[go: up one dir, main page]

WO2019150339A1 - Contact sensor, particularly for a robot foot - Google Patents

Contact sensor, particularly for a robot foot Download PDF

Info

Publication number
WO2019150339A1
WO2019150339A1 PCT/IB2019/050894 IB2019050894W WO2019150339A1 WO 2019150339 A1 WO2019150339 A1 WO 2019150339A1 IB 2019050894 W IB2019050894 W IB 2019050894W WO 2019150339 A1 WO2019150339 A1 WO 2019150339A1
Authority
WO
WIPO (PCT)
Prior art keywords
contact
support element
longitudinal direction
probe
contact sensor
Prior art date
Application number
PCT/IB2019/050894
Other languages
French (fr)
Inventor
Yifu Gao
Claudio Semini
Michele Focchi
Darwin Gordon Caldwell
Original Assignee
Fondazione Istituto Italiano Di Tecnologia
Universita' Degli Studi Di Genova
Priority date (The priority date is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the date listed.)
Filing date
Publication date
Application filed by Fondazione Istituto Italiano Di Tecnologia, Universita' Degli Studi Di Genova filed Critical Fondazione Istituto Italiano Di Tecnologia
Publication of WO2019150339A1 publication Critical patent/WO2019150339A1/en

Links

Classifications

    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01L—MEASURING FORCE, STRESS, TORQUE, WORK, MECHANICAL POWER, MECHANICAL EFFICIENCY, OR FLUID PRESSURE
    • G01L5/00—Apparatus for, or methods of, measuring force, work, mechanical power, or torque, specially adapted for specific purposes
    • G01L5/0004—Force transducers adapted for mounting in a bore of the force receiving structure
    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01L—MEASURING FORCE, STRESS, TORQUE, WORK, MECHANICAL POWER, MECHANICAL EFFICIENCY, OR FLUID PRESSURE
    • G01L5/00—Apparatus for, or methods of, measuring force, work, mechanical power, or torque, specially adapted for specific purposes
    • G01L5/0028—Force sensors associated with force applying means
    • G01L5/0038—Force sensors associated with force applying means applying a pushing force
    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01L—MEASURING FORCE, STRESS, TORQUE, WORK, MECHANICAL POWER, MECHANICAL EFFICIENCY, OR FLUID PRESSURE
    • G01L5/00—Apparatus for, or methods of, measuring force, work, mechanical power, or torque, specially adapted for specific purposes
    • G01L5/0052—Apparatus for, or methods of, measuring force, work, mechanical power, or torque, specially adapted for specific purposes measuring forces due to impact

