Tactile sensor and manipulator

Abstract

The present invention discloses a tactile sensor and a manipulator thereof. The tactile sensor includes an ultrasonic sensor, which is provided with a probe connected to a flexible tube, so that the ultrasonic wave generated by the ultrasonic sensor propagates along the inner cavity of the flexible tube; a contact portion is formed on the side wall of the flexible tube, which is contacted by an object, causing the contact portion to deform and reflect the ultrasonic wave in the inner cavity of the flexible tube to obtain a tactile signal. A manipulator includes the above-mentioned ultrasonic sensor. The tactile sensor and manipulator of the present invention use the flexible tube to direct the distance measurement of the ultrasonic sensor. When the flexible tube is compressed and closed due to contact with an object, the ultrasonic wave propagating along the flexible tube is reflected back to the ultrasonic sensor, thereby detecting contact between the flexible tube and the object. Furthermore, the ultrasonic sensor's distance measurement function can be used to determine the position of the object relative to the flexible tube.

Description

Technical Field

[0001] The present invention belongs to the field of detection and control, and in particular relates to a tactile sensor and a manipulator thereof. Background Art

[0002] Mechanical grippers are generally operated by human operators through direct visual observation or camera monitoring to perform grasping, or by robots that process image information obtained through a vision system for intelligent grasping.

[0003] If encountering an unstructured environment, such as one without light, visual perception will be difficult to play a role. Considering that mechanical grippers based on force sensing are better at grasping special objects that are not hard, soft, or brittle, robots should rely more on touch to grasp general objects in unstructured environments.

[0004] In recent years, mainstream tactile sensors are mainly divided into five categories according to their working principles.

[0005] (1) Capacitive tactile array sensor. Its principle is that external force changes the relative displacement between the plates, thereby changing the capacitance. The tactile force is measured by detecting the change in capacitance.

[0006] (2) Inductive tactile sensor. It uses the principle of electromagnetic induction to convert pressure into changes in the self-inductance and mutual inductance of the coil, and then converts the circuit into a voltage or current change output.

[0007] (3) Photoelectric tactile sensor. It is developed based on the principle of total internal reflection and is usually composed of a light source and a photodetector. When the pressure applied to the interface changes, the reflection intensity of the sensor's sensitive element and the frequency of the light source will also change accordingly.

[0008] (4) Piezoresistive tactile sensor. This device is made based on the piezoresistive effect of semiconductor materials. Its substrate can be directly used as a measuring sensor element, and the diffused resistors are connected in the substrate to form a bridge. When the substrate is deformed by external force, the resistance values will change, and the bridge will produce a corresponding unbalanced output.

[0009] (5) Piezoelectric tactile sensor: Under the action of pressure, a potential difference appears between the two end surfaces of the piezoelectric material; conversely, mechanical stress is generated when voltage is applied.

[0010] However, the above-mentioned conventional mechanical grippers based on contact perception are expensive, and the multi-sensor fusion makes the mechanical structure and control system of the robot very complex, with low stability, making it difficult to promote and use. Summary of the Invention

[0011] The present invention provides a tactile sensor and a manipulator thereof to solve the technical problem of high detection cost of existing tactile sensors mentioned in the background art.

[0012] To achieve the above objectives, the specific technical solutions of the tactile sensor and the manipulator thereof of the present invention are as follows:

[0013] A tactile sensor includes an ultrasonic sensor, which is provided with a probe connected to a hose so that the ultrasonic waves generated by the ultrasonic sensor propagate along the inner cavity of the hose; a contact portion is formed on the side wall of the hose, and the contact portion is contacted by an object, causing the contact portion to deform and reflect the ultrasonic waves in the inner cavity of the hose to obtain a tactile signal.

[0014] Furthermore, the ultrasonic sensor outputs ultrasonic waves in a PW output mode.

[0015] Furthermore, a first failure end is provided at one end of the hose close to the ultrasonic sensor, a second failure end is provided at one end of the hose away from the ultrasonic sensor, and the contact portion is located between the first failure end and the second failure end.

