Reducing rotational inertia in skinner machines

Abstract

For a skinner or flaying machine used by an operator, an emergency stopping time in response to proximity of a hand to the knife is decreased by reducing the rotational inertia of those components that are connected to the feeder roller. Operator safety is enhanced. The components connected to the stripper roller and driven by the same motor may be reversibly disconnected from the motor, or a different motor may be used to drive the stripper roller.

Description

[0001] Title: REDUCING ROTATIONAL INERTIA IN SKINNER MACHINES.

[0002] Background:

[0003] The invention relates to manually operated configurations of the machines known as “skinners” or as “flaying machines” used for processing parts of carcasses in meat or other flesh processing plants where they serve to separate layered parts of carcasses. In particular the invention relates to enhancement of safety measures initiated upon optical detection of an operator’ s coloured- gloved finger within a hazardous area near a blade under camera surveillance, or when a gloved and conductive finger in a conductive glove makes contact with the sharp blade; the enhancements being related to effecting an abrupt stop to feeder roller movement.

[0004] Definitions

[0005] A “freewheel clutch” is also known (among further names) as a sprag clutch, one-way clutch or an over-running clutch. Freewheel is the selected manufacturer’s preferred term.

[0006] A “stopped response time” is the time taken for the skinner machine to recognise a danger to the operator and then bring the feeder roller to a halt. This machine uses no physical friction brake.

[0007] “Pulley” describes a driving or driven wheel linked by a belt. Some pulleys in this description may be replaced by sprocket wheels linked by chains, or intermeshed cog wheels.

[0008] Prior Art

[0009] The Applicants describe a skinner or derinder including an optical safety protection apparatus in PCT / NZ2020 / 050142 (herein ‘142). The present invention uses a variation of the Applicant’s imaging optical sensing systems adapted to detect an operator's hand close to, even in dangerous proximity to a bandsaw blade, as in WO2017196187A1 by at least one camera that looks down on to the bandsaw table, and causes the bandsaw blade to be stopped within 20 milliseconds. Bergman et al (US 2008 / 0079590) describes protection for an operator when using a skinner. A processor determines the position of a physical sensor, worn on the operator’s body, that senses generated fields and carries an output to the processor. A magnetic field, generated sequentially in several dimensions, is preferred. The position of the sensor in relation to a hazard; in particular a skinner knife, is calculated. An alarm may be sounded and the skinner machine is slowed or stopped. ‘590 describes a sensor not using an imaging optical sensing system, nor is the sensor described as being sensitive to electrical contact.

[0010] Technical Problem to be Solved.

[0011] As the stopped response time tends to zero, the motor power rating required to bring a rotating mass to a stopped halt (which can be regarded as a powered deceleration) for the purpose of better operator protection increases. Yet a practical motor would have a power rating of under 3 kW; typically 1.6 kW. Reduction of rotational inertia of the parts that must be brought to a stopped halt is desirable to provide a desired response time, given a practical limit to motor power. A servo motor is preferred because at the time of filing other types of electric motor such as the internally braked induction motor do not have a sufficiently fast response.

[0012] Constraints.

[0013] It is believed that any solution should retain the original configuration of the skinner, and should not require the operator to take special steps. Intrinsic also to the Applicant’s earlier citation is the use of standard glove materials as variously coloured latex. Since some operators have been trained with, and have trust in conductive gloves as the sensing means, the solution should be compatible with conductive gloves that may also be coloured.

[0014] The skinner machine as described does not use a physical brake.

[0015] Statement of Invention.

[0016] In a first broad aspect the invention provides a skinner machine having a fixed blade for skinning an article placed upon a feeder roller by an operator and carried toward the blade, a first drive motor connected through a drive path in order to, when in use, rotate a set of rotatable driven components, the skinner machine also having an operator safety protection apparatus including at least one sensor capable in use of detecting the operator’s hand in relation to a defined hazardous proximity zone about the fixed blade; the operator safety protection apparatus then creating and sending a SIGNAL to an actuator in order to bring the feeder roller to a stopped halt wherein the set includes (A) a first group of rotatable components having a first rotational inertia and including the motor and the feeder roller, (B) a second group of rotatable components having a second rotational inertia and including a stripper roller, and (C) a reversible disengagement apparatus capable, when in use, of decoupling the first group from the second group, so that a torque derived from rotational inertia within the second coupled group will be disconnected from the motor if the motor is commanded to stop.