Definitions

  • the present invention relates to a contact sensor, in particular for use on a robot provided with legs for sensing the contact of the foot of each leg of the robot with the ground.
  • anthropomorphous robots generally have six-axis force sensors posi- tioned in the ankle of each leg to measure the reaction forces generated by the ground, thereby allowing to determine the state of contact between the foot and the ground by comparison of the value of the normal force (i.e. of the force orthogonal to the ground) measured by the sensor with a given threshold value.
  • multiple-axis force sensors in the feet of four-legged robots. Such force (or torque) sensors are typically based on the use of strain gauges and are, therefore, very expensive.
  • force (or torque) sensors based on the use of strain gauges are very delicate, and therefore suscepti- ble to be damaged or loose precision in case of strong contacts, which are rather frequent in a four-legged robot that walks or trots. Therefore, the use of sensors of this type is prob- lematic on robots intended to move on rough terrains, even more so if said robots must also be able to jump.
  • US 2003/0213623 Al discloses a sensor intended to be used on a vehicle seat do determine the weight and the position of an occupant of the seat.
  • the sensor basically comprises a contact element, an elongated transmission member rigidly connected to the contact ele- ment, a ball coupling device having a first part, that is rigidly connected to the transmission member and has a conical seat, and a second part, that is made as a ball and is partially ac- commodated in said seat, an elastic disk having a further conical seat where the ball is par- tially accommodated, and a strain gauge for sensing the load exerted on the elastic disk via the contact element, the transmission member and the ball coupling device.
  • EP 1 462 784 Al discloses a device for measuring the reaction force transmitted by the ground to the foot of a walking robot, comprising a casing adapted to be mounted in a point of the foot of the robot facing the ground, a movable unit mounted in the casing and adapted to move rela- tive to the casing when a reaction force is transmitted by the ground to the foot of the ro- bot, and a sensor mounted in the casing to measure the reaction force of the ground trans- mitted via the movable unit.
  • EP 1 462 784 A 1 is only capable of sensing and measuring axial reaction forces, transmitted by the ground to the robot foot.
  • Figure 1 is an axial section view of a contact sensor according to an embodiment of the present invention
  • Figures 2 and 3 are a perspective view and a front elevation view, respectively, of the elastic support element of the contact sensor of Figure 1 ;
  • Figure 4 shows the detail A of Figure 1 on an enlarged scale
  • Figure 5 is a perspective view of the transmission member of the contact sensor of Figure 1.
  • a robot foot is indicated with 10 and is mounted at the bot- tom end of a tubular element 12 forming part of the structure of a leg of the robot.
  • the lon- gitudinal axis of the tubular element 12 is indicated x.
  • the direction of the axis x will be hereinafter referred to as axial or longitudinal direction.
  • the foot 10 is provided with a contact sensor, generally indicated with 14, for sensing a condition of contact of the foot 10 with the ground.
  • the contact sensor 14 (hereinafter simply referred to as sensor) comprises, first of all, a support element 16, preferably made of metal.
  • the support element 16 is mounted at the bottom end of the tubular element 12.
  • the support element 16 comprises a disk-shaped first portion l6a, extending in a plane perpendicular to the longitudinal axis x, and a cylindrical second portion (bottom portion) l6b, extending along the longitudinal axis x, the foot 10 being rigidly connected to said second portion, for example by threaded coupling.
  • the first portion l6a of the support element 16 is made as an elastically deformable portion, in particular in the axial direction, and to this end it preferably has one or more slits, conveniently shaped (for example, coil-shaped) and positioned. In the embodiment pro- posed herein, the first portion l6a has three coil-shaped slits, indicated with 18i, 1 82 and 183, respectively.
  • the second portion 16b of the support element 16 forms a rigid body that is movable (to- gether with the foot 10, to which, as already mentioned above, it is rigidly connected) rela- tive to the tubular element 12 as a result of the elastic deformability of the first portion l6a.
  • the second portion 16b along with the foot 10, is displaceable both axially (that is, along the direction of the longitudinal axis x) and radially (that is, along any direc- tion lying on a plane perpendicular to the longitudinal axis x), and is also tiltable about a centre of rotation R placed at the intersection of the longitudinal axis x with a median plane P of the first portion l6a perpendicular to the longitudinal axis x, as shown in Figures 1 and 4.
  • the second portion 16b of the support element 16 is movable, as a result of the elastic deformability of the first portion l6a, not only along the direction of the longitudinal axis x, but also along a direction having a component perpendicular to the longitudinal axis x.
  • annular abutment surface lOa of the foot 10 rests on a shoulder 17 of the second portion l6b of the support element 16.
  • the support element 16 further comprises a plurality of radial protrusions that protrude ra- dially from the outer edge of the first portion 16a of this element.
  • the support element 16 comprises three radial protrusions (indicated with 20 ] , 20 2 and 20 3 , respectively), angularly spaced by 120° from one another.
  • the radial protrusions 20i, 20 2 and 20 3 are slightly thicker than the first portion 16a of the support element 16, i.e. they have a greater size in the axial direction than the first portion l6a, on both sides (top and bottom sides) of the first portion l6a.
  • each radial protrusion 20i, 20 2 and 20 3 may protrude about 0.1 mm, both upwards and downwards, relative to the first portion l6a.
  • the support element 16 further comprises, on the side axially opposite to the second portion 16b with respect to the first portion 16a, a third portion 16c, of cylindrical shape, that in the mounted condition of the contact sensor 14 on the foot 10 extends upwards relative to the first portion 16a.
  • the third portion 16c forms a rigid body together with the second portion 16b and is, therefore, also movable together with the second portion 16b relative to the tubular element 12 as a result of the elastic deformability of the first portion l6a.
  • the first portion 16a of the support element 16, with the respective radial protrusions 20i, 20 2 and 20 3 , as well as the second portion 16b and the third portion l6c, are made in a sin- gle piece.
  • the contact sensor 14 further comprises an electronic switch 22, preferably a uniaxial one, that is accommodated inside the tubular element 12 in the mounted condition of the sensor 14 on the foot 10 of a robot.
  • the switch 22 is accommo- dated, at least partially, in a sleeve 24 and is rigidly connected thereto, for example by means of screws 26.
  • the connection between the switch 22 and the sleeve 24 by means of the screws 26 provides the advantage of allowing adjustment of the relative axial position of the switch with respect to the sleeve.
  • the sleeve 24 is, in turn, accommodated in the tubular element 12 and is constrained there- to by means of a ring nut 28 that is screwed to the bottom end of the tubular element 12.
  • the ring nut 28 clamps the first portion 16a of the support element 16 and a flange 24a of the sleeve 24 against the bottom face (indicated with 12a) of the tubular element 12, thereby exerting an axial locking force onto the first portion 16a and the flange 24a.
  • the switch 22 is provided at its bottom, that is on the side facing towards the foot 10 and the support element 16, with a probe 30 having a spherical coupling surface 30a.
  • An elec- tric wire 32 extending inside the tubular element 12 is connected to the switch 22.
  • the switch 22 is configured to generate a contact signal when the displacement of the probe 30 exceeds a given threshold value.
  • the switch 22 may, for example, be a contact switch or a proximity switch arranged to measure the variation of capacitance resulting from the displacement of the probe.
