EP2078125B1

EP2078125B1 - Wire tying machines

Info

Publication number: EP2078125B1
Application number: EP07824085A
Authority: EP
Inventors: Ian David Coles; Graham Frank Barnes
Original assignee: Tymatic Ltd
Current assignee: Tymatic Ltd
Priority date: 2006-10-09
Filing date: 2007-10-09
Publication date: 2011-12-14
Anticipated expiration: 2027-10-09
Also published as: WO2008044002A2; GB0619947D0; ATE537317T1; EP2078125A2; WO2008044002A3

Abstract

A machine for tying a wire around one or more objects (2) comprises a wire sensing arrangement (68, 76) for sensing the presence of the wire in a predetermined part of the machine, the wire sensing arrangement being configured to detect presence of the wire (46, 52) when the wire closes an electrical circuit so that an electrical current passes through part of the wire (46, 52). The electrical resistance of the wire may be measured to determine the wire type.

Description

This invention relates to machines for tying a length of wire around two or more objects to bind them together. It relates particularly to wire tying machines for use in binding steel reinforcing bars into a lattice as part of construction of reinforced concrete structures.
Such tying machines are known - see for example WO 2004/083559 . The tying machine generally comprises a wire feed mechanism which draws the wire from a spool and feeds the wire in a loop around the intersection of the bars until the wire returns back to the machine. The wire is then cut and the two ends are gripped by a rotating head which rotates to twist the wire.
For a successful tying operation the twisting action must not be commenced until both ends of the wire have been properly gripped and the wire has been cut. For example, if the wire should get stuck somewhere in the machine or run out, then if the head starts to turn damage to the machine can be caused which could put the machine out of use and require costly repairs.
There have been previous proposals to overcome this problem. For example, EP-A-0822303 discloses the idea of measuring the torque generated by a motor driving the twisting mechanism and halting the twisting if the torque (as measured by the current drawn by the motor) is not seen to be increasing after a predetermined time. It is inferred from this that the wire is not being properly twisted. However, this solution is not ideal as it only gives an indirect indication of the proper progression of the wire and could still lead to damage caused by the attempted initial rotation of the head before it is halted.
The applicant has also recognised a further problem with prior art tying machines. In order to load a new spool of wire into such machines it is necessary to release the rollers forming part of the wire feed mechanism so there is not too much friction to allow the end of the wire to be inserted into it. The applicant has appreciated that this requirement gives rise to more parts than would otherwise be necessary and also places a significant strength requirement on the surrounding structure since a relatively high force is required to overcome the gripping force.
It is an object of the invention in its various aspects to alleviate the problems set out above.
The present invention provides a machine for tying a wire around one or more objects comprising a wire sensing arrangement for sensing the presence of the wire in a predetermined part of the machine, the wire sensing arrangement being configured to detect presence of the wire when the wire closes an electrical circuit so that an electrical current passes through part of the wire.
Thus it will be seen by those skilled in the art that in accordance with the invention the wire itself is used as part of the sensing arrangement which gives a straightforward, direct and reliable way of detecting the presence or absence of the wire in a particular part of the machine.
In one set of preferred embodiments of the invention the sensing arrangement is configured to sense the presence of the wire in a part of the machine to which the wire is returned after passing around the object(s) to be tied. In other words, the sensing arrangement in such an embodiment is configured to detect when the wire has been properly looped around the object so that e.g. twisting can commence. It will be appreciated that this gives a positive, reliable indication of the presence of the wire so that the risk of damage being caused by twisting before the end of the loop has been properly received can be avoided.
The sensing arrangement in such embodiments could comprise a wiper electrode adapted and positioned to contact the edge of the wire when it is in the predetermined correct position. However, in accordance with preferred embodiments the sensing arrangement comprises an electrode surface which is adapted to contact the end of the wire when the wire has been received at the predetermined part of the apparatus. By contacting the end of the wire, the electrode can be made extremely robust for example by incorporating it as part of a surface of the apparatus. This obviates the risk associated with a resilient wiper contact of the contact becoming bent or damaged when struck by the end of the wire.
It is preferred that the machine is configured so that if the wire is not sensed within a predetermined time an error signal is given and normal operation is suspended. This allows the operator for example to put the machine into a maintenance model which will be described later.
