Cable tie installation tool

An automatic cable tie installation tool that conveys the cable tie by pressurized air includes a pressure differential sensing mechanism constructed so as to identify blockages in the transfer tube to prevent subsequent propulsion of the next cable tie into the tube.

TECHNICAL FIELD 
The present invention relates generally to a tool for the automatic 
installation of a cable tie around a bundle of wires, and more 
specifically to a tool that utilizes pressurized air as a means to convey 
the individual cable ties and includes an improved sensing mechanism for 
avoiding cable tie jams resulting from blockages occurring within a 
transfer tube of the tool. 
BACKGROUND OF THE INVENTION 
A wide variety of cable tie application tools are known and some are 
complicated multiple operation tools that provide individual cable ties 
from a remote dispenser having a cartridge or reel containing a large 
number of cable ties to a conveyance mechanism for provision to the 
application tool. 
One special type of cable tie application tool has utilized the application 
of pressurized air to convey the individual cable ties from the dispenser 
to a hand manipulated application tool for application to a bundle of 
wires. See, for example, U.S. Pat. No. 3,946,769 to Caveney et al. 
These remote dispenser air convey tools are very desirable and have been 
highly successful for situations where maximum volume and speed of 
application is necessary. However, multiple cable tie jams within the 
transfer hose or tube could lead to potential destruction and subsequent 
replacement of the transfer tube which may result in extensive delays and 
repair costs which can be very significant. Therefore it is critical to 
the avoidance of these problems that once a first cable tie is jammed or 
some other blockage occurs within the transfer tube of the tool, that a 
second cable tie is not loaded and fired through the tube. Prior tools 
used sensors positioned near the entrance end and exit end of the transfer 
tube such that the sensors detected whether a fired cable tie passed the 
first sensor but not the second sensor, indicating that the tie never 
reached the tool. However, this still resulted in situations where the 
user or a different user could turn the tool off and on or remove and 
reapply the tube to the tool while a cable tie was still blocked within 
the tube and load and fire a second cable tie resulting in a costly jam. 
Therefore, further improvements in the art of avoiding multiple cable tie 
jams within the transfer tube of air convey cable tie application tools is 
still needed. 
SUMMARY OF THE INVENTION 
It is an object of the present invention to provide an improved cable tie 
installation tool having a cable tie blockage preventing mechanism. 
It is further an object of the present invention to provide an improved air 
convey cable tie installation tool having a sensing mechanism for 
preventing the firing of a cable tie when an initial blockage in the 
transfer tube is sensed. 
In general, an automatic cable tie installation tool for fastening an 
individual cable tie around a bundle of wires or the like includes cable 
tie application means for application of the cable tie around a bundle, 
cable tie receiving means for receiving and positioning the cable tie for 
transportation to the cable tie application means, cable tie advancing 
means utilizing pressurized air for advancing the cable tie from the 
receiving means through a transfer tube to the application means, control 
means for controlling the receiving means, sensing means for sensing the 
presence of a blockage within the transfer tube, and, signaling means for 
signaling the control means in response to a blockage indicated by the 
sensing means to prevent the positioning of a next cable tie for 
transportation to the application means.

