Knotter trip mechanism with cooperating clutch mechanism

In a baler having a plunger reciprocating in a bale case and knotters for tying strands of twine around bales, two trip mechanisms are provided for automatic actuation of the knotters. A first trip mechanism is capable of preventing operation of the knotters until a bale of desired length is formed. A clutch mechanism for driving the knotters includes a pawl assembly with an abutment tab. A second trip mechanism holds the pawl assembly in a position where it prevents the knotters from being driven when the plunger is retracted. The initial displacement of the second trip mechanism toward a position where the knotters are driven is in substantially the same direction as the initial displacement of the pawl assembly abutment tab.

BACKGROUND OF THE INVENTION 
This invention relates generally to agricultural balers and, in particular, 
to knotter trip mechanisms for such balers. 
In a conventional type of baler, a plunger reciprocates in a bale case to 
form crop material into rectangular bales. Tying mechanisms comprising 
needles and knotters are provided to tie several strands of binding 
material such as twine around the bales, and a trip mechanism is employed 
for automatically actuating the knotters when bales reach a desired 
length. Such trip mechanisms are disclosed in U.S. Pat. No. 2,897,748 and 
British application 1,169,137. 
Conventionally, the knotter drive shaft controlling the operation of both 
the needles and the knotter mechanisms is rotated at the same rotational 
speed as the plunger crank arm so that the knot tying cycle is completed 
only when the plunger is retracting, or while the bale, which previously 
has been compressed in the bale chamber, is springing back thereby 
resulting in the bale being of relatively low density as it exits from the 
bale chamber. This characteristic causes low energy efficiency as crop 
material has to be compressed much harder to obtain a given density in the 
finished bale. This characteristic also may cause problems with the knot 
tying operation as knots may not hold firmly after completion. 
Although these problems are not critical in conventional, small rectangular 
balers which produce bales typically weighing in the range of 20 to 30 kg, 
the situation is different with medium and large rectangular balers which 
produce bales weighing in the range of 200 up to 1000 kg. In such medium 
and large square balers, the problems described above that are caused by 
the bales expanding in the bale case prior to the knotting cycles being 
completed are much more noticeable. The springing back of crop material 
prior to the knotting cycle being completed is much more significant 
causing bales of relatively low density and resulting in power 
inefficiency. Also, the knot tying operation is often adversely affected 
resulting in frequent misties. 
It has already been proposed in the art, as disclosed in German patent 
1,095,044, to rotate the tying mechanism drive shaft at twice the 
rotational speed of the plunger crank arm. Others also have already 
proposed, as disclosed in German patent 804,616, to rotate the tying 
mechanism main shaft through only one half or one third of a complete 
revolution during the tying cycle. With both of these proposals, the tying 
operation is completed in less than one complete reciprocating cycle of 
the plunger thereby greatly reducing the above-described problems. 
However, these proposals have caused another problem which is concerned 
with timing the operation of the tying mechanism with the plunger 
movement. In conventional hay balers, the knotter drive shaft is rotated 
at the same rotational speed as the plunger crank arm when the knotter 
trip mechanism is tripped. Therefore, timing the knotter operation with 
the plunger movement is very simple. As is generally known in the art, the 
knotter trip mechanism is operable to always trip the knotter cycle at 
precisely the same point in the plunger cycle. Incorrect timing between 
the plunger movement and the knotting cycle would disturb and make the 
knotter operation ineffective. Unless special precautions are taken, such 
incorrect timing easily could occur in arrangements where the tying cycle 
is completed in less than a full reciprocating cycle of the plunger. 