In a further set of preferred embodiments the sensing arrangement is arranged to detect when the end of a wire spool has been reached and/or there is a break in the wire on the spool. In accordance with such embodiments the sensing arrangement would therefore be configured such that wire coming off the spool normally closes an electrical circuit so that when the wire breaks or runs out the circuit is broken which can be detected to allow appropriate action to be taken. This reduces the possibility of the end of the wire becoming trapped in the machine which might be difficult to remove and/or cause damage if the machine is used. In such embodiments a resilient wiper contact is preferred.
The two particular applications set out above are not the only possibilities for where the presence or absence of the wire can be detected using the principles disclosed herein; the sensing arrangement could be employed in any other desired part of the machine. More importantly, the two sensing arrangements described above, and indeed any others, are not mutually exclusive. For example, a voltage could be applied to the wire which is sensed in any of several locations.
In order for the wire to close part of an electrical circuit two electrical connections must be made to it. In some embodiments envisaged this is effected by means of making electrical contact to the wire at two discrete points, e.g. with two discrete electrodes contacting the wire. The Applicant has realised that this gives a further benefit in some circumstances in that the electrical conductivity of the wire is characteristic of the type of wire. Thus the electrical conductance of the wire between the two discrete points can be measured to verify the type of wire by comparing it against an expected value for the correct wire.
Preferably the machine is configured to operate normally if the measured conductance is within a predetermined range of the reference conductance but to cease normal operation or give an error signal if it is outside that range.
In other embodiments of the invention the wire is simply allowed to contact a conductive part of the structure of the apparatus so that the wire is at the same potential as the body of the apparatus - e.g. 0 volts or +/-12 volts. The electrode or plurality of electrodes need(s) then only to measure the presence or absence of this voltage to determine the presence or absence of the wire. This is advantageous in requiring only a single electrode but more generally it means that it is not necessary to isolate the wire electrically from the body of the machine which simplifies the machine design.
Using the electrical conductance.of the wire to detect when a spool is empty is a convenient and reliable method when the end of the wire comes away from the spool. However some spools are wound so that the end of the wire remains attached to the spool. The conductance detector would not detect such a condition and so the Applicant has devised a further arrangement which may be used alone or in conjunction with electrical conductance detection. This is based on the recognition that under such circumstances the resistance to movement encountered by the wire feed mechanism will rise significantly as it tries to draw the wire off the wheel. Thus in at least some preferred embodiments of the invention the wire feed means of the machine is configured to detect the drawing resistance presented by the wire and to cease feeding the wire when said drawing resistance or rate of rise thereof is above a threshold value.
Preferably the drawing resistance is measured by measuring the current drawn by a motor driving the wire feed means.
A tying machine in accordance with at least some embodiments of the invention is able reliably to detect when the wire on a spool has ruh out. Preferably the machine is arranged in such a way that normal operation is ceased when it is detected that the wire has run out This reduces the danger of wire becoming entangled in the machine and potentially causing damage. Preferably the rotating head of the machine is locked to prevent rotation under such circumstances. In particularly preferred embodiments the machine is arranged to reverse the wire feed mechanism to return the short length of wire which was drawn into the machine back into the vicinity of the spool for easy removal. Preferably the machine is configured thereafter to enter a maintenance mode. In such a maintenance mode the machine is preferably configured, upon suitable actuation, to advance a wire feed mechanism in a manner allowing a new wire to be threaded into the machine e.g, at a lower speed than the wire feed usually operates at. It will be appreciated that this obviates the need to release any part of the wire feed mechanism to insert a new wire manually. This avoids the disadvantages of having such a manual release mechanism which were set out earlier.
Of course, once the new wire has been introduced sufficiently into the machine it will be necessary at some stage to revert to normal operation. This could be achieved in many ways, for example, a manual intervention could be required such as operating a switch. Alternatively the presence of the wire in part of the machine could be detected and the presence either indicated to the user or used to switch the machine automatically back into a normal use mode. This presence detection could preferably be in accordance with the first aspect of the invention - i.e. namely using the wire itself to close an electrical circuit. Other alternatives would include measuring the drain current of the wire feed means, other ways of sensing the presence of wire or simply operating the wire feed mechanism at the lower speed for a fixed period of time.
Preferred embodiments of the invention will now be described, by way of example only, with reference to the accompanying drawings in which:

