Abstract:
A meat encasing machine has a looper horn, linking chain and conveyor which, prior to production, have home positions which are determined. A pulsed signal is generated as the looper horn rotates and is transmitted to an amplifier from an encoder on the servo motor for the looper horn and the conveyor. The output pulse signal is then reduced in frequency so that it can be read by a PLC. The PLC counts the pulses in the signal and can determine the relative position of the looper horn based on the count and can therefore minimize the rotation of the looper horn in the home position at the beginning of each new cycle.

Description:
This application is based upon the applicants&#39; provisional application Ser. No. 60/047,487 filed May 23, 1997. 
    
    
     BACKGROUND OF THE INVENTION 
     Meat encasing machines have a linker which uses a meat emulsion pump connected to a stuffing tube upon which a shirred casing is mounted. Meat emulsion is extruded from the stuffing tube into the casing and the filled casing is rotated by means of a chuck and delivered to a linker for creating a linked strand of sausages. The linked strand then passes through a rotating looping horn and loops of sausages from the strand are deposited on hooks of a conveyor located downstream from the horn. These conventional machines mechanically connect the operation of the horn and the conveyor to coordinate their respective functions. Special attention then must be given to coordinate the action of the pump with respect to the horn and the conveyor. 
     A cycle of the foregoing machine is completed as each &#34;stick&#34; of shirred casing is filled, and the pump is disengaged. The &#34;stopped&#34; portion of the horn needs to be assessed before a new cycle with a new shirred casing stick is implemented. While the down time between cycles is brief, in the order of 2 to 4 seconds or more of an 18 second cycle, this down time contributes to the inefficiency of the overall operation. 
     It is therefore a proposed object of this invention to reduce the down time between cycles in the operation of a sausage encasing machine. 
     It is a further object of the invention to simplify the operation of the pump clutch from cycle to cycle so as to reduce the down time between cycles. 
     SUMMARY OF THE INVENTION 
     The home position of the looper horn, linking chain and conveyor prior to production of a meat encasing machine are determined. A pulsed signal is generated as the looper horn rotates and is transmitted to an amplifier from an encoder on the servo motor for the looper horn and the conveyor. The output pulse signal is then reduced in frequency so that it can be read by a PLC. The PLC counts the pulses in the signal and can determine the relative position of the looper horn based on the count and can therefore minimize the rotation of the looper horn in the home position at the beginning of each new cycle. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is a schematic drawing of the components of a meat encasing machine of the prior art; 
     FIG. 2 is a schematic front elevational drawing of the looper horn of FIG. 3; 
     FIG. 3 is a schematic front elevational drawing of the looper horn of FIG. 1 showing variable positions thereof; and 
     FIG. 4 is a schematic drawing of the components of a meat encasing machine of this invention. 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
     While FIGS. 1 and 2 have been characterized as prior art, they actually only preceded in time the invention of FIG. 3 and 4, and are not deemed to be prior art in a 35 U.S.C. § 102 or 103 sense. 
     FIGS. 1 and 2 show a prior art machine of which the instant invention is an improvement. FIG. 1 is a diagram showing a linking machine 10, a looper 12, and a conveyor 14. As shown, the linker 10 includes a pair of pump metering gears 16 which are engaged or disengaged by a pump clutch 18. The pump motor 20 is used to drive the pump metering gears 16. The linker 10 also includes a twister 22 positioned upstream from the linking chains 24. The linking chains 24 are driven by a linker motor 26. As the links of meat product are linked by the linker 10, they are fed through a looper horn 28 which rotates in order to hang a predetermined number of links between a number of hooks 30 which are formed on the conveyor 14. As the horn 28 rotates, the conveyor moves so that the hooks 30 pick up a loop comprised of a predetermined number of links. 
     FIG. 1 also shows the system that controls the linker 10, the looper 12, and the conveyor 14. The looper 12 and conveyor 14 are both precisely controlled by a servo motor 32. Operatively coupled to the servo motor 32 is a servo encoder 34 which creates a quadrature feedback pulsed signal to the servo amplifier 36 which controls the operation of the servo motor 32. 
     The looper 12 includes a proximity sensor 38 which is operatively connected to a programmable logic controller (PLC) 40. The PLC 40 is also operatively connected to the pump clutch 18. 