DESCRIPTION OF THE PREFERRED EMBODIMENT 
A remote dispenser type cable tie application tool system utilizing the 
application of pressurized air to convey individual cable ties to the hand 
manipulated tool having a blockage sensing mechanism embodying the concept 
of the present invention is designated generally by the reference numeral 
10 in the accompanying drawings. 
As shown in FIG. 1, a cable tie application tool system using a blockage 
sensing mechanism according to the present invention includes a cable tie 
application tool 12, a cable tie dispenser 14 connected to the tool 12 via 
a transfer tube 22. The dispenser 14 is connected to a cable tie reel 16 
and receives the individual cable ties 20 through a receiving drum 18. The 
drum 18 of the dispenser 14 receives and positions the individual cable 
ties 20 for transfer into and through the transfer tube 22 into position 
within the application tool 12 for application by the tool jaws 26 around 
a bundle of wires 24. 
As can be seen in FIGS. 2 and 6, the blockage sensing mechanism 25 is 
disposed generally between the receiving drum 18 and the inlet area 30 of 
the transfer tube 22 and in addition to the control circuitry (not shown) 
is comprised of a connector block assembly 28, an air inlet 36 a pair of 
pressure taps 44, 46 and a pressure regulator 34. This positioning of the 
connector block assembly 28, the pressure taps 44, 46 and the circuitry of 
the control unit 35 allows a user to obtain a differential pressure 
reading to indicate the presence of a blockage in the transfer tube 22 
prior to loading and firing of the next cable tie 20. 
As can be seen in FIGS. 7 and 8, the connector block assembly 28 includes a 
passageway 60 aligned between the receiving drum 18 and the transfer tube 
22 through which cable tie 20 is loaded into tube 22. The assembly 28 
further includes a first bore 40 into which air flows from the air inlet 
36 as regulated by pressure regulator 34. Assembly 28 also includes a 
sliding piston 48 which has a second bore 50 aligned with first bore 40 
and ending in a right turn at its distal end. The connector block assembly 
28 and sliding piston 48 also include a plurality of O-ring seals 52 which 
seal around the piston to prevent air leakage and to ensure proper 
operation. The first bore 40 includes an orifice 42 of a smaller diameter 
and the pair of pressure taps 44, 46 opening into the bore from the top. 
The two pressure taps 44, 46 located upstream and downstream from orifice 
42 respectively and are electrically connected to a differential pressure 
transducer of the control unit 35. There is also a valve 38 which can be 
switched so that downstream tap 46 is connected to the differential 
pressure transducer of the control unit 35 or is switched so that the 
downstream tap 46 is blocked and that side of the pressure transducer 
vents to atmosphere. Additionally, positioned at the exit area of 
passageway 60 is a first optical sensor 32 which indicates when the tie 20 
has passed into the inlet area 30 of the transfer tube 22. Finally, there 
is a second optical sensor situated near the exit end of tube 22 (not 
shown) that indicates when a tie has passed and that a proper firing has 
occurred. 
As can be seen in FIGS. 7-9, during a normal cycle of advancing a cable tie 
through the tube 22 to tool 12, when the user activates the trigger, a 
primary air burst is sent through the drum 18 to move the loaded tie 20 
through a cable tie passageway 60 past first optical sensor 32 and into 
position for advancement through tube 22. As seen in FIGS. 7 and 8, 
sliding piston 48 initially rests on a first surface for correct alignment 
of the piston bypass cable tie passageway 62 with the cable tie passageway 
60. When first optical sensor 32 detects that tie 20 has passed, it sends 
a signal to the control unit 35 which stops the primary air blast from the 
drum to prevent the tie 20 from moving too far down into the transfer tube 
22 and to allow for the loading of the next tie 20 into position in the 
drum 18. The signal from first optical sensor 32 that the tie has passed 
also results in the control unit 35 initiating the secondary air burst 
which goes through air inlet 36 into first bore 40 which hits the far wall 
and moves the sliding piston 48 into the position shown in FIG. 9 which 
aligns the distal end of second bore 50 with passageway 60 and pushes the 
tie 20 through the tube 22 to the tool 12. The secondary burst of air from 
inlet 36 pushes the sliding piston 48 into the sealed position and 
simultaneously seals the passage and conveys the cable tie 20. An 
anti-rotation pin 54 is engaged with piston 48 to prevent rotation and 
misalignment of the piston 48. After the second optical sensor (not shown) 
at the tool end of the tube signals that the tie has passed, the control 
unit knows that the tool is ready for another normal cycle. If, however, 
the tie does not pass the second optical sensor (not shown) or the control 
unit is otherwise in a state in which it tells the tool to operate a test 
cycle, then the user will not be able to fire another tie into the tube. 
The test cycle consists of only sending the secondary air burst through 
inlet 36 such that piston 48 will move and bore 50 will align with 
passageway 60. The primary air burst which moves the tie from the drum 
into the transfer tube has not been sent and therefore the tie 20 was not 
loaded into the entrance end of the transfer tube 22 for advancement by 
this secondary air burst. The pressure taps 44, 46 will take pressure 
readings which will be checked by the control circuit. If there exists a 
blockage, the pressure differential across the orifice will be smaller 
than in the condition of no blockage, because flow is restricted by the 
blockage. The control unit receives and checks the pressure differential 
information from the taps 44 and 46 and controls the operations of the 
tool accordingly. 
It is to be noted that the initial test air burst to check the pressure 
differential is not performed before every cycle, but only under certain 
conditions indicated to the control circuit such as each time the system 
is first powered up, each time the cable tie convey tube is disconnected 
from the system and reconnected and any time the control does not see the 
proper input from the cable tie convey optical sensors. As can be seen 
from the schematic of FIG. 10, the control circuit checks the status of 
the cable tie conveyance tube as follows. The electronic control unit 35 
first opens up a convey air inlet valve (not shown) which sends air 
through air inlet 36, and into bore 40 and through the orifice 42. The 
valve 38 is initially positioned to vent the low side of the differential 
transducer to atmosphere, in order to indicate to the control the convey 
air inlet pressure setting. Next, valve 38 is switched connecting the low 
pressure side of the transducer to the downstream tap 46 so that the 
differential pressure across the orifice by taps 44, 46 is noted by the 
electronic control. The electronic control consults a table in memory to 
compare the convey air inlet pressure to the indicated differential 
pressure across the orifice. The result of this comparison indicates to 
the electronic control whether the cable tie convey tube is clear or 
obstructed. 
The precise positioning of the respective pressure taps 44, 46 can be 
determined for different specific bore sizes and specific orifice sizes by 
using standard calculations to optimize the readings. 
It is also noted that the transfer tube 22 in the preferred embodiment of 
the present invention has an interior profile contoured to surround in 
relatively close proximity the circumference of the cable tie head as can 
be seen in FIG. 5. Close contouring of the internal profile of the tube 22 
to the cable tie head minimizes air leakage around the cable tie head 
within the tube so that the maximum differential pressure reading is 
obtained to accurately identify a cable tie presence within the transfer 
tube. FIG. 3 shows the internal contour of a prior art transfer tube which 
allows more air to pass unimpeded around the cable tie which results in a 
smaller pressure differential reading thus making the precise 
determination of a blockage less accurate and more difficult. FIG. 4 shows 
a prior tube in the undesired state of having a multiple cable tie jam. 
While the particular embodiments of the present invention have been shown 
and described, it will be obvious to those skilled in the art that changes 
and modifications may be made without departing from the invention in its 
broader aspects. The matter set forth in the forgoing description and 
accompanying drawings is offered by way of illustration only and not as a 
limitation. The actual scope of the invention is intended to be defined in 
the following claims when viewed in their proper perspective based on the 
prior art.