Figure 1A is a perspective view of a wire tying machine of the general type to which the invention may be applied;
Figure 1B is a view similar to Figure 1A with a mounting (removed);
Figure 2 is a sectional view through the machine shown in Figures 1A and 1B;
Figure 3 is a view of the machine from underneath;
Figure 4 is a partial perspective view of part of the machine showing wire detection means embodying the invention; and
Figure 5 is a partial perspective view of another part of the machine showing another wire presence detector in accordance with the invention.

Referring first to Figs. 1a, 1b and 2 there is shown two perspective views and a sectional view of part of a tying machine of the general type to which the invention can be applied with certain parts such as the housing, handle, battery, controls and wire spool removed for clarity. The apparatus is shown situated over a junction where two steel bars 2 cross over each other at right angles. The steel bars 2 are intended to form a rectangular grid to be embedded in a concrete structure in order to reinforce it.
Sitting in use above the uppermost bar 2 is the rotary head of the apparatus 4. This includes a horizontal circular base plate 6 extending up from which is a channel 8 which is approximately semi-circular in vertical section and of approximately constant width in the orthogonal direction. In the centre of base plate 6 is a part-spherical depression 9. The underneath of the base plate 6 is shown in Fig. 3 from which it will be seen that on one side there is a narrow slot 10 corresponding to one end of the semi-circular channel and on the other side of the plate 6 corresponding to the other end of the channel is a funnel region 12.
Returning to Figs. 1a, 1b and 2, attached to the semi-circular channel 8 is the upper cylindrical portion of the head 14 which is rotatably mounted in the cylindrical portion 16a of a bracket member mounted to the housing (not shown) by a flange portion 16b (omitted from Fig. 1b). The upper head portion is supported by two rotary bearings 18. A toothed gear wheel, 20 is provided fixed at the top of the head to allow it to be driven by a motor 22 via a worm gear.
Extending through the gear wheel 20 into the open upper end of the head 4 is a solenoid assembly comprising a cylindrical outer tube 26 housing the coil and an inner plunger 28 which is able to slide vertically relative to the coil 26. At the bottom end of the plunger 28 is an actuating disc 30, which is used to operate wire gripping clutch mechanisms.
The internal construction of the head 4 will now be described. On the left hand side as seen from Fig. 2, there may be seen a pivotally mounted angled clutch lever 32. A pair of compression springs 36 act on the longer, upper arm of the lever 32 so as to bias the lever in an anti-clockwise direction in which the shorter, lower arm is pressed downwardly. Of course any number of springs might be used. To the right of the clutch lever 32 are a series of roller wheels 38a,38b,38c the purpose of which will be explained below. A similar clutch lever is provided, displaced approximately 180 degrees around the head. This is not therefore visible in the sectional view.
To the left of the upper head portion 14 connected to the main bracket flange portion 16b is a wire feed inlet guide 40 which receives the free end of wire 46 which has been unwound from the spool (not shown).
Figure 4 shows in detail a wire-spool-empty detector embodying the invention. The tying machine on which the detector is employed is a little different to that described with reference to Figs. 1a, 1b, 2 and 3 but operates in essentially the same way. In Fig. 4 there may be seen a wire spool 50 around which is wound circular diameter steel wire 52. The wire spool 50 is mounted via a spindle (not shown) to a spool support bracket 54. This bracket 54 is connected to the metal frame of the machine, indicated generally by the reference numeral 56.
Part of a wire feed mechanism may be seen which comprises a pair of opposed rollers 58, 60, one or both of which may be driven. Conveniently just the lowermost roller 60 is driven in this embodiment. In the drawing, the uppermost roller 58 is shown mounted on a spindle 62 which is supported between a pair of arms 64 which are themselves pivotally mounted to the frame to allow the upper wheel 58 to move up and down although a spring (not shown) biases the reel 58 down onto the opposing reel 60 in order to ensure that the wire 52 passing between the rollers 58, 60 is firmly gripped. A funnel element 66 is provided immediately upstream of the rollers 58, 60 to facilitate insertion of the end of the wire from a new spool.
Upstream of the funnel member 66 is a wiper contact member 68 which is mounted to a support post 70 extending from the main body 56. An electrically insulated plastic layer (not clearly visible) is sandwiched between the contact member 68 and the post 70 so that they are electrically isolated from one another. As will be seen, the contact member 68 comprises a gently curved portion which is positioned to press resiliently against the wire 52 as it comes off the spool, past the contact 68 into the funnel member 66.
The body of the machine 56 is connected to the common voltage rail of the circuit board controlling the machine (not shown). The wire is in physical and therefore electrical contact with several metal parts of the machine body 56, most of which are not shown in Figure 4 although these could include the funnel member 66. The wire 52 is therefore at the same electrical potential as the body 56 i.e. the common rail voltage of the circuit board.
