JPS62274230A - Force/torque sensor having overload protection - Google Patents

Abstract

(57) [Summary] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

[Detailed Description of the Invention] 3. Detailed Description of the Invention The present invention detects a load and divides it into three mutually orthogonal
that is, perpendicular X, Y, and z01], i.e., a sensor that allows the decomposition into components of forces and moments oriented along and around Cartesian coordinates. The invention is more particularly concerned with protecting such one degree of freedom 6'' sensors from being damaged by subjecting them to loads greater than for which they were previously designed.

Force/torque sensors with six degrees of freedom are known in the art.

U.S. Pat. Nos. 4,094,192, 4,259,863, and 4,448,080 disclose depictions. Such a sensor is a load cell.
) or similar object to which is fastened a strain gauge that emits an electrical signal proportional to the load applied to the body. The signals are preferably directed to a microprocessor or similar electronic device so that they automatically and rapidly resolve each applied load along and around three mutually perpendicular axes. perform mathematical calculations. Although the body of the sensor may be of various shapes, a rectangular "cross" type sensor, such as that shown in US Pat. No. 4,448,083, is preferred. The sensor consists of a central hub section interconnected to a surrounding rim section by means of which the sensor strain gauges are fastened.A rectangular cross-shaped sensor body is described in U.S. Pat. No. 4,259,863 and U.S. Pat. It has better inherent symmetry with respect to any arrangement of Cartesian coordinates or orthogonal axes than a "delta" or three-spoke sensor unit as shown in the above patent.

A significant drawback of each of the prior art sensors is that if the loads applied to the sensor during use were of an excessive magnitude, the strain gauges and/or other components thereof could suffer structural damage. It is the lack of any means to prevent it. In addition to the possibility of sustaining severe structural damage, sensors lacking overload protection must be exposed to loads much greater than the actual loads to which the sensor could be safely accommodated, to give a reasonable margin of safety. A lower maximum load rating must normally be provided.

A preferred type of overload protection means consists of a cylindrical pin placed concentrically within an oversized hole in the form of a circular cut surface. This type of overload protection element is relatively easy to construct and install and has been used to date in sensors with six or fewer degrees of freedom. For example, U.S. Pat. Nos. 3,646,809 and 428
See No. 3941. However, attempts to use previous types of elements in six degrees of freedom sensors have been unsuccessful due to premature engagement of one or more of the pin/hole elements under the additional loads involved. In an effort to eliminate previous problems, the use of oval or other non-circular shaped pins or holes has been proposed. This approach is not recommended for sensors with six degrees of freedom, which are suitable for sensing very small magnitude distortions. The cost of manufacturing and assembling a six degree of freedom sensor with a non-circular shaped overload pin is too high and the results achieved thereby are often far from satisfactory.

The present invention provides structurally simple and economical, yet highly reliable and efficient overload protection for a six degree of freedom force/torque sensor of the type with spoke-like elements, each of which The central hub part of the center main body and the surrounding lip part are designed to act as if they were supporting a strain gauge that interconnected them. The sensor body is designed and constructed such that a moment applied to the hub portion of the sensor body about any one of three orthogonal axes results in an angular hub deflection of approximately the same magnitude. Thus, if the central longitudinal axis of the sensor is designed as a biaxial axis, the internal hub deflection caused by a moment about the z-axis will be caused by a moment of the same magnitude about either the x-axis or the y-axis. The angular deviation caused by this would be almost the same. The foregoing provides that the sensor overload protector is in the form of a cylindrical pin element extending between and placed within aligned cylindrical holes provided in the rim and hub portions of the sensor body. Forgive yourself for being A pin-receiving hole in one of the parts, preferably the rim part of the body, has a larger diameter than that of the pin part received therein, so that it mates with the opposing cylindrical surface of each pin. The holes are radially spaced from each other during normal use and loading of the sensor. The overload-induced engagement between the facing surfaces of the pin and its associated oversized hole is
Limiting the maximum stress imposed on the sensor spoke elements and the strain gauges fixed thereto, thus preventing damage and/or possible breakage to them.

In a preferred embodiment of the sensor, the body portion thereof is “
It is of the "square cross" type, with its four spoke elements extending radially around its periphery at 90° intervals between the hub and rim of the body. are provided, and they are spaced radially between the rim and hub portions of the sensor body, equally spaced 90' apart with respect to each other, and 45° apart with respect to the spoke elements. It's growing.

Other features of the invention will become apparent from the following description of preferred embodiments thereof.

