WO2025215553A1

WO2025215553A1 - Impact control method for a robotic gripper

Info

Publication number: WO2025215553A1
Application number: PCT/IB2025/053735
Authority: WO
Inventors: Simone CORTINOVIS; Rocco Antonio ROMEO; Marco Rossi
Original assignee: Fondazione Istituto Italiano di Tecnologia; Camozzi Automation SpA
Current assignee: Fondazione Istituto Italiano di Tecnologia; Camozzi Automation SpA
Priority date: 2024-04-09
Filing date: 2025-04-09
Publication date: 2025-10-16
Anticipated expiration: 2026-10-09

Abstract

A method for controlling the impact between the gripping fingers of a robotic gripper and an object to be gripped comprises the steps of : a) setting a set-point value of the gripper closing speed; b) controlling the movement of the gripper at the closing speed set-point value; c1) calculating a speed datum representative of the closing speed; c2) comparing said speed datum with a speed threshold value; d1) calculating a datum for the current absorbed by the gripper; d2) comparing said absorbed current datum with a pre- established absorbed current threshold value; e) determining whether the gripping fingers have impacted upon the object when the speed datum is lower than the speed threshold value or when the absorbed current value is above the absorbed current threshold value; f) activating a braking device as soon as an impact is detected.

Description

"Impact control method for a robotic gripper" DESCRIPTION

[0001] The present invention relates to the field o f robotic grippers and relates in particular to a method for controlling the impact between the gripping fingers of a robotic gripper and an obj ect to be gripped .

[0002] In recent decades , with the aim of creating machines that are able to interact with humans in unstructured environments , robotics has seen considerable progress in both design and control algorithms . In this context , numerous methods have been developed for managing impacts or collisions between robots and the surrounding environment [ 1 ] .

[0003] However, the development and control of robotic grippers has received relatively little attention compared to other aspects of robotics . The gripping of obj ects is often uncontrolled, especially due to a lack of control over the gripping force . Elastic components are usually pre ferred over algorithmic solutions . For example , the patent publication [ 2 ] demonstrates how an 0-ring, suitably integrated into the mechanical transmission of a gripper , may reduce the peak force resulting from an impact .

[0004] Although elastic components may help to dampen impact forces , the use of such components also has several disadvantages. In particular:

[0005] - a reduction in the precision of the force: elasticity may cause unpredictable deformations thereby compromising precise controlling of the force;

[0006] - inconsistent gripping: variability in the elastic response may lead to less repeatable gripping forces;

[0007] - a prolonged settling time: oscillations deriving from elastic elements may delay system stabilization;

[0008] - an increase in mechanical complexity: elastic components have to be appropriately arranged within the mechanical transmission.

[0009] The present invention instead proposes a method for managing the force exerted at the point of contact between the robotic fingers and objects of unknown size during the gripping process, regardless of the hardness of the object. The main challenge is to develop an algorithm that is capable of detecting impacts that occur between the fingers and the object thereby allowing the hardware, i.e., the robotic gripper, to react quickly and avoid damage to the mechanical transmission or to the object itself.

[0010] A previous study [3] presented a gripper design and a method for detecting and managing unforeseen impacts between the fingers and the surrounding environment. The problem of impacts between gripping fingers and gripped obj ects has not however been addressed .

[0011] Regarding the detection of impact with gripped obj ects and the consequent containment of force spikes , an approach has been described in [ 4 ] that provides for optimi zation of the contact area of the gripper fingers .

[0012] In [ 5 ] , a collision between the gripping fingers and the obj ect is detected using force and torque information .

[0013] One obj ect of the present invention is to propose a method for controlling the impact between the gripping fingers of a robotic gripper and an obj ect to be gripped, which does not require the use of force or torque sensors and which nonetheless avoids the risk of damage to the gripper and/or the gripped obj ect due to impact .

[0014] Another obj ect of the invention is to control the impact between the gripping fingers of a robotic gripper and an obj ect to be gripped, which, in addition to not requiring the use of force or torque sensors , may be used ef fectively even without knowing the si ze of the obj ect to be gripped .