U.S. Pat. No. 4,503,762 discloses means for timing the tying cycle with the 
movement of the plunger in the direction to compress crop material in the 
bale case. A tying mechanism is provided with a drive line including a 
clutch mechanism having a pawl assembly, the position of which is 
controlled by a first trip mechanism coupled to a bale length metering 
apparatus. In addition, a second trip mechanism is cooperable with the 
pawl assembly and operatively associated with the baler plunger in a 
manner such that the pawl assembly, when tripped by the first trip 
mechanism to a drive engaging position, is returned to its drive 
interrupting position when the plunger is retracting in the bale case. The 
second trip mechanism, however, is continuously oscillated between a pawl 
assembly holding position and a pawl assembly releasing position during 
the entire bale compressing cycle preceding the tying cycle of the formed 
bale. This manner of operation is very inefficient considering that the 
second trip mechanism only has to interfere once in a complete bale 
forming cycle, and more specifically, during the tripping of the tying 
mechanism. Unnecessary wear of the components of the second trip mechanism 
results therefrom, requiring increased maintenance. Furthermore, the 
structure operatively connecting the baler plunger to the second trip 
mechanism is located close to the plunger compressing area where the 
structure is subjected to dirt and crop resulting in abrasion and possible 
lack of operation. The second trip mechanism is positioned such that, upon 
the first trip mechanism being tripped, it cannot prevent an initial 
coupling between the tying mechanism and its drive line. Such an initial 
coupling is prevented after a short angular displacement of the tying 
mechanism drive shaft provided the baler plunger is retracting in the bale 
case. Accordingly, energy is lost in setting the tying mechanism in motion 
for a small initial displacement. This initial displacement results in the 
tying mechanism being removed from its optimum start position thereby 
causing high inertia forces when it is actuated a second time to complete 
the tying cycle. 
SUMMARY OF THE INVENTION 
It is an object of the present invention to overcome the aforementioned 
problems and more specifically to provide a baler with improved power 
efficiency and fewer continuously oscillating elements. 
According to the present invention, a baler comprises a bale case, a 
plunger reciprocable in the bale case for compressing crop material into 
bales, a tying mechanism mounted on the bale case for tying a strand of 
binding material around a bale, and drive means for driving the tying 
mechanism. This drive means includes a clutch mechanism which has a pawl 
assembly movable between a drive interrupting position and a drive 
engaging position. The pawl assembly has an abutment tab. The baler also 
comprises bale length metering means, and first trip means operatively 
associated with the bale length metering means and cooperable with the 
pawl assembly abutment tab. The metering means is operable, until a bale 
of predetermined length is formed, to locate the first trip means in a 
pawl assembly holding position maintaining the pawl assembly in its drive 
interrupting position and, when a bale of predetermined length is formed, 
to retract the first trip means to a pawl assembly releasing position 
permitting the pawl assembly to move to its drive engaging position. The 
baler further comprises second trip means also cooperable with the pawl 
assembly abutment tab and movable between a pawl assembly holding position 
for maintaining the pawl assembly in its drive interrupting position and a 
pawl assembly releasing position for permitting the pawl assembly to move 
to its drive engaging position. The second trip means is operatively 
associated with the plunger in a manner so that the second trip means is 
positioned in its pawl assembly holding position when the plunger is 
retracted. 
The initial displacement of the second trip means, when moved from its pawl 
assembly holding position towards its pawl assembly releasing position, is 
oriented substantially in the same direction as the initial displacement 
of the pawl assembly abutment tab, when the pawl assembly is moved from 
its drive interrupting position toward its drive engaging position. 
The present invention may be used on all types of square balers, including 
conventional or small rectangular balers. However, the present invention 
is particularly useful on medium and large square balers.

DESCRIPTION OF THE PREFERRED EMBODIMENT 
Referring to FIG. 1, a baler 10 includes a bale case 12 mounted on a frame 
14 which is supported by wheels 16. A tongue 18 extends forwardly from the 
bale case 12 for attachment to a tractor (not shown). A plunger 20 is 
reciprocably disposed in the bale case 12 to form crop material into 
rectangular bales. The plunger 20 is attached by a connecting rod 22 to a 
crank arm 24 fixed to a shaft 26 on which a sprocket 28 is fixedly 
mounted. The connecting rod 22 has a pivotal connection 30 at one end with 
the plunger 20 and another pivotal connection 32 at the other end with the 
crank arm 24. 
A drive shaft 34 is connected at one end to a gearbox 36 carried on the 
baler 10 and is adapted for connection at the other end to the PTO of a 
tractor (not shown). The drive shaft 34 causes clockwise rotation, as 
viewed in FIG. 1, of a double sprocket 38 which is fixed to the output 
shaft 40 of the gearbox 36. The double sprocket 38 is connected via a 
chain 42 to a sprocket 44 of larger diameter. A sprocket 46 is fixed to 
rotate with the sprocket 44. This arrangement of sprockets provides a 
speed reduction from the double sprocket 38 to the sprocket 46. A chain 48 
connects the sprocket 46 to the sprocket 28 to cause clockwise rotation of 
the sprocket 28, as viewed in FIG. 1, in order to cause reciprocation of 
the plunger 20 in a fore-and-aft direction in the bale case 12. 
