Measuring and testing – Dynamometers – Responsive to multiple loads or load components
Patent
1996-11-27
1998-10-13
Noori, Max H.
Measuring and testing
Dynamometers
Responsive to multiple loads or load components
73862044, G01L 116, G01L 122
Patent
active
058214313
DESCRIPTION:
BRIEF SUMMARY
BACKGROUND OF THE INVENTION
The present invention relates to a measurement sensor for a linking wrench between two mechanical parts.
The sensor proposed by the invention is designed to enable the measurement of a full force wrench, that is: three force components and three moment components exerted between two mechanical parts.
A measurement sensor for a full force wrench is notably described in document EP-A-0 396 568. This sensor is formed of a single metallic part which has two end faces and a central part. The two end faces are intended to be respectively fastened onto a reference body and onto a body generating the forces and the moments. The central part is formed of six beams which longitudinally are in the shape of a spiral. These six beams are placed according to a triangulate architecture closed between the two end faces. Each beam supports means to measure the deformations, these means being formed of strain gauges.
Such a measurement sensor is notably characterised by a relatively low stiffness because of the measurement principle itself which is based on the use of strain gauges. Indeed, for a strain gauge to operate correctly there has to be a certain elasticity in the metal forming the central part of the sensor.
This results in several drawbacks, among which:
a pass-band limited by the sensor's own frequency and by the additional elasticity introduced for the use of the strain gauges, and
a displacement along six degrees of freedom or compliance which can be incompatible with certain uses.
In addition, a certain area for bonding and cabling is required in order to set the strain gauges into place on the beams thereby limiting the minimal size of these sensors.
Lastly, once again because of the strain gauge technology, these measurement sensors have fracture safety coefficients which are under 5, which can be very insufficient in certain cases, robotics, for example, or can require the use of oversized sensors with the resulting loss of sensitivity that this solution implies.
SUMMARY OF THE INVENTION
The aim of the invention is to meet the drawbacks of these strain gauge measurement sensors whilst providing other advantages.
To this end, the invention proposes a measurement sensor for a linking wrench between two mechanical parts, which is characterised in that it comprises six piezoelectric cylinders, whose axes are directed along six directions, two support plates mounted facing one another and respectively in contact with the two end faces of each piezoelectric cylinder, and means to mount and fasten the six piezoelectric cylinders between the two plates.
According to one embodiment of the measurement sensor according to the invention, the axes of the six piezoelectric cylinders are directed according to a triaxial structure of ternary symmetry, and the six piezoelectric cylinders are evenly spaced towards the periphery of the two support plates.
To be able to align the piezoelectric cylinder axes along six predetermined directions, the two support plates respectively have two roughly planar main faces facing one another, and six cavities are arranged on each of the main faces, two cavities from each of these faces which are intended to accommodate the ends of a piezoelectric cylinder each having a bearing surface which is perpendicular to the direction along which the piezoelectric cylinder is to be aligned.
According to another characteristic of the sensor according to the invention, each piezoelectric cylinder is axially pierced by a screw forming a means to fasten the cylinder onto the two plates, each screw also forming a prestressing element of the cylinder against the two main faces of the two support plates.
To enable these fastening screws to be mounted, two axially aligned passages are drilled respectively in the two support plates for each screw, the passage which receives the threaded part of the screw being tapped.
Advantageously, an insulating washer is brought around each of the end faces of the piezoelectric cylinders.
The fact of designing a sensor made up of several
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patent: 3939704 (1976-02-01), Zipin
patent: 4688421 (1987-08-01), Pzsolla
patent: 4793193 (1988-12-01), Borgudd
patent: 4802371 (1989-02-01), Calderara et al.
patent: 5063788 (1991-11-01), Ch'Hayder et al.
Giat Industries
Noori Max H.
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