GB2042180A - Measuring dimensions of workpieces - Google Patents

Abstract

A method of displaying a size function of each of a series of workpieces comprises sensing the value of a size dependent parameter of a workpiece while it is in a machine to give an electrical signal which is stored; removing the workpiece from the machine and physically determining the size function and feeding the stored signal to a display device and adjusting the display device until it indicates the physically determined size, so that the display will indicate the correct size function of each subsequent workpiece. The workpiece is typically a flexible bearing shell having an inner cylindrical surface. The size function is displayed on a broaching or boring machine and preferably the average value obtained from a succession of shells is displayed on a preceding machine such as an edge surface shaving machine to control the size function which is determined in the broaching machine. <IMAGE>

Description

SPECIFICATION Workpiece manufacturing & testing methods The invention relates to a method of displaying a function relating to the size of a series of workpieces during the course of their manufacture on a machine or press. The invention also relates to a method of controlling the manufacture of such workpieces in dependence on the size function displayed.

The invention has been developed in relation to the manufacture of flexible bearing shells but is not limited thereto.

Aflexible bearing shell hastheform of a hollow semicylinder and two such shells are located in a bearing housing to form a bearing. The shells engage one another along edge surfaces which are parallel to the longitudinal axis of the bearing, such edge surfaces engaging along the so called parting line. The circumferential length of a shell is measured along the outer cylindrical surface of the shell.

A dimension related to the circumferential length is the parting line height which is the measured perpendicular distance between a plane containing said edge surfaces and a parallel plane tangent to the outer cylindrical surface of the shell when the shell is located in a parting-line inspection fixture as described below and a predetermined load is applied to said edge surfaces.

In our British Patent No. 1,463,092 we have described and claimed a method of testing the size of a flexible bearing shell by measuring a distance having a known relation to the parting line height of the shell, characterised in that the said measurement is effected while the shell is clamped in a support in a machine tool arranged to machine the inner cylindrical surface of the shell while clamped in said support and before said inner surface is machined.

In our British Patent Application No. 3470/78 (Serial No. 1560611 ) we have described and claimed that the above method may be carried out by measuring said distance while the shell is clamped in said support and during or after said inner surface is machined.

In said Patent we have also described and claimed apparatus for machining the inner cylindrical surface, and testing the size of, a flexible bearing shell and comprising a support having a semi-cylindrical recess to receive the shell so that one or both parting line edge surfaces of the shell are outside the recess, clamp jaws to clamp the shell in the recess and arranged so as partially to overlie said surfaces, means for measuring the stand-off distance that the or each such surface stands proud of the support and means for machining the inner cylindrical surface of the shell while clamped in said recess.

The present invention has been developed in relation to displaying the value of a parameter related to the parting line height of a flexible bearing shell while in apparatus described in said complete specification. However, the invention is not so limited and it may be used for displaying a size function of a different type of workpiece.

Broadly considered, the invention comprises a method of displaying a function relating to the size of each of a series of workpieces while each workpiece is located in a machine in which it is operated upon, the method comprising sensing the value of a parameter of a workpiece while the latter is located in the machine, the parameter being directly related to a size function whose value is to be displayed; deriving an electrical signal from said sensed value; storing the signal; removing the workpiece from the machine; physically determining the desired size function of the removed workpiece by measurement or comparison; feeding the stored signal to an electric, size-function-indicating display device; and adjusting an electric circuit driving said display device until the latter indicates the size function of the workpiece as physically determined, and subsequently sensing the value of said parameter for each of the series of workpieces while each is located in the machine and displaying the required size function of each workpiece on the display device, the device and circuit being such that when the latter has been so adjusted, the sensed value of said parameter for each of said further workpieces will result in a derived electric signal of such magnitude as to indicate the correct size function of each workpiece on the display device.

If the workpieces to be measured are flexible bearing shells, as described in said Patent No.

1,463,092 the procedure is as follows: a first bearing shell is placed in the machine in which the inner cylindrical surface thereof is to be machined and, preferably after such machining, a distance having a known relation to the parting line height of the shell is measured as described in said patent. The measurement results in an electric signal. This signal is stored. The shell is then removed from the tool and said distance is determined in a parting-line inspection fixture.

The fixture comprises a block having a semicylindrical recess in the upper surface thereof dimensioned to receive the bearing shell. The circumferential length of the recess in the block is slightly less than the circumferential length of the shell to be measured. Afixed abutment is provided along one edge of the recess which engages one of the edge surfaces of the shell on the parting line and the other edge surface of the shell on the parting line stands proud of the upper surface of the block. A predetermined load is applied to the edge which stands proud of the block and the stand-off distance by which the edge surface is spaced from the upper surface of the block is measured.In practice the stand-off distance is measured by measuring between the upper surface of the block and the lower surface of the member which applies the load to the projecting edge surface of the shell. This measurement can be made by a dial gauge or by an electrical transducer. In setting up the fixture it is necessary to calibrate the measuring means and this is effected by the use of a solid master gauge of semicylindrical form which mates exactly with the recess in the block and engages the fixed abutment along one edge and has the operating load applied to the other edge. Since the dimensions of the master gauge are known and the stand-off distance is known a calibration of the measuring means can be made.