The body of the sensor, generally indicated by the numeral 1° in Figures 1-3, is generally of the shape of a square cross. consisting of an element 14, a hub element 16' and an overlying hub plate 16'' secured to each other in any suitable manner, such as by screw fasteners 18;
Contains. The hub portion 16 and the rim portion 12 of the main body 1o are placed in a concentric relationship with the central vertical axis of the sensor main body, and spaced from each other in the radial direction. Such axes are the Cartesian coordinate system or orthogonal axes shown in the figure.
7 and 2 are indicated by the letter 2. Hub element 16
' and the major planes of the hub plate 16'' are perpendicular to such axes and parallel to the plane containing the x+7 axis of the coordinate system. Four bosses or protrusions 17 extend downwardly from the interior major surface of the plate 16''. They protrude equally spaced around the edges of it. Spoke elements 14 are interconnected and extend radially between hub element 16' and rim portion 12 at equal 900 spacings around the circumference of body 1o. For descriptive convenience, a pair of spoke elements 14 in a -line arrangement are shown extending along the X-axis of the depicted coordinates;
Sometimes hereinafter referred to as X-axis spoke elements, while the other pair of spoke elements 14 extend along the y-axis and are sometimes hereinafter referred to as y-axis spoke elements. Each spoke element 4 is formed integrally with the central portion of a combination of four flexure elements 20 formed in the wall of the rim portion 12 around its periphery at 90' intervals. Each bending element 20 forms a circular cord around the two axes of the sensor and has a length dimension that is significantly larger than the width dimension of the bend, i.e. its dimension parallel to the z-axis. have.

The width dimension of each bend, in turn, is significantly larger than its thickness dimension, ie, parallel to the X or y axis. Y
The flexure element 20 in combination with the axial spoke element 14 has a relatively low stiffness in the y-axis direction and a relatively high stiffness in the x- and/or two-axis direction. Similarly, the flexure element 20 in combination with the X-axis spoke element 4 has a relatively low stiffness in the x-axis direction, but a relatively high stiffness in the y-axis and/or bi-axes.

Four strain gauges 22 are fixedly coupled to each spoke element 14. The gauges 22 associated with each element are each approximately centered on a respective one of the four external surfaces of the element. The gauge extends longitudinally to the spoke elements with which it is assembled and is of a type sensitive to tension strains as a result of compression and/or bending of those assembled spoke elements.

The sensor rim portion 12 of the body 10 is suitable for being fixed to any desired support, which may for example be a robot arm (not shown). The exposed external major surface of the plate 16'' of the hub portion 16 is a device or structure, such as a robot wrist or hand, that applies loads to be sensed and resolved into forces and moments. the load applied to the hub portion 16, provided that it is of a size within the range for which the sensor is designed to fit. causes a deflection of the hub portion relative to the rim portion 12, a bending-type deformation of at least some of the spoke elements 14, and the initiation of electrical signals from at least some of the strain gauges 22.

By suitably processing the strain gauge output signals in a suitably programmed microprocessor (not shown) combined with the sensor, the load forces and The components of moments can be quickly calculated and identified. A detailed explanation of how the load components are resolved mathematically is given below.
Don't hope, hag, here is the previously listed U.S. Patent No. 4094.
It can be obtained from No. 192.

According to the invention, in combination with the sensor body 10, means are provided on the hub portion 16 to protect the sensor against damage caused by experiencing excessive loads.

Such overload protection means include four cylindrical pin elements 24 extending radially between the hub portion 16 and the rim portion 12.
Contains. The pins 24 are spaced approximately 45 degrees apart from each other around the periphery of the body 10 and approximately 45 degrees apart from circumferentially adjacent spoke elements 14 . The protrusions 17 on the inner surface of the hub plate 16'' have holes 30 which allow spaced entry into each of the protrusions from the surface thereof facing the inner cylindrical surface of the rim portion 12 of the body 10. The holes 30 are axially aligned with each one of four radially extending holes 32 provided in the rim portion of the body 10.

The radially innermost end of the pin 24 is connected to the hole 30 in the hub portion.
are fixedly attached, such as by push-fitting, into each of the parts. Opposing, radially outermost pin ends 24 are disposed concentrically within each one of the holes 32 in rim portion 12 . The outer end of each pin 24 has a hole 32
has a smaller diameter than the hole 32 in which the pin 24 is concentrically received, and during normal operation of the sensor an annular gap or space 34 (exaggerated in FIG. 5). ) exists in between. If an overload is applied to the sensor body, the hub portion 16 will be overloaded with respect to the rim portion 12! II deflection occurs, which causes engagement between at least some opposing cylindrical surface portions of pin element 24 and rim hole 32. Such engagement prevents the relative deflection between the bodies 12.16 from exceeding predetermined safety limits and thus prevents the spoke elements 14, flexure elements 20 and/or the frangible sensor components from exceeding predetermined safety limits.
or prevent damage to things such as the strain gauge 22.

An overload force applied in any direction along any one of the three drawn X and Z axes will cause the four pin elements 24 to
will be reacted to by all of them. An overload force applied in any direction along an axis coinciding with the solid axes of two pin elements 24 in any in-line arrangement will be responded to only by the other two pin elements 24. Similarly, an overload moment applied in any direction about either of the drawn 7 and z axes will be reacted to by all four pin elements 24, whereas any of the aligned pin elements 24 An overload mormont applied in either direction of the axis coinciding with the solid axis of either pair will only be reacted by the other two pin elements.