  • the contact sensor 14 further comprises a transmission member 34 which extends along the axial direction x and is axially interposed between the support element 16 and the switch 22, so as to transmit to the switch 22, or, more precisely, to the probe 30 thereof, the small movements (in the order for example of tenths of a millimetre) of the assembly formed by the foot 10 and the portions 16b and l6c of the support element 16, which small movements are allowed by the elastic deformability of the portion 16a of the support ele- ment 16, when a force generated by the contact with the ground acts on the foot 10.
  • a transmission member 34 which extends along the axial direction x and is axially interposed between the support element 16 and the switch 22, so as to transmit to the switch 22, or, more precisely, to the probe 30 thereof, the small movements (in the order for example of tenths of a millimetre) of the assembly formed by the foot 10 and the portions 16b and l6c of the support element 16, which small movements are allowed by the elastic deformability of the portion 16a of
  • the transmission member 34 is rigidly connected, at a bottom end portion 34c thereof, to the support element 16, in particular to the third portion l6c of said element, so as to be movable like a rigid body together with said portion, and together with the second portion 16b of the support element 16 and the foot 10. Also the transmission member 34, as well as the portions 16b and l6c of the support element, is thus movable not only along the direc- tion of the longitudinal axis x, but also along a direction having a component perpendicular to the longitudinal axis x.
  • the transmission member 34 has, at a top end portion thereof (that is, the end portion axi- ally facing towards the switch 22), a conical coupling surface 34a, with which the spherical coupling surface 30a of the probe 30 cooperates.
  • the transmission member 34 further comprises an intermediate portion 34b, preferably of cylindrical shape, extending along the longitudinal axis x between the bottom end portion 34c and the top end portion defining the conical seat 34a.
  • Such a coupling between the switch 22 and the transmission member 34 allows to convert the dis- placements along multiple directions of the assembly formed by the portions l6b and l6c of the support element 16 and the foot 10, due to the fact that the contact force acting on the foot 10 is not necessarily directed along the axial direction x, but may have a non-axial component, into an axial displacement of the probe 30. Therefore, it is possible to sense contact forces acting on the foot 10 in more directions, rather than along the axial direction only, with the use of a simple uniaxial switch.
  • the transmission member 34 acts as an "amplifier" for amplifying the radial displacements of the assembly formed by the portions 16b and l6c of the support element 16 resulting from the deformation of the first portion 16a of the support element 16 due to the contact forces acting on the foot 10.
  • Such an amplification effect may be adjusted by acting on the one hand on the opening angle (indicated with a in Figure 1) of the conical seat 34a, and on the other on the length of the intermediate portion 34b of the transmission member 34, or, more precisely, on the ratio of the distance (indicated with Li in Figure 1) of the point of contact between the spherical coupling surface 30a of the probe 30 and the conical seat 34a of the transmission member 34 from the plane P (which distance depends, of course, on the length of the intermediate portion 34b of the transmission member 34) to the distance (indicated with L 2 in Figure 1) of the bottom end of the support element 16 from the plane P.
  • the angle a is comprised between 10 and 70 de- grees, more preferably between 20 and 60 degrees.
  • the ratio LI/L 2 is preferably comprised between 0.5 and 2. The change in the angle a, that affects the sensitivity of the sensor to a greater extent, will be used for a coarse adjustment, while the change in the distance Li, with the distance L 2 remaining unchanged (that is, with the length of the second portion 16b of the support element 16 remaining unchanged), will be used for a fine tuning.
  • the contact sensor 14 preferably further comprises a stop member 36 axially inter- posed between the first portion l6a of the support element 16 and the sleeve 24 to limit the axial movement of the assembly formed by the second portion l6b and the third portion 16c of the support element 16 and thus prevent excessive axial deformation of the first por- tion l6a of the support element 16. In this way, when an excessive force is exerted on the foot 10, the first portion l6a of the support element 16 goes into abutment against the stop member 36 and cannot therefore deform further.
  • the contact sensor 14 is assembled by mounting in order, at the bottom end of the tubular element 12, the various components of the sensor itself, namely the switch 22 with its sleeve 24, the transmission member 34, the stop member 36 (that may also be mounted in advance on the sleeve 24), the support element 16 and the ring nut 28, and then by screw - ing the ring nut 28 onto the bottom end of the tubular element 12 to hold the various com- ponents mentioned above in position. Finally, the foot 10 is rigidly connected to the sup- port element 16, in particular to the second portion 16b thereof.
  • the radial protrusions 201 , 20 2 and 20 3 of the support element 16 have a greater thickness than the first portion 16a of said element (for example, 0.1 mm thicker both on the upper side and on the lower one), so that a certain axial clearance is provided (for example, 0.1 mm) both on the upper side, between the first portion l6a of the support element 16 and the stop member 36, and on the lower one, between the first portion l6a of the support element 16 and the ring nut 28.
  • Said axial clearance allows the first portion l 6a of the support element 16 to elastically deform as a result of the contact force transmitted by the ground to the foot 10 and, thus, by the foot 10 to the support element 16.
  • a small radial clearance (for example, 0.1 mm) is provided between the trans- mission member 34 and the internal cylindrical surface of the sleeve 24 to limit the angular deformation of the first portion 16a of the support element 16 (resulting from the applica- tion of forces having non-axial components on the foot 10, and thus on the support element 16), and thus prevent the risk of damaging the first portion l 6a of the support element 16 due to excessive deformation.
  • the contact sensor 14 according to the invention operates therefore as follows.
  • the contact force exerted by the ground on the foot 10 is transmitted by the foot 10 to the support element 16 and causes, as a result of the elastic deformation of the first portion l6a of said element, a displacement of the assembly formed by the portions 16b and l6c of said element.
  • the direction and the amount of the elastic deformation of the portion l6a, and therefore also the direction and the amount of the displacement of the assembly formed by the portions 16b and 16c, will depend on the direction and the intensity of the contact force.
  • the first portion l6a is con- figured to deform also as a result of non-axial contact forces, i.e. of contact forces having non-axial components.
  • the contact sensor according to the invention comprises few pieces, that can be manufactured in a very simple and inexpensive way, and is therefore much simpler and less expensive than a conventional contact sensor using strain gauges.
  • a simple contact or proximity switch which does not require particularly complicated signal processing electronics, may be used as electronic switch.
  • the sensor further has a remarkably short response time, by virtue of the very small elastic deformation (and the high stiffness) of the elastically deformable portion of the support element, as well as by virtue of the reduced mass (and, therefore, reduced inertia) of the movable parts of the sensor. Since the deformability is obtained by virtue of the stiffness and shape of the support element itself, and not by virtue of an additional separate component (like, for example, a spring), the hysteresis effects are reduced.
  • all the components of the sensor can be mounted inside a tubular element, for example the tubular element forming the leg structure in case the contact sensor is used to sense the contact of a robot foot with the ground, and thus be protected from the outer environment. Therefore, the sensor can even be used in particularly hostile environments.

