A METHOD OF FORMING A COLOUR GRADUATED PICTURE FROM A BLACK-WHITE GRADUATED PICTURE AND IN PARTICULAR A METHOD OF PRODUCING A COLOUR GRADUATED ISOBAR REPRESENTATION OF A PRESSURE DISTRIBUTION

Abstract: A method of forming a colour graduated isobar picture, particularly of the footprint of a pneumatic tire, in which a black-white graduated picture of the pressure distribution is made by loading a tire (16) against an elastomeric mem­ brane (10) having a plurality of shaped projections (12) on one side thereof which contacts a transparent plate (15). A picture of the contact pattern formed by the projections with the plate is photographed. The black-white picture is then placed in iuxtaposition with a heat sensitive liquid crystal sheet which is activated by directing radiant heat onto the liquid crystal sheet throuoh the black-white picture. The image of the activated liquid crystal sheet is recorded preferably by colour photography.

Description: A METHOD OF FORMING A COLOUR GRADUATED PICTURE FROM A BLACK-WHITE GRADUATED PICTURE AND IN PARTICULAR A METHOD OF PRODUCING A COLOUR GRADUATED ISOBAR REPRESENTATION OF A PRESSURE DISTRIBUTION The present invention in its broadest sense relates to a method of obtaining a colour picture from a black and white representation thereof, and in particular to a method of obtaining a colour graduated isobar picture of a pressure distribution. A paper entitled 'Measuring of Pressure Forces in Sitting' by B Rosemeyer and W Pfijringer (Arch. Orthop. Traumat. Surg 95 167-171, 1979) discusses an analytical technique for measuring the pressure distribution on different parts of the body when sitting in a working seat. The measurement of load distribution was done on a transparent plate with a rubber membrane having pyramidal points on its underside adjacent the plate. A contrasting fluid between the membrane and the transparent plate shows up the points where they contact the plate. These points are distributed at a density of 25/cm2. When a load was placed on the membrane, the points as viewed from underneath show up as points of different size, whose overall matrix gives a picture the impression of which is of varying black-white graduation. The load distribution picture is then observed by mirror and photographic pictures taken. These pictures are then scanned by TV camera which electronically transforms the black-white graduation into colour graduated isobar pictures. A refinement of this technique was to use a digital measuring video system which also allowed automatic area analysis on the single points of the load distribution picture. It can be seen that a disadvantage of the above method is that it requires expensive electronic equipment to convert the black-white graduated picture to a colour isobar picture. By contrast the present invention provides a simple and relatively cheap method of converting a black-white picture into a colour representation thereof. Accordingly there is provided in its broadest sense a method of obtaining a colour graduated picture from a black-white representation thereof, characterized by the steps of (1) placing the black-white graduated picture into juxtaposition with a heat sensitive liquid crystal sheet, (2) directing a radiant heat source on to the black-white graduated picture onto the liquid crystal sheet which changes colour in relation with localized temperature of the sheet as determined by the black/white graduations in the picture, (3) recording the coloured image, preferably by colour photography, of the activated liquid crystal sheet. More particularly there is provided a method of obtaining a colour graduated isobar picture comprising the steps of (A) placing an elastomeric membrane having a plurality of shaped projections on one side thereof against a transparent plate, the projections being adjacent the plate, (B) placing a load on the other side of the elastic membrane to deform the projections against the plate, (C) observing through the plate and recording a black-white graduated picture of the image formed by the contact areas of the projections against the transparent plate, and (D) forming a colour graduated picture from the black-white graduated picture of step (C) by a method in which the black-white graduated picture is converted to a colour isobar picture as described above. The above method is particularly useful for obtaining a colour graduated isobar picture of the footprint of a pneumatic tire in which the tire is loaded against said other side of the membrane, and a contrasting medium is used between the membrane and the transparent plate. The applicant has found that an unexpectedly good contrast medium is a translucent sheet material such as semi-transparent draughting paper, for example Diamant Extra Nr 102 glatt 70/75 g/m2, or polyester draughting sheets sold under trade name 'Mylar'. Also according to the present invention there is provided a method of forming a black-white graduated picture of a pressure distribution in the footprint of a pneumatic tire and comprising the steps of (A) placing an elastomeric membrane having a plurality of shaped projections on one side thereof adjacent a transparent plate, the projections being towards the plate, (B) placing a contrast medium, in the form of a thin translucent sheet material having a matt surface finish, between the-membrane and the transparent plate, (C) loading a pneumatic tire against the other side of the elastomeric membrane to deform the projections against the contrast medium and the plate, and (D) observing through the plate and recording