In ordinary use as shown in Figure 4 the wire 52 completes an electrical circuit between the body of the machine 56 (e.g. via the funnel member 66) and the contact member 68. This means that the common rail potential will be detected at the contact member 68 which allows the presence of the wire 52 to be detected. As long as the wire is detected, the machine will operate normally. However, when the wire on the spool 50 runs out, the common rail potential will no longer be detected at the contact member 68 and this change of potential can be detected by the control circuit. As a consequence of such detection, the wire feed rollers 58, 60 are immediately stopped and reversed so that the short length of wire which has been drawn into the machine body is returned into the spool cavity from where it is easy to remove when the spool is changed.
After returning the end of the wire, the machine is automatically put into maintenance mode. In maintenance mode the rotary head (see item 4 in Figs. 1a to 2) may be locked into position or at least prevented from rotating in the direction of twisting as a further protective measure. Furthermore the control circuit alters the way in which the wire feed roller 60 is driven so that when the trigger or other actuation switch is operated, the roller is driven only slowly compared to its normal speed. This allows a new spool 50 to be inserted. The end of the wire on the new spool is manually fed into the funnel member 66 and the trigger operated so as to take up the end of the wire into the machine. This is continued until the wire reaches the ordinary readiness position for the tying operation, as sensed by a wire presence sensor which conveniently comprises a further electrode similar to the spool-empty electrode member 68. Thereafter the control circuit causes the machine to revert to normal mode.
The spool-empty detection mechanism described above works well for spools where the inner end of the wire is freed when the spool runs out Sometimes however spools are wound so that the inner end is attached to the spool. For example this can make the spool easier to wind. The afore-described mechanism will not work in such circumstances. However in this embodiment the control circuit also monitors the current drawn by the motor driving the lower roller 60. When a spool runs out with the end of the wire remaining attached and the rollers 58, 60 continue to try to draw the fixed wire in, the drawing resistance which is encountered by the rollers will rise rapidly, and so therefore will the electrical current drawn by the associated motor. When this rapid rise in current is detected (e.g, as an absolute value or a threshold rate of rise is exceeded) the roller 60 is stopped and reversed exactly as it is when the electrode 68 detects the end of the wire. Again after the wire is returned the machine automatically enters maintenance mode.
A further wire presence sensor embodying the invention is shown in Fig. 5. The Figure shows in close-up detail the rotary head 70 of the machine shown in Fig. 4. The head 70 comprises a disc 72 with two opposed radial slots through which the wire 52 passes when pulled taut for twisting. Situated above the head base plate 72 is a curved wire guide surface 74. At one end (the right end as viewed) the surface drops away to allow the wire to slide along it easily. At the other end is disposed a planar surface electrode 76 on one face of a support column 78. An electrically insulating plastic film layer is provided between the electrode 76 and the support column 78 in order to electrically isolate them from one another.
In use the wire 52 is issued by wire issuing means (not shown) to the left side of the head 70 (as viewed), it executes a loop around the reinforcing bars (also not shown) and re-enters the machine to the right of the head 70. It then slides over the guide surface 74 until it abuts the electrode 76. At this point the electrode detects the common rail potential at which the wire is by virtue of its contact with the body elsewhere (e.g. the guide surface 74) which causes the wire issuing rollers to stop and the wire clamps (not shown) to grip the wire. The wire issuing rollers are then reversed to retract the wire and pull it taut. Thereafter the head 70 can rotate to twist the wire as is known.
If there should be a problem preventing the wire passing around the bars and re-entering the machine, e.g. being kinked or getting caught, the wire will not be detected and so the twisting operation will not be attempted, thereby avoiding the possibility of damage to the machine or injury to an operator. If the wire is not detected within a predetermined time from beginning the wire issuing, an alarm signal is given and the machine can be put into maintenance mode by the operator. It will further be appreciated that since the electrode 76 is located on the nonrotating support column 78 of the machine body, the disclosed arrangement will also prevent the twisting operation from being attempted should the head 70 not be in the correct rotary orientation for any reason.
It will be appreciated that the embodiments shown are simply examples of how the principles of the invention can be embodied. The presence or absence could be detected at any desired part of the machine.