[0017] Preferably the first group includes the first drive motor, a rotatable distribution shaft driven by the motor, a first pulley, a first belt, a first belt tensioning pulley, a feed roller pulley and the feeder roller together having a first rotational inertia; all of which rotate as one unit.

[0018] Preferably the second group includes the second pulley, a second belt, a second belt tensioning pulley, a feeder roller pulley and a stripper roller; said second subgroup having a second rotational inertia, and the invention includes a reversible disengagement apparatus capable of rapidly disengaging the first group from the second group.

[0019] In one option, the first drive motor of the skinner machine is a servo motor and the SIGNAL is carried to a connected servo motor controller for use as a stop signal; the motor controller thereby serving as a first actuator to cause the first group to stop within a stopped response time following detection of the hand during which time the reversible disengagement apparatus decouples the first group from the second group so that, when in use, the torque derived from rotational inertia within the second group does not tend to maintain rotation of the servo motor.

[0020] Preferably the first drive motor of the skinner machine is coupled to a rotatable distribution shaft carrying a first pulley coupled with a first belt to the feeder roller and carrying a second pulley coupled to a stripper roller; the shaft also carrying a first reversible disengagement apparatus of the type known as a freewheel clutch, also known as a one-way clutch or as an over-running clutch, is built into a hub of the second pulley situated on the rotatable distribution shaft and disposed in order to disconnect the second pulley and associated components from the rotatable distribution shaft whenever the second pulley is rotating more quickly than the rotatable distribution shaft, thereby reversibly isolating the rotational inertia of the second group associated with the second pulley from the first drive motor.

[0021] In an alternative aspect, a second reversible disengagement apparatus of the skinner machine is disposed between the second pulley and the stripper roller and comprises a moveable belt tensioning pulley and a second actuator capable when in use of moving the tensioning pulley from a first or normal operating position, in which the pulley applies a tensioning contact with the second belt, to a second disengaged position in which the tensioning pulley does not apply a tensioning contact with the second belt; whereupon loss of tension in the belt causes a loss of frictional grip between the second belt and the second pulley, thereby disconnecting the second group rom the first group.

[0022] Note that in this option the second pulley becomes part of the first group.

[0023] Preferably the second actuator and the first actuator are activated at the same time.

[0024] In a second broad aspect, at least one of the stripper roller and the feeder roller is constructed to have a reduced rotational inertia as compared to that of a solid cylindrical roller comprised of a stainless-steel alloy by a process selected from the following range: use of a material having a lower density, construction of the roller in the form of a hollow cylinder, filling that hollow cylinder with a stiff material having a lower mean density, and removal of material from an interior of the roller with a tool during manufacture , thereby reducing rotational inertia associated with the second group and thereby allowing the controller for the servo motor to halt the motor in a given time with less power.

[0025] Optionally, a radial array of bored holes may be drilled within the wall and along a length of the roller after the cylinder surface has been machined.

[0026] Alternatively, hollow rollers may be formed by spin casting within a mould.

[0027] Optionally, the hollow interior of the cylinder may receive a stiffening filling of a plastics, carbon, or light metal, sealed in place inside the roller.

[0028] In a third broad aspect, the stripping roller is connected to a separate second motor, thereby disconnecting the second group from the first group.

[0029] NOTICES:

[0030] Reference numerals, including those appearing in the Summary of Invention, are provided for clarification only and are not intended to restrict the scope of the invention to the particular embodiments of the components in conjunction with which the reference numerals are used. Throughout this specification unless the text requires otherwise, the word "comprise" and variations such as "comprising" or "comprises" will be understood to imply the inclusion of a stated integer or step or group of integers or steps but not the exclusion of any other integer or step or group of integers or steps. Each document, reference, patent application or patent cited in this text is expressly incorporated herein in their entirety by reference. Reference to cited material or information cited in the text should not be understood as a concession that the material or information was part of the common general knowledge or was known in New Zealand or in any other country.

