanent despite efforts to make them so. 
In the semiconductor industry there is a need to mark housings for 
transistors and integrated circuits with some of the information mentioned 
above. Machines have been developed for this purpose which have printing 
elements which transfer ink obtained from a die directly onto the 
semiconductor container in one stroke. One such machine has two marking 
elements, each mounted on opposite ends of a shaft. On an upstroke, the 
upper element contacts a die and receives ink, after which the downstroke 
is commenced. Approximately midway through the downstroke the shaft is 
rotated about a horizontal axis so that the upper element is now coming 
downward for contacting a housing. The downstroke continues for a 
predetermined distance, the extent of which is sufficient to permit the 
marking element to come into contact with the object housing. The marking 
element in such machines is a pad which serves not only to momentarily 
retain ink transferred from the die, but also to provide a slight amount 
of shock absorption. 
One problem experienced in the semiconductor industry in using this type of 
marking machine is that the shock absorption character of the marking pad 
is insufficient to protect some of the fragile semiconductor housings 
which are used. For example, ceramic housings are favored in those 
applications where high temperatures are expected. A ceramic housing is 
quite brittle compared to a plastic housing, yet is much more expensive 
than plastic. It has been found that ceramic housings are subject to 
cracking under the impact of a marking machine. Sometimes these cracks are 
discovered by optical inspection by a marking machine operator, but in 
other instances the cracks are microscopic and are only discovered after 
failure of a device in the hands of a customer, even after final 
inspection and testing indicate a good part. Replacement of a device in 
the hands of a customer is very time consuming and expensive both for the 
customer and the manufacturer. 
Accordingly, it is an object of the present invention to devise a printing 
and marking element for use with fragile goods and other items. 
SUMMARY OF THE INVENTION 
The above object has been achieved in a printing and marking element by 
providing a shock absorbing yoke for a marking element. The yoke features 
a zone for allowing relative free motion of the element with respect to 
the yoke. The yoke receives energy for reciprocal motion involved in 
printing from an arm. A slider block, transferring power from the arm to 
the yoke, moves within the yoke with an adjustable amount of drag. This 
allows the printing element, which is fixed relative to the yoke, to 
remain at rest after gently contacting the printed object, with the slider 
block continuing motion in the yoke, dissipating the remaining driving 
impact. 
There are three principal benefits realized by this invention. First, 
fragile objects and goods, specifically housings for integrated circuits 
are not cracked or damaged by marking or printing. Second, the marking or 
printing machine receives less wear due to less reaction to the impact 
against the printed object. Third, the printing or marking machine does 
not have to be perfectly aligned with the printed object for good quality 
printing, i.e., there is less blurring of the print.

DESCRIPTION OF THE PREFERRED EMBODIMENT 
With reference to FIG. 1 a marking element assembly 11 is shown. This 
assembly features a yoke 13 having connected marking elements 15 and 17. 
The marking elements are moved up and down in a direction indicated by the 
arrowheads A and rotated in the direction indicated by the arrowheads R. 
The manner of motion will be explained below. 
The assembly further includes a driving arm 19 for causing both the up and 
down motion and the rotational motion mentioned above. Force is 
transmitted to the driving arm 19 by means of at least one driving journal 
21 which transmits both the rotational force and the up and down motion. 
Power is applied to the journal 21 by an external motor. The manner of 
applying power to a marking element assembly 11 is well known. For 
example, a machine sold by Markem Corporation of New Hampshire employs 
marking elements similar to marking elements 15, 17 shown herein. Power is 
transmitted to a yoke holding the marking elements by means of arm 19 and 
journal 21. 
The difference between the prior art and the present invention is the 
provision of a shock absorbing element in the present invention. Shock 
absorption is achieved by the novel yoke of the present invention. This 
yoke features the slider block 23 which is connected to driving arm 19. 
The slider block may be a solid mass of material having a keyed hole 
therethrough, into which arm 19 snugly fits. A key on arm 19 fits into the 
keyed hole. Slider block 23 has side edges, 25, 27 such that the slider 
block can move vertically in the direction indicated by the arrowheads A 
between the inside of the yoke sidewalls 31, 33. The width of slider block 
23 is slightly greater than the width of the top wall 45 and bottom wall 
47 of yoke 13, both of which have equal widths. The fact that slider block 
23 has a slightly wider width, say by 1 mm, places the slider block in a 
position to readily contact the sidewalls. 
Support for the slider block is achieved by means of vertical rails 32, 34 
which are integrally formed on the inside surfaces of the opposed 
sidewalls 31, 33, respectively, in order to maintain the slider block 23 
in the proper orientation. These rails define the path for slider block 
vertical motion within the yoke. The rails extend through grooves defined 
on opposite sides of the block. Slider block 23 is made of metal and the 
edges 25, 27 are generally lubricated to promote sliding action, even 
though drag is applied to the slider block. 
The opposed walls 31, 33 of the yoke can be brought into close proximity to 
the slider block by means of screws 35, 37, 39, plus a fourth screw not 
shown, on one side. These screws extend through the sidewall 31 of the 
yoke into opposite top and bottom walls. For example, the screws 35, 37 
are threaded into bottom wall 47, while screw 39 and the fourth screw (not 
shown) extend into the top wall 45. Between the head of each screw and the 
screw shank, not shown, is a spring washer. For example, the screws 35, 
37, 39 have the spring washers 36, 38, 40 respectively between the screw 
head and shank of the washer such that the spring washer exerts force 
between the screw head and the sidewall of the yoke. 
