Profile Checking Apparatus

The present invention relates to a method of and apparatus for checking the profile of an element.

The method and apparatus has particularly, but not exclusive, application to the checking of the profiles of the cams of a camshaft. At the present time, this checking is carried out either manually, which is a tedious repetitive and time consuming operation, or automatically with complex and expensive equipment. This equipment comprises stepping motors for turning the shaft angularly through predetermined angular steps and taking measurements at each step.

According to one aspect of the present invention there is provided a method of checking the profile of an element including the steps of advancing a detection head up to the element, determining a reference point on the profile, producing continuous relative movement between the detection head and the element continuously taking profile readings from the reference along the profile and feeding these readings at selected spaced intervals to a computer for subsequent manipulation.

According to another aspect of the present invention, there is provided apparatus for checking the profile of an element comprising a support, a transducer for producing a signal in dependence upon the position of the profile, a drive associated with the support for producing continuous relative movement between an element being checked and the transducer and means for feeding signals from the transducer to a computer for subsequent manipulation.

In order that the invention may be more clearly understood, one embodiment of the invention will now be described by way of example with reference to the accompanying drawings, in which:

FIG. 1 is a diagrammatic view of a camshaft measuring apparatus,

FIG. 2 shows a plot of the ideal profile of the cam and of the profile error of the actual cam obtained using the apparatus of FIG. 1, and

FIG. 3 shows an acceleration and velocity plot for the cam of the profile error of which is shown in FIG. 2.

Referring to FIG. 1, the apparatus comprises a rigid, straight and flat base 1 upon which is mounted a headstock 2, a tailstock 3 and carriage 4 for a lift measuring transducers. The tailstock 3 is movable to accommodate camshafts of different lengths and the headstock 2 incorporates a motor drive 6 for rotation. A high resolution rotary encoder 7 records angular displacement in steps of 0.001.degree. and cam lift is measured with the aid of a 30 mm displacement transducer having a resolution of 1 micron. The camshaft to be checked is mounted between centres and a steady is used on the journals to correct any sag or eccentricity. A cam follower, which may be the flat type or spherical as required, is disposed between the cam and the transducer 5. Measuring pressure is maintained constant during the measuring process.

The transducer 5 and rotary encoder 7 are connected, via respective digital readout devices 8 and 9 and an interface 10 to a central processing unit 11. Device 8 provides a continuous digital readout of the lift measured by transducer 5 and device 9 a continuous digital readout of the angle measured by the rotary encoder 7. The interfaces 10 match the outputs from the devices 8 and 9 to the I/O interface of the central processing unit. Unit 11 is a microcomputer and is provided with peripheral equipment which includes a dual disc-drive memory module, a dot matrix printer and A3 8-pen plotter.

The above described apparatus is used in the following manner. With the camshaft to be checked mounted between centres of the headstock 2 and tailstock 3 and drive coupling attached the cam journals are checked for any eccentricity and a steady is fitted as required. The cam follower, referenced 20 in FIG. 1, is then adjusted on the cam form referenced 21 on FIG. 1 (in this case a flat follower is set normal to the cam face.) The cam peak is then estimated by finding the reversal point of the lift and then using this figure, lift is recorded 30.degree. on either side. (For this particular cam, the profile is symmetrical for 32.degree. either side of the peak.) The true position of the cam peak is then found by subtracting the difference in lift at these points and winding the cam 21 to the required lift value noting the angular change on device 9. The true value for the peak is then entered into the computer and the motor drive 6 started. The measured values for angle and lift are displayed on a V.D.U. associated with the computer at 1 degree intervals for the full 360.degree. of rotation. Both disc-drives are used during measurement, programmes being retained on one drive unit and measured data stored on the other. The software programme controls the data collection sequence and after one full revolution of the cam, re-adjusts the measured data to put the cam peak at zero degrees.

The software programme which is shown at the end of the specification has been written so that it is user friendly and does not require any specialist computer knowledge. Simple questions are displayed on the screen such as "Is the measurement to be a new one or a plot of existing data?" Options are then provided by using the special function keys to produce the following.

(i) Profile, velocity and acceleration diagrams of cam form.

(ii) Error plot of cam form--deviations from a straight line and errors depicted over camshaft sectional view.

(iii) An A4 size view of cam with errors plotted over nominal shape.

(iv) Angular error results printed for one camshaft the (camshaft for the present embodiment has 16 cam lobes.)

(v) Printout of measured cam data at one degree increments.

(vi) Continuation key to start the measurement sequence again.

(vii) Plot showing all cam errors in the form of deviations from a straight line, plotted on one A3 size sheet of paper.

FIG. 2 shows an error plot of the cam greatly magnified together with a plot of the ideal cam profile. The ideal profile is referenced I and the Error plot is referenced E.

FIG. 3 shows a plot of the lift, velocity and acceleration diagrams of the cam. These are respectively referenced L, V and A.

The data collection operation takes 10 minutes and then after re-adjustment to format the peak at zero degrees the error plot may be drawn on the V.D.U. screen. Upon pressing the `continue` key the data is stored on disc and then the options via the special function keys appear as already described above. Numerical differentiation of the measured cam lift value may be carried out to produce velocity and acceleration data. These results together with the cam profile are then plotted on A3 cartridge type paper using 4 different pen colours. The plots are fully labeled with the angular scale marked from -180 to +180 degrees and the lift from -0.05" to 0.30". The plots can be produced for any camshaft without reference to any known data, the only limiting factor being maximum value of lift which is programmed to be 0.3" but this can be easily changed if required.

The error plot of cam form (also on A3 paper) is fully labelled and uses four different pen colours. This routine makes use of camshaft drawing data already stored in the machine. Errors are shown as deviations from a straight line but a section view showing the greatly magnified error is also plotted on the left-hand side of the paper.

It will be appreciated that after initially establishing the cam peak, the shaft is rotated continuously and the measured data (lift and angle) is sent simultaneously and continuously to the central processing unit 11. The measured signals from both the angles and lift transducers are sent whether the cam is rotating or static. The software programme reads the values and determines whether to accept or reject dependant upon the tolerances set in the programme. The data accepted by the computer is stored for later manipulation and calculation before being outputted to the peripheral devices.

This method of data acquisition permits a simpler and therefore less expensive arrangement as compared with machines which make use of stepping motors and control circuits between the central processing unit and the camshaft driving device. ##SPC1##