[0016] Furthermore, the diameter of the hose is less than or equal to half the wavelength of the ultrasonic wave, and greater than that of the ultrasonic wave. Please add based on the thermal adhesion effect.

[0017] Furthermore, an adapter is provided between the ultrasonic sensor and the probe; a first socket is formed at one end of the adapter and is sleeved outside the probe, and a second socket is formed at the other end of the adapter and is sleeved outside the hose.

[0018] A robot arm comprises the ultrasonic sensor mentioned above.

[0019] Furthermore, it also includes centrally symmetrical gripper fingers, which are closed to grip objects; and a hose is arranged on the inner wall of the gripper fingers to detect the gripping status of objects by the gripper fingers.

[0020] Furthermore, the gripper finger includes a straight end, and an inwardly curved arc segment is formed at the end of the straight end so that the arc segment can cover the grasped object.

[0021] Furthermore, an embedding groove extending along the length direction is provided on the inner wall of the gripper finger, and the side surface of the hose is fixed on the embedding groove.

[0022] Furthermore, the manipulator also includes a mounting frame and a driving frame that can move coaxially relative to the mounting frame; the end of the gripper finger is hinged on the mounting frame; a connecting rod is provided on the driving frame, one end of the connecting rod is hinged to the mounting edge, and the other end of the connecting rod is hinged to the gripper finger, so that the gripper finger, the connecting rod and the driving frame form a crank rocker mechanism.

[0023] Furthermore, the manipulator also includes a fixed seat, on which a guide rod is fixedly connected along the axial direction. The guide rod passes through the drive frame at one end away from the fixed seat and is fixed to the mounting frame, so that the drive frame can slide along the guide rod.

[0024] Furthermore, an auxiliary seat is provided on one side of the fixed seat close to the driving frame, and the auxiliary seat is fixed to the guide rod; a driver is installed between the fixed seat and the auxiliary seat, and the driver drives the driving frame to slide.

[0025] The tactile sensor and the manipulator thereof of the present invention have the following advantages:

[0026] 1. Use a hose to direct the distance measurement of the ultrasonic sensor. When the hose is closed due to pressure caused by contact with an object, the ultrasonic wave propagating along the hose is reflected back to the ultrasonic sensor, so that it can be known that the hose and the object are in contact. The ultrasonic sensor's distance measurement function can also be used to obtain the position of the object relative to the hose.

[0027] 2. The robotic arm draws on the fly-catching strategy of the Venus flytrap, repeatedly trying to grasp objects through touch. In response to the need to grasp objects in special environments, a robotic gripper integrating tactile sensing functions is designed to solve the problem of gripper applicability in low-light environments. BRIEF DESCRIPTION OF THE DRAWINGS

[0028] Figure 1 A line graph showing the experimental results of the effect of the hose diameter on the accuracy of the ultrasonic sensor of the present invention;

[0029] Figure 2 A line graph showing experimental results of the effect of bending on the accuracy of an ultrasonic sensor according to the present invention;

[0030] Figure 3 It is a schematic diagram of the structure of the manipulator of the present invention;

[0031] Figure 4 It is the working flow diagram of the robot of the present invention.

[0032] Description of the marks in the figure:

[0033] 1. Gripper finger; 11. Straight end; 12. Arc segment; 2. Mounting frame; 3. Drive frame; 4. Connecting rod; 5. Fixed seat; 51. Guide rod; 6. Auxiliary seat; 7. Linear push rod; 8. Ultrasonic sensor; 81. Hose. DETAILED DESCRIPTION

[0034] The technical solution of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the embodiments described are only some embodiments of the present invention, not all embodiments. All other embodiments obtained by ordinary technicians in this field based on the embodiments of the present invention without making any creative efforts shall fall within the scope of protection of the present invention.