[0031] Figures

[0032] Fig 1: Oblique midline section through a portion of a complete skinner (Prior art ‘142) Fig 2: Cross section of a modified roller.

[0033] Fig 3. Block diagram showing principal components.

[0034] Fig 4: Oblique side view of the skinner, showing the motor, rotatable distribution shaft, and belt drives to rollers.

[0035] Fig 5: Elevation side view showing belt drives to the roller.

[0036] Fig 6: Altered portion of Fig 5, showing a stripper roller belt drive disengagement device.

[0037] Introduction

[0038] The inventors have taken several steps to reduce the rotational inertia of the stripper, including separating the group including the feeder roller and motor from the group including the stripper roller and reducing the rotating mass.

[0039] Fig 1 (from ‘142 ) shows the overall layout as an oblique view 100 of a cross-sectioned skinner of the type to which this document is directed. The skinner provides an operator (standing to the left beyond 101) with a top working surface or operating area 102, a horizontal feeder roller 103 to the rear of that surface, behind which is a fixed knife 105. The exposed upper surface of the feeder roller is detailed in order to engage with an underneath surface of an item. In use, the operator presses by hand a carcass portion or item against the feeder roller which steadily turns clockwise (with reference to this diagram) and draws the item to be skinned toward the rear knife 105.

[0040] A skinner machine is usually optimised to remove a thin layer perhaps 1 mm thick at each pass of the piece, by mounting the knife close to the surface of the feeder roller. Example: removal of the skin and fascia covering the muscle of a bovine tongue. The fixed horizontal knife 105, parallel to and close to the feeder roller, will cut the item apart along planes of relative weakness. The upper cut part becomes the useful product. The lower part comprises unwanted layers such as fascia which are drawn beyond the knife 105, around the feeder roller 103 and are removed from roller 103 by the stripper roller 104 which turns typically about 4 times faster and consigns the unwanted material to a disposal bin. Both rollers are conveniently driven by the same motor. The feeder roller surface moves at typically 700 mm per second.

[0041] A derinder is a similar machine having a similar mode of operation, but in contrast is able to remove a much thicker layer, although a skinner may be modified to work as a derinder. A derinder does not employ a stripper roller, instead using fixed metal fingers to dislodge material from underneath the feeder roller 103 which may have circumferential grooves to fit ends of the fingers.

[0042] Operator risk arises because the operator holds the carcass portion to be skinned with his or her gloved hands. Hands are at some risk of being inadvertently fed on to the knife 105 by rotation of the feeder roller, or the gloves may be caught against the roller. For safety protection, the operator wears the usual blue (or another colour, such as green) latex gloves, allowing detection by the optical warning system. The operator may prefer that the gloves are also conductive, which is a well-known sensing method. In that case apparatus is provided with connections to detect a change of current if any part of the glove touches the blade in particular, or any other part of the machine and to send a SIGNAL to the motor controller, as secondary protection.

[0043] This document is not limited to skinners using optical glove-sensing apparatus. Nor is it limited to skinners using servo-controlled motors.

[0044] Rotational inertia in a skinner of the type described resides in a set of rotatable parts, treated as two groups.

[0045] Group 1. Motor 304 shaft, drive belt 503 to the pulley 504 on the distribution and clutch shaft 305 and 20-tooth reduction pulley 306, belt tensioner pulley 505, and toothed belt 404a to the feeder roller, and the feeder roller 103 itself.

[0046] Group 2. Stripper roller drive pulley 307 on the distribution and clutch shaft 305, pulley (405c) on the stripper roller shaft, stripping roller 104, drive belt 405a, and tensioner pulley or wheel 405d. In the prototype, the stripping roller 104 is rotated about 3.6 times faster than the feed roller. A reversible disengagement apparatus 309 may separate the components of Group 2 from those of Group 1.

[0047] (Note that the stripper roller drive pulley 307 becomes part of Group 1 in Example 2 below.)

[0048] The inventors believe that completion of a stopped halt for a skinner starting from hand proximity detection should be within the range of 5 to 20 milliseconds. A fast response is particularly desirable if electric glove conduction is used, because the glove and the fixed blade have already made contact. Optical detection allows the stopped halt a freedom to take longer.