[0015] Such obj ects are achieved using a control method according to claim 1 and a robotic gripper according to claim 7 . The dependent claims describe preferred or advantageous embodiments of the control method and of the robotic gripper . [0016] Further features and advantages of the control method and of the robotic gripper according to the invention shall be made readily apparent from the following description of preferred embodiments thereof , provided purely by way of non-limiting example , with reference to the accompanying figures , wherein :

[0017] - Figure 1 is a flow chart of the method for controlling the impact between the fingers of the robotic gripper and an obj ect to be gripped, in one embodiment ;

[0018] - Figure la is a flow diagram of the control method, in an embodiment variant of the control method of Figure 1 ;

[0019] - Figure 2 is a flowchart of the control method, in another embodiment ;

[0020] - Figure 3 is a flowchart of the control method, in a further embodiment ;

[0021] - Figures 4 and 4a are a perspective view and a cross section of an example of a robotic gripper that implements the control method according to the invention; [0022] - Figure 5 shows a comparison between graphs of the position, speed and gripping force curves , obtained from experimental data and simulations , in the case of an impact at 500 rpm ( revolutions per minute ) with a rigid obj ect , in the absence ( Figure 5 ( a ) ) and in the presence ( Figure 5 (b ) ) of the control method according to the invention;

[0023] - Figure 6 represents the same comparison between the graphs of Figure 5 , but in the case of impact at 1000 rpm;

[0024] - Figure 7 represents graphs obtained from experimental data and simulated data of the position, speed, current and gripping force curves , obtained from experimental data and simulations , in the case of an impact with a so ft obj ect and using the impact control method according to the invention; and

[0025] - Figure 8 shows a diagram of the detected speed signal and the set-point speed and a diagram of the relative acceleration signal .

[0026] In the description that follows , all directional references ( for example , upper, lower, upward, downward, left , right , towards the left , towards the right , at the top, at the bottom, above , below, vertical , hori zontal , clockwise and counterclockwise ) are used only for identi fication purposes in order to help the reader understand the described embodiments and do not create limitations , in particular with regard to the position, orientation or use of the described embodiments .

[0027] The j oining references ( for example , fixed, coupled, connected, and the like ) must be interpreted broadly and may include intermediate elements between a connection of elements and a relative movement between elements . The j oining references do not there fore necessarily imply that two elements are directly connected in a fixed relationship therebetween .

[0028] Embodiments of the method for controlling the impact between the gripping fingers of an electrically operated robotic gripper and an obj ect to be gripped will be described below .

[0029] In the following description, the impact control method will refer to a rigid item to be gripped and a soft item to be gripped . The term " rigid obj ect" is intended to identi fy an obj ect that , at the moment of impact using the gripping fingers of the robotic gripper, does not substantially deform and wherein stopping the stroke of the fingers or the movable finger of the gripper, could instead cause , at least under certain conditions , damage to the gripping fingers and/or to the system for transmitting the motion from the actuator of the gripper to the gripping fingers . I f the obj ect is rigid but fragile , being impacted by the gripping f ingers may also cause the obj ect to break .

[0030] The term " soft obj ect" instead refers to an obj ect that , at the time of impact with the gripping fingers of the robotic gripper, may deform and not therefore provoking the instantaneous arrest of the stroke of the gripping fingers, or of a movable finger of the gripper. Also in this case, however, the impact control method described below makes it possible to avoid, or in any case limit, deformation of the object.

[0031] The impact control method described below applies to a robotic gripper 100 comprising an electric gripper actuator 102 which controls the movement of one or more gripping fingers 112.

[0032] In fact, the proposed impact control method is based upon the fact that, at the time of impact with an object, in the case of a rigid object, the speed of the gripping fingers undergoes a drastic reduction, while in the case of a soft object the current absorbed by the gripper actuator increases significantly in order to keep the speed of the gripping fingers constant whilst the object deforms .

[0033] In the remainder of the description, for simplicity of presentation, reference will be made to a robotic gripper having two or more gripping fingers 112, translatable along a translation direction X between an inactive position (i.e., object released) and an active position (i.e., gripping the object) . However, it is clear to the person skilled in the art that the proposed impact control method may also be used, in addition to the case of a single finger that is movable with respect to at least a second fixed finger, in robotic grippers wherein one or more gripping fingers may be controlled in order to perform a non-rectilinear gripping movement.