A feed chamber 50 is mounted underneath the bale case 12 and includes a 
curved duct 52 having top and bottom walls 54 and 56, respectively, and 
sidewalls. The top wall 54 is formed of a series of curved channel 
members, of inverted generally U-shaped cross-section, which are arranged 
side-by-side so that there are slots defined between adjacent channel 
members. The bottom wall 56 is formed primarily of a single curved, 
continuous panel member. The curved duct 52 is open at its lower end 58 
and at its upper end 60 and communicates at its upper end 60 with an inlet 
opening formed in the bottom wall of the bale case 12. A pickup device 62 
of a conventional type is pivotally connected at 64 to the feed chamber 50 
and is supported by wheels 66. The pickup device 62 includes a plurality 
of fingers 68 which are rotatable in the direction indicated in FIG. 1 for 
lifting crop material from the ground and delivering it toward the feed 
chamber 50. 
A feeder mechanism 70 is provided in the feed chamber 50 for moving crop 
material toward the lower end 58 of the duct 52, then through the duct 52 
from its lower end 58 to its upper end 60, and then into the bale case 12 
through the inlet opening in the bottom wall thereof. The feeder mechanism 
70 includes two sets of feeder elements or tines 72,74 arranged to project 
through the slots in the top wall 54 of the duct 52. 
The double sprocket 38 is connected to a sprocket 76 mounted on the side of 
the bale case 12 by a chain 78 in a backwrap manner to cause rotation of 
the sprocket 76 in a counterclockwise direction as indicated. The chain 78 
also extends around idlers 80. Another sprocket 82 fixed to rotate with 
the sprocket 76 is connected by a chain 84 to a sprocket 86 to cause 
counterclockwise rotation of the sprocket 86 and thus operation of the 
feeder mechanism 70. A belt 88 extends around a sheave 90 that is 
connected to the sprocket 86 in a backwrap manner and around another 
sheave 92 on the pickup device 62 to rotate the sheave 92 in a clockwise 
direction and thus operate the pickup device 62. The belt 88 also extends 
around idlers 94, the forward one of which is preferably spring loaded to 
allow vertical movement of the pickup device 62 and to allow the belt 88 
to slip if the pickup device 62 is overloaded. 
The baler 10 includes a system for tying several strands of twine around a 
completed bale. This system includes a plurality of conventional knotters 
96 (two of which are partially shown in phantom in FIG. 3) mounted above 
the bale case 12. The knotters 96 are driven by a shaft 98 on which a 
sprocket 100 is rotated. A chain 102 extends around the sprocket 100 and 
another sprocket 104 that is connected to rotate with the sprockets 76 and 
82. The various sprockets are sized so that the sprocket 100 rotates twice 
as fast as the sprocket 28. Accordingly, the knotters 96 and needles 110, 
when actuated as explained later, advantageously will be driven at twice 
the speed of the plunger crank arm 24. A yoke 106 is pivoted on stub 
shafts 108 carried on the sides of the bale case 12. The yoke 106 carries 
a plurality of twine needles 110 for delivering strands of twine to the 
knotter 96 which form knots therein. As also seen in FIGS. 2 and 3, a link 
112 is pivotally connected at one end to a crank arm 114 by a pin 116. The 
crank arm 114 is clamped to the shaft 98 by a bolt 118. The other end of 
the link 112 is pivotally connected by a pin 120 to a bracket 121 carried 
on the yoke 106. A tripping device for actuating the tying system includes 
a star wheel 122 fixed on a shaft 124 that is rotatably supported in 
brackets 126 mounted on the upper corner rails 127 of the bale case 12. 
The tripping device also includes an arm member 128 operatively coupled to 
the shaft 124 in a conventional manner, such as disclosed in U.S. Pat. No. 
2,897,748. 
Referring now to FIGS. 2 and 3, it will be seen that the arm member 128 has 
a plate 130 pivoted thereto at its forward end by a pin 129. The plate 130 
is pivoted on a pin 132 carried on a frame member 133 of the bale case 12. 