[0035] In the description of the present invention, it should be noted that the terms "center," "upper," "lower," "left," "right," "vertical," "horizontal," "inner," and "outer," etc., indicating orientations or positional relationships, are based on the orientations or positional relationships shown in the accompanying drawings and are intended solely to facilitate and simplify the description of the present invention. They are not intended to indicate or imply that the devices or components referred to must have, be constructed, or operate in a specific orientation, and therefore should not be construed as limitations on the present invention. Furthermore, the terms "first," "second," and "third" are used for descriptive purposes only and should not be construed as indicating or implying relative importance.

[0036] In the description of the present invention, it should be noted that, unless otherwise clearly specified and limited, the terms "installed", "connected", and "connected" should be understood in a broad sense. For example, it can be a fixed connection, a detachable connection, or an integral connection; it can be a mechanical connection or an electrical connection; it can be a direct connection, or it can be indirectly connected through an intermediate medium, or it can be internal communication between two components. For ordinary technicians in this field, the specific meanings of the above terms in the present invention can be understood according to specific circumstances. In addition, the technical features involved in the different embodiments of the present invention described below can be combined with each other as long as they do not conflict with each other.

[0037] Those skilled in the art will appreciate that although some embodiments herein include certain features included in other embodiments but not other features, the combination of features from different embodiments is intended to be within the scope of the present invention and to form different embodiments. For example, in the claims, any one of the claimed embodiments may be used in any combination.

[0038] The tactile sensor of the present invention can acquire tactile signals. Therefore, the extraction and quantification of tactile information are key to the present invention. By adopting the fly-catching strategy of a bionic Venus flytrap and applying the ultrasonic ranging principle to a robotic gripper, the gripper acquires a tactile signal when a grasped object touches the gripper in the dark.

[0039] Specifically, the tactile sensor includes an ultrasonic sensor, which is provided with a probe connected to a hose so that the ultrasonic waves generated by the ultrasonic sensor propagate along the inner cavity of the hose; a contact portion is formed on the side wall of the hose, and the contact portion is for an object to contact, causing the contact portion to deform to reflect the ultrasonic waves in the inner cavity of the hose to obtain a tactile signal.

[0040] Ultrasonic sensors are non-contact, range-finding sensors that detect and locate objects within a defined range in an airborne medium. Ultrasonic sensors are unaffected by the color or other visual characteristics of the object being measured. They use high-frequency sound to detect and locate objects in a variety of environments.

[0041] 2d=cΔt

[0042] Where: d is the distance between the sensor surface and the surface of the object being measured;

[0043] c—speed of sound;

[0044] Δt—the propagation time of ultrasonic waves in the medium;

[0045] Ultrasonic sensors emit ultrasonic pulses, which travel through the air and reflect when they encounter an object. When the pulse is reflected back to the sensor, the time difference Δt between the transmitted pulse and the received reflected pulse is measured. The distance d to the reflecting object can be calculated using the above formula, thereby determining the object's position relative to the contact part.

[0046] The ultrasonic sensor used in this invention is an existing commercial ultrasonic ranging module that uses the aforementioned principle to measure distance. However, these modules are typically used for outdoor sensing and cannot be applied to equipment such as robotic arms. Therefore, a flexible tube is required to directionalize distance measurement.

[0047] The hose can be made of a standard rubber tube. By encapsulating the ultrasonic sensor at one end of the hose, the ultrasonic wave's sensing volume is confined to a narrow path, converging the ultrasonic pulses emitted by the ultrasonic sensor. This allows the ultrasonic wave to be guided along the hose and prevented from being reflected or interfered with by objects in the environment. In a pipe-based configuration, the ultrasonic pulse will continue to propagate until it is blocked and reflected by a discontinuity in the tube or deformation caused by an external object. The blocked and reflected ultrasonic pulse carries the distance information between the contact point of the measured object and the sensor. Distance is measured by outputting an electrical signal converted from this distance information at a certain ratio. This transforms the ultrasonic sensor's distance measurement function into tactile information.