The stand-off distance as measured is then set on the display device by adjusting an electric circuit driving the display device. This adjustment of the circuit is such that when a further shell is measured while located in the machine, the actual stand-off distance which would have been determined by use of the fixture is indicated on the display device. It follows, therefore, that when a bearing shell is measured in the machine the stand-off distance will be indicated on the display device and can be inspected by the machine operator. If the stand-off distance is less than that permitted by the tolerance range then the operator can discard the shell whereas if it is within the tolerance range the shell can pass onwards for further treatment.If the parting line height is greater than that permitted by the tolerance range then the shell can be returned for remachining i.e. shaving of the parting line edge surfaces.

In British Patent No. 1,463,092 we describe that the stand-off distance was measured before the shell was broached or bored. We have now found that we can measure the stand-off distance or parting line height during or after the shell has been machined.

Preferably we measure the distance shortly after machining of the bore and while the shell is dimensionally stable. We have found that by measuring the stand-off distance while the shell is dimensionally stable very good reproducability is obtained. However, it is within the invention to measure the parameter before machining.

The method described may be applied to the manufacture of workpieces in which case the derived signals may operate audible or visual warnings if the parameter as measured is not within the permitted tolerance range. This makes it easy for the operator to reject the non-acceptable workpieces.

Alternatively, automatic means may be provided for rejecting workpieces which are outside the permitted tolerance range.

The method of control of manufacture may be extended where, as in the case of bearing shells, a further machine referred to as the "preceding machine" acts on each workpiece to control the parameter which is determined in the first mentioned machine, referred to as the "succeeding machine". Thus with flexible bearing shells, a shaving machine will shave the parting line edge surfaces and each shell will then pass to a broaching or boring machine where the bore of the shell is machined. In the broaching or boring machine the parting line height or stand-off distance determined by operation of the shaving machine is measured and displayed according to the invention.The derived signals from measuring a series of workpieces may be averaged and fed to a display device on the preceding machine, the shaving machine in the case of bearing shells, so the operator of the preceding machine can determine the effect of that machine.

Thus where the workpieces are flexible bearing shells, the average is taken of the stand-off distance or parting line heights which were measured on the broaching or boring machine and this average value is displayed on the shaving machine. It is found in practice that the shaving machine tends to drift out of tolerance and by displaying the measured and averaged figures from the broaching or boring machine the operator can decide when the shaving machine requires resetting. The average of the parameters measured on the first machine tool, ke.

the parting line height or stand-off distance of the bearing shell, may be a "rolling average" and may for example be the average of the last five workpieces or shells measured on the first mentioned machine tool.

In a modification of the method of the invention the average value determined as above is used to control the setting of the preceding machine, i.e. the shaving machine when the workpieces are flexible bearing shells. Such shaving machines are set manually but contain pneumatic or hydraulic actuators which give some small adjustment on the operation of the machine and such actuators can be controlled by the average determined from the broaching or boring machine so as to vary the setting of the shaving machine so that the parting line height or stand-off distance ultimately obtained is within the desired tolerance range.

The invention has been described specifically in relation to the manufacture of flexible bearing shells but may equally be applied to the manufacture of other workpieces where a size-function parameter has to be measured. Similarly if the workpiece has to be acted upon by two machines an average can be taken from the size parameter measured from the succeeding machine and fed back to the preceding machine to enable the latter to be controlled either manually or automatically on the basis of the average measurement obtained.

Where the workpieces are flexible bearing shells then these will be measured in the manner described in our British Patent No. 1,463,092 or as modified as described in our British Patent Application No.

3470/78. (Serial No.1560611) The invention will now be described in detail by way of example with reference to the manufacture of a flexible bearing shell. The machines which operate on the shell to determine its bore and parting line height are a broaching or boring machine and a shaving machine respectively. The shell is shaved and then bored or broached. In carrying out the invention the parting line height measuring means as described in British Patent No. 1,463,092 will be connected via an electric circuit to a display device on the broaching or boring machine and via an averaging circuit to a display device on the shaving machine.

At the start up of a run, a production bearing shell is shaved in the shaving machine and then passed to the broaching or boring machine and is then broached or bored. Immediately after broaching or boring, e.g. within one hundredth of a second, (or within such time limit as the dimensions of the shell are stable) the parting line height or stand-off distance is measured and this produces an electrical signal. As described in said prior specification, the measurement is effected by an eddy current displacement transducer. The electrical signal derived is stored. The signal may or may not cause a reading on the display device depending on how the latter has been set initially.The shell is then removed and measured by use of the fixture in the manner described above and the electric circuit driving the display device is then adjusted so that the display device indicates the actual stand-off distance measured by use of the fixture.