Since the screw shank extends into either a top wall or a bottom wall of 
the yoke, the spring allows a magnification pressure to be exerted between 
a sidewall, through which the screw is connected, and a top or bottom 
wall. This magnification permits careful turning of the screws such that 
the pressure between sidewall 31 on the one hand and the top and bottom 
walls 45 and 47, on the other hand, to be carefully controlled. This 
allows for gradual adjustment of the sidewall drag against slider block 23 
such that a desired amount of drag may be readily achieved. The spring 
washers 36, 38, 40 need only be positioned on screws extending into one of 
the sidewalls. It is generally easier to make drag adjustments from only 
one side of the yoke. These spring washers define a pressure means for 
varying sidewall spacing relative to the slider block whereby the amount 
of sliding friction contact between the sidewalls and the slider block may 
be varied. Screws 41, 43 and two other screws, not shown, at the bottom of 
sidewall 33 secure the sidewall to the top and bottom walls 45 and 47. The 
screws are fasteners and not used for drag adjustments. 
The marking elements 15 and 17 are fixed with respect to the top and bottom 
walls 45 and 47. In other words, the marking element 15 is fixed with 
respect to top wall 45, while marking element 17 is fixed with regard to 
bottom wall 47. The marking elements have identical constructions which 
include central shafts 51, 51' which are rigid and usually made of metal. 
Pad backing members 53, 53' are connected to the respective shafts 51, 
51'. Adhesively connected to the backing members 53, 53' are ink retaining 
pads 55, 55' respectively, which are somewhat resilient and may have some 
shock absorption qualities, especially if made from an elastomeric 
material such as rubber. 
The driving arm 19 extends through hole 61 defined in the sidewall 31 and 
is connected to slider block 23, as previously mentioned. The hole 61 is 
oversize relative to the diameter or thickness of driving arm 19. For 
example, the diameter of hole 61 may be 50% greater than the diameter of 
driving arm 19. The exact extent to which the diameter of hole 61 is 
oversize depends upon the amount of free motion that is desired. The arm 
19 emerges through a similar hole, not visible, in the sidewall 33. 
Preferably, driving arm 19 is a single metal bar which extends completely 
through yoke 13. A single bar is not necessary since two parallel colinear 
bars could be joined within slider block 23. It should be noted that the 
hole 61 is circular, merely as a matter of convenience. The hole could be 
elliptical, elongated in the vertical direction with opposite elliptical 
ends which are sufficiently wide to accommodate the driving arm 19 within 
the opposite ends. 
In operation, the marking elements 15 and 17 move upward in unison in the 
direction indicated by the top arrowhead A until the pad 55 contacts an 
ink transfer die, not shown, which places an ink pattern on pad 55 
corresponding to a mark to be made. The steel transfer die, containing the 
indicia to be marked receives ink from an inked roller. The die and roller 
are represented diagrammatically by the block 58, labeled "inked die" in 
FIGS. 2-4. The ink pattern transfer from the die to pad 55 may be any 
combination of letters, symbols, or other marks which can be formed on a 
die. Such dies and ink transfer methods are well known. Pad 55 is adjusted 
to contact the die lightly such that the slider block is centered in the 
yoke. Centering of the slider in the vertical direction is desirable in 
order to reset the slider block for the next down stroke. Only a light 
inking of pad 55 is required on the upstroke. This is unlike the 
downstroke in which firm contact with the marked object is required. 
After ink is received by pad 55, the yoke is rotated about the axis of 
symmetry of arm 19. This rotational force may be transmitted to arm 19 by 
means of a gear, not shown, on the far side of journal 21. A cam, not 
shown, on the side of arm 19 opposite journal 21 has detents which index 
the rotational position of arm 19 such that the marking elements 15 and 17 
will be vertically aligned. Rotation of yoke 13 is achieved at the 
beginning of a down stroke such that the pad 55 which has just received 
ink, now faces a device to be marked. This situation is shown in FIG. 2. 
With reference to FIG. 2, pad 55 is travelling in a downward direction 
indicated by the arrow B toward the article to be marked M. The slider 
block 23 is in a relatively low position after rotation and ready to be 
pushed upward by the reaction of the yoke 13 after impact of the pad 55 on 
the article M. 
In FIG. 3, the pad 55 has continued motion in the direction indicated by 
the arrow B, until coming into contact with the article M. After making 
contact, marking element 15 stops, but arm 19 continues its downward 
motion, with the slider block in sliding friction contact with the 
sidewalls of the yoke. Arm 19 is initially approximately centered in hole 
61 when contact is first made by the pad 55 with the article M, but as the 
arm moves downward, it assumes the position indicated by the dashed line 
19'. This position may be seen more clearly with reference to FIG. 4. 
In FIG. 4 slider block 23 is shown to be at its lowermost position between 
the opposed sidewalls 31, 33 of yoke assembly 13. At this points, downward 
force has ceased and the yoke 13 has been successful in dissipating the 
downstroke energy after the pad 55 has contacted the object M. Upward 
motion will now occur which will center the yoke with respect to the arm 
19 after contact with the inked die such that the slider block 23 is 
approximately midway between the walls 45 and 47. A yoke rotation then 
follows. The yoke assembly after rotation is in the position shown in FIG. 
1. 
While the preferred embodiment has been described with reference to a 
single yoke, a plurality of similar yokes could be arranged on an arm 19 
for simultaneously marking a plurality of parallel articles.