A spring 134 is connected between the arm member 128 and a transverse beam 
135 on the bale case 12 to urge the arm member 128 in a forward direction 
relative to the bale case 12. A ramp 136 is pivoted at one end on a pin 
138 on the side of the bale case 12, and a roller 140 carried by the 
plunger 20 is positioned to roll underneath the lower surface of the ramp 
136. A rod 142 is connected at its lower end to the ramp 136 and at its 
upper end to one arm of a bell crank lever 144 fulcrumed at 146 to the 
side of the bale case 12. A link 148 extends between the other arm of the 
bell crank lever 144 and a further link 150, which is pivoted by a pin 152 
to a support 154 on the bale case 12. A spring 156 is connected between 
the further link 150 and a vertical beam 162 for urging the further link 
150 in a clockwise direction around the pin 152 as seen in FIG. 2. As best 
can be observed in FIG. 3, the shaft 98 is rotatably supported at its ends 
in bearings 164, 166 carried by brackets 168, 170. Bracket 168 is secured 
to a beam 171 extending between the transverse beam 135 and another 
transverse beam 158 on the bale case 12, and bracket 170 is secured to the 
bale case corner rail 127. 
Referring to FIG. 4, a hub 172 shown in cross-section is bolted to the 
sprocket 100 (not shown in FIG. 4). The hub 172 has a cam lobe 174 welded 
to its inner surface, and the hub 172 is rotated in the direction 
indicated by the arrow 176. A disk 178 is keyed to the shaft 98 behind the 
hub 172 as also seen in FIG. 3. A pawl assembly 180 is pivoted at 182 on 
the disk 178, and carries a roller 184 at one end for engagement with the 
cam lobe 174 on the hub 172. The end of the pawl assembly 180 opposite the 
roller 184 is formed with a tab 186. A spring 188 is connected between the 
pawl assembly 180 and the disk 178 to urge the pawl assembly 180 in a 
counter-clockwise direction about pivot 182 as viewed in FIG. 4. The plate 
130 carries a first trip means, hereinafter referred to as the tab 190 
disposed to engage the tab 186 on the pawl assembly 180. The link 150 is 
extended with a second trip means, called the tab 192, also for engagement 
with the pawl assembly tab 186. A locking means in the form of an extended 
arm 194 welded or otherwise secured to the plate 130 is operable, under 
certain operating conditions which will be described later, to engage the 
link 150 for maintaining the tab 192 in abutment with the pawl assembly 
tab 186. 
In operating the baler 10, crop material is delivered into the bale case 12 
by the feeder mechanism 70 where it is then compressed into bales by the 
plunger 20. While a bale is being formed, the arm 128 is in the position 
shown in FIGS. 2 and 4 so that the tab 190 thereon is located in a pawl 
assembly holding position, engaging the tab 186 on the pawl assembly 180. 
By the same token, the arm 194 locks the tab 192 in the position as shown 
in FIGS. 4 equally in engagement with the pawl assembly tab 186. The pawl 
assembly 180 is thereby held in a drive interrupting position where the 
roller 184 is out of the path of movement of the cam lobe 174 on the hub 
172 which is constantly rotated with the sprocket 100 in the direction 
indicated by the arrow 176. Therefore, the disk 178 and the shaft 98 are 
stationary and the knotters 96 are idle for the time being. Meanwhile, the 
reciprocating movement of the plunger 20 in the bale case 12 causes the 
roller 140 to roll back and forth underneath the lower surface of the ramp 
136. It will be observed that the connecting structure between the ramp 
136 and the tab 192, being the rod 142, the bell crank 144 and the links 
148, 150, are dimensioned in a manner such that the ramp 136 is out of the 
path of movement of the reciprocating roller 140 when the tab 192 is 
locked in the position as shown in FIGS. 2 and 4. In other words, although 
the roller 140 of the reciprocating plunger 20 is constantly moved 
underneath the ramp 136, the latter remains stationary for as long as the 
pawl assembly 180 is held in its drive interrupting position. 
