Method for detecting obstructed nozzles

A method of detecting whether a vacuum nozzle on a high speed component placement machine is obstructed. A vacuum nozzle (10) has a hollow tube with a vacuum port (25) and an opening (12) at one end. The hollow tube having a fiber optic wire (20) located within it such that one end of the fiber optic wire is exposed to be illuminated (50) by a remote light source (30). The fiber optic wire transmits light to illuminate the opening from the interior of the vacuum nozzle. The amount of light exiting the illuminated opening is measured (55) by a remotely located light detector (35). A decision (60) is made as to whether the opening is obstructed by comparing the measured illuminated opening to a predetermined standard.

TECHNICAL FIELD 
This invention relates in general to methods of vacuum pick-up of 
components. 
BACKGROUND 
All electronics assembly manufacturing lines require some form of component 
placement system. The simplest component placement equipment is a steady 
hand and a pair of tweezers. More complex systems use automatic component 
placement machines, and, as in manual placement, the object is to pick up 
a part from a certain position and place it at a new location on a 
substrate. Pick-up is normally achieved either in manual or automated 
systems by using a vacuum chuck which is sized to suit the component. 
Components are presented to the pick-up position using an automatic 
component feeder. In all cases, two important criteria for component 
placement are accuracy and reliability. The ability to repetitively place 
the component in the desired location on the substrate. Repeatability of 
component placement is typically aided by the use mechanical centering 
jaws on the placement head. The placement head then typically moves from 
the pick up position to the desired location on the substrate and deposits 
the component on the substrate by releasing the vacuum, thus allowing the 
component to gently fall into the desired location. Components are 
typically placed, in to an adhesive or a solder paste that prevents the 
movement of the component during subsequent operations. Both the solder 
paste and the adhesive have a certain degree of tackiness which tends to 
hold the component in position. 
Two major approaches are typically taken on automated pick and place 
equipment for surface mount technology. The first is to use a dedicated 
head for each component. This head transfers components from a feeder to 
the substrate or printed circuit board (PCB). A conveyer moves the boards 
past a line of placement heads which progressively populate the board. 
This type of system is typically used for very high volume, long run 
situations. The second approach is a single head machine which is 
microprocessor controlled and contains numerous interchangeable chucks 
which can rapidly pick parts from a variety of feeders and populate a 
single board at a time. This approach is more appropriate for short to 
medium runs with many different assemblies, since set-up time is 
relatively short and the machines are very flexible. 
The level of "user friendliness" should be considered in any decision as to 
which type of component placement head to use. While some machines require 
technician level personnel to program and edit machine functions, others 
require more skilled engineering level assistance. The trade off between 
flexibility and cost of maintenance must be considered by the user. 
In the case of single head component placement machines with multiple 
chucks, 100 or more vacuum chucks are on a single head. It is extremely 
important that each of the chucks be maintained in a pristine operating 
condition. If any of the chucks is misaligned or inoperative, the 
placement of the components will be in error or the component will be 
missing from the circuit board. High speed machines that have turret heads 
are capable of placing very high numbers (5000-8000 per hour) of small 
components, and the problem of vacuum chuck or vacuum nozzle clogging is a 
significant one. The small orifice in the vacuum chuck is easily 
obstructed by environmental debris or particulates. In order to ensure 
continued up-time and reliability of machines, the vacuum chucks must be 
scrupulously cleaned on a regular basis. In addition, there is no way of 
determining whether a vacuum nozzle is obstructed until it becomes 
completely inoperative, at which time defective product has already been 
manufactured. 
It would be desirable and a significant improvement in the state of the 
art, if a system could be devised that could detect a clog or obstructed 
vacuum nozzle in a proactive manner. Such a method would reduce the cost 
of maintenance of the high speed component placement machines and increase 
the quality of the assembled electronic product.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
Clogged vacuum nozzles on high speed component placement systems contribute 
to the placement defects and cycle time increase of an automated 
production line. The method of detecting whether of not a vacuum nozzle 
opening on a high speed component place machine is obstructed encompasses 
illuminating the vacuum nozzle with a remote light source. The vacuum 
nozzle contains a fiber optic cable or bundle that is embedded within the 
vacuum nozzle, in such a manner that the other end of the fiber optic 
bundle illuminates the interior of the vacuum nozzle and thus the vacuum 
nozzle opening. As the rotary machine passes by the remote light source 
the interior of the nozzle is illuminated by the fiber optic. As the 
turret on the placement continues to rotate the nozzle passes over a 
measuring device, typically a camera. The measuring device measures the 
amount of light, if any, emanating from the illuminated vacuum nozzle 
opening. This measurement is compared to a set of standard criteria, and a 
determination is then made as to whether or not the opening is clogged. If 
the opening is not obstructed, it will be seen as a bright light. If the 
opening is completely obstructed the bore of the nozzle will not be seen 
and it will be dark. If the nozzle is partially obstructed, a combination 
of light and dark areas will be seen that represents the amount and degree 
of obstruction of the nozzle. 
