fig1 is a longitudinal sectional front view showing a first embodiment of the present invention , and in which a hopper - shaped charge port 11 is provided above a casing 1 , and discharge ports 13 , 14 with a partition 12 therebetween are provided . a pair of rotary shafts 21 , 22 are rotatably supported in the casing , and rotatable knives 23 , 24 and spacer rings 25a , 25b are respectively mounted on the rotary shafts in an alternate manner , thus forming a crushing section 2 . the rotational direction and frequency ( rpm ) of the rotary shafts 21 , 22 are independently changeable . a feed plate 3 is vertically disposed from the casing at a portion obliquely above the rotatable knife 23 , and a cutter 4 is also vertically disposed from the casing at a portion obliquely above the rotatable knife 24 but in an opposite direction . fig2 ( a ) and 2 ( b ) are developed views showing the feed plate 3 and the cutter 4 intersecting the rotatable knives 23 , 24 , and showing cutout portions 31 , 41 , through which the top end of the locus of each rotatable knife passes at the time of rotation of the knives . these cutout portions are provided along the full length of the knives in a comb - like manner as is shown by the line formed by the points l , m , n , p , q , r and s . fig1 and fig2 ( a ) both show a state of normal operation of the crusher , and in which an object m to be crushed such as municipal waste thrown into a charge port 11 is guided to a gap formed between the rotatable knife 23 rotating clockwise and the rotatable knife 24 rotating counterclockwise . the object m is bit and crushed or shredded shearingly into small pieces to be discharged from the discharge port 13 to the outside of the crusher . since the partition 12 is disposed between the two knives 23 , 24 , the crushed waste does not move toward the discharge port 14 but is delivered to the next step . with the lapse of a long operation time , however , abrasion of the rotatable knives 23 , 24 proceeds gradually to the extent of enlarging the gap between one rotatable knife and the counter spacer ring as shown in fig2 ( b ), whereby such waste as used tire 0 or vinyl chloride e , for example , is not shearingly shredded or crushed but merely bit between the two knives and sent out as it is . waste such as small cartridge cylinders may also pass through the gap without being sufficiently compressed or crushed because of the abraded and enlarged gap . even when the mentioned state of an enlarged gap is found , the waste can be shearingly crushed between the rotatable knives and the cutter just by setting clockwise the rotational direction of both rotary shafts 21 , 22 . at the same time when turning the end of the feed plate 3 upwardly to disengage the rotatable knife 23 from the cutout 31 and extending the feed plate 3 obliquely crossing the charge port as shown in fig3 so as to extend above the center portion of the two rotatable knives like a hood , relatively small waste to be crushed , such as a cartridge cylinder , a spray can , come in contact with the upper face of the feed plate 3 and slidingly drops to be bitten between the cutout portions 41 of the cutter 4 and the rotatable knife 24 , whereby the bitten waste is completely crushed and discharged without fail , thus solving the problem mentioned with reference to fig2 ( b ). in this respect , it is certain that not only the rotatable knives but also the cutter is exposed to the abrasion conditions , but the cutter 4 acts as a scraper during normal operation and suffers less from the abrasion , and therefore when comparing a gap t1 formed between the rotatable knives with a gap t2 formed between the rotatable knife and cutout portion , a large difference is found between the two gaps t1 , t2 , and this difference is increased all the more with the progress of abrasion , from which it is understood that the arrangement shown in fig3 provides a peculiar technical advantage . in the same manner , if any troublesome waste such as used a tire , vinyl bag , a fiber product like carpet or underwear , stick to or twine itself around the rotatable knives making it impossible to shearingly crush them , they are exactly crushed shearingly by the sharp edge of the cutter . furthermore , since the collection of classified waste has become prevalent recently to a certain extent as mentioned above , a desirable advantage may be expected , if the shape and nature of the waste are preliminarily acknowledged and the arrangement shown in fig3 is made to correspond to such shape and nature of the waste . fig4 shows a function of the invention performed when a highly rigid material such as steel balls which are impossible to crush is mixedly thrown in the crusher . in such a case , both rotary shafts 21 , 22 are rotated counterclockwise and the end of the feed plate 3 is turned downward so as to disengage the rotatable knife 23 from the cutout portion 31 in reverse arrangement from that shown in fig3 whereby the rigid material s is guided to the left side of the crusher while rolling over the top of the rotatable knives and drops down to be selectively discharged from the discharge port 14 after being classified by the partition 12 . as a result , it is now possible to protect the crusher against the problem caused by overload . in addition , the rigid material removed as mentioned above will no longer be delivered mixedly to the next process but is held to await a different disposal . fig5 shows a function of the invention which is required to be performed in the event that waste thrown into the crusher is caught by a portion such as the upper corners of the rotatable knives 23 , 24 beneath the charge port and retained during the normal operation shown in fig1 . in the state shown in fig5 when turning the feed plate 3 and the cutter 4 suddenly many times through a small angle toward the center of their rotary shafts , the retained waste is bumped off by the shocks from such sudden movements and drops down to the center portion of the engaging section to be