Tire Uniformity Machine, LIBROTA - KOBELCO

f structureand manufacturing technology.The electromagnetic valves used for the aircircuit shown in Fig. 6 were chosen to respond toinput signals faster than the previous machines. Inaddition, the electric pneumatic (EP) regulators andpressure sensors used for the tire pressure controlwere selected on the basis of their excellent accuracyand repeatability. Moreover, the high-speed controlcycle of the controller has improved the pressurerepeatability, reducing pressure fluctuation duringthe test. In the end, the control cycle necessary tostabilize tire pressure was found.2.3.2 Measures against electric noiseA TUM uses a number of servo motors for2.2.1 Drum structurePrevious machines employ bearings with taperedrollers, and the axial load received by the drum israther small. Librota, on the other hand, employsbearings that have been changed to an angular type,the same type as adopted in the spindle, to reducethe vibration of the drum.Moreover, its rib structure was completelyrevised to minimize the amount of drumdeformation when the load is applied to the tire.Fig. 5 Drum structure2.2.2 Manufacturing technologiesA drum requires a drum shaft that serves as therotating axis. The drum shaft is fitted with a loadcell for detecting the reaction force from each tire.In the case of Librota, a jig was devised to finish thedrum shaft with high accuracy and to reduce therunout of the drum shaft itself. For the drum, thecircumference polishing process to finish the shapewas revised.A prototype drum (Fig. 5) incorporating thesemeasures of drum vibration reduction was made toverify that the drum vibration had been reduced toless than half of that of previous machines.Fig. 6 Air circuit for tire inflationKOBELCO TECHNOLOGY REVIEW NO. 36 NOV. 201852

Fig. 7 Tire pressure before noise reductionFig. 9 Mechanism of spindle elevatorFig. 8 Tire pressure after noise reductionmachine operation. It was found that the electricnoise generated from these servo motors adverselyaffects the control of tire pressure. As shown inFig. 7, mixed noise makes it difficult to suppressthe fluctuation of inner pressure to within 0.05% ofthe set value. To this end, a study was conducted toreduce the noise generated from the servo motorsand to prevent the noise from intruding into thecontrol equipment.As a result of implementing various measuresthat were required, it was confirmed that the tirepressure variation at the time of inspection had beendecreased to allow the pressure to be controlledwithin 0.05% of the parameters, as shown in Fig. 8.3. Cycle timePassenger vehicle tires produced at tire factoriesare subjected to 100% inspection, and thus theshortening of cycle time is directly linked withproductivity improvement. Therefore, a TUM isrequired to operate with as short a cycle time aspossible.3.1 Downsizing of machine 3)In the development of Librota, the workingstrokes and weight of the apparatus were reviewedin pursuit of thorough downsizing. The revisionof the elevation mechanism of the spindle is anexample. In the measurement zone of a TUM, afunction for raising and lowering the spindle isrequired to chuck the tire with the rim. Kobe Steel'sprevious TUMs and those of competitors usehydraulic power to raise and lower the spindle.Librota has a structure in which ball screws arrangedin the left and right guide frames are synchronicallycontrolled by their respective servo motors toraise and lower the upper spindle. The separating53KOBELCO TECHNOLOGY REVIEW NO. 36 NOV. 2018force caused by tire pressure is retained by a brakemechanism. Fig. 9 shows the elevating mechanismof the spindle in Librota. This structure has increasedthe ascending and descending speed of the spindleand thus shortened the cycle time. Moreover,the use of servo motors has eliminated the needfor a hydraulic system, facilitating maintenance.Furthermore, without the risk of oil leakage, it isnow possible to install the spindle lifting/loweringunit on top of the machine. This has successfullyeliminated the need for a floor pit.The revision of these mechanical structureshas led to the reduction of the occupied volume toapproximately 30% of that of the previous machines.3.2 Adopting high-speed controllerAs shown in Fig. 10, the operation of the machinefollows the program in the controller, which repeatsthe sequence of the status check (thick horizontalline) and action (shaded box). Here, the delay timedue to the fieldbus communication cycle consists of:・ the time from the detection of the actual state tothe detection of the condition by the controllerand・ the time from the operation command by thecontroller to the actual start of the operation.The TUM operation related to cycle time includeshundreds of status checks and actions, which leadsto cycle time delay for the number of fieldbuscommunication cycles. The cycle time is also affectedby the processing capacity of the controller CPU,which influences the program execution speed.Therefore, a decision was made to construct acontrol unit with a controller capable of high-speedprocessing with a short task cycle and a high-speedcommunication fieldbus with a short communicationcycle (Fig. 11).Performance evaluation by a breadboard testconfirmed the cycle time of 18 seconds.

ConclusionsFig.10 Flow of elevating operation for spindleKobe Steel resolved the trade-off betweenimproved measurement repeatability and shortcycle time, and since Librota's commercialization in2013, more than 70 units have been sold, mainly inChina and Southeast Asia. It can respond to diverseneeds with the optional apparatuses required for tirequality inspection, including a sheet-of-light lasergeometry system, which inspects a tire's circularityand concave/convex abnormality on a plane, and ashoulder grinder, which grinds the edge of a tire toreduce vibration and noise.Kobe Steel will strive to expand the lineup ofTUM responding to the wide range of customerneeds, while developing the market in Europe andthe U.S., and continue its activities to take the lead inthe world market.References1) K. Goto, SHINKO TECHNO ENGINEEING REPORTS,2015, Vol.43.2) Kobe Steel. SPINDLE STRUCTURE AND TIRE TESTINGMACHINE HAVING THE SAME. JP2012145503. 2012-0802.3) Kobe Steel. TIRE TESTING MACHINE. JapaneseUnexamined Patent Application Publication No. Hei6-317504. 1994-11-15.Fig.11 Controller configurationKOBELCO TECHNOLOGY REVIEW NO. 36 NOV. 201854

TUMs have been sold mainly in Japan and Southeast Asia so far, and, to win the leading spot, there has been a need to commercialize new TUMs applicable everywhere, including China, Europe, and the U.S., the markets currently dominated by competitors. In a TUM, two capabilities are emphasized, i.e.,