The critical overload component associated with this type of force/torque sensor is the moment rather than the force. If such a sensor is properly protected from damage due to the moment component of an overload, failure due to the force component of such a load will always be rare. protect this type of sensor from damage caused by moment components from excessively applied loads in a suitable and sufficient manner;
On the other hand, at the same time it has hitherto been difficult to avoid unduly limiting the useful load range of the sensor. The foregoing desired results, of course, do not occur as a matter of course when using a co-cylindrical mating hole with an overload pin. this is,
The angular deflection experienced by the central hub of a conventional sensor of the type in question in response to a moment applied about two axes of the sensor occurs when the moment is about either the x-axis or the y-axis. It is of a completely different size. Compensation for the different biases mentioned earlier is
It was hypothesized that this could be achieved by the use of overload pins with specially calculated oval or other non-circular cross-sectional shapes. However, even if one were to believe that such pins would produce the desired results, it is far from certain, and the cost of their manufacture and assembly would make their use impractical.

Achieving the desired overload protection with the use of cylindrical pins and hole elements in the sensor of the present invention is achieved because the angular deflection experienced by the sensor hub portion 16 is limited to three orthogonal axes about which such moments are applied to the hub portion! ,7. This is made possible in a substantial part by the fact that, irrespective of the particulars of H, are essentially the same. The above is the drawing'! JI7 and 8
Schematically depicted in fig. As shown in FIG. 7, a moment of a fixed magnitude around the z-axis is
6' yields an angular deviation of the hub element parallel to the x,y plane of the coordinate system of magnitude zero. As shown in FIG. 8, the addition of a moment of the same magnitude applied about either the The angular deviations are of approximately the same magnitude, 0. The aforementioned desired result can be achieved by selecting appropriate values during the design of the sensor of the type in question, or of the various dimensions of the centimeter body parts, including in particular the spoke elements 14 and the flexure elements 20. can be obtained.

Although preferred embodiments of the invention have been shown and described, this is for purposes of illustration only and not as a limitation, and the scope of the invention is to be defined by the claims as filed.

[Brief explanation of the drawing]

FIG. 1 is a rear elevational view of the main body of a sensor according to the invention. FIG. 2 is a side elevational view of the sensor body. FIG. 3 is a front elevational view of the sensor body, with portions thereof partially broken away to better disclose the structural details. FIG. 4 is an enlarged fragmentary view, partially in elevation and partially in vertical section, taken along line 4--4 of FIG. 3, showing the relationship between one of the spoke elements and the rim of the sensor body; It shows the connection between. FIG. 5 is an enlarged fragmentary elevation, partially vertical section taken along line 5--5 of FIG. One end of the Hoto pin is shown. FIG. 6 is an exploded perspective view of a portion of the sensor shown in FIGS. 1-3. Figures 7 and 8 are schematic diagrams depicting the angular excursions experienced by the hub portion of the sensor body in response to moments applied thereto. Patent applicant Lord Corporation Showa//year? Month 1'2 day 3. The number of persons making the amendment ÷ 4. Agent

Claims (1)

Claims: 1. A six-degree-of-freedom sensor for detecting additional loads resolvable into forces and moments along and about orthogonal axes 16), an annular rim portion (12) surrounding the hub portion, and a plurality of radial elements (14) interconnecting the portions (12, 16). , the hub part (
16) is angularly deflectable with respect to said rim (12) by an applied load and is caused by a moment applied to it about any one of said axes. the angular deflection of the hub portion (16) is approximately the same magnitude as the angular deflection caused by the application of the moment about any other of the axes, and the sensor is one of which can engage the other of said part under overload conditions, thereby reducing the angular deflection of said hub part (16) to said rim part (12).
sensor 2, characterized in that the radiation element (14) is generally parallel to a plane containing the X and Y axes, and is adapted to limit 2. A sensor according to claim 1, wherein the sensors are arranged to be spaced apart from each other by substantially equal angular spacing. 3. The load loading pins (24) are generally parallel to a plane containing the X and Y axes, and are spaced about the Z axis at substantially equal angular intervals with respect to each other. The sensor according to claim 2, which is . 4. The transmission element (14) and the overload pin (24) are connected to the Z
4. The sensor of claim 3, wherein the sensor extends generally radially relative to an axis and is spaced at substantially equal angular intervals relative to each other about the Z-axis. 5. The overload pin (24) and the radiation element (14) are connected to the Z
5. The sensors of claim 4, wherein the sensors are arranged alternately about the axis in substantially equally spaced relation to each other. 6. The sensor according to claim 5, wherein there are four radiation elements (14) and four overload pins. 7. Each of the rim and hub portions (12, 16) has a plurality of holes (32, 30) therein;
Each of one hole (32, 30) of the portion (16)
, 12) is axially aligned with one of the holes (30, 32) of the other and not axially aligned with the hole associated with each of said pin elements (24). The pin elements (24) each form a first pin element (24) closely received in one of the holes (30, 32) of its associated pair of holes. and is received within the surface of the other of the paired holes (30, 32) and is generally radially spaced therefrom. A sensor according to claim 1, characterized in that it has two parts. 8. The sensor according to claim 7, wherein the hole receiving the second part of the pin element (24) is adapted to be a hole (32) in the rim part (12). .