Landscapes

  • Physics & Mathematics (AREA)
  • General Physics & Mathematics (AREA)
  • Chemical & Material Sciences (AREA)
  • Analytical Chemistry (AREA)
  • Push-Button Switches (AREA)
  • Manipulator (AREA)

Abstract

The sensor (14) comprises: a contact element (10) arranged to receive a contact force; a switch (22) comprising a probe (30) arranged to undergo a displacement along a longitudinal direction (x) as a result of the application of a force on the contact element (10), the switch (22) being configured to generate a contact signal when the displacement of the probe (30) along the longitudinal direction (x) exceeds a given threshold value; a support element (16) to which the contact element (10) is rigidly connected, the support element (16) comprising a first portion (16a) configured to elastically deform as a result of the application of a force on the contact element (10); and a transmission member (34) rigidly connected to the support element (16) and extending along the longitudinal direction (x) between the support element (16) and the probe (30) to transmit a displacement to the probe (30) as a result of the elastic deformation of the first portion (16a) of the support element (16). The probe (30) and the transmission member (34) have respective coupling surfaces (30a, 34a) cooperating one with the other, wherein one (30a) of said surfaces has a spherical shape while the other one (34a) has a conical shape.

Description

Contact sensor, particularly for a robot foot
The present invention relates to a contact sensor, in particular for use on a robot provided with legs for sensing the contact of the foot of each leg of the robot with the ground.
It is known to use, on robots provided with legs, such as anthropomorphous robots or four- legged robots, contact sensors for sensing the contact of each foot of the robot with the ground. For example, anthropomorphous robots generally have six-axis force sensors posi- tioned in the ankle of each leg to measure the reaction forces generated by the ground, thereby allowing to determine the state of contact between the foot and the ground by comparison of the value of the normal force (i.e. of the force orthogonal to the ground) measured by the sensor with a given threshold value. It is also known to use multiple-axis force sensors in the feet of four-legged robots. Such force (or torque) sensors are typically based on the use of strain gauges and are, therefore, very expensive. Furthermore, force (or torque) sensors based on the use of strain gauges are very delicate, and therefore suscepti- ble to be damaged or loose precision in case of strong contacts, which are rather frequent in a four-legged robot that walks or trots. Therefore, the use of sensors of this type is prob- lematic on robots intended to move on rough terrains, even more so if said robots must also be able to jump.
US 2003/0213623 Al discloses a sensor intended to be used on a vehicle seat do determine the weight and the position of an occupant of the seat. The sensor basically comprises a contact element, an elongated transmission member rigidly connected to the contact ele- ment, a ball coupling device having a first part, that is rigidly connected to the transmission member and has a conical seat, and a second part, that is made as a ball and is partially ac- commodated in said seat, an elastic disk having a further conical seat where the ball is par- tially accommodated, and a strain gauge for sensing the load exerted on the elastic disk via the contact element, the transmission member and the ball coupling device.
Such known contact sensor is configured to sense axial loads only, i.e. loads transmitted to the contact element in the direction of the axis of the transmission shaft, by decoupling the (undesired) radial loads from the (desired) axial loads. EP 1 462 784 Al, on which the preamble of the appended independent claim 1 is based, discloses a device for measuring the reaction force transmitted by the ground to the foot of a walking robot, comprising a casing adapted to be mounted in a point of the foot of the robot facing the ground, a movable unit mounted in the casing and adapted to move rela- tive to the casing when a reaction force is transmitted by the ground to the foot of the ro- bot, and a sensor mounted in the casing to measure the reaction force of the ground trans- mitted via the movable unit.
Also the device known from EP 1 462 784 A 1 is only capable of sensing and measuring axial reaction forces, transmitted by the ground to the robot foot.
It is an object of the present invention to provide a contact sensor that has a high precision, that is simple and inexpensive to manufacture, and that is able to sense not only axial loads but also non-axial loads transmitted, for example by the ground, to the contact element of the sensor.
This and other objects are fully achieved according to the present invention by means of a contact sensor having the features set forth in the appended independent claim 1.
Advantageous embodiments of the present invention are defined in the dependent claims, the subject-matter of which is to be considered as forming an integral part of the following description.
The features and the advantages of the present invention will be clear from the following detailed description, given purely by way of non-limiting example with reference to the attached drawings, wherein:
Figure 1 is an axial section view of a contact sensor according to an embodiment of the present invention;
Figures 2 and 3 are a perspective view and a front elevation view, respectively, of the elastic support element of the contact sensor of Figure 1 ;
Figure 4 shows the detail A of Figure 1 on an enlarged scale; and
Figure 5 is a perspective view of the transmission member of the contact sensor of Figure 1.
The following description refers to the case of a contact sensor used in a robot foot, but it is clear that the invention is not to be intended as being limited to this specific application only.
With reference first to Figure 1, a robot foot is indicated with 10 and is mounted at the bot- tom end of a tubular element 12 forming part of the structure of a leg of the robot. The lon- gitudinal axis of the tubular element 12 is indicated x. The direction of the axis x will be hereinafter referred to as axial or longitudinal direction.
The foot 10 is provided with a contact sensor, generally indicated with 14, for sensing a condition of contact of the foot 10 with the ground.
The contact sensor 14 (hereinafter simply referred to as sensor) comprises, first of all, a support element 16, preferably made of metal. The support element 16 is mounted at the bottom end of the tubular element 12.
As shown in Figures 2 and 3, the support element 16 comprises a disk-shaped first portion l6a, extending in a plane perpendicular to the longitudinal axis x, and a cylindrical second portion (bottom portion) l6b, extending along the longitudinal axis x, the foot 10 being rigidly connected to said second portion, for example by threaded coupling.