[0048] In order to adapt the hose and the probe, an adapter can be installed between the ultrasonic sensor and the probe. One end of the adapter is formed with a first socket that is sleeved outside the probe, and the other end is formed with a second socket that is sleeved outside the hose.

[0049] Below, the selection and structural adjustment are carried out based on the various characteristics of ultrasonic sensors.

[0050] 1. About the output mode of ultrasonic sensor

[0051] Existing ultrasonic sensors generally have two output modes: analog voltage output (AN) and pulse width output (PW).

[0052] If the AN output port remains open or continuously at a high level, the sensor will convert the detected distance information to an analog voltage output. The output analog voltage has a certain proportional relationship with the actual distance to the measured object.

[0053] For example, when the power supply is 5V, the output analog voltage is proportional to the measured distance at 4.9mV / cm. When the power supply is 3.3V, the ratio is 3.2mV / cm. The hardware limits the maximum range of the analog voltage output conversion to 700cm for 5V and 600cm for 3.3V. If the PW output is left open or held high, the sensor will output pulse width to indicate distance. The ratio is 58µS per pulse width, representing 1cm, and there is no limit on the maximum range of the output conversion.

[0054] Therefore, the PW output mode has higher accuracy and better stability, so the ultrasonic sensor of the present invention adopts the PW output mode to output ultrasonic waves.

[0055] 2. About the detection range and error of ultrasonic sensors

[0056] When the test point is too far from the sensor and the sensor cannot obtain a valid reflected signal, the measurement result output by the console suddenly changes to the sensor's maximum ideal measurement distance. This output remains unchanged regardless of how far the test point is moved. By exploiting this characteristic, the distance from the test point to the starting end face is continuously extended until the distance reading at a certain point suddenly reaches the sensor's default maximum measurement distance. This point represents the critical point where the actual distance measurement function fails, i.e., the sensor's maximum measurement distance within the constricted sensing volume of the catheter.

[0057] Similarly, when the test point is too close to the sensor, the console output shows the sensor's default minimum distance.

[0058] Therefore, the hose has a first inoperative end at the end closest to the ultrasonic sensor and a second inoperative end at the end farther from the ultrasonic sensor, with the contact portion located between the first and second inoperative ends. Furthermore, the second inoperative end can be cut off to make the hose shorter than the ultrasonic sensor's measuring distance.

[0059] The following is an ultrasonic sensor with a first failure end of 20CM to test the performance of the tactile sensor and conduct a feasibility analysis of the ultrasonic sensor.

[0060] Comparative Experiment 1

[0061] like Figure 1 As shown in the figure, experiments were conducted on hoses with inner diameters of 3mm, 4mm, 6mm, and 8mm. The experimental data is presented as a line graph, with the abscissa representing the average distance from the three measurement points to the end face of the tube, as determined by each marked point. The ordinate represents the average difference between the average actual distance measured three times and the average measured distance of the three measurements at each point, which is considered the error.

[0062] Experimental results show that a 6mm inner diameter tube has better stability than an 8mm inner diameter tube, with a generally stable error within a 100mm measurement range. Tubes with inner diameters of 3mm and 4mm have smaller errors than those with inner diameters of 6mm and 8mm, but a smaller maximum measurement range. The 4mm inner diameter tube has the smallest error and a larger measurement range than the 3mm inner diameter tube. Therefore, the 6mm outer diameter, 4mm inner diameter hose offers the best performance. Using it in a robotic gripper can yield more accurate measurement data, meeting the need for providing decision-making information for grasping by the gripper.

[0063] Analysis shows that the diameter of the hose connected to the sensor affects the accuracy of the ultrasonic sensor. Over short distances, smaller-diameter hoses provide more accurate measurements. Over longer distances, measurements are only possible with larger-diameter hoses, as they couple better with the ultrasonic sensor, providing more reflected input. However, large-diameter hoses are bulky and difficult to route. From a theoretical perspective of waveguide ultrasound, hose diameter significantly affects wave propagation. A hose with a diameter greater than half a wavelength will conduct complex sound patterns, resulting in echoes with multiple peaks. On the other hand, narrow hoses can cause losses due to thermoviscous effects.