     It is very important that the linking chains 24, looper 12, and conveyor 14 are precisely synchronized prior to production cycles. In order to set the correct positioning relationship between the linker chains 24 and the conveyor 14, a simple homing routine is performed. The linking chains 24 first jog at a predetermined slow constant velocity, while a photoelectric fixed field sensor waits to sense a butterfly (not shown) mounted on the linking chains 24. The butterfly elements are conventional (see U.S. Pat. No. 3,191,222, FIGS. 9 and 18). When a butterfly is sensed and passes by the sensor, a timer is started and eventually times out. When the timer times out, the linking chains are stopped with the intent of stopping a butterfly close to the twister chuck (not shown). The conveyor 14 also starts a homing routine after the linking chains 24 are finished homing. 
     FIG. 2 is a diagram of the looper 12. As shown, the looper horn 28 includes a stainless steel screw 42 which rotates along with the looper horn 28. At the beginning of the homing routine, the conveyor 14 jogs at a predetermined slow constant velocity while the sensor 38 waits to sense the passing of the stainless steel screw 42. When the screw 42 passes, a timer 41 is started and eventually times out. When the timer 41 times out, the conveyor 14 and looper horn 28 are stopped. One example of this routine is illustrated in FIG. 2. At the beginning of a cycle, the looper horn 28 must rotate around until the screw 42 encounters the proximity switch 38. This rotation is designated in FIG. 2 as the line &#34;1&#34;. The looper horn 28 must then rotate to the virtual home position which is designated in FIG. 2 as the line &#34;2&#34;. In the example shown in FIG. 2, the looper horn 28 must rotate almost two entire turns before reaching the virtual home position. 
     FIGS. 3 and 4 show an improved control system of the present invention. FIG. 3 is a diagram of the linker 10, looper 12, and conveyor 14 which are substantially the same as that shown in FIG. 1. However, the system shown in FIG. 3 homes and synchronizes the conveyor and looper in an improved manner. Like the system shown in FIG. 1, the looper 12 and conveyor 14 are driven by a servo motor 32 which includes a servo encoder 34 and a servo amplifier 36. Again, a quadrature pulsed signal created by the servo encoder 34 is fed back to the servo amplifier 32. 
     With the present invention, this pulsed signal is used by the PLC 40 to anticipate the looper horn 28. The feedback quadrature pulsed signal from the servo encoder 34 is preferably reduced in frequency to a level more usable by the PLC 40. To accomplish this, the servo amplifier divides the pulsed signal by eight and sends the signal to a divider 44 which divides the signal by four resulting in a pulsed signal having a frequency 1/32 of the frequency of the feedback signal from the servo encoder 34. This divided pulsed signal is then provided to the PLC 40 and used as follows. 
     FIG. 4 is a diagram of the looper horn 28 and is structurally similar to that shown in FIG. 2. As shown in FIG. 4, a stainless steel screw 42 is coupled to the looper horn 28 and is rotatable with the looper horn 28. Also shown is a stationary proximity switch 38 which defines a reference point. The proximity switch 38 is operatively connected to the PLC 40. When the stainless steel screw 42 passes the proximity switch 38, a counter is reset to 0. As the looper horn 28 rotates, the pulses from the divider 44 are counted by the PLC 40. In the preferred embodiment, one full rotation of the looper horn 28 results in 750 pulses being counted. Since the number of pulses per rotation are constant, by counting the number of pulses, the PLC 40 will always know the relative position of the looper horn 28. At the beginning of each cycle, the looper horn 28 can then be positioned to the virtual home position without first rotating past the proximity sensor 38 like the prior art system shown in FIGS. 1 and 2. 
     In the example shown in FIG. 4, the proximity switch 38 is shown at the relative location of 0 and 750 pulses. If the looper horn 28 is stopped at the end of a cycle at the position designated as &#34;1&#34;, the PLC 40 would have counted 50 pulses since the counter was zeroized when the screw 42 passed the proximity sensor 38. At the beginning of the next cycle, the PLC can bring the looper horn 28 to the virtual home position by rotating the looper horn until 625 more pulses are counted (in this example, the equivalent of 675 total pulses since the counter was zeroized). Note that the virtual home position is relative and therefore may be located at any other position. In the worst case scenario, the looper horn 28 would need to rotate slightly less than one full rotation before reaching the virtual home position. 
     In an alternative embodiment, the looper 12 is controlled such that upon reaching the end of a cycle, the looper horn 28 continues to rotate until it reaches the virtual home position or a predetermined position. In this way, at the beginning of the next cycle, the looper horn 28 will not have to be homed since it is already located at the virtual home position.