The measurement system is shown in the accompanying block diagram. The sensors are the transducers referred to in specification No. 1,463,092 and their outputs are summed in a summing amplifier and then passed to a store amplifier and through a gain amplifier to the size-function display unit. The gain amplifier is associated with an offset control whose purpose is described below.

The output from the gain amplifier is also fed to an averaging unit associated with a counter fed from a trigger via a gate control also connected to the store amplifier. The average unit produces a control signal based on the average of the last five signals fed to the size display unit from the gain amplifier. This averaged signal is fed to a second display unit for the averaged size and this control signal may also be used to control a shaving machine as will be described.

The operation of the circuit will now be explained with reference to the accompanying graph which shows the derived signal shown as a voltage V plotted against size S.

The characteristic of the circuit is linear as indicated by the dash line 10 and this intercepts the voltage axis at Vo. The signal measured is indicated by the line 11 representing a voltage Vm1. The intersection of the lines 10 and 11 at 12 will result in an indicated size So. This size may or may not be on the indicating dial of the display device according to the latters initial setting of the offset control. The size of the shell as measured is indicated at S1 and if the line 13 is drawn upwardly from S1 to intersectthe line 11 at 14 this indicates the position at which the line 10 should be located.The offset control of the gain amplifier is then operated to modify Vo to a value of Vo' which displaces the line 10 to the full line position indicated at 10' passing through the point 14 and having voltage Vml for the size S'. It follows that whenever a bearing shell is measured which produces a derived signal Vm1 a size S1 will be indicated on the display device. If, however, the derived signal measured is Vm2 then the size indicated will be S2 as obtained by following the chain lines 15 and 16. The display device and circuit are so arranged as to give a linear characteristic 10, 10' so that an appropriate value will be displayed on the display device.

It will be seen, from the foregoing, that one can set up the display device using a production bearing rather than having to use masters or sub-masters as described in said prior specification. It will of course be necessary to calibrate the fixture in which the size of the shell is physically determined.

The electric circuit produces an average of the last five derived signals measured, when each new signal is derived the first signal in the average is discarded. Thus, one has a "rolling average" and this value is displayed on a second display device on the shaving machine and gives an indication to the operator of that machine whether or not it is operating with the required tolerance range. If desired, as described above, this average signal may be used to control the shaving machine to ensure that the parting line height does stay within the required tolerance.

Reverting now to the display device on the broaching or boring machine. This is provided with visual warning means which indicates to the operator if a bearing shell is over or undersize. If the shell is undersize then it is scrapped. If it is oversize it is put through the shaving machine once more.

In our British Patent Application No. 3471/78 we have described the control of a shaving machine from the measurements taken in a broaching or boring machine in the manufacture of flexible bearing shells.

It will be seen that the invention provides a simple method for indicating the measurement of the parting line height of bearing shells. This method is, however, applicable to other workpieces as described above.

Claims (9)

1. A method of displaying a function relating to the size of each of a series of workpieces while each workpiece is located in a machine in which it is operated upon, the method comprising sensing the value of a parameter of a workpiece while the latter is located in the machine, the parameter being directly related to a size function whose value is to be displayed; deriving an electrical signal from said sensed value; storing the signal; removing the workpiece from the machine; physically determining the desired size function of the removed workpiece by measurement or comparison; feeding the stored signal to an electric, size-function-indicating display device; and adjusting an electric circuit driving said display device until the latter indicates the size function of the workpiece as physically determined, and subsequently sensing the value of said parameter for each of the series of workpieces while each is located in the machine and displaying the required size function of each workpiece on the display device, the device and circuit being such that when the latter has been so adjusted, the sensed value of said parameter for each of said further workpieces will result in a derived electric signal of such magnitude as to indicate the correct size function of each workpiece on the display device.

2. A method of controlling a first machine wherein the size function of a workpiece is measured and displayed on a second machine in accordance with the method claimed in claim 1 and said first machine acts on each workpiece to control the parameter which is determined in said second machine.

3. A method according to claim 2 wherein the average of the values of said parameters obtained from a pluralityofworkpieces is displayed on said first machine.

4. A method according to claim 3 wherein said average of the values of said parameters is used to control said first machine.

5. A method according to claim 1 wherein each said workpiece comprises a flexible bearing shell whose inner cylindrical surface is to be machined, the said size function to be displayed being related to the parting line height of the shell and said machine comprises a broaching or boring machine for machining said inner cylindrical surface of each said shell.

6. A method according to any one of claims 2 to 4 wherein each said workpiece comprises a flexible bearing shell whose inner cylindrical surface is to be machined, the said size function to be displayed being related to the parting line height of the shell; said second machine comprises a broaching or boring machine for machining said inner cylindrical surface of said shell and said first machine comprises a shaving machine for shaving the parting line edge surfaces of each said shell.

7. A method of displaying a function relating to the size of each of a series of workpieces substantially as hereinbefore described with reference to the drawings.

8. A method of controlling a machine substantially as hereinbefore described with reference to the drawings.

9. A workpiece whenever produced in a machine employing the method claimed in any one of the preceding claims.