The first portion l6a of the support element 16 is made as an elastically deformable portion, in particular in the axial direction, and to this end it preferably has one or more slits, conveniently shaped (for example, coil-shaped) and positioned. In the embodiment pro- posed herein, the first portion l6a has three coil-shaped slits, indicated with 18i, 1 82 and 183, respectively.
The second portion 16b of the support element 16 forms a rigid body that is movable (to- gether with the foot 10, to which, as already mentioned above, it is rigidly connected) rela- tive to the tubular element 12 as a result of the elastic deformability of the first portion l6a. In particular, the second portion 16b, along with the foot 10, is displaceable both axially (that is, along the direction of the longitudinal axis x) and radially (that is, along any direc- tion lying on a plane perpendicular to the longitudinal axis x), and is also tiltable about a centre of rotation R placed at the intersection of the longitudinal axis x with a median plane P of the first portion l6a perpendicular to the longitudinal axis x, as shown in Figures 1 and 4. In general, therefore, the second portion 16b of the support element 16 is movable, as a result of the elastic deformability of the first portion l6a, not only along the direction of the longitudinal axis x, but also along a direction having a component perpendicular to the longitudinal axis x.
Furthermore, as shown in Figure 4, an annular abutment surface lOa of the foot 10 rests on a shoulder 17 of the second portion l6b of the support element 16.
The support element 16 further comprises a plurality of radial protrusions that protrude ra- dially from the outer edge of the first portion 16a of this element. Preferably, as in the pre- sent embodiment, the support element 16 comprises three radial protrusions (indicated with 20] , 202 and 203, respectively), angularly spaced by 120° from one another. For the reasons that will be explained more in detail below, the radial protrusions 20i, 202 and 203 are slightly thicker than the first portion 16a of the support element 16, i.e. they have a greater size in the axial direction than the first portion l6a, on both sides (top and bottom sides) of the first portion l6a. For example, each radial protrusion 20i, 202 and 203 may protrude about 0.1 mm, both upwards and downwards, relative to the first portion l6a.
The support element 16 further comprises, on the side axially opposite to the second portion 16b with respect to the first portion 16a, a third portion 16c, of cylindrical shape, that in the mounted condition of the contact sensor 14 on the foot 10 extends upwards relative to the first portion 16a. The third portion 16c forms a rigid body together with the second portion 16b and is, therefore, also movable together with the second portion 16b relative to the tubular element 12 as a result of the elastic deformability of the first portion l6a.
The first portion 16a of the support element 16, with the respective radial protrusions 20i, 202 and 203, as well as the second portion 16b and the third portion l6c, are made in a sin- gle piece.
The contact sensor 14 further comprises an electronic switch 22, preferably a uniaxial one, that is accommodated inside the tubular element 12 in the mounted condition of the sensor 14 on the foot 10 of a robot.
More specifically, in the embodiment shown in the drawings, the switch 22 is accommo- dated, at least partially, in a sleeve 24 and is rigidly connected thereto, for example by means of screws 26. The connection between the switch 22 and the sleeve 24 by means of the screws 26 provides the advantage of allowing adjustment of the relative axial position of the switch with respect to the sleeve.
The sleeve 24 is, in turn, accommodated in the tubular element 12 and is constrained there- to by means of a ring nut 28 that is screwed to the bottom end of the tubular element 12. In the assembled condition, as shown in detail in Figure 4, the ring nut 28 clamps the first portion 16a of the support element 16 and a flange 24a of the sleeve 24 against the bottom face (indicated with 12a) of the tubular element 12, thereby exerting an axial locking force onto the first portion 16a and the flange 24a.
The switch 22 is provided at its bottom, that is on the side facing towards the foot 10 and the support element 16, with a probe 30 having a spherical coupling surface 30a. An elec- tric wire 32 extending inside the tubular element 12 is connected to the switch 22.
The switch 22 is configured to generate a contact signal when the displacement of the probe 30 exceeds a given threshold value. The switch 22 may, for example, be a contact switch or a proximity switch arranged to measure the variation of capacitance resulting from the displacement of the probe.
The contact sensor 14 further comprises a transmission member 34 which extends along the axial direction x and is axially interposed between the support element 16 and the switch 22, so as to transmit to the switch 22, or, more precisely, to the probe 30 thereof, the small movements (in the order for example of tenths of a millimetre) of the assembly formed by the foot 10 and the portions 16b and l6c of the support element 16, which small movements are allowed by the elastic deformability of the portion 16a of the support ele- ment 16, when a force generated by the contact with the ground acts on the foot 10.
The transmission member 34 is rigidly connected, at a bottom end portion 34c thereof, to the support element 16, in particular to the third portion l6c of said element, so as to be movable like a rigid body together with said portion, and together with the second portion 16b of the support element 16 and the foot 10. Also the transmission member 34, as well as the portions 16b and l6c of the support element, is thus movable not only along the direc- tion of the longitudinal axis x, but also along a direction having a component perpendicular to the longitudinal axis x.
The transmission member 34 has, at a top end portion thereof (that is, the end portion axi- ally facing towards the switch 22), a conical coupling surface 34a, with which the spherical coupling surface 30a of the probe 30 cooperates. The transmission member 34 further comprises an intermediate portion 34b, preferably of cylindrical shape, extending along the longitudinal axis x between the bottom end portion 34c and the top end portion defining the conical seat 34a.
Such a coupling between the switch 22 and the transmission member 34 (i.e. by means of a spherical surface on one side and a conical surface on the other) allows to convert the dis- placements along multiple directions of the assembly formed by the portions l6b and l6c of the support element 16 and the foot 10, due to the fact that the contact force acting on the foot 10 is not necessarily directed along the axial direction x, but may have a non-axial component, into an axial displacement of the probe 30. Therefore, it is possible to sense contact forces acting on the foot 10 in more directions, rather than along the axial direction only, with the use of a simple uniaxial switch.