finally crushed . fig6 shows a further function of the invention which is required to be performed when bulky waste such as a refrigerator , a washing machine or the like is longitudinally thrown in and the rotatable knives run idly . to meet this situation , it is desirable to have the feed plate suddenly vibrated to repeatedly generate shocks to one side of the bulky waste to deform it , then a part of the side near the bottom is drawn in to be easily dragged in with the cutting edge of the rotatable knives and finally crushed shearingly thereby . fig7 shows another embodiment which is an improvement of those shown in the foregoing fig1 to 6 , and in which a feed roller 37 is rotatably attached to a leg section 32 in order to perform more exactly the function described mainly with respect to fig6 . fig8 shows a further embodiment in which a feed roller 38 is rotatably attached , in place of the cutter 4 described with reference to fig1 to the casing side facing the feed plate 3 . in both of the foregoing second and third embodiments , the ability to bite bulky waste between the rotatable knives for shearing is further increased by providing projections on the periphery , so that those projections may push aside of the bulky waste toward the center portion . moreover in the case of the embodiment shown in fig8 the attached feed roller 38 serves as a scrapper in the same manner as mentioned in the foregoing first embodiment . when required , it is also preferable to rotatably attach another feed roller on the upper part so as to further increase the pushing and collapsing performance . for turning the feed plate 3 , one end thereof is attached with a pin 33 to the leg section 32 provided with a back plate as shown in fig1 and the other end makes use of the telescopic action of a cylinder 35 attached to the casing with a pin 34 . when telescopically moving the cylinder 35 , the feed plate 3 turns around a fulcrum pin 36 , thus the cylinder serves as an actuator . in the same manner , for turning the cutter 4 , the telescopic action of a cylinder 42 is utilized , thereby the cutter is permitted to turn around a fulcrum pin 43 . though rotational direction of the two rotary shafts can be changed in both the forward and backward directions , when establishing a program so as to be automatically changed by combining such rotational directions and actuation of the cylinder on certain conditions , it becomes possible to achieve sufficient maintenance and crushing efficiency by computer control . fig9 is a flow chart showing an outline of a control procedure for the embodiment shown in fig7 and on which requirements for initialization is shown as an example hereunder : optimum rotation frequency , position and movement of feed plate , and frequency of reverse rotation after stoppage due to overload for each classified waste ; condition of detection of foreign materials , frequency of reverse rotation , and position of feed plate ; based on the initial conditions mentioned above , controls for each section including emergency stop , oil quantity , oil temperature , oil filter , change in operating conditions , discharge conveyor , feed plate , feed roller can be set and executed . fig1 shows a flow chart with respect to the detection of mixed rigid material and separate discharge thereof as a representative control , and in which ps denotes a set output , ts denotes a set torque , vs denotes a set speed , pa denotes a real output , ta denotes a real torque , and va denotes a real speed . fig1 shows an example of such control , and in which detector section 5 of the crusher for detecting the rotation frequency r comprises hydraulic motors 28 , 29 for driving the rotary shafts of the crushing section , and axial piston pumps 53 , 54 attached to the hydraulic pressure section by way of oil pipes 51 , 52 . these pumps indicate the discharge quantity and discharge direction of oil in the form of inclinations ∠ θa , ∠ θb of an inclined plate in the pump . with an increasing discharge quantity , the rotation frequency of the hydraulic motors 28 , 29 is also increased , and turning θ ° from positive to negative results in reversal of the rotational direction . torque ta applied to the rotary shafts can be recognized by checking the differential pressures a , b from oil pressure indicators 55 , 56 attached to the oil pipes 51 , 52 . a potentiometer 57 attached to the fulcrum pin 36 detects the inclination angle of the feed plate 3 . holding pressure of the feed plate 3 is indicated by an oil pressure indicator 60 attached to an oil pipe 59 connected to the hydraulic cylinder 35 on the backside of the feed plate . detection of the cutter 4 is performed in the same manner as the feed plate . to operate a desired section according to instructions from the control section 6 , the mentioned drive motors 28 , 29 , connected to the axial piston pumps 53 , 54 by way of an oil pipe and the hydraulic cylinder 35 connected to a hydraulic pump 58 by way of an oil pipe , are driven . an example of a transmission sequence of actual drive instruction in the detecting section 5 and control section 6 is described hereinafter with reference to fig1 and 13 . ( 1 ) initialization is conducted before starting the operation of the crusher . generally , the initialization depends upon whether the material m to be crushed is bulky or not . when the material m is relatively bulky , an angle formed by inclination of the feed plate 3 is set to be large . on the other hand , when the material m is of relatively small bulk , the angle ∠ φ is set to be small so that the material m to be crushed may be guided to the crossover line of the two rotary shafts , i . e ., to the center portion during the crushing operation . ( 2 ) optimum workload w is selected among the levels classified from experience into several grades depending upon the performance of the drive motor for driving the rotary shafts , and the size , the material , the shape , the nature of the material m to be crushed including whether or not an