[0049] Example 1.

[0050] Hand 301 is shown in a proximity to the blade of knife 105. 301a is an information path: the view of the hazardous volume about the blade, presented to the optical warning system 302 which surveils a volume in proximity to the knife blade along the length of the knife. 301a may also represent an electrical contact between a conductive glove on the hand 301 and the knife. Both forms of sensing may be co-enabled. Whether or not that presence is a hazardous proximity is evaluated by controller 302.

[0051] For the preferred servo-motor option, the servo-motor controller drawn within the motor block 304 is activated by a SIGNAL transmitted in line 303 in order to stop the motor 304. That motor is a relatively powerful servo motor as described in PCT / NZ2020 / 050142. The related Ethernet- compatible motor controller can actively bring rotation to a halt in 10-15 milliseconds of receiving the SIGNAL. A preferred motor is an AM8052-3F10 servomotor having a power rating of 1.6 kW. (Manufacturer: Beckhoff, Germany. Beckhoff also supplies the motor controller). Driven axle 305 carries a pulley 306 for a belt drive to feeder roller 103 and a second pulley 307 for a belt drive to the stripper roller 304.

[0052] Block 309 of Fig 3 represents a freewheel clutch orientated in order to drive the second pulley if the drive axle 305 is turning faster than pulley 307, allowing the pulley 307 to coast to a halt without significant drag if the drive axle 305 is slowed or stopped by a SIGNAL within 303. No external control for that type of clutch is required, and its action is immediate.

[0053] A preferred clutch is the “combined bearing freewheel” product Stieber CSK30PP (Stieber; Munich, DE) which has a key way on both the inner and the outer races. The freewheel clutch is installed to allow pulley 307 to turn freely over a slower-turning distribution and clutch shaft thereby isolating the Group 2 (as listed above) components if the shaft 305 stops. The site of the clutch is indicated in Fig 4 at 309, upon the distribution and clutch shaft, between the hub of the pulley 307 and the shaft 305. Pulley 307 is partly supported on the clutch which has an external form resembling that of a roller or ball bearing. A conventional bearing (not shown) is also used to support the pulley 307 when the clutch is not engaged.

[0054] During a stopped halt, the stripping roller and associated components of Group 2, which are in any case concealed from the operator, freewheel about the clutch and coast to a stop in a few seconds. The clutch has the effect of preventing the rotational inertia of the stripper roller section (group 2) from tending to maintain rotation of the stopping servo motor which is part of Group 1.

[0055] No physical brake device is included.

[0056] Fig 4 is an oblique side view of a prototype skinner drive. A shaft 402 turned by servo-motor 304 drives a first reduction belt drive with pulley 403 connected to 80 tooth pulley 504 by toothed drive belt 503 in order to turn the distribution and clutch shaft 305 (end shown). That extra shaft is not shown in the schematic of Fig 3. A speed reduction of about 1:4 from the motor is obtained. Belt 503 has a resiliently mounted belt tensioning pulley 405.

[0057] Shaft 305 drives the feed roller 103 directly with belt 404a, using a 20 teeth pulley 306 (obscured in Fig 4). Shaft 305 is also fixed to the internal or drive ring of the clutch 309 (see above). The decouplable outer ring of that clutch is fixed to the pulley 307. 404a indicates the feeder roller drive belt driven by a small toothed pulley (obscured). Toothed belt 405a (such as type HTD- 8M-20W) is driven by a toothed pulley 307, and turns the stripping roller 104 for a speed increase of 3.64:1. The 80-toothed pulley 307 drives the stripper roller pulley 504 having 22 teeth. Part 407 is a mounting plate.

[0058] Fig 5 is an elevation view of an interior of a prototype skinner from the left side with respect to the operator, showing the belt drives. Plate 407 supports a bearing for the distribution and clutch shaft 305. In Fig 5, the 80-tooth pulley 307 for the stripper roller conceals the attached clutch 309 and conceals the drive pulley 306 for the feeder roller. The belt 405a drives the stripper roller on pulley 504. Belt tension is maintained by resiliently mounted idler pulley or wheel 501. The belt that drives the feeder roller is 404a; it passes around a tensioning idler wheel 505 and around a pulley 503 attached to an end of the feeder roller 103 (not identified here). Each idler wheel 501, 505 uses a presettable spring tensioning device 502. Example 2.