a black-white picture of the image formed by the contrast areas of the projections against the plate. Preferably a layer of lubricant e.g. silicone oil is placed between the translucent sheet and the membrane. The invention will be described by way of example and with reference to the accompanying drawings in which: - Figure 1 is a portion of an elastomeric membrane as is used in the method of the present invention - Figure 2 is a schematic drawing of the loading of the membrane in order to obtain a graduated black-white picture of the pressure distribution on the membrane - Figure 3 is a typical graduated black-white pressure distribution picture for the footprint of a pneumatic tire - Figure 4 is a schematic drawing of the conversion of the black-white graduated picture into a colour isobar picture - Figure 5 is a black-white graduated picture of a second tire footprint pressure distribution - Figure 6 is a black-white reproduction of a colour graduated isobar picture of said second footprint picture shown in Figure 5. - Figure 7 is a black-white graduated picture of a tire footprint pressure distribution according to the second embodiment of this invention is which a sheet material contrasting medium is used between the elastomeric membrane and the glass plate. With reference to Figure 2 there is illustrated a portion of an elastomeric membrane as is utilized in the present method. The membrane 10 comprises an elastomeric mat 11 of a thickness tt t of about 1 mm. One side of mat II is covered in a plurality of shaped projections, preferably pyramidal projections 12, which each have a square base of 2 mm x 2 mm and have a population density of 25 projections/cmz. The included angle alpha between adjacent edges at the apex of each pyramidal projection is 900. The preferred elastomeric material for the elastomeric membrane is a low hysterisis carbon black filled natural rubber compound. It has been found that for the measurement of pressure distribution in the footprint of passenger tires which may exert a maximum pressure of about 7 bars, and truck tires which may exert a maximum pressure of about 15 bars, the elastomeric membrane should have a hardness of about 60 -65 Shore A for passenger tires and 75 -80 Shore A for truck tires. With reference now to Figure 2 and Figure 3, there is illustrated the way in which graduated black-white picture of a pressure distribution is obtained. The elastomeric membrane 10 is placed on top of a transparent plate 15, preferably glass, with the pyramidal projections 12 adjacent the plate 15. A contrast medium in the form of fluorescene dyed water is placed between the membrane and the glass plate in order to highlight the contact areas between the projections 12 and the glass plate 15. A pneumatic tire 16 under load is driven across the membrane and causes the pyramidal projections to distort against the plate 15. The resultant image is viewed from underneath the glass plate i.e. in the direction of arrow A. Each pyramidal projection 12 will distort against the glass plate 15 in relation to the load on the projection, i.e. a heavier load on the projection will form a larger contact area with the glass plate than a lighter load. These differences are shown at 17 in Figure 2. The pressure distribution in the footprint of a tire will therefore cause the large number of projections 12 to form an overall black-white graduated image in which the black/white ratio in any area is representative of the pressure. A permanent black and white record of the pressure distribution is made by synchronous flash photography of the footprint taken through the glass plate in the direction of arrow A. The photographic conditions were a shutter speed of 1/5ooth of a second using high contrast film with a dual flash, preferably using diffused light. When pictures were taken of the footprint of a tire on a moving vehicle the camera was triggered by an electronic eye which sensed the vehicle. Figure 3 is a black-white graduated picture of a tire footprint pressure distribution of a typical pneumatic tire, and which has been made by the above described method. The black-white picture is printed onto normal photographic printing paper, however, care should be taken that the photographic developing and printing conditions are standardized so that different pictures reflect different footprint pressures and not different photographic processing conditions. The black and white photograph can be further copied onto photocopy paper or onto thin Agfa-Geveart copy paper. With reference to Figure 4, there is illustrated in schematic form the very simple method by which the black-white graduated picture of the tire pressure distribution in the footprint is converted into a colour isobar picture. The black-white picture of the footprint is printed onto a sheet of paper 20 which is placed in juxtaposition with a sheet of liquid crystal film 21 of the type used in contact thermography. The two sheets 20 and 21 are held together in a surrounding frame 22. A suitable liquid crystal film is sold under the trade name 'ThermodetectR - SaprocilR' and is available from SAPROCIL, 217 Rue Clemenceau, F-68160 Ste Marie-aux-Mines, France. The liquid crystal sheet is basically microencapsulated liquid crystals disposed between two polyester films. The colour of the liquid crystal film is dependent upon the temperature of the liquid crystals. Thus if a portion of the film is heated locally it will change colour relative to the rest of film. The black and white picture 20 of the footprint of a tire, for example