EP 1 790 459 A22510152025303540455055DescriptionBACKGROUND OF THE INVENTION1. Field of the Invention?[0001] The present invention relates to an abnormalitydetecting apparatus for a mold clamping device in anelectric injection molding machine.2. Description of the Related Art?[0002] In an electric injection molding machine, themovable part of the injection molding machine is drivenby a motor. Typically, the torque of the motor is transmit-ted to the movable part of the injection molding machinethrough a belt transmission mechanism. Even in a moldclamping mechanism that uses a toggle mechanism, themotor torque is converted by a conversion mechanismfrom the rotary movement of a ball screw/nut mechanismor the like to straight-?line movement, moving a crossheadof the toggle mechanism so as to move a movable oneof mold halves to perform closing, clamping and openingof the mold halves.?[0003] When a toggle-?type clamping mechanism isdriven by a motor via a belt and a ball screw/nut mech-anism or the like, after the movable one of the mold halvestouches the stationary one of the mold halves, a largeload is put on the belt during the clamping that generatesa clamping force (the interval from mold touch to the at-tainment of a predetermined clamping force) and whilethe mold is being opened (the interval from the positionat which the clamping force is generated to the openingof the mold), abnormalities such as breakage of the beltsometimes occur. As a result, despite the occurrence ofan abnormality such as the broken belt and the fact thatthe mold clamping device has become inoperable, thecontinuous injection molding operation is continued andthe injection molding machine malfunctions.?[0004] Accordingly, a technology has been developedthat has as its object to detect an abnormality such as abroken belt or the like and to prevent the malfunctioningof the injection molding machine.?[0005] For example, a method is known that mounts apulse generator on the crosshead of a toggle-?type clamp-ing mechanism, counts a number of pulses generated inproportion to the amount of movement of the crosshead,compares this detected pulse number with a secondpulse number that is proportional to a detected numberof revolutions of a motor generated by a pulse generatorprovided on the driving side motor, and detects an ab-normality when the ratio exceeds a predetermined range(JP 7-16901A), as is a method that provides a first pulsegenerating means that detects the rotation of a drivingshaft (on the motor side), a second pulse generatingmeans that detects the rotation of a driven shaft that isdriven via a power transmission belt, counts the numberof clock pulses in the interval between pulses generatedfrom the first and second pulse generating means re-spectively, obtains and compares the rotation speeds ofthe driving shaft and the driven shaft, and detects anabnormality when the difference between the two ex-ceeds a threshold value (JP 2003-174786A).?[0006] In addition, a method is known that links a drivenpulley and a driving pulley mounted on the motor by abelt and provides one or more projections on that drivenpulley, and also provides a proximity switch that detectsthese one or more projections and detects a breakageof the belt by the presence of ON-?OFF signals from thatproximity switch (JP 2003-74649A), as are such methodsas detecting tooth-?skipping of a timing belt by the pas-sage of projections detected by a proximity switch (JP2003-184967A), detecting an abnormality in the belt bydetecting the tension on the belt (JP 11-262932A), andusing the fact that the torque of the motor that drives thebelt transmission mechanism declines when the beltbreaks to detect belt breakage by the torque of the motor(JP 6-182845A).?[0007] However, in the methods described in JP7-16901 A and JP 2003-17478A, which provide meas-uring means such as pulse generators on each of themotor side and the driven side and detect abnormalitiesin the belt transmission mechanism, the cost of the in-jection molding machine increases by the extent to whichmeasuring means such as pulse generators must be pro-vided. In addition, with the method described in JP2003-74649A, which detects abnormalities of the belt bywhether or not the driven-?side pulley is rotating, even ifthe driven-?side pulley is rotating there is no guaranteethat the crosshead and the movable mold are movingproperly, and consequently, there are times when thismethod cannot detect abnormality in the movement ofthe crosshead or the movable mold due to some abnor-mality with the transmission mechanism. Further, themethods described in JP 2003-184967A and JP11-262932A require tension detection means or meas-uring means that detect the amount of rotation, whichincreases the cost of the injection molding machine.Moreover, in the method described in JP 6-182845A, ifthe mold clamping device uses a toggle mechanism, ina state in which the toggle mechanism extends and gen-erates a predetermined clamping force, the toggle mech-anism itself generates a clamping force that sharply re-duces the output torque of the motor that drives the cross-head of that toggle mechanism, making it difficult to de-tect any abnormality in the belt transmission mechanism(such as breakage of the belt) from the motor outputtorque.SUMMARY OF THE INVENTION?[0008] The present invention provides an abnormalitydetection apparatus for a mold clamping device, capableof reliably detecting abnormalities in a driving force trans-mission mechanism such as a belt transmission mech-anism at low cost.1 2
