WO2017194527A1

WO2017194527A1 - A task-custom finger device for kinesthetic and cutaneous feedback

Info

Publication number: WO2017194527A1
Application number: PCT/EP2017/061032
Authority: WO
Inventors: Domenico PRATTICHIZZO; Monica MALVEZZI; Francesco CHINELLO; Claudio PACCHIEROTTI
Original assignee: Università Degli Studi Di Siena
Priority date: 2016-05-09
Filing date: 2017-05-09
Publication date: 2017-11-16
Also published as: ITUA20163624A1

Abstract

A finger exoskeleton device (1) providing both kinesthetic stimuli along the finger and three-dimensional cutaneous force on the fingertip surface, either generated independently to each other or at the same time, which can be used for rehabilitation purposes, teleoperation, telecommuting, gaming, comprises a proximal portion, apt to be worn at the first phalanx of a finger, and a fingertip portion, apt to be fixed to a distal phalanx and provided with a distal clamp (2), wherein the proximal portion comprises a proximal servomotor (4), acting on a link (6) having an elongated rod (7) connected to said fingertip portion, and at least one potentiometer (11) to sense the rotation of said link (6) with respect to the proximal portion. The fingertip portion comprises three different distal servomotors (22, 23, 24), displaced to form a triangle by their respective axes, and a platform (28) rotatably linked to the axes of said distal servomotors (22, 23, 24) through the respective rigid and articulated arms (25, 26), the platform (28) being positioned to contact the finger pulp.

Description

A TASK-CUSTOM FINGER DEVICE FOR KINESTHETIC AND CUTANEOUS

FEEDBACK

Description

The present invention is related to a task-custom haptic finger exoskeleton device able to apply both kinesthetic stimuli along the finger and three-dimensional cutaneous forces on the finger pulp, either generated independently to each other or at the same time, which can be used in a rehabilitative scenario and/or in robotic control.

In this connection, several finger exoskeletons are known, which can be used to transmit or sense forces, i.e. either to a single finger or to the whole human hand .

US patent No. 5,516,249 A discloses a wearable master system and methods to remotely control an industrial machine as a slave robot. The device can provide kinesthetic force feedback to the operator to return a physical sensation of the resistive forces encountered by the slave side. This device can be applied to two opposed human fingers, i.e., the index finger and the thumb. However, it cannot independently provide a cutaneous feedback to the operator's fingertips. Moreover, the disclosed structure does not present a modular mechanics, which enable the user to wear the device in different fingers and to select the use of the kinesthetic module and/or the cutaneous module.

Chinese patent No. 10-3,251,494 B discloses an active/passive cable-driven exoskeleton finger for rehabilitation, comprising mechanics and drivers designed to be worn and provide force feedback. This device can assist the patient in rehabilitative tasks for finger articulations using force feedback to help motor control modulation. However, again, no independent cutaneous stimulation is provided to the operator, either referred to the fingertip or to the phalanges. Also in this case, it is not modular.

International patent application No. WO 2014/033613 discloses a hand exoskeleton having four finger exoskeletons independent to each other, which can assist the rotation of each single finger joint in a rehabilitative scenario. The device is designed to be worn by the user and to independently control each finger. However, it is not possible to separate each finger from the main structure.

International patent application No. WO 2014/068509 disclose a hand exoskeleton device for handwriting rehabilitation .

In this connection, the aim of the presented invention is to devise a finger exoskeleton that can overcome the drawbacks shown in the prior art, i.e., the absence of cutaneous feedback connected to finger kinesthetic device; the lack of modularity, in order to let the user choose the type of feedback for each application; and the need of a low-power device with a simple and portable mechanical design.

This aim is achieved by a finger device as defined in appended claim 1. Further details of the present invention are referred in the accompanying dependent claim.

According to the present invention, the finger exoskeleton device can provide, either at the same time or independently to each other, both cutaneous and kinesthetic feedback, through specifically provided end- effectors. This feature enriches the variety of the applicable haptic stimuli. Moreover, it overcomes the impedance control stability problems due to rigid contacts and time delays since providing solely cutaneous stimuli does not affect the stability of the teleoperation system.

It is also possible to adapt the exoskeleton to fit different finger lengths, thanks to the presence of a passive prismatic joint placed along the finger.

The presented finger device can use commercial servomotors to provide the required forces to the flexion-extension finger movement. The actuators are located along the finger to provide kinesthetic and/or the cutaneous feedback on each finger in the most unobtrusive way.

The modularity of this exoskeleton allows the user to choose the best configuration related to the task he/she needs to perform.