When a bale has reached the desired length, the starwheel 122 and the shaft 
124 will have rotated far enough to cause the arm 128 to be pivoted 
upwardly about the pin 129 to a point where a slot 131, that is defined 
between the end of the arm 128 and a bracket 137 which is attached 
thereto, receives the shaft 124. The arm 128 is then moved forwardly with 
respect to the bale case 12 by the spring 134 thereby resulting in 
rotation of the plate 130 about the pin 132 to a pawl assembly releasing 
position shown in FIG. 5 where the tab 190 on the plate 130 is out of 
engagement with the tab 186 on the pawl assembly 180. This tripping action 
most frequently occurs when the baler plunger 20 is approaching its 
maximum compaction position as at this point in the cycle an additional 
charge of crop material is added to the bale under formation whereafter 
the desired bale length is obtained. Occasionally however, this tripping 
action equally may occur at any other point of the reciprocating cycle of 
the plunger 20 and is then caused e.g. by machine vibrations. In any 
event, it will be appreciated that rotation of the plate 130 around the 
pin 132 equally will procure rotation of the arm 194 therearound as the 
arm 194 is firmly connected to the plate 130. Consequently, the link 150 
carrying the tab 192 is permitted to rotate about the pin 152 under action 
of the spring 156, but not necessarily will do so under all operating 
positions of the plunger 20 as will be explained hereinafter. 
As already mentioned, it is generally known in the art that the knotter 
cycle of a baler should be tripped always at precisely the same point in 
the plunger cycle i.e. when the plunger is approaching its full compaction 
position. In conventional balers where the knotter drive shaft is rotated 
at the same rotational speed as the plunger, timing of the knotter 
operation with the plunger movement is quite simple. Yet, the baler 10 
presently under consideration is provided with a knotter shaft 98 driven 
at twice the rotational speed of the plunger crank shaft 26. That is, the 
knotters 96 and the needles 110 each make one complete knot tying cycle 
while the plunger 20 makes one-half of a complete stroke (i.e. 180.degree. 
rotation of the plunger crank arm 24), which is in contrast with prior art 
balers of which the knotters and needles make one complete knot tying 
cycle while the plunger makes a complete stroke (i.e. 360.degree. rotation 
of the plunger crank arm). As a result, the knotter tripping mechanism 
according to the invention should be synchronized with the plunger 
movement in order to ensure that the knot tying operation is carried out 
only when the plunger 20 is moving through the rearward half of its path. 
This timing requirement between the plunger movement and the knotter 
operation has necessitated the provision of the additional means according 
to the invention, which are an improvement in comparison with the 
embodiment depicted in U.S. Pat. No. 4,503,762. Said additional means are 
in the form of the structure comprising the roller 140 on the plunger 20, 
the ramp 136, the link 150 with the tab 192 thereon and the arm 194 on the 
plate 130. 
The hub 172 and the plunger 20 are synchronized in their respective 
movements in a manner such that, as the plunger 20 reaches its maximum 
compaction position, the leading edge of the cam lobe 174 just has moved 
past the roller 184. In case the tab 190 is tripped upon the plunger 20 
reaching said maximum compaction position, then the tab 192 equally will 
be tripped out of engagement with the pawl assembly tab 186 since the ramp 
136 is free to pivot downwardly under influence of the spring 156. Indeed, 
since the plunger 20 is located in its rearmost position, the roller 140 
thereon does not prevent downward rotation of the ramp 136. At this point 
in the cycle (i.e. when the plunger 20 is positioned in or close to its 
maximum compaction position) the link 150 with the tab 190 thereon is 
situated in the retracted position shown in phantom lines in FIG. 5. As 
both tabs 190, 192 are now freeing the tab 186, the pawl assembly 180 is 
pivoted in an anticlockwise direction around pivot 182 thus allowing the 
roller 184 to engage the inner surface of the cam lobe 174. Further 
rotation of the hub 172 in the direction 176 during the further movement 
of the plunger 20 allows the roller 184 to ride over the inner surface of 
the cam lobe 174 until it is allowed to "drop outwardly" and against the 
inner surface of the hub 172 behind the cam lobe 174. Consequently the 
roller 184 now is positioned in a drive engaging position i.e. in the path 
of movement of the cam lobe 174 as observed in phantom lines in FIG. 5. 