[0034] With reference to the flow chart of Figure 1, in one embodiment the impact control method 1 provides for setting a set-point value v_sp of the closing speed of the gripping fingers on the object to be gripped, at least in an end part of the finger closing stroke (step 10) .

[0035] In one embodiment, the fingers 112 of the gripper are controlled so as to begin their displacement from the inactive starting position towards the gripping position of the object with a first rapid acceleration step.

[0036] After this first rapid acceleration step, if provided, the gripping fingers are controlled so as to move with a constant speed corresponding to the set-point speed (step 12) , at least in the end part of the finger closing stroke.

[0037] In one embodiment, the set-point value of the closing speed is different depending upon whether the object to be gripped is rigid or soft. In the first case, in fact, the set-point speed (V_sp,hard) is lower, so as to keep the force of impact within a safety range, i.e., so as to protect the mechanics of the gripper from possible damage. In the case of a soft object, the set-point speed (V_sp, soft) may be determined according to the maximum force of impact that the soft object may withstand without undergoing excessive deformation, i.e., in such a way as to prevent the risk of damage to the object or plastic deformations .

[0038] If the object to be gripped is a rigid object, a speed datum (F(wfb) ) is calculated, at least in the end part of the closing stroke, that is representative of the closing speed Ma. For example, the speed datum is obtained by sampling the closing speed of the gripping fingers and calculating the maximum value or average value of a set of detected samples.

[0039] For example, in the case of using a rotating electric motor as an actuator for moving the gripping fingers, the angular velocity of the motor is monitored (step 14 ) .

[0040] For example, the closing speed is obtained by calculating the derivative of the position values of the gripping fingers, for example measured using an encoder associated with the motor shaft.

[0041] The speed datum obtained is then compared with a speed threshold value wth calculated as a function of the set-point value v_st (step 16) .

[0042] For example, the speed threshold value wth is calculated as a percentage of the set-point value, for example 90% of the set-point value. [0043] If the object to be gripped is instead a soft object, an absorbed current datum is calculated, at least in the end part of the closing stroke ( f ( I f b ) ) , that is representative of the current absorbed by the electric actuator (step 18) .

[0044] The absorbed current datum ( f ( I f ) ) is compared with a pre-established absorbed current threshold value Ith (step 20) .

[0045] If the absorbed current datum is above the absorbed current threshold value, then it may be determined that the gripping fingers have impacted upon the object to be gripped .

[0046] In fact, the softness, i.e., the elasticity of the object to be gripped, would make it more complicated to use the speed datum as an indicator of impact. The fingers could in fact maintain the desired set-point speed, or a value very close thereto, even after contact. However, the speed controller adjusts the current by increasing it in order to overcome the resistance of the object. In this case, an impact is therefore identified when the result of a current function, for example the average or maximum over a certain number of samples, exceeds the predetermined threshold value.

[0047] In both cases, when an impact is detected, a finger movement braking function may be activated (step 22) .

[0048] Such activation preferably occurs in a substantially instantaneous manner as soon as the impact is detected.

[0049] In particular, the braking function is implemented by activating a dedicated braking device.

[0050] In fact, immediate activation results in a significant decrease in the peak force and the steady state gripping force. Once the brake is actuated, the gripped object remains locked with a gripping force that is determined by the impact speed and the stiffness of the body of the object.

[0051] For example, a more elastic object absorbs the impact better and gives the impact control algorithm more time to activate, thereby significantly reducing the force of impact.

[0052] If the gripping force obtained is already sufficient, the actuating power may be reduced to zero (step 24) . For example, in the case of an electric gripper, the motor current may be reduced to zero.

[0053] Alternatively, it is possible to release the brake in order to manage the gripping power so as to obtain the desired gripping force, for example by modulating the motor current.

[0054] In an embodiment illustrated in the flow chart examples in Figures 1 and 2 , the impact control method provides for establishing the rigidity of the obj ect to be gripped before performing the steps of monitoring the closing speed and the absorbed current . In this case , in fact , the method could perform either only the monitoring of the closing speed or only the monitoring of the absorbed current , depending upon whether the obj ect to be gripped is rigid or soft , respectively .

[0055] According to one aspect of the invention, the impact control method does not include the acquisition of information concerning the rigidity of the obj ect to be gripped and both monitoring of the closing speed and monitoring of the absorbed current are performed .