In particular, the transmission member 34 acts as an "amplifier" for amplifying the radial displacements of the assembly formed by the portions 16b and l6c of the support element 16 resulting from the deformation of the first portion 16a of the support element 16 due to the contact forces acting on the foot 10. Such an amplification effect may be adjusted by acting on the one hand on the opening angle (indicated with a in Figure 1) of the conical seat 34a, and on the other on the length of the intermediate portion 34b of the transmission member 34, or, more precisely, on the ratio of the distance (indicated with Li in Figure 1) of the point of contact between the spherical coupling surface 30a of the probe 30 and the conical seat 34a of the transmission member 34 from the plane P (which distance depends, of course, on the length of the intermediate portion 34b of the transmission member 34) to the distance (indicated with L2 in Figure 1) of the bottom end of the support element 16 from the plane P. By changing the ratio LI/L2, together with the angle a, it is possible to control the level of sensitivity of the sensor to the radial forces, keeping the sensitivity to the axial forces unchanged. Preferably, the angle a is comprised between 10 and 70 de- grees, more preferably between 20 and 60 degrees. The ratio LI/L2 is preferably comprised between 0.5 and 2. The change in the angle a, that affects the sensitivity of the sensor to a greater extent, will be used for a coarse adjustment, while the change in the distance Li, with the distance L2 remaining unchanged (that is, with the length of the second portion 16b of the support element 16 remaining unchanged), will be used for a fine tuning.
Finally, the contact sensor 14 preferably further comprises a stop member 36 axially inter- posed between the first portion l6a of the support element 16 and the sleeve 24 to limit the axial movement of the assembly formed by the second portion l6b and the third portion 16c of the support element 16 and thus prevent excessive axial deformation of the first por- tion l6a of the support element 16. In this way, when an excessive force is exerted on the foot 10, the first portion l6a of the support element 16 goes into abutment against the stop member 36 and cannot therefore deform further.
The contact sensor 14 is assembled by mounting in order, at the bottom end of the tubular element 12, the various components of the sensor itself, namely the switch 22 with its sleeve 24, the transmission member 34, the stop member 36 (that may also be mounted in advance on the sleeve 24), the support element 16 and the ring nut 28, and then by screw - ing the ring nut 28 onto the bottom end of the tubular element 12 to hold the various com- ponents mentioned above in position. Finally, the foot 10 is rigidly connected to the sup- port element 16, in particular to the second portion 16b thereof. As explained above, the radial protrusions 201 , 202 and 203 of the support element 16 have a greater thickness than the first portion 16a of said element (for example, 0.1 mm thicker both on the upper side and on the lower one), so that a certain axial clearance is provided (for example, 0.1 mm) both on the upper side, between the first portion l6a of the support element 16 and the stop member 36, and on the lower one, between the first portion l6a of the support element 16 and the ring nut 28. Said axial clearance allows the first portion l 6a of the support element 16 to elastically deform as a result of the contact force transmitted by the ground to the foot 10 and, thus, by the foot 10 to the support element 16.
In addition, a small radial clearance (for example, 0.1 mm) is provided between the trans- mission member 34 and the internal cylindrical surface of the sleeve 24 to limit the angular deformation of the first portion 16a of the support element 16 (resulting from the applica- tion of forces having non-axial components on the foot 10, and thus on the support element 16), and thus prevent the risk of damaging the first portion l 6a of the support element 16 due to excessive deformation.
The contact sensor 14 according to the invention operates therefore as follows.
When the foot 10 comes in contact with the ground, the contact force exerted by the ground on the foot 10 is transmitted by the foot 10 to the support element 16 and causes, as a result of the elastic deformation of the first portion l6a of said element, a displacement of the assembly formed by the portions 16b and l6c of said element. The direction and the amount of the elastic deformation of the portion l6a, and therefore also the direction and the amount of the displacement of the assembly formed by the portions 16b and 16c, will depend on the direction and the intensity of the contact force. The first portion l6a is con- figured to deform also as a result of non-axial contact forces, i.e. of contact forces having non-axial components. The displacement of the assembly formed by the portions 16b and l 6c of the support element 16 is transmitted by the transmission member 34 to the probe 30 and causes, by virtue of the engagement between the coupling surface 30a of the probe 30 and the coupling surface 34a of the transmission member 34, an upward axial displace ment of the probe 30. Such a displacement, if large enough, will cause triggering of the switch 22 and, thus, the generation of an electric contact signal. In view of the above description, the advantages obtainable with a contact sensor according to the present invention are clear.
First of all, the contact sensor according to the invention comprises few pieces, that can be manufactured in a very simple and inexpensive way, and is therefore much simpler and less expensive than a conventional contact sensor using strain gauges.
In addition, a simple contact or proximity switch, which does not require particularly complicated signal processing electronics, may be used as electronic switch.
The sensor further has a remarkably short response time, by virtue of the very small elastic deformation (and the high stiffness) of the elastically deformable portion of the support element, as well as by virtue of the reduced mass (and, therefore, reduced inertia) of the movable parts of the sensor. Since the deformability is obtained by virtue of the stiffness and shape of the support element itself, and not by virtue of an additional separate component (like, for example, a spring), the hysteresis effects are reduced.
Furthermore, all the components of the sensor can be mounted inside a tubular element, for example the tubular element forming the leg structure in case the contact sensor is used to sense the contact of a robot foot with the ground, and thus be protected from the outer environment. Therefore, the sensor can even be used in particularly hostile environments.
Naturally, the principle of the invention remaining unchanged, the embodiments and the constructional details may vary widely from those described and illustrated purely by way of non-limiting example, without thereby departing from the scope of the invention as defined in the appended claims.