Figure 6, is placed against the liquid crystal sheet 21 to form a laminate in which the printed side of the paper faces away from the liquid crystal sheet. The paper sheet on which the black and white picture is printed should be as thin as possible so that the paper itself does not act as a heat sink. A suitable paper has been found to have a weight of 80-100 grim2. A pair of radiation heat sources 22 are directed onto the film sheet 21 through the black-white footprint picture 20. A pair of heat sources 22 are used to get a more even spread of radiant heat. The radiation heat source 22 could be an electric white light bulb, for example two tubular bulbs having a single 30 Watt filament, or preferably an infrared bulb. The heat source 22 is located in a surrounding housing 24 to minimize any convection effects. The black areas of the black-white footprint picture preferentially absorb heat and cause the adjacent liquid crystal sheet 21 to change colour in accordance with heat absorbed by the black area. The image of the coloured liquid crystal sheet is permanently recorded from above by colour photography. The coloured photograph of the image of the liquid crystal sheet obtained from the black-white footprint in Figure 6 is reproduced in black and white in Figure 5. Thus a permanent colour graduated isobar picture of the tire footprint pressure distribution is obtained. The colour of each isobar can be dependent upon room temperature, the density of the paper layer 20, the length of time for which the liquid crystal sheet/black and white picture laminate is exposed to the radiant heat, and also the intensity of the radiant heat. However, it has been found that for a given intensity of radiant heat, with the other parameters being constant, the colour of each isobar will stabilize after a certain time period. The intensity of the radiation could be varied by altering the power of the radiation source 22 or by altering the distance 'd' of the radiation source 22 from the two sheets 21 and 20. In the present example, using paper 20 as specified overleaf, a distance 'd' of 120 mm and a pair of heat sources 22 of 30 Watts each, it has been found that the colour of each isobar will stabilize after about 1 minute. For a given set of time/intensity parameters the different colour isobars can be calibrated. A series of different known weights is placed on the membrane 10 in spaced locations and the above described procedure is carried out to obtain a colour isobar picture for pressure exerted by the known weights on the membrane 10. The pressures exerted by the known weight can be calculated from the known weights and the areas over which they bear and hence an approximate pressure can be assigned to each colour of the isobar picture. A slight disadvantage of the above described method for obtaining a colour isobar picture of the pressure distribution in the footprint of a tire is in the use of a liquid contrast medium i.e. fluorescene dyed water. Because the membrane 10 has a large number of downwardly pointing projections 12 it is difficult to remove all the air entrapped by the liquid from between the membrane and the glass plate. Furthermore the maximum road speed for which the pressure distribution in the footprint of a tire mounted on a vehicle can be measured, when a tire is driven across the membrane, is limited by the interaction between the elastomeric membrane and the liquid. This in practical terms mean that the use of the elastomeric membrane 10 combined with a liquid contrast medium is only good for measurements for tires mounted vehicles travelling up to about 40 kph. Therefore in a preferred embodiment of a method according to this invention the contrast liquid, is replaced by a thin translucent sheet material having a matt finish. An example of a suitable material is draughting paper, for example Diamant ExtraR type 102, having a thickness such that it weights about 70/75 gr/m2, or polyester draughting sheet which is a polyester film having a matt finish on both sides and which is between 50-80 microns thick and which is used by draughtsmen; such a sheet is sold under the tradenames Mylar TM or Omnigraphic TM It has been found that if a sheet of translucent paper, or Mylar film is placed between the pyramidal projections and the glass plate that it can act as a contrast medium. It is thought that the projections 12 press the thin sheet material against the glass and cause an interference with the reflective or light scatter properties at the glass/sheet material interface. If photographed from below by synchronous flash photography, a black and white photograph of the footprint reveals a black/white graduated pressure distribution picture similar to that shown in Figure 7. This picture can be converted to a colour isobar picture by the techniques previously described. It is considered that because the interaction between the elastomeric membrane and the sheets of paper/Mylar is much faster than the interaction with a liquid contrast medium, that this preferred embodiment could be used to obtain a black-white graduated picture of a pressure distribution on tires mounted on vehicles travelling in excess of 100 kph and perhaps over 200 kph, when they are driven across the elastomeric membrane. Hence, a colour isobar pressure distribution can be obtained from this black and white picture. The reaction of the elastomeric membrane against the sheet paper/Mylar can be enhanced by placing a thin layer of lubricant, such as silicone oil, between the projections on the membrane and the sheet.