According to the invention, cutaneous force is rendered by a mobile flat platform placed under the fingertip. The mobile platform can translate and orient in three- dimensional space, independently from the kinesthetic force generated by the kinaesthetic module on the finger.

According to the invention, the herein disclosed device represents an easy-to-wear and low-cost system for virtual interaction, gaming, rehabilitation, and teleoperation . It has a design that can be easily extended to the whole hand: the compact form factor enables, in fact, the user to easily worn five exoskeletons on one hand. The finger exoskeleton of this invention will be disclosed hereinafter with reference to a preferred embodiment thereof, given with exemplificative and no limitative purpose in connection with the annexed drawings wherein:

· Figure 1 shows a perspective view of a finger exoskeleton device according to the present invention; • Figure 2 shows an exploded perspective view of the finger exoskeleton device of Figure 1;

• Figure 3 shows an exploded perspective view of a proximal portion of the finger exoskeleton device of figure 1; and

• Figure 4 shows a partially exploded perspective view of a fingertip portion of the finger exoskeleton device of figure 1.

With reference to the figures, a finger exoskeleton device is indicated as 1. It comprises a portion related to the proximal phalanx (Figure 3) , apt to be grounded at the first portion of any operator' s finger, and a fingertip side (Figure 4), apt to be fixed to the distal phalanx, wherein a mobile platform is located to provide cutaneous stimuli to the user's finger pulp.

This last structural element is connected to the finger by a clamp 2 enveloping the joint finger between the middle and the distal finger phalanges. The information provided to the finger pulp includes an orientation (roll and pitch) and a compression provided by the surface which is virtually in contact with the finger pulp.

At the proximal portion, the device 1 comprises a proximal ring 3, or an equivalent proximal clamp, to secure the device on the finger. The ring 3 may be provided with two separated branches linked by a hinge, to fit different finger sizes. An elastic and deformable ring can be used as well.

The proximal ring 3 supports a first servomotor 4 apt to provide a force at the proximal end 5 of a prismatic passive link 6 embodied by an elongated rod 7 having a longitudinal slit 8 wherein a proximal pin 9 is inserted to rotate and slide along the elongated rod 7, whose length corresponds to the finger length.

The first servomotor 4 can exert a reaction force at the proximal ring 3, while a proximal plate 10, below the first servomotor 4, is rigidly connected to a first potentiometer 11 to sense any rotation between the prismatic link 6 and the proximal ring 3. To this purpose, the first potentiometer 11 is connected to said proximal pin 9 by a proximal rotating arm 12.

At the distal clamp 2, the device 1 comprises a second potentiometer 13, namely a rotational passive joint potentiometer, which may allow the relative rotation of a distal end 14 of the prismatic link 6 through a distal pin 15.

In turn, the distal clamp 2, comprising two separate distal branches 16, works as a fastener around the distal phalanx so as to obtain a rigid connection, and it is hingedly connected to a distal assembly 20, apt to carry out a haptic device providing a cutaneous feedback at the finger pulp.

Clamp 2 and distal assembly 20 are connected through a rigid member 17 parallel to the prismatic link, when the finger is extended and straight, to place the distal assembly 20 at the finger pulp.

Such a distal assembly 20 (Figure 4) comprises a support plate 21 on which three different distal servomotors are mounted, namely a first distal servomotor 22 at the right side of the finger, a second distal servomotor 23 at the left side of the finger, and a third distal servomotor 24 at the distal end of the finger, displaced on the supporting plate to form an equilateral triangle.

Each distal servomotor shaft is connected to a distal rigid arm, namely a first distal rigid arm 25, a second distal rigid arm (not shown, on the opposite side of the first distal arm 25) and a third distal rigid arm 26, through a respective double rotational joint 27 having an input axis corresponding to the servomotor axis and an output axis which is parallel to the input axis (Figure 4) .

Each distal arm is then rotatably articulated to a mobile haptic platform 28 by universal joints 29, i.e., joints allowing a rotation around any axes, so as to have the axes of said distal servomotors and said haptic platform 28 linked together.

It should be noted that the output axes of each rotational joint 27 form together a triangle on a single plane (Figure 4) .

Between the support plate 21 and the mobile haptic platform 28, there is a space to house the distal phalanx of the finger, so that the pulp is in contact with the upper side of the mobile haptic platform, and a cutaneous force may be applied to the pulp when the said distal servomotors are activated. To sense the forces applied by the mobile haptic platform 28 on the finger pulp, a pressure sensor, possibly a piezo-resistive sensor 30, is placed on the upper side of the mobile platform 28.

On the upper side of the distal portion, a three-arm cross 31 is placed to secure the distal servomotors.

The above described exoskeleton structure has six freedom degrees, and three of them are motorised.