[0056] In this case , with reference to the flow chart o f Figure la, the method for controlling the impact between the gripping fingers of the robotic gripper and an obj ect to be gripped wherein the rigidity thereof is unknown, comprises the steps of :

[0057] - setting a set-point value V_sp for the closing speed of the at least one movable finger on the obj ect to be gripped, at least in an end part of the closing stroke of the movable finger ( step 10 ) ;

[0058] - controlling the movement of the at least one movable finger at the closing speed set-point value at least in the end part of the closing stroke ( step 12 ) ; [0059] - calculating, at least in the end part of the closing stroke, a speed datum F(wfb) that is representative of the closing speed (step 14) ;

[0060] - comparing such speed datum with a speed threshold value wth calculated as a function of the set-point value (step 16) ;

[0061] - calculating, at least in the end part of the closing stroke, an absorbed current datum f (Ifb) that is representative of the current absorbed (laa) by the electric actuator (step 18) ;

[0062] - comparing said absorbed current datum with a pre- established absorbed current threshold value Ith (step 20) ;

[0063] - determining whether the gripping fingers have impacted upon the object when the speed datum is lower than the speed threshold value or when the absorbed current datum is above the absorbed current threshold value ;

[0064] - activating a braking device for braking the movement of the at least one movable finger in a substantially instantaneous manner as soon as the impact is detected (step 22) .

[0065] The method may then include a step for managing the actuation energy (step 24) .

[0066] Therefore, by using both speed and current absorption signals simultaneously, i.e., in parallel, by implementing an OR logic gate, the algorithm is able to control the force of impact upon the object regardless of the type thereof, in particular regardless of the rigidity of the object.

[0067] It is therefore not necessary to provide the algorithm with the datum for the stiffness of the object and the algorithm may autonomously determine which object has been gripped (also in order to adapt subsequent control actions to the type of object, for example the management of the actuation energy) based on which activation occurred first, between the two comparisons with the speed threshold value and the current absorption threshold value.

[0068] In an embodiment illustrated in the flow chart of Figure 2, the control method la provides for acquiring the size of the object to be gripped, at least in the direction of movement of the gripping fingers (step 8) .

[0069] In this case, the control method provides for setting a maximum closing speed value v_max. (step 10a) and controlling the movement of the fingers at the maximum closing speed value (step 12a) before the fingers enter an end part of the closing stroke, i.e. before the fingers are in proximity to the object to be gripped.

[0070] In other words, if the size of the object to be gripped is known, it may be more efficient to approach the object as quickly as possible, for example by controlling the position thereof.

[0071] After placing the fingers very close to the object, the final gripping step is performed by means of controlling the speed, with a set-point speed (v'_sp) that is significantly lower than the maximum speed (step 12b) . [0072] In one embodiment, having moved the gripping fingers of the gripper close to the object very quickly, in the end part of the closing stroke, in the absence of information concerning the size of the object, so as to avoid any risk of damage to the gripper (in the case of a rigid object) or to the object (in the case of a soft object) , the fingers may be moved at a set-point speed (v'_Sp) that is lower than the applied set-point value (v_sp) .

[0073] In this case, the speed threshold value o' th may be chosen to be very low, close to zero.

[0074] From this point on, the control method continues as described above, both as regards the embodiment of Figure 1 and the embodiment of Figure la.

[0075] The flow diagram in Figure 3 shows, by combining them, the same steps as the control methods 1, 1' described above, in the cases of a rigid or soft object and of known or unknown object size. The speed control block 30 refers to the determination of the closing speed of the fingers and the consequent actuation of the fingers in the three cases of a rigid object, a soft object (thus providing for a different, in particular lower, set-point speed for a rigid object than the set-point speed for a soft object) , and an object of known size.

[0076] The impact detection block 40 refers to the comparison between the speed and current values and the respective threshold values, as described above.

[0077] In one embodiment, in order to prevent the gripping fingers from colliding with each other when there is no object between them, the speed set-point value may be chosen so that the fingers stop in proximity to the completed gripper closing stroke (for example, at 99% of the complete stroke) .

[0078] In one embodiment, the control algorithm may also employ an acceleration datum obtained from the speed datum that is representative of the closing speed.

