Measuring and testing – Testing of material
Reexamination Certificate
1998-10-20
2001-03-20
Williams, Hezron (Department: 2856)
Measuring and testing
Testing of material
C073S012120, C073S054010, C073S054230, C073S054360
Reexamination Certificate
active
06202496
ABSTRACT:
The present invention relates to an apparatus for the measurement of viscoelastic characteristics of bodies, in particular of bodies of elastomeric materials such as rubber, comprising a measurement body which is displaceably mounted relative to the holder and which has a measuring head which can be placed onto a sample body and means for the to and fro movement of the measurement body and means for the measurement of the path of displacement of the measurement head and/or of the force acting on the measurement head during the to and fro movement of the measurement body.
An apparatus of this kind is known from DE 40 40 786 A1. In this known apparatus a sample body is laid for the measurement on a measurement table which is provided beneath the holder with the measurement body. The holder must be rigidly supported relative to the measurement table in order to achieve reproducible results during the measurement.
This apparatus admittedly has the advantage, when compared with other apparatuses for the measurement of viscoelastic characteristics, that no special test preparation and in particular no clamping of the sample to a clamping fixture is required. Nevertheless, this apparatus has disadvantages in its utility, because the samples must be arranged on the sample table beneath the measurement head. The arrangement of the sample body on the sample table requires time and is not possible for all sample bodies, in particular when these have no reasonably flat contact surface.
The invention is based on the object of further developing an apparatus of the initially named kind so that these disadvantages do not arise. In particular the possibilities of use should be enlarged and the handling should be simplified.
This object is satisfied in that the measurement body is mounted in a freely movable housing with an opening for the passage of the measurement head and with an abutment surface which can be placed onto the sample body.
In contrast to the known apparatus the sample body is, in accordance with the invention, not brought into a specific position relative to the apparatus, but rather the freely movable housing of the apparatus of the invention is placed onto the sample body for the measurement of the viscoelasticity. The abutment surface thereby ensures that the sample body adopts a defined position relative to the housing with the measurement body. In this way it is possible to dispense with a rigid sample support table opposite the holder for the measurement body and to make measurements directly at the sample. The apparatus of the invention can thus be formed as a hand apparatus which can be used directly on location.
The measurement of viscoelastic characteristics is of particular importance amongst other things for vehicle tires, for example during the testing of new tire mixtures. Hitherto, sample bodies were made of the respective tire material and fixedly clamped into a measuring apparatus in accordance with DIN 53513. The disadvantage of this is that sample bodies must first be manufactured or cut out of an available tire before a measurement can take place. This has, moreover, the disadvantage that a tire is destroyed after the measurement has taken place. Thus, it is not possible to measure one and the same tire after different running periods.
The invention now makes it possible to measure the viscoelasticity of different components of the tire, such as for example the tread and the side wall without destroying the tire. For this purpose the housing with the abutment surface is placed onto a suitable position of the vehicle tire and the measurement is carried out. After the measurement has been completed the tire can be used again, for example in order to make a renewed measurement of the viscoelasticity and also of measurements of another kind after a longer running period. In just the same way it is possible with the hand apparatus of the invention to carry out measurements on a tire mounted on a vehicle. A measurement can thus for example also be carried out directly after a conclusion of a test run on the still hot tire, whereby a much simpler, or a more rapid measurement of the viscoelasticity of a heated tire close to reality is possible than with an independently heated sample body of tire material.
In accordance with a development of the invention means are provided by which it is ensured that the abutment surface of a housing sits firmly on the sample body during a measurement procedure. Through this feature the use of the apparatus of the invention as a hand device is improved, in that the housing with the measurement body is prevented from moving relative to the sample body during the measurement procedure. In this way it is ensured that reproducible results of high quality can be achieved even with a hand device.
One possibility for such means consists in forming the abutment surface as a standing surface of defined size. The housing with the measurement body can then be placed with its standing surface on the sample body, so that firm contact between the abutment surface and the sample body is ensured by the self-weight of the housing. The housing can for example have a weight between ca. 0.5 and 1 kp.
Another possibility consists in providing a pressure sensor which detects a pressing contact of the abutment surface on the sample body. A pressure sensor of this kind can for example be a planar pressure disk clamped between two mutually confronting flat surfaces of two parts of the housing. A valid measurement is only present when the pressure sensor detects a contact pressure above a specific threshold value. The selection of valid measurements can in this arrangement take place either via corresponding automatic means or however simply manually in that a suitable indicator device, for example a lamp, indicates when a sufficient contact pressure of the housing at the sample body is present.
In accordance with a further embodiment of the invention the zero position of the measurement head is determined by a predetermined depth of penetration. Other than in the apparatus known from DE 40 40 786 A1 the zero position is thus not determined via the indentation force of the measurement head into the sample body. This has the advantage, in particular with relatively soft sample bodies, that a penetration of the measurement head which is too deep and thus the danger of destroying the sample body is avoided. This is amongst other things also important because the apparatus of the invention is to be used on a final product on location, and not only on a specially manufactured sample body.
The depth of penetration in the zero position is preferably so selected that the deflection of the measurement head during the measurement lies in a range of at least approximately linear force-displacement ratio. In this way the reliability of the measured value obtained is increased. On measuring a body of elastomeric material the depth of penetration in the zero position amounts for example to ca. 100 to ca. 500 &mgr;m, when measuring tire mixtures, in particular to ca. 500 &mgr;m. These values can however also be selected differently, particularly in dependence on the shape of the penetration body. It is advantageous to determine suitable values by preliminary tests.
In accordance with a further embodiment of the invention the measurement head projects beyond the abutment surface of the housing in accordance with the desired depth of penetration. By placement of the abutment surface of the housing onto the sample body the penetration of the measurement head into the sample body by the desired amount is thus achieved in a simple manner. Another possibility consists in providing means by which the measurement head can be moved out of the housing into its zero position before the measurement is started. In both cases the zero position of the measurement head is preferably selectable. The zero position can thus be set at the apparatus, in a suitable manner, in particular in dependence on the material of the sample body.
In accordance with a further embodiment of the inventio
Fuchs Hans-Bernd
Herrmann Volker
Jakob Karlheinz
Unseld Klaus
Dunlop GmbH
Fitch Even Tabin & Flannery
Tran Thuy Vinh
Williams Hezron
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