As the shaft 98 is driven at twice the rotational speed of the crank shaft 
26, the cam lobe 174 approaches the pawl assembly 180 already again as the 
plunger is approaching its fully retracted position. As explained 
hereabove, at this point in the cycle the knotter mechanism may not be 
actuated and this is guaranteed by the following. 
When the plunger 20 is moved forwardly in the bale case 12 in a subsequent 
retracting stroke towards the phantom position of FIG. 2, the roller 140 
pushes the ramp 136 upwardly about the pin 138. Caused thereby, the rod 
142 is pushed upwardly, effecting the bell crank 144 to pivot around its 
fulcrum 146 and pulling the link 148 forwardly with respect to the bale 
case 12. As such, the link 150 with the tab 192 thereon is returned to the 
full line position of FIG. 5. In so doing, the tab 192 again engages the 
pawl assembly tab 186 whereby the pawl assembly 180 is pivoted opposite to 
the force of the spring 188 in the clockwise direction around pivot 182 to 
the full line position of FIG. 5 whereby the pawl assembly 180 is pivoted 
out of the path of movement of the approaching cam lobe 174. It thus will 
be appreciated that while the plunger 20 is performing a retracting stroke 
in the bale case 12, the pawl assembly 180 always is prevented from 
coupling the continuously rotating hub 172 to the disk 178 since under 
those operating conditions of the plunger 20, the tab 192 forces the pawl 
assembly 180 from its drive engaging position towards its drive 
interrupting position. 
When the plunger 20 subsequently moves toward the end of its rearward or 
compacting stroke, the ramp 136 again is permitted to pivot downwardly, 
thereby pushing the link 150 to the pawl assembly releasing position 
abutting against the arm 194 as shown in FIG. 6 and moving the tab 192 on 
the link 150 out of engagement with the pawl assembly tab 186. The spring 
188 again urges the pawl assembly 180 to the position where the roller 184 
is in the path of movement of the cam lobe 174. As the plunger 20 is 
approaching its maximum compaction position, the cam lobe 174 is moved a 
second time towards the intercepting area with the roller 184. This time, 
the cam lobe 174 engages the roller 184 and remains in contact therewith 
for a full revolution of the disk 178. During this revolution of the disk 
178 and the shaft 98 supporting the latter the tying system is operated. 
That is, the needles 110 are moved through the bale case 12 to deliver 
twine to the knotters 96 which are driven to form knots in the twine. 
The disk 178 carries a cam track 196 which engages a roller 198 on the 
plate 130 as the disk 178 is rotated. This serves to reset the arm 128 to 
the position shown in FIG. 2 after one complete (360 degree) revolution of 
the disk 178. The tab 190 on the plate 130 is returned to the position 
shown in FIG. 4 so that it re-engages the tab 186 on the pawl assembly 
180. Concurrent therewith and by intermediary of the locking arm 194, the 
tab 190 equally is repositioned in its pawl assembly holding position. The 
pawl assembly 180 thus is returned to the position as seen in FIG. 4 
following a single revolution of the disk 178 and the shaft 98. 
As already discussed, it occasionally may happen that the tripping action 
of the tab 190 is not effected when the plunger 20 is close to its full 
compaction position, but equally could occur e.g. when the plunger 20 has 
only commenced its compaction stroke. In the latter case, the operating 
cycle of the knotter mechanism varies substantially from the one already 
depicted hereabove since actuation of the knotters 96 is not delayed any 
longer by the plunger cycle. Indeed, tripping of the tab 190 permits the 
tab 192 equally to trip as soon as the compressing plunger 20 has 
disengaged the ramp 136 whereby the pawl assembly roller 184 is permitted 
to move to the position shown in FIG. 6 i.e. ready to be intercepted by 
the cam lobe 174. Upon the plunger 20 approaching its full compaction 
position, the cam lobe 174 engages the roller 184 thereby coupling the hub 
172 to the disc 178 thereby initiating the tying operation. It accordingly 
will be understood that in the above situation the coupling between the 
cam lobe 174 and the pawl assembly roller 184 is effected immediately, 
without the hub 172 having to perform another full rotation as was the 
case with the first explained situation. 