[0079] In this case, the algorithm determines that the gripping fingers have impacted the object when the acceleration datum assumes a negative value, for example lower than a predetermined deceleration threshold value.

[0080] The acceleration datum may be used as a further control signal in parallel with the speed and current signals , therefore as a third input of the OR logic gate , or else , in order to render the algorithm even more robust , in series with the control based upon the speed datum, for example by implementing an AND logic gate that has the controls based on the speed and acceleration data as inputs .

[0081] In fact , it has been experimentally determined that the use of the acceleration signal of fers optimal results both in the case of rigid obj ects and in the case of soft obj ects .

[0082] The graphs of Figure 8 show an example of the correlation between the speed signal and the acceleration signal . As may be seen, when the detected speed drops sharply to zero , the acceleration signal shows a negative impulse spike which may be used to detect when the obj ect has been impacted .

[0083] The invention also relates to a robotic gripper 100 comprising a gripper actuator 102 of the electric type , at least two gripping fingers 112 , at least one finger of which i s a movable finger operatively connected to the gripper actuator 102 to be moved with respect to the other one .

[0084] The gripper 100 is also equipped with at least one position or speed sensor - not shown - adapted to detect the position or speed of the at least one movable finger 112, a current sensor not shown adapted to detect the current absorbed by the electric actuator 102, and a braking device 104 adapted to brake the movement of the at least one movable finger.

[0085] The gripper 100 is equipped with an electronic control unit 120 operatively connected to the gripper actuator 102, the position or speed sensor, the current sensor, and the braking device 104.

[0086] The electronic control unit 120 is configured to implement the impact control method described above in its possible embodiments.

[0087] In one embodiment, the gripper 100 is driven by a brushless motor 102, for example a 24 V motor, i.e., a synchronous permanent magnet motor (PMSM) . The angular position of the motor 102 may be detected by means of an incremental encoder (for example with a resolution of 2048 cpt) , mounted on an electronic board of the motor.

[0088] For example, the electronic board may be provided with three Hall effect sensors.

[0089] The braking device 104 may be connected to a planetary gear reducer 106, for example with a reduction ratio T = 28:1. The planetary gear reducer 106 actuates a rack and pinion mechanism 108 that synchronizes the movement of two jaws 110 of the gripper 10. A gripping finger 112 is fixed to each aw 110. [0090] For example , each j aw 110 slides along a respective T-shaped guide 114 .

[0091] In one embodiment , by virtue of the impact control method according to the present invention, the mechanical connection system between the actuator 102 and the gripping fingers 112 is completely rigid, i . e . , there are no elastic elements between the components of the mechanical connection system that are adapted to cushion or dampen the impact between the gripping fingers and the obj ect . Such elastic elements may in fact be avoided seeing that their function of canceling or reducing the force spikes due to the impact with the obj ect is performed by the proposed impact control method, and in particular by the substantially instantaneous activation of the braking device .

[0092] Therefore , for example , the mechanical connection system comprising :

[0093] - an actuator 102 , for example in the form of a synchronous electric motor with permanent magnets ;

[0094] - a transmission system 106 , 108 , for example in the form of toothed wheels , a rack and pinion, adapted to transmit the torque generated by the aforementioned actuator 102 ;

[0095] - j aws 110 moved by means of said transmission system; [0096] - gripping fingers 112, associated with said jaws 110,

[0097] is a rigid system, i.e., devoid of elastic elements, such as spring devices or gaskets.

[0098] Figure 5 represents a comparison between the graphs of the position, speed and gripping force curves, obtained from experimental data and simulations, in the case of an impact at 500 rpm (revolutions per minute, or 8.25 mm/ s in terms of the linear speed of the finger) with a rigid object, in the absence of the IDA ("Impact Detection Algorithm") algorithm which implements the impact control method according to the invention (Figure 5 (a) ) and in the presence of the IDA algorithm (Figure 5 (b) ) .

[0099] The objective of these experiments is in particular to demonstrate how the IDA algorithm is capable of containing the force of impact even without information concerning the size of the object.

[00100] In the graphs the dashed curves represent simulated data, while the curves with continuous lines represent experimental data. The marker ID indicates the instant of the impact.