Claims

A machine for tying a wire (52) around one or more objects (2) comprising a wire sensing arrangement for sensing the presence of the wire (52) in a predetermined part of the machine (4), the wire sensing arrangement being configured to detect presence of the wire (52) when the wire closes an electrical circuit so that an electrical current passes through part of the wire (52).
A machine as claimed in claim 1 wherein the sensing arrangement is configured to sense the presence of the wire (52) in a part of the machine (4) to which the wire is returned after passing around the object(s) (2) to be tied.
A machine as claimed in claim 2 wherein the sensing arrangement comprises an electrode surface (68, 76) which is adapted to contact the end of the wire (52) when the wire has been received at the predetermined part of the apparatus (4).
A machine as claimed in any preceding claim configured so that if the wire (52) is not sensed within a predetermined time normal operation is suspended.
A machine as claimed in any preceding claim wherein the sensing arrangement is arranged to detect when the end of a wire spool (50) has been reached and/or there is a break in the wire (52) on the spool (50).
A machine as claimed in claim 5 comprising a resilient wiper contact (68) for carrying out said detection.
A machine as claimed in any preceding claim wherein the sensing arrangement is configured to make electrical contact to the wire (52) at two discrete points.
A machine as claimed in any preceding claim wherein the sensing arrangement is configured to make electrical contact to the wire (52) by allowing the wire to contact a conductive part of the structure (56) of the apparatus so that the wire is at the same potential as said structure.
A machine as claimed in any preceding claim comprising wire feed means (58,60) configured to detect a drawing resistance presented by said wire (52) and to cease feeding the wire when said drawing resistance or rate of rise thereof is above a threshold value.
A machine as claimed in claim 9 wherein said drawing resistance is measured by measuring the current drawn by a motor driving the wire feed means (58, 60).
A machine as claimed in any preceding claim comprising means for detecting when the wire (52) on a spool (50) has run out and configured such that normal operation is ceased when it is detected that the wire has run out.
A machine as claimed in claim 11 comprising a rotating head (4) and being configured such that said rotating head is locked to prevent rotation when it is detected that the wire (52) has run out.
A machine as claimed in claim 11 or 12 arranged to reverse a or the wire feed mechanism (58, 60) to return a length of wire (52) which was drawn into the machine back into the vicinity of the spool (50) for easy removal.
A machine as claimed in claim 11, 12 or 13 configured to enter a maintenance mode that after is detected that the wire (52) has run out whereby in said maintenance mode the machine is configured, upon suitable actuation, to advance a wire feed mechanism (58, 60) in a manner allowing a new wire to be threaded into the machine.