Claims

1. Contact sensor ( 14) comprising:
a contact element (10) arranged to receive a contact force, in particular in case of contact with the ground;
a switch (22) comprising a probe (30) arranged to undergo a displacement along a longitudinal direction (x) as a result of the application of a force on the contact element (10), said switch (22) being configured to generate a contact signal when the displacement of the probe (30) along said longitudinal direction (x) exceeds a given threshold value; a support element (16) rigidly connected to the contact element (10);
elastically deformable means (l6a) which are configured to elastically deform as a result of the application of a force on the contact element (10) and are operatively associat- ed with the support element (16) so as to allow a displacement of the support element (16), together with the contact element (10), as a result of the application of a contact force on the contact element (10); and
a transmission member (34) which is rigidly connected to the support element (16) and extends along said longitudinal direction (x) between the support element (16) and the probe (30) of the switch (22) to transmit a displacement to the probe (30) as a result of the elastic deformation of said elastic means (l6a);
wherein the probe (30) and the transmission member (34) have respective coupling surfaces (30a, 34a) cooperating one with the other;
characterized
in that said elastically deformable means (l6a) are formed by a first portion (l6a) of the support element (16),
in that the transmission member (34) is configured and mounted so that it is movable not only along said longitudinal direction (x), but also along a direction having a component perpendicular to said longitudinal direction (x), and
in that one of said coupling surfaces (30a, 34a) has a spherical shape, while the other one (34a) has a conical shape.
2. Contact sensor according to claim 1 , wherein the opening angle (a) of the conical coupling surface (34a) is comprised between 10 and 70 degrees, preferably between 20 and 60 degrees.
3. Contact sensor according to claim 1 or claim 2, wherein the spherical coupling sur- face (30a) is formed by the probe (30), while the conical coupling surface (34a) is formed by the transmission member (34).
4. Contact sensor according to any one of the preceding claims, wherein said first por- tion (l6a) of the support element (16) is a disk-shaped portion extending in a plane per- pendicular to said longitudinal direction (x) and having a plurality of slits (181, 182, l 83).
5. Contact sensor according to claim 4, wherein the support element (16) further corn- prises a second portion ( 16b) extending along said longitudinal direction (x) from said first' portion (l6a) towards the contact element (10), the contact element (10) being rigidly con- nected to the support element (16) at said second portion ( 16b).
6. Contact sensor according to claim 4 or claim 5, wherein the support element (16) further comprises a third portion (l 6c) extending along said longitudinal direction (x) from said first portion (l 6a) towards the probe (30), the transmission member (34) being rigidly connected to the support element (16) at said third portion (l 6c).
7. Contact sensor according to claim 4 or claim 5, wherein the ratio of the distance (Li) of the point of contact between said coupling surfaces (30a, 34a) from a median plane (P) of said first portion (l 6a) of the support element (16) perpendicular to said longitudinal direction (x) to the distance (L2) of the end of said second portion (16a) of the support ele- ment (16) facing towards the contact element (10) from said median plane (P) is comprised between 0.5 and 2.
8. Contact sensor according to any one of the preceding claims, further comprising a sleeve (24) which extends along said longitudinal direction (x) and in which the probe (30) and the transmission member (34) are accommodated.
9. Contact sensor according to claim 8, wherein the switch (22) is rigidly connected to the sleeve (24) by connection means (26) adapted to allow adjustment of the relative posi- tion of the switch (22) with respect to the sleeve (24) along said longitudinal direction (x).
10. Contact sensor according to any one of the preceding claims, wherein the switch (22) is a contact switch or a proximity switch.
1 1. Robot leg comprising a foot (10) and a contact sensor (14) according to any one of the preceding claims, wherein the foot (10) forms the contact element of the contact sensor (14).
PCT/IB2019/050894 2018-02-05 2019-02-05 Contact sensor, particularly for a robot foot WO2019150339A1 (en)