[00101] The effectiveness of the algorithm that implements the impact control method is evident, as the force decreases from over 300 N, in the case of absence of an algorithm, to about 150 N, in the presence of an algorithm. It should also be noted that the speed setpoint (dashed and dotted line) is reset only when an impact is detected, i.e. when the motor speed drops below the predetermined threshold value.

[00102] It should be noted that the simulated and actual data are very similar, with the only discrepancy observable being in the motor speed curve, which has oscillations in the case of the experimental data. The strong correlation between the model and the experiments has made it possible to predict the actual behavior of the gripper. It was therefore possible to identify the maximum impact speed in order to keep the gripping force within the safety limit (i.e. 300 N) : such speed was 1000 rpm, i.e. 16.5 mm/ s .

[00103] Figure 6 shows the same graphs as Figure 5, but in the case of an impact at 1000 rpm. It should however be noted that in the case of absence of an IDA algorithm, only the simulated data are reported, insofar as the expected maximum gripping force was found to be 150% of the safety limit.

[00104] As envisaged by the model, the gripping force using the IDA algorithm never exceeded 300 N, reaching a maximum of 285 N. The IDA has made it possible to double the speed of the motor, i.e. to move the fingers up to 16.5 mm/ s (1000 rpm) .

[00105] Figure 7 represents graphs obtained from experimental data and simulated data of the position, speed, current and gripping force curves, but only in the presence of the IDA algorithm and in the case of a soft, i.e., deformable object, for example a plastic bottle.

[00106] In this case, a threshold value for activating impact detection is applied to the measured absorbed current. An impact is detected when the current measured falls for between 0.7 and 0.8 seconds.

[00107] Also in this case, the simulated and experimental data coincide perfectly, including the very low gripping force (about 5 N) .

[00108] By virtue of the elasticity of the object, the speed may follow the desired set-point value even after contact between the finger and the object. However, in order to overcome the resistance of the object, the speed controller increases the delivered current. The IDA algorithm detects this alteration in the current value, thereby resulting in effective impact detection.

[00109] The proposed method therefore achieves the objective of allowing the robotic gripper to move its gripping fingers at a high closing speed and to maintain an optimal gripping force.

[00110] The method provides for maintaining a constant closing speed until the impact detection algorithm identifies a collision between the fingers and the object; at this point the brake is activated and the actuation power is managed based upon the application. [00111] The proposed method works without the aid of force sensors, also regardless of the size and rigidity of the object (insofar as it adapts according to the rigidity of the object) .

[00112] The proposed control method therefore makes it possible to manage the force exerted at the point of contact between the gripping fingers of a robotic gripper and an object to be gripped, even if said object is of unknown size during the gripping process, thereby adapting to the stiffness of said object.

[00113] The proposed method is capable of allowing the robotic gripper to promptly detect impacts that occur between the fingers and the object, consequently reacting instantaneously in order to avoid damage to the gripper's mechanical transmission or to the object itself.

[00114] It should be noted that the approach illustrated in the present invention exceeds that adopted in previous studies for the same purposes of managing the force of impact, insofar as it does not require the optimization of the contact area of the gripper fingers, nor does it require information concerning force and torque in order to detect a finger-obj ect collision, nor does it require the use of flexible f ingers .

[00115] It should be noted that the proposed control method and gripper provide for actively actuating a dedicated braking device as soon as an impact has been detected in such a way as to instantly stop the movement of the at least one movable finger and thus prevent damage to the gripped obj ect and/or to the mechanical transmission caused by inertial force spikes .

[00116] In other words , the braking mechanism, based upon a dedicated braking component , which makes it possible to brake the at least one movable finger substantially instantaneously, makes it possible to avoid or reduce spikes in the gripping force that could be generated during impact between the fingers and the ob j ect .

[00117] Furthermore , the braking function ensures that the obj ect is gripped with a repeatable and stable force . [00118] After the brake has been activated, the motor current may be reset to zero thereby minimi zing unnecessary energy consumption and ensuring gripping stability without loss of force .

[00119] A person skilled in the art may make several changes , adj ustments , adaptations , and replacements of elements with other functionally equivalent ones to the embodiments of the impact control method and of the robotic gripper according to the invention in order to meet incidental needs , without departing from the scope of the following claims . Each of the features described as belonging to a possible embodiment may be obtained independently of the other described embodiments .