[0059] See Figs 3 and 6. The dashed line 308 actively controls a solenoid 601 when the controller performs a sudden or stopped halt. Fig 6 is a diagram taken from part of Fig 5 showing the solenoid. When energised, the armature 602 pulls the idler wheel 501 that maintains tension in the stripper roller belt 405a away from the belt so that the belt can slip against the pulleys, acting as a clutch. Outline 501 indicates the belt tensioning pulley position when extended and applying tension; 501a indicates a retracted position for the belt tensioning pulley as dashed lines when the solenoid is activated and tension is thereby removed from the belt. The armature 602 is attached to a movable mount, sliding within a frame and supporting the idler wheel. A spring for maintaining belt tension during normal use is not shown. For this option, the pulleys are preferably not toothed. An effect of unexpected lubrication of the non-toothed gripping surfaces during use by contaminants from the items being skinned has not been explored.

[0060] In an alternative configuration, the solenoid is always energised when tension is applied to the belt during normal use. During a stopped halt the solenoid current is cut so that the armature moves to disengage the idler wheel 501 with assistance from the spring and belt tension.

[0061] Example 3.

[0062] See Fig 2. Steps taken during manufacture of the stripper roller in particular reduce its rotational inertia. Prior-art rollers are solid cylinders of a selected stainless steel alloy typically grade 316 stainless steel, and may be 500 mm long and 70 mm in diameter, plus axles, and with machined outer walls for providing an engaging or gripping surface of the formed surface ridges. Feeder and stripping roller positions are controlled in a skinner in order that the rollers closely pass each other at a “stripping site”, and pass the fixed knife with a clearance of perhaps 0.1 mm. In this invention the stripper roller material may be replaced by 17-4PH castings for increased hardness, though having a similar mass.

[0063] An Example 3 stripper roller 103 is a hollow cylinder of unchanged external dimensions, with caps across each end for support by bearings. Preferably the same stainless alloy is used. The roller diameter is 68 mm. The wall thickness is indicated by the branched indicum 204. As shown in Fig 2, both ends of the hollow cylinder are machined (as at 202a) in order to accept a circular cap or adaptor that is a dilated part of an axle 202, 203. Axle 201 includes a key way for accepting the stripper roller drive pulley 504. After machining a selected material - for instance a thick- walled tube of type 316 stainless steel, the detailed wall section of the prototype stripping roller may have an about 8.6 mm thickness. The roller mass has been reduced to about one third of that of the solid version. It was found that even a thick-walled tube tended to flex during machining of the exterior profile, and therefore a tightly fitting, stiff insert can be used to temporarily increase stiffness, or to provide a lighter, yet stiff core for the roller during use. The stiff insert may comprise a plastics, carbon, or light metal rod, sealed in place at each end of the roller, or a strong metal including a stainless steel, formed into a stiff skeleton.

[0064] Alternatively, a cylinder that received a machined surface when solid may have internal material removed longitudinally under the surface using a long twist drill or a similar tool.

[0065] A stripper roller may be spin-cast inside a mould having an internal impression of the desired ridges. The surface detail may be finished to the required tolerance by subsequent precise machining. Use of SAE Type 630 stainless steel (more commonly known as 17-4 PH; also known as UNS S 17400) material for castings would provide an increased hardness for the roller surface.

[0066] At this time, stainless steel is thought to be incompatible with an extrusion process in which a circular orifice, provided with profile-forming teeth and an internal plug, could extrude lengths of straight stripper roller. A lighter material such as aluminium is well known to be extrudable in that way, but is presumably unable to meet food safety requirements even if the surface is treated for increased hardness. It may be useful to also reduce the mass of the slower-turning feeder roller in a similar way.

[0067] Example 4.