Claims: CLAIMS: 1. A method of forming of colour graduated picture from a black-white graduated picture including the steps of (1) placing the black-white graduated picture into juxtaposition with a heat sensitive liquid crystal sheet, (2) directing a radiant heat source on to the black-white graduated picture onto the liquid crystal sheet, which changes colour in relation with localized temperature of the sheet as determined by the black/white graduations in the picture, (3) recording the coloured image of the activated liquid crystal sheet. 2. A method of forming a colour graduated isobar picture of pressure distribution comprising the steps of (A) placing an elastomeric membrane having a plurality of shaped projections on one side thereof against a transparent plate, the projections being adjacent the plate, (B) placing a load on the other side of the elastic membrane to deform the projections against the plate, (C) observing through the plate and recording a black-white graduated picture of the image formed by the contact areas of the projections against the transparent plate, (D) forming a colour graduated picture from the black-white graduated picture of step (C) by a method as claimed in Claim 1. 3. A method as claimed in Claim 1 or Claim 2 characterized in that the colour image of the activated liquid crystal sheet is recorded by colour photography. 4. A method as claimed in anyone of Claims 1 to 3 characterized in that the black-white graduated image is recorded via photographic techniques onto paper, and the paper is placed adjacent the liquid crystal sheet with the black-white image on the side of the paper facing the heat source. 5. A method as claimed in Claim 3 characterized in that the paper onto which the black-white graduated image is transposed is thin paper having a density of less than 100 gr/m2. 6. A method of forming a colour isobar picture of the pressure distribution in the footprint of a pneumatic tire, and including the method of Claim 2, and Claims 3, 4, and 5 when dependent upon Claim 2, in which a pneumatic tire is loaded against said other side of the membrane and a contrasting medium is used between the membrane and the transparent plate in order to highlight the contact areas of the projections. 7. A method as claimed in Claim 6 characterized in that the tire is a passenger car tire and that the elastomeric membrane is made from a rubber compound having a hardness of about 60 -65 Shore A. 8. A method as claimed in Claim 6 characterized in that the tire is a truck tire and the elastomeric membrane is made from a rubber compound having a hardness of 75 -80 Shore A. 9. A method according to anyone of Claim 6, 7, or 8, characterized in that the contrasting medium is a thin translucent sheet material having a matt surface finish. 10. A method according to Claim 9 characterized in that the sheet material is ttylarR polyester drawing sheet. 11. A colour graduated isobar picture of the pressure distribution in the footprint of a tire, characterized in that the colour graduated isobar picture was formed by a method as claimed in anyone of the preceding claims. 12. A method of forming a black-white graduated picture of a pressure distribution in the footprint of a pneumatic tire and comprising the steps of (A) placing an elastomeric membrane having a plurality of shaped projections on one side thereof adjacent a transparent plate, the projections being towards the plate, (B) placing a contrast medium, in the form of a thin translucent sheet material having a matt surface finish, between the membrane and the transparent plate, (C) loading a pneumatic tire against the other side of the elastomeric membrane to deform the projections against the contrast medium and the plate, and (D) observing through the plate and recording a black-white picture of the image formed by the contrast areas of the projections against the plate. 13. A method as claimed in Claim 12 characterized in that the contrast medium is a thin polyester sheet having a thickness of between 50-80 microns. 14. A method as claimed in Claim 12 or Claim 13 characterized in that a thin layer of lubricant is placed between the translucent sheet and the membrane. 15. A method as claimed in Claim 12 or 13 characterized in that the lubricant is silicone oil. 16. A method of obtaining a picture of a footprint of a tire on a vehicle which is travelling in excess of 100 kph and including a method as claimed in any preceding claims.

Inventors: BREEDIJK, FRANS N.
Applicants: THE GOODYEAR TIRE & RUBBER COMPANY
Application year: 1985
Main classification: G01L1
IPC codes: G01L1, G01L17