References cited

1] S. Haddadin et al., "Robot collisions: A survey on detection, isolation, and identification, " IEEE

Trans. Robot., vol. 33, no. 6, pp . 1292-1312, Dec. 2017. [2] S. Hideaki, "Electric gripper," no. JP2021053786A,

October 1, 2019.

[3] F. Ostyn et al., "Design and control of a quasidirect drive robotic gripper for collision tolerant picking at high speed." IEEE Robotics and Automation Letters 7.3 (2022) : 7692-7699.

[4] G. Vitrani et al., "Improving the grasping force behavior of a robotic gripper: model, simulations and experiments", MDPI Robotics, 2023.

[5] J. Becedas et al., "Two-Flexible-Fingers Gripper Force Feedback Control System for Its application as End Effector on a 6-DOF Manipulator", IEEE Transactions on Robotics, 2011.

Claims

1 . A method for controlling the impact between the gripping fingers of a robotic gripper and an obj ect to be gripped, wherein the robotic gripper comprises a gripper actuator of the electric type and at least two gripping fingers , at least one finger of the at least two gripping fingers being a movable finger operatively connected to the gripper actuator to be moved with respect to the other one , the control method compris ing the steps of : a ) setting a set-point value of the closing speed of the at least one movable finger on the obj ect to be gripped, at least in an end part of the closing stroke of the movable finger ; b ) controlling the movement of the at least one movable finger at the closing speed set-point value at least in the end part of the closing stroke ; cl ) calculating, at least in the end part of the closing stroke , a speed datum representative of the closing speed; c2 ) comparing said speed datum with a speed threshold value calculated as a function of the set-point value ; dl ) calculating, at least in the end part of the closing stroke , an absorbed current datum representative of the current absorbed by the electric actuator ; d2 ) comparing said absorbed current datum with a pre- established absorbed current threshold value ; e ) determining whether the gripping fingers have impacted upon the obj ect when the speed datum is below the speed threshold value or when the absorbed current datum is above the absorbed current threshold value ; f ) activating a braking device for braking the movement of the at least one movable finger in a substantially instantaneous manner as soon as the impact is detected .

2 . Method according to claim 1 , wherein, from said speed datum representative of the closing speed, an acceleration datum is obtained, and wherein it is determined whether the gripping fingers have impacted upon the obj ect when the acceleration datum as sumes a negative value .

3 . Method according to any one of the preceding claims , wherein the speed datum representative of the closing speed is obtained by means of the steps of :

- sampling the closing speed of the at least one movable finger ;

- calculating the maximum value or the mean value of a set of detected samples .

4 . Method according to any one of the preceding claims , wherein the speed threshold value is calculated as a percentage of the set-point value .

5 . Method according to any of the preceding claims , wherein : step a ) is preceded by a step of acquiring at least the si ze of the obj ect to be gripped in the movement direction of the at least one movable finger ;

- step a ) compri ses a sub-step al ) of setting a maximum closing speed value ; and

- step b ) comprises a sub- step bl ) of controlling the movement of the at least one movable finger at the maximum closing speed value before the movable finger enters an end part of the closing stroke .

6 . Method according to claim 5 , wherein the set-point value of the clos ing speed in the end part of the closing stroke is lower than a set-point value of the closing speed set in the case of unknown si ze of the obj ect .

7 . A robotic gripper, comprising a gripper actuator of the electric type , at least two gripping fingers , at least one finger of the two gripping fingers being a movable finger operatively connected to the gripper actuator to be moved with respect to the other one , at least one position or speed sensor suitable for detecting the position or speed of the at least one movable f inger, a current sensor suitable for detecting the current absorbed by the electric actuator, a braking device suitable for braking the movement of the at least one movable finger, and an electronic control unit operatively connected to the gripper actuator, the position or speed sensor, the current sensor and the braking device , the electronic control unit being configured to implement the control method according to any one of the preceding claims .

8 . Robotic gripper according to the preceding claim, wherein the electronic control unit is configured to calculate the movement speed of the at least one movable finger as a derivative of a position datum measured by the position sensor .

9 . Robotic gripper according to claims 7 or 8 , comprising a mechanical connection system that connects the gripper actuator to the at least one movable finger, wherein the said connection system is devoid of elastic elements .