Weight sensor suitable for use under a bed with a deformable plate mounted to a base at three contact points
A weight sensor may include a weighing platform and a load cell coupled to the platform to sense a weight applied to the platform. The load cell may include a deformable plate with one or more strain gauges arranged to provide an electrical signal representing the weight applied to the platform, and a base supporting the load cell, wherein the deformable plate is movably mounted to the base at only three contact points, the contact points allowing lateral movement of the plate relative to the base when the plate deforms in response to a weight applied to the platform. The weight sensor makes it possible to independently monitor the weight and weight shifting of two people sharing the same bed. The weight sensor is self-centering when a load is applied off-center to the platform, which is particularly beneficial when such a weight sensor is used underneath a bed, e.g., under a bed leg or other support member which may not be aligned centrally over the weight sensor. Beneficially the sensor is not unduly affected by minor misalignment of the leg of a bed relative to the load cell.
1. A weight sensor, comprising: a weighing platform and a load cell coupled to the platform to sense a weight applied to the platform, the load cell comprising a deformable plate with one or more strain gauges arranged to provide an electrical signal representing the weight applied to the platform, and a base supporting the load cell, wherein the deformable plate is movably mounted to the base at only three contact points, the contact points allowing lateral movement of the plate relative to the base when the plate deforms in response to a weight applied to the platform.
2. A weight sensor according to claim 1 , wherein the deformable plate is substantially triangular in plan view.
3. A weight sensor according to claim 2 , wherein the three contact points are arranged at apices of the triangle.
4. A weight sensor according to claim 1 , wherein multiple sets of strain gauges are positioned symmetrically about the centre of the deformable plate.
5. A weight sensor according to claim 4 , wherein each one of three sets of strain gauges is arranged symmetrically around one of the three contacts points.
6. A weight sensor according to claim 4 , wherein each set of strain gauges comprises a pair of flexure beams that are arranged to bend into symmetrical double cantilever S-shapes in the plane of the deformable plate.
7. A weight sensor according to claim 1 , wherein the platform and deformable plate are coupled by a single central coupling.
8. A weight sensor according to claim 7 , wherein the central coupling comprises a rounded protrusion extending from a surface of the plate towards a facing surface of the platform.
9. A weight sensor according to claim 1 , wherein the deformable plate comprises three rounded protrusions arranged to contact a surface of the base as the three contact points.
10. A weight sensor according to claim 1 , wherein the deformable plate is movably mounted to the base by three ball bearings arranged between the deformable plate and the base as the three contact points.
11. A weight sensor according to claim 1 , further comprising means for sensing when a periphery of the deformable plate is moved in contact with the base.
12. A weight sensor according to claim 11 , wherein the sensing means comprises a pair of peripheral contacts on facing surfaces of the deformable plate and the base.
13. A weight sensor according to claim 1 , wherein the platform comprises an upper surface or cover made of a resilient or gripping material.
14. A weight sensor according to claim 1 , wherein the platform includes a recess positioned centrally on its upper surface.
15. A system for monitoring loads, comprising a plurality of the weight sensors according to claim 1 and a data hub electrically connected to each of the weight sensors.
16. A system according to claim 15 , wherein the data hub is arranged to continuously collect load data from the weight sensors during use.
17. A system according to claim 15 , wherein the data hub comprises a processor arranged to record load data relating to a change in load.
18. A system according to claim 17 , wherein the data hub comprises a memory arranged to store only the recorded load data.
19. A system according to claim 15 , wherein the data hub comprises wireless data connection means.
20. A system according to claim 15 , wherein the weight sensors are positioned on the ground under a free-standing bed to monitor loads from the bed.
21. A system according to claim 15 , comprising a first set of weight sensors arranged under a first side of a bed, and a second set of weight sensors arranged under a second side of a bed, wherein the data hub is arranged to record a differential measurement of the loads between the first and second sets of weight sensors.