GB2075184A - Monitoring rotor vibration - Google Patents

Abstract

To determine when a rotating body 1 is not rotating truly, a beam of visible, IR or UV radiation 4 is reflected off a reflective surface 5 on the rotating body to a sensor 6. When the body is not rotating truly, the sensor detects a variation in the reflected beam and, if this exceeds a certain value the driving power rotating the body is switched off. <IMAGE>

Description

SPECIFICATION Detector device The present invention reiates to a method for determining when a rotating body is not rotating truly and to a device for use therein.

Where bodies are rotated at high speeds, e.g. as with a centrifuge rotor, imbalances in the body, e.g.

due to unequal loading of sample tubes in a centrifuge rotor, cause the body to vibrate during rotation. This is undesirable and may cause overstressing of the device and failure of, for example, the drive shaft on which the body is mounted.

Various methods have been proposed for monitoring the vibration of a rotating body so as to switch off the rotation drive means if the vibration exceeds a given level. However, these methods have relied upon physical contact between the body and the sensor to sense the vibration. This requires individual setting-up of the sensor for each rotor and gives rise to problems due to erosion at the point of contact between the body and the sensor.

We have now devised a method for monitoring the vibration of a rotating body which reduces the above problems.

Accordingly, the present invention provides a method for monitoring the vibration of a rotating body, which method comprises shining a beam of radiation onto a surface on the body and monitoring the direction of reflection of that radiation from the surface.

The invention is of especial use in monitoring the vibration of a centrifuge rotor and, for convenience, the invention will be described in terms of this use.

To aid understanding of the invention, a preferred form thereof will be described by way of example with respect to the accompanying drawings in which Figure 1 is a diagrammatic view from one side of a centrifuge for present use; and Figure 2 is a typical signal produced from the device of Figure 1.

A centrifuge rotor 1 is mounted on a drive shaft 2 within a rotor chamber 3. A source 4 of radiation is provided to direct a beam of radiation onto a reflective surface 5 of the rotor 1. Infra red or ultra violet radiation sources can be used. However, it is preferred to use a light source, e.g. a lamp or a light emitting diode, as the radiation source and that the beam be parallel or have a small angle of divergence, e.g. from 0 to 60". Alternatively, the light beam can be focussed on the reflective surface 5 of the rotor when the latter is running true. The beam of light is directed onto the reflective surface at any suitable angle, typically at an incident angle of from lotto 80" e.g. 30 to 60" to the plane of the reflective surface.

The reflective surface 5 on the rotor 1 is a planar surface which can be located at any convenient portion of the rotor which has a substantially uniform circular cross-section coaxial with the axis of rotation of the rotor. Thus, the radiation can be reflected off a band around the waist of the rotor.

However, rotors come in various different shapes and sizes and it is preferred to use a reflective portion of the rotor which is common to the majority of rotors, thus minimising the need to reset the radiation source/sensor alignment when changing rotors. The base of many rotors is fitted with a reflective disc or annular track, substantially coaxial with the axis of rotation, for speed control purposes and these conveniently also serve to reflect the radiation from the source 4. Alternatively, a reflective annular track 5 can be mounted on the drive shaft 2 substantially coaxial with the axis of rotation.

The beam of radiation reflected from reflective surface 5 is sensed by a suitable sensor 6. Where a visible light beam is used, the sensor conveniently takes the form of a photoelectric cell. The sensor 6 is positioned so as to receive a substantially uniform signal reflected from surface 5 when the rotor 1 is running truly. When the rotor is vibrating the orientation of the surface 5 with respect to the sensor changes and the surface 5 deflects the light beam (as shown dotted in Figure 1). This results in a rise and fall in the signal generated by sensor 6 as the light beam swings to and fro across the sensor due to the wobble of the rotor during its vibration. A typical series of signals from a sensor using a sectored reflective disc as the surface 5 is shown in Figure 2. The wave curve indicates the variation in signal due to the vibration.The permitted fluctuation of the signal about that given when the rotor is running true can be selected and the power to the motor is cut off using conventional means, e.g. using a comparitor circuit to determine when the signal from the sensor exceeds the acceptable level, the comparitor circuit then activating a relay to cut off the power supply to the motor.

By using the method of the invention, erosion of the sensor is avoided as are other mechanical problems, and by using a reflective disc in the base of the rotor the method can be applied to a wide range of shapes and sizes of rotor without the need for adjusting the light source/sensor alignment.

The invention also provides a device which comprises a body which is to be rotated about an axis and which is provided with a reflective portion; a source of radiation adapted to direct a beam of radiation onto the reflective portion; and a radiation sensor adapted to receive radiation reflected from the reflective portion.

The invention further provides as a specific embodiment thereof a centrifuge having a rotor adapted to be rotated about an axis by an electric motor, the rotor having an annular reflective surface on the base thereof substantially co-axial with the axis of rotation of the rotor; a light source adapted to direct a beam of light at an incident angle of from 10 to 80" to the plane of the reflective surface; a light sensor positioned to receive light reflected from the reflective surface; comparison mean for comparing the light actually falling on the sensor with the reference amount of light falling on the sensor when the rotor is rotating truly; and means for switching off the power to the electric motor when the difference between the actual reflected light and the reference light values exceeds a given value.

Claims (6)

1. A method for monitoring the vibration of a rotating body, which method comprises shining a beam of radiation onto a surface on the body and monitoring the direction of reflection of that radiation from the body.

2. A device which comprises a body which is to be rotated about an axis and which is provided with a reflective portion; a source of radiation adapted to direct a beam of radiation onto the reflective portion; and a radiation sensor adapted to receive radiation reflected from the reflective portion.

3. A method or device as claimed in either of claims 1 or 2 wherein the body is a centrifuge rotor.

4. A method or device as claimed in claim 3 wherein the base of the rotor carries a reflective disc or annular track substantially co-axial with the axis of rotation of the rotor.

5. A method or device as claimed in either of claims 1 or 2 wherein the source of radiation is a light source and the radiation sensor is a photoelectric cell.

6. A centrifuge having a rotor adapted to be rotated about an axis by an electric motor, the rotor having an annular reflective surface on the base thereof substantially co-axial with the axis of rotation of the rotor; a light source adapted to direct a beam of light at an incident angle of from 10 to 800 to the plane of the reflective surface; a light sensor positioned to receive light reflected from the reflective surface; comparison mean for comparing the light actuaily falling on the sensor with the reference amount of light falling on the sensor when the rotor is rotating truly; and means for switching off the power to the electric motor when the difference between the actual reflected light and the reference light values exceeds a given value.