The communication between the finger exoskeleton device and an external terminal can be realized through a USB cable, while the power may be supplied by an external AC- DC converter. The firmware is installed on-board, possibly written in Arduino^® C-like language, while an external library is used to communicate with an external computer .

The device can use two different levels of control. A low-level control is characterized by the position regulation of each servomotor, i.e., the controller is installed inside - each servomotor and it regulates the motors position.

A possible prototype of the present invention can employ a HS-40 servo motor by Hitec RCD, to generate kinaesthetic force on the finger On the other hand, it can use a HS5035HD servo motor by Hitech RCD to move the mobile platform at the fingertip.

In order to set the target motor position, a high-level controller is implemented on the Arduino board. A specific controller, e.g. a controller by Atmega, is installed on such board to read the force measured by the piezoelectric sensor placed on the haptic platform, compensating the error between the desired force and the current one .

Moreover, the controller reads the position of the kinesthetic finger exoskeleton using the potentiometer. This allows the user to monitor the actual position of the finger.

In Table 1, an example of the exoskeleton device elements is detailed through its feature and performance thereof.

Motor HS-40 HS-5035HD

Motor type Analog, 3 poles Digital, 3 poles

Speed (4,8 V) 0,10 s/60° 0,10 s/60°

Stall-torque 0,6 kg · cm 0,8 kg · cm

Size (mm) 20x8, 6x17 18, 6x7, 6x15, 5

Weight (g) 4,8 4,5

(Table 1) The maximum force applicable on the fingertip is 4.5 N, when all the three motors are pulling the platform together. The maximum force on the kinaesthetic exoskeleton depends on the length at which the prismatic link has to be set. The prismatic link on the kinesthetic exoskeleton has two roles: allowing to the device to fit different fingertip sizes and providing kinesthetic force, also enabling the flexion-extension movements with difference impedance levels.

Both in the kinesthetic (proximal) and cutaneous (distal) elements, the force is provided by controlling the position of the servomotors.

As it is apparent from the above description, the haptic finger exoskeleton is easily wearable on a finger, since its structure can be achieved with light and small components, and it may be rigidly connected to further different apparatuses, like a desktop haptic interface.

To the above-described haptic finger exoskeleton device a person skilled in the art, with the purpose of satisfying additional and contingent needs, could introduce several additional modifications and variants, however all comprised within the protective scope of the present invention, as defined by the enclosed claims.

Claims

1. A finger exoskeleton device (1) comprising a proximal portion, apt to be worn at the first phalanx of a finger, and a fingertip portion, apt to be fixed to a distal phalanx and provided with a distal clamp (2), wherein the proximal portion comprises a proximal servomotor (4), acting on a link (6) having an extensible rod (7) connected to said fingertip portion, and at least one potentiometer (11, 13) to sense the rotation of said link (6) with respect to the proximal portion,

characterised in that the fingertip portion comprises:

• three different distal servomotors (22, 23, 24), displaced to form a triangle by their respective axes; and

· a haptic platform (28), linked to the axes of said distal servomotors (22, 23, 24) through respective distal rigid arms (25, 26), positioned to contact the finger pulp,

wherein each rigid distal arm (25, 26) is rotatably articulated to the respective distal servomotor axis through a respective double rotational joint (27) having an input axis corresponding to the servomotor axis and an output axis which is parallel to the input axis, and to the haptic platform (28) by corresponding universal joints (29) allowing a rotation around any axis, the output axes of each rotational joint (27) forming a triangle on a single plane.

2. The finger exoskeleton device according to claim 1, comprising, at the proximal portion, a proximal ring (3) supporting said proximal servomotor (4) .

3. The finger exoskeleton device according to claim 1, wherein said elongated rod (7) has a longitudinal slit (8) wherein a proximal pin (9) is inserted to rotate and slide along the elongated rod (7), the pin (9) being connected to said proximal servomotor (4) .

4. The finger exoskeleton device according to claim 1, comprising a first potentiometer (11) at the proximal portion, to sense any rotation of the link (6), and a rotational passive joint (13) at the fingertip portion, to sense the relative rotation of a distal end (14) of the link (6) .

5. The finger exoskeleton device according to claim 1, wherein said distal servomotors (22, 23, 24) are mounted on a support plate (21) connected to said clamp (2), between the support plate (21) and the haptic platform (28) a space being provided, said distal arms (25, 26) acting as spacers, to house the distal phalanx of the fingers, so that the pulp is in contact with the upper face of the haptic platform (28) .

6. The finger exoskeleton device according to claim 1, wherein, on a upper face of the haptic platform (28), a pressure sensor is placed, possibly a piezo-resistive sensor (30), in contact to the finger pulp.