explosive substance is mixed , though this step can be omitted so long as the conditions are fixed at all times . ( 3 ) reading of a real torque ta is performed by conversion from the differential pressures a , b of the oil pressure indicators 55 , 56 . ( 4 ) if the torque ta is larger than the allowable limit tm , it means occurrence of something abnormal , and a different process is needed . for example , it is preferred to shift the process to ( a ) shown in fig1 . ( 5 ) when the torque ta is within the limit , a desirable rotation frequency r is calculated from an express w = f ( ta , r ). high torque results in low rotation frequency , and low torque results in high rotation frequency . ( 6 ) reading of a rotation frequency ra is performed by conversion from the angles ∠ θa , ∠ θb of the inclined plates of the axial piston pumps 53 , 54 . when the inclined plates are neutral , θ ° is 0 and the rotary shafts 21 , 22 are not operated . under normal operation , if the clockwise direction is set to be positive , the counterclockwise direction becomes negative as a matter of course . since the rotation of the two rotary shafts is a uniform rotational motion in opposite direction from each other , ∠ θa =-∠ θb and usually | θ °| is constant . ( 7 ) real workload is obtained by substituting ta , ra into the mentioned expression of the optimum workload w . if the workload is smaller than the allowable minimum workload wm , it means the occurrence of something abnormal , and a different process is needed . thus the process is to be shifted to another flow chart ( b ). ( 8 ) if the workload is not smaller , ra is compared with the allowable minimum workload rm to inspect whether the workload is larger than rm . when the rotation frequency is so high as to be over the limit , there is a possibility of explosion during crushing , and therefore the rotation frequency is lowered at least to rm . and a signal is sent to the axial pamps 53 , 54 . ( 9 ) to ( 11 ) to achieve a maximum workload under normal operation , a signal for coinciding the real workload ra with r is sent to the axial pumps 53 , 54 . this cycle is repeated to continue a crushing operation with the best efficiency . in this connection , the flow sheet is fig1 ( a ) shows a process in the event of mixing some rigid substance impossible to be crushed such as steel ingot and possible to cause a problem with the machine if the operation is continued . ( 12 ) if the torque ta is over tm and an overload occurs , the inclinations , ∠ θa , ∠ θb becomes 0 , whereby the drive motors 28 , 29 stop and their rotation frequency becomes 0 . ( 13 ) a signal for increasing the differential pressure c in the oil pressure indicators 60 , 61 is sent to the hydraulic cylinder 35 . ( 14 ) the feed plate 3 turns around the support pin 36 until the angle ∠ φ formed with a horizontal plane becomes maximum ( perpendicular in this example ). ( 15 ) a signal for changing the angle of the inclined plate of the axial pump 53 is sent so that the two axial pumps 53 , 54 may both be inclined at the same negative angle . in other words , the two rotary shafts 21 , 22 rotate in the same direction ( clockwise , for example ) at the same speed , thereby removing the rigid material causing the overload . ( 16 ), ( 17 ) after conducting a reverse rotating for a predetermined time , the rotation mentioned in ( 15 ) is stopped and again started . this operation is repeated a predetermined number of times n ( three times , for example ). ( 18 ) to ( 21 ) after reading the rotation torque ta to acknowledge that ta is lower than tm , the process is returned to the flow chart in fig1 . in the example shown in fig1 ( b ), the waste to be crushed is so small as to escape from the crushing area thereby causing idle running , otherwise waste such as string or cloth twines itself around the rotatable knives without being shredded thereby also causing idle running and falling into a state of reduce the inclination φ formed with respect to the horizontal plane of the feed plate 3 to compensate the crushing center , whereby the crushing operation is changed so as to be performed between the shaft and the cutter . after overcoming the mentioned problem of deficient load , the process is returned to the flow shown in fig1 , the detailed description of which is omitted herein . the algorithm shown herein is just an example , and , as a matter of course , there are a number of other automatic control methods for various operations of maintaining optimum crushing conditions and necessary security by selecting several required input factors such as adjustment of other cutters , hopper level , holding pressure of feed plate , etc . the rotatable shafts are entirely formed of plate - like materials and it is preferable that , as shown in fig1 in the combination of the two rotatable knives , the rotatable shaft 23 is provided with a spiral projecting cutting edge 26 having a surface extending from the outer periphery toward the center on one side , while the rotatable shaft 24 is provided with a circular arc projecting cutting edge 27 having a surface extending from the outer periphery toward the center on two sides . the number of engagements of the mentioned projecting edges is a product of the number of each projecting cutting edge and rotation frequency if the two rotary shafts have been set to rotate at the same rotation frequency . however , if the rotation frequency of a pair of rotary shafts are set to be different from each other , then the number of engagements of the projecting cutting edges is a product of number of respective projecting edges and rotation frequency . accordingly , it is possible to use properly this relation of number of engagement depending upon whether crushing of a waste is easy or difficult . as various different embodiments of the invention may be made without departing rom the spirit and scope thereof , it is to be understood that the invention is not limited to th specific embodiments thereof except as defined in the appended claims .