To facilitate the disengagement of the pawl assembly roller 184 from the 
cam lobe 174, special attention has to be given to the finishing of the 
surface of the leading edge of the latter. In prior art balers the radius 
of curvature of said leading edge normally equals the radius of the pawl 
assembly roller for holding the latter firmly in engagement. Yet, during 
disengagement, this roller has to be pivoted tangentially out of the arc 
formed by the cam lobe leading edge. Accordingly, the roller is forced to 
roll over the inner edge of said arc, bringing a relative displacement 
about between the hub 172 and the disc 178; a displacement which has to be 
neutralized e.g. by strain in the chains in the knotter drive line. The 
leading edge of the cam lobe 174 according to the invention has been 
provided with a radius of curvature which is fairly larger than the radius 
of the roller 184 so that during disengagement of the two elements, the 
roller 184 smoothly can roll over the leading surface of the cam lobe 174 
and out of engagement therewith without creating the aforementioned 
relative displacement between the hub 172 and the disc 178. 
From what precedes it thus will be appreciated that the second trip means 
192 is held in a pawl assembly holding position for as long as the first 
trip means 190 engages the pawl assembly tab 186 and this by the 
intermediary of the locking means 194. In other words, the second trip 
means 192 is held stationary during the entire bale forming cycle even 
though the plunger 20 continuously is reciprocating in the bale case 12. 
Only under the combined condition of the first trip means 190 being 
tripped and the plunger 20 being located close to its maximum compression 
position, the second trip means 192 is allowed to assume a pawl assembly 
releasing position thereby initiating the tying operation. 
According to present invention, the second trip means 192, when pivoted 
from its pawl assembly holding position towards its pawl assembly 
releasing position, is initially moved substantially in the same direction 
as the tab 186 carried by the pawl assembly 180, when the latter is 
pivoted from its drive interrupting position towards its drive engaging 
position. This is in contrast with the prior art baler described in U.S. 
Pat. No. 4,503,762, of which the second trip means is pivotable in a 
generally perpendicular direction to the path of movement referred to 
hereabove of the pawl assembly tab 186. The foregoing prior art 
arrangement has necessitated the second trip means to be positioned a 
short distance past the first trip means when seen in the direction of 
rotation of the pawl assembly in order to allow the second trip means to 
move in front of the pawl assembly tab when the latter is released by the 
first trip means. A serious drawback results therefrom however in that 
upon tripping of the first trip means and while the plunger is performing 
a retracting stroke, the knotters and needles are actuated for a very 
short period of time immediately whereafter the coupling between the drive 
and the tying mechanism is disengaged again by the interference of the 
second trip means. It will be understood that this disengaging of the 
drive may be acceptable functionally on the one hand, but is 
energy-consuming and effects premature wear of components on the other 
hand. Indeed, energy is spent to set the tying mechanism in motion, not 
for a complete tying cycle, but only for a very short angular displacement 
whereafter the tying mechanism is completely halted again. Upon the 
plunger performing, a subsequent compaction stroke, the tying mechanism 
then has to be actuated for a second time, now effecting a full tying 
cycle. 
The arrangement according to the present invention has overcome the 
mentioned drawbacks by selecting a specific location of the pivot pin 152 
of the second trip means 192 and the pivot 182 of the pawl assembly 180 
with respect to the orientation of the abutment tab 186, respectively the 
second trip means 192. As already indicated, the abutment tab 186 is 
provided on the outer end of a pawl assembly crank arm 181. While the 
second trip means 192 engages the pawl assembly abutment tab 186 to hold 
the pawl assembly 180 in its drive interrupting position, the pawl 
assembly crank arm 181 is virtually aligned with the link 150. It will 
also be observed that under this operating condition of the pawl assembly 
180, the contact surface of the abutment tab 186 normally engaging the 
first and second trip means 190, 192 is oriented generally parallel to the 
connecting line between the pin 152 around which the link 150 pivots and 
the pivot 182 of the pawl assembly 180. To some extent, the same can be 
said about the tab 192 so that in effect, one could consider the second 
trip means 192 on the link 150 to be arranged 37 radially" with respect to 
the abutment tab 186 and the crank arm 181. Due to the foregoing 
configuration and when the tab 192 is pivoted to its pawl assembly 
releasing position allowing the pawl assembly to assume its drive engaging 
position, the tabs 186 and 192 initially are moved substantially in the 
same direction whereafter they flare outwardly with respect to each other 
in a manner comparable to the swinging movement of a double swing door as 
can be observed in FIG. 5. Upon the plunger 20 retracting in the bale case 
12, the link 150 carrying the tab 192 is pivoted in a counter-clockwise 
direction around pin 152, as already described, while contacting the tab 
186 and accordingly forcing the pawl assembly 180 back to its drive 
interrupting position as seen in FIG. 5. In other words, before the cam 
lobe 174 has reached the intercepting area with the pawl assembly roller 
184, the latter already has been swung completely out of the way 
permitting the cam lobe 174 to pass underneath without any contact being 
made. This contact is only effected during the subsequent compaction 
stroke of the plunger 20, whereby a full tying cycle is initiated. 