Applications Claiming Priority (2)

Application Number Priority Date Filing Date Title
IT102018000002407 2018-02-05
IT201800002407A IT201800002407A1 (en) 2018-02-05 2018-02-05 Contact sensor, especially for robot foot.

Publications (1)

Publication Number Publication Date
WO2019150339A1 true WO2019150339A1 (en) 2019-08-08

Family

ID=62044896

Family Applications (1)

Application Number Title Priority Date Filing Date
PCT/IB2019/050894 WO2019150339A1 (en) 2018-02-05 2019-02-05 Contact sensor, particularly for a robot foot

Country Status (2)

Country Link
IT (1) IT201800002407A1 (en)
WO (1) WO2019150339A1 (en)

Citations (2)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
DE4416874A1 (en) * 1994-05-13 1995-11-16 Univ Freiberg Bergakademie Edge tension measuring device for contact-point between workshop tool and workpiece
EP1462784A1 (en) * 2003-02-27 2004-09-29 Samsung Electronics Co., Ltd. Ground reaction force measuring module for walking robot and robot foot structure adopting the same

Family Cites Families (2)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
JP2005517951A (en) * 2002-02-21 2005-06-16 インテリジェント メカトロニック システムズ インコーポレイテッド Vehicle seat (preload) load cell with lateral and angular adjustment
US9513721B2 (en) * 2013-09-12 2016-12-06 Microsoft Technology Licensing, Llc Pressure sensitive stylus for a digitizer

Patent Citations (2)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
DE4416874A1 (en) * 1994-05-13 1995-11-16 Univ Freiberg Bergakademie Edge tension measuring device for contact-point between workshop tool and workpiece
EP1462784A1 (en) * 2003-02-27 2004-09-29 Samsung Electronics Co., Ltd. Ground reaction force measuring module for walking robot and robot foot structure adopting the same

Also Published As

Publication number Publication date
IT201800002407A1 (en) 2019-08-05

Similar Documents

Publication Publication Date Title
US4747313A (en) Tactile sensor
US4811608A (en) Force and torque converter
EP1880163B1 (en) Dimensional measurement probe
US9823144B2 (en) Load sensor
EP0740768B1 (en) Touch probe
JP3400377B2 (en) Foot sensor and humanoid robot having the same
US8502776B2 (en) Joystick controller
JPH0139522B2 (en)
CA2907581A1 (en) High density actuator with minimal lateral torsion
US7317167B2 (en) Weighing module with precisely-positionable overload protection device
CN113525549B (en) Robot foot and robot with same
WO2019150339A1 (en) Contact sensor, particularly for a robot foot
KR20200129047A (en) Dual mode sensing joystick assembly
JP2024534244A (en) Scanning Probe
WO2002043984A3 (en) Weight sensor assembly with overload spring
KR100813681B1 (en) Force sensor
US20150192484A1 (en) Device for detecting the state of a machine element
EP1595116A1 (en) Method and devices for measuring weight
US4977775A (en) Torque transducer
Hosseini et al. Design and implementation of a simple and low-cost optoelectronic force sensor for robotic applications
RU2296307C1 (en) Device for checking drawing-up force of threaded connection
JP2520050B2 (en) Pressure sensor
JP7631550B2 (en) TRAILER LANDING GEAR HAVING FORCE MEASURING ELEMENTS - Patent application
JP5402675B2 (en) Joystick device for vehicle control
JP5889039B2 (en) Shock absorber and built-in weighing device using it

Legal Events

Date Code Title Description
121 Ep: the epo has been informed by wipo that ep was designated in this application

Ref document number: 19710133

Country of ref document: EP

Kind code of ref document: A1

NENP Non-entry into the national phase

Ref country code: DE

122 Ep: pct application non-entry in european phase

Ref document number: 19710133

Country of ref document: EP

Kind code of ref document: A1