[0068] The stripper roller is driven by a second motor so that the stripper roller and the feeder roller are separate systems. As a result, the components of Group 2 are never connected with those of Group 1. The time taken to stop the concealed stripper roller does not affect operator safety. The Applicants had thought it preferable but not essential to use only one motor, for reasons of simplicity, cost, and power requirements. Example 4 is not illustrated. Advantages: Advantages of the various modifications described include that the desired duration of the stopped halt in particular relation to the feeder roller is reduced to under 20 ms, yet without use of an unduly powerful option for the servo motor.

[0069] There is less risk that the rotor of the servo motor will escape from servo control during stopping. That contributes to the objective of avoiding injury to the operator’s hand. An advantage of the freewheel clutch option is that no active control is required.

[0070] Finally it will be understood that the scope of this invention as described and / or illustrated herein is not limited to the specified embodiments. Those of skill will appreciate that various modifications, additions, known equivalents, and substitutions are possible without departing from the scope of the invention as set forth in the following claims.

Claims

We Claim1. A skinner machine having a fixed blade for skinning an article placed by an operator upon a feeder roller and carried toward the blade, a first drive motor connected through a drive path in order to, when in use, rotate a set of rotatable driven components, the skinner machine also having an operator safety protection apparatus including at least one sensor capable in use of detecting the operator’s hand in relation to a defined hazardous proximity zone about the fixed blade; the operator safety protection apparatus then creating and sending a SIGNAL to an actuator in order to bring the feeder roller to a stopped halt characterised in that the set includes (A) a first coupled group having a first rotational inertia and including the motor and the feeder roller, (B) a second, independently coupled group having a second rotational inertia and including a stripper roller, and (C) reversible disengagement apparatus capable, when in use, of decoupling the first coupled group from the second coupled group, so that a torque derived from rotational inertia within the second coupled group will not be connected to the motor if the motor is commanded to decelerate to a stop.

2. The skinner machine of claim 1 characterised in that the first drive motor of the skinner machine is a servo motor and the SIGNAL is carried to a connected servo motor controller for use as a stop signal; the motor controller thereby serving as a first actuator to cause the first group to stop within a stopped response time following detection of the hand while the reversible disengagement apparatus decouples the first group from the second group so that, when in use, the torque derived from rotational inertia within the second group does not tend to maintain rotation of the servo motor.

3. The skinner machine of claim 1 characterised in that the first drive motor of the skinner machine is coupled to a rotatable distribution shaft carrying a first pulley coupled with a first belt to the feeder roller and carrying a second pulley coupled to a stripper roller; the shaft also carrying a first reversible disengagement apparatus of the type known as a freewheel clutch, also known as a one-way clutch or as an over-running clutch is built into a hub of the second pulley situated on the rotatable distribution shaft and disposed in order to disconnect the second pulley and associated components from the rotatable distribution shaft whenever the second pulley is rotating more quickly than the rotatable distributionshaft, thereby reversibly isolating the rotational inertia of the second group associated with the second pulley from the first drive motor.

4. The skinner machine of claim 1 characterised in that a second reversible disengagement apparatus of the skinner machine is disposed between the second pulley and the stripper roller and comprises a moveable belt tensioning pulley and a second actuator capable when in use of moving the tensioning pulley from a first or normal operating position, in which the pulley applies a tensioning contact with the second belt, to a second disengaged position in which the tensioning pulley does not apply a tensioning contact with the second belt; whereupon loss of tension in the belt causes a loss of frictional grip between the second belt and the second pulley, thereby disconnecting the second group from the first group.

5. The skinner machine of claim 4 characterised in that the second actuator and the first actuator are activated at the same time.

6. The skinner machine of claim 1 characterised in that at least one of the stripper roller and the feeder roller is constructed to have a reduced rotational inertia as compared to that of a solid cylindrical feed roller comprised of a stainless- steel alloy by a process selected from the following range: use of a material having a lower density, construction of the roller in the form of a hollow cylinder, replacement of that hollow interior of the cylinder with a stiff material having a lower mean density, and removal of material from an interior of the roller with a tool during manufacture, thereby reducing rotational inertia associated with the second group.

7. The skinner machine of claim 1 characterised in that the stripping roller is connected to a separate second motor, thereby separating rotational inertia associated with the second group from the first group.

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