Twin-disc tribometer

1. A twin-disc tribometer assembly comprising:

a first sample drive shaft arranged to receive a first sample disc;

a second sample drive shaft arranged to receive a second sample disc;

a first drive motor configured to rotate the first drive shaft; and

a second drive motor arranged to rotate the second drive shaft;

wherein the first and second drive shafts positioned relative to each other such that a sample disc mounted on the first drive shaft will make a point contact with a sample disc on the second drive shaft as the drive shafts rotate; and

wherein the shafts rotate relative to each other in a continuous rotational motion and in a non-continuous reciprocating motion,

wherein a motor control is provided to perform a first motor drive operation where the first and second motors drive the first and second shafts in a continuous rotational motion and to perform a second motor drive operation where the first and second motors drive the first and second shafts in a reciprocating motion relative to each other;

wherein the second motor drive operation uses a sinusoidal drive signal of fixed magnitude and frequency; and

wherein the sinusoidal frequency is the same for each of the first and second motors, but the magnitude is different.

2. A twin-disc tribometer as claimed in claim 1 , wherein:

the shafts rotate the samples in a non-collinear motion where one sample disc is tilted with respect to the other; and

the non-collinear motion is provided by one or both of the drive shafts being configured to carry the samples such that one sample is tilted with respect to the other so that the sample discs do not rotate around parallel axes.

3. A twin-disc tribometer assembly comprising:

a first sample drive shaft arranged to receive a first sample disc;

a second sample drive shaft arranged to receive a second sample disc;

a first drive motor configured to rotate the first drive shaft; and

a second motor arranged to rotate the second drive shaft;

wherein the first and second drive shafts are positioned relative to each other such that a sample disc mounted on the first drive shaft will make a point contact with a sample disc on the second drive shaft as the drive shafts rotate;

wherein the assembly is configured to allow the shafts to rotate relative to each other in a continuous rotational motion and in a non-collinear motion where one sample disc is tilted with respect to the other, wherein non-collinear motion is provided by one or both of the drive shafts being configured to carry the samples such that one sample is tilted with respect to the other so that the sample discs do not rotate around parallel axes;

wherein the second motor drive operation uses a sinusoidal drive signal of fixed magnitude and frequency; and

wherein the sinusoidal frequency is the same for each of the first and second motors, but the magnitude is different.

4. A method of operating a tribometer, the method comprising:

driving two sample discs in a first motion mode whereby the discs rotate continuously and collinearly with respect to each other; and

selectively rotating the two sample discs in a second mode in a continuous rotational motion and in a reciprocal motion relative to each other and/or about non-parallel axes with respect to each other;

wherein the second motor drive operation uses a sinusoidal drive signal of fixed magnitude and frequency; and

wherein the sinusoidal frequency is the same for each of the first and second motors, but the magnitude is different.