Referring now to FIG. 1, a pictorial schematic view of a nozzle in 
accordance with the invention is show. A vacuum nozzle 10 typically 
consists of a hollow tube having a concentric bore down the center of the 
tube. One end of the nozzle 10 has an opening 12 that serves as the vacuum 
chuck to pick up the component (not shown). Although the drawing figure 
shows the tip of the nozzle as tapered, this is clearly an option and it 
may be cut off square if desired. The other end of the vacuum nozzle 10 is 
used to attach the nozzle to the turret head (not shown) of the component 
placement system. This end of the nozzle is typically called the nozzle 
block 14. In one particular application, that is component placement 
machines made by Sanyo of Japan, the nozzle block 14 is attached to the 
replaceable vacuum nozzle 10 by means of a retaining screw 16. The nozzle 
block 14 serves to fixture and align the nozzle 10 in proper orientation 
in the turret head. Passing through the nozzle block 14 is a fiber optic 
bundle 20. Fiber optics are known by a number of names, such as fiber 
optic bundles, fiber optic wires, light pipes, or simply a fiber optic and 
are well known in the modern world. Fiber optics provide an efficient 
transmission of light through the bundle with minimal attenuation. One end 
21 of the fiber optic bundle is arranged so that it is exposed to the 
exterior of the nozzle. The other end 22 of the fiber optic is arranged so 
that it lies in embedded or within the interior of the vacuum nozzle tube 
10. Exact placement of this end of the fiber optic is not critical, 
however, it is important that it be arranged within the interior of the 
vacuum nozzle in such a manner that light emanating from the fiber optic 
bundle 20 can illuminate the interior of the vacuum nozzle and 
specifically the opening 12. A vacuum port 25 is also located in the 
vacuum nozzle and is used to draw the vacuum on the nozzle to pick up the 
component. A light source 30 is located remotely to the vacuum nozzle. The 
light source 30 is not physically connected to the vacuum nozzle in any 
manner. This enables the vacuum nozzle to freely rotate and move on the 
turret without encumbrance by wires or other power sources. The remote 
light source may be a dedicated light or simply ambient light provided by 
lighting fixtures or exterior illumination. An optical measuring device 35 
is also mounted remotely to the vacuum nozzle 10 and is used to determine 
whether or not the opening 12 is obstructed. The optical measuring device 
35 may consist of any number of means which can measure light, such as a 
camera, a light meter, a photo diode, etc. and need not be restricted to 
the visible range of the electromagnetic spectrum. The use of ultraviolet 
and/or infrared light is an equally acceptable alternative to the use of 
visible light. Advantages accrued by remotely locating the optical 
measuring device 35 away from the nozzle are similar to those accrued by 
the use of the remote light source 30. Since the optical measuring device 
is not attached to the nozzle in any way, it does not encumber the nozzle 
and allows unrestricted freedom of movement. 
Referring now to FIG. 2, in practice the remote light source illuminates 
the fiber optic bundle (step 50). Light passes down through the bundle and 
exits at the opposite end of the fiber optic bundle and illuminates the 
interior of the vacuum nozzle. The amount of light exiting the vacuum 
nozzle is measured (step 55) by the remotely located optical measuring 
device. The decision is then made as to whether or not the nozzle is 
obstructed (step 60). The measurement of light emanating from the nozzle 
opening is an inverse function of the degree of obstruction of the nozzle 
opening. That is, obstructed nozzles pass little or no light, and clear or 
unobstructed nozzles pass a great deal of light. The decision mechanism 
employed in step 60 is typically a software algorithm resident in the 
machine operating system. However, in less sophisticated systems it may be 
manually performed. By comparing to a set of standards, (typically the 
software algorithm will use a look-up table). A decision is made as to 
whether or not the nozzle is clogged. If the nozzle is obstructed, an 
attempt may be made to clear the nozzle by pressurizing it with a 
pressurized gas such as air or nitrogen at a level above ambient pressure 
(step 65). At this point the process is repeated, that is the nozzle is 
again illuminated and light coming out the opening is measured and a 
decision is made as to whether the nozzle is obstructed. The intent is 
that the use of pressurized air will dislodge and blow out any debris that 
may be blocking the nozzle. If the attempt to clear the nozzle was 
successful, the machine turret continues in its normal way of picking 
components off of a feeder and placing them on the substrate (step 70). It 
should be obvious to the reader that the iteration of steps can be 
performed a number of times. For example, the operator may set the machine 
parameters to make three attempts to clear the nozzle and if it is not 
clear on the third attempt, then the nozzle is flagged or labeled by the 
software as being inoperative. This takes the nozzle out of the system and 
does not permit it to be used for subsequent assembly operations. If 
desired the machine operator may be alerted through the red warning light 
resident on the placement machine. At this point the operator has the 
option of removing the nozzle and replacing it with a new one or simply 
bypassing that nozzle and continuing on with production. 
FIG. 3 shows three typical cases of nozzle conditions. An unobstructed 
nozzle 80 appears to the camera to be completely white, that is the light 
shines through the nozzle and no obstruction is seen. A partially 
obstructed nozzle 82 shows a pattern of black in one or more portions of 
the nozzle. This pattern may extend from simply a partial obstruction 
(less than 10%) to nearly total obstruction (approaches 80-90%). A 
completely clogged nozzle 84 does not have any light exiting the nozzle 
opening, and thus appears as a black spot on the video camera. 
In summary, a non contact method for determining whether or not a vacuum 
pick up nozzle on a component placement machine has been obstructed has 
been shown. This method provides significant advantages over the prior art 
in that the vacuum nozzle and the machine turret are not hindered or 
encumbered by any additional wires or connections. The remotely located 
light source and remotely located camera provide complete freedom of the 
machine turret to operate in the normal fashion. In addition, since most 
component placement machines typically have a camera for inspection of the 
part orientation prior to placement on the substrate this same camera can 
be used to verify the condition of the nozzle. A remote light source is 
easily mounted in any number of locations on the machine, and thus a cost 
effective, simple and highly reliable system has been created that 
provides a significant increase in the reliability and repeatability of 
high speed component placement machines. 
While the preferred embodiments of the invention have been illustrated and 
described, it will be clear that the invention is not so limited. Numerous 
modifications, changes, variations, substitutions and equivalents will 
occur to those skilled in the art without departing from the spirit and 
scope of the present invention as defined by the appended claims.