The present embodiment in this manner avoids a temporarily purposeless 
coupling being made between the knotter mechanism and its drive as was the 
case with the baler shown in U.S. Pat. No. 4,503,762. The present baler 
thus is substantially more energy-efficient and more durable in 
construction as the knotter components are less subjected to wear. 
Turning now to FIGS. 7, 8 and 9 of the drawings, an alternative embodiment 
is shown in which the connecting structure between the ramp 136 and the 
second trip means or tab 192 is modified in order to render the overall 
construction more compact. Also the first trip means and cooperating 
locking means have been altered substantially as will be described 
hereafter. The ramp 136 is extended with an upwardly directed rod 143 
which is pivotable in unison therewith around the pivot pin 138. A link 
149 is provided between the rod 143 and the lower end of a further link 
151, which carries the second trip means 192 at its upper end for 
engagement with the pawl assembly tab 186. The further link 151 is 
pivotably attached to the bale case 12 by means of an intermediate pivot 
153. The second trip means 192 is urged towards its pawl assembly 
releasing position by a spring 157, which by the same token aims to swing 
the ramp 136 into the path of movement of the roller 140 on the 
reciprocating plunger 20. 
Referring more specifically to FIGS. 8 and 9, it will be observed that the 
plate 130, forming a link between the bale length metering means 122 and 
the pawl assembly 180, has been modified when compared to the first 
embodiment to the extent that no tab is provided thereon any longer for 
directly engaging the pawl assembly tab 186. Instead, a tab 193 firmly 
secured to the 10 plate 130, has taken over the function of as well the 
tab 190 as the locking arm 194 of the first embodiment. In as much as said 
tab 190 and said arm 194 were rigidly connected to each other by the 
intermediary of the plate 130, movement of the one element resulted in 
movement of the other element and vice versa. As a consequence, the pawl 
assembly 180 was held in its drive interrupting position directly by the 
tab 190 on the one hand, and indirectly by the locking arm 194 through the 
tab 192 on the other hand. Also, upon the tab 190 being tripped, the 
locking arm 194 equally was withdrawn from the tab 192, taking no part any 
longer in the actual tripping of the tying mechanism. The alternative 
embodiment now proposes to provide the tab 193 on the plate 130 in a 
manner such that the back side of the tab 192 is engageable by the tab 193 
for controlling on the one hand, the position of the tab 192, and, on the 
other hand, the position of the pawl assembly 180 via said tab 192. In 
FIG. 8, the arrangement is shown in its idle position before any tripping 
has occurred while FIG. 9 depicts the pawl assembly 180 in a condition 
ready to drive the tying mechanism. In essence, the working principle of 
the alternative arrangement is identical to the one already described in 
connection with the first embodiment and therefore will not be repeated 
here. 
It will be appreciated that in the alternative embodiment, the overall 
number of elements synchronizing the movement of the plunger with the 
tying mechanism has been reduced further in order to obviate the necessity 
of maintenance and readjustments. 
The foregoing description illustrates preferred embodiments of the 
invention. However, concepts employed may, based upon such description, be 
employed in other embodiments without departing from the scope of the 
invention. 
It, for example, will be apparent that the coupling mechanism between the 
plunger 20 and the tab 192 may be modified so that the second trip means 
192 is held stationary in the pawl assembly holding position until a 
complete bale has been formed The tripping of the tying mechanism by the 
conventional trip mechanism including the starwheel 122 and the components 
coupled thereto is neutralized unless the plunger 20 is located at or 
adjacent its full compaction position. 
The present invention may be used on a wire tie mechanism including wire 
twisters instead of knotter mechanisms.