[0064] Therefore, the diameter of the hose should not be greater than half the wavelength of the ultrasonic wave and should be greater than the acoustic boundary layer of the inner wall of the hose. The acoustic boundary layer consists of two parts: the viscous boundary layer and the thermal boundary layer. Beyond the acoustic boundary layer, the thermal viscous effect weakens and no longer interferes with the transmission of sound waves in the pipe.

[0065] Comparative Experiment 2

[0066] The hose was spiraled into three nested coils with a maximum diameter of 40 cm, which served as a curved tube for comparison with a straight tube of the same model.

[0067] The result is as follows Figure 2 The experimental results show that the error values and directions of the two broken lines are very similar, indicating considerable accuracy. This experiment demonstrates that ultrasonic sensing within a flexible tube is unaffected by tube curvature, as long as the tube is not bent to the point of deformation and causing echoes. Therefore, it is feasible to appropriately bend the flexible tube within the manipulator structure.

[0068] After the above research and analysis, silicone hoses can be used to improve ultrasonic sensors, so it is feasible to integrate ultrasonic sensors into the mechanical gripper system.

[0069] like Figure 3 As shown, the present invention also discloses a manipulator, comprising the above-mentioned ultrasonic sensor 8, so that the manipulator can obtain tactile sensation.

[0070] The manipulator comprises a centrally symmetrical gripper finger 1, which is closed to grasp an object. A hose 81 is provided on the inner wall of the gripper finger 1 to detect the grasping status of the object by the gripper finger 1.

[0071] To accommodate the aforementioned tactile sensors, the gripper fingers 1 must be strong and wide enough. They must also have smooth transitions, without sharp protrusions or depressions, to prevent blind spots where parts of the gripper fingers 1 cannot make contact with the object, potentially hindering tactile perception.

[0072] Specifically, the gripper finger 1 includes a straight end 11 terminated by an inwardly curved arc segment 12, ensuring that the arc segment 12 covers the object being grasped as closely as possible. A longitudinally extending groove is defined on the inner wall of the gripper finger 1, into which the hose 81 is secured, providing a tactile feel. A through-groove is defined on the end of the straight end 11, distal from the arc segment 12, for the hose 81 to pass through, preventing it from interfering with the movement of the gripper finger 1.

[0073] To drive the movement of the gripper fingers 1, the manipulator also includes a mounting frame 2 and a drive frame 3 that can move coaxially relative to the mounting frame 2. The ends of the gripper fingers 1 are hinged to the mounting frame 2. The drive frame 3 is equipped with a connecting rod 4, one end of which is hinged to the edge of the mounting frame 2 and the other end of which is hinged to the gripper fingers 1. The gripper fingers 1, connecting rod 4, and drive frame 3 thus form a crank-rocker mechanism. By axially moving the drive frame 3 along the mounting frame 2, multiple gripper fingers 1 can be synchronously driven to close.

[0074] To connect the mounting frame 2 and the driving frame 3, the manipulator further includes a fixing base 5. A guide rod 51 is axially fixed to the fixing base 5. The end of the guide rod 51, which is away from the fixing base 5, passes through the driving frame 3 and is fixed to the mounting frame 2, allowing the driving frame 3 to slide along the guide rod 51. The guide rod 51 can be fixed using a variety of fixing methods, such as clamps, threads, welding, etc., which will not be detailed in this embodiment.

[0075] To move the drive frame 3, a driver is mounted on the fixed base 5. This driver is typically a pneumatic cylinder or linear push rod, equipped with a piston rod. The end of the piston rod is hingedly connected to the mounting base 2, pushing the drive frame 3 to translate along the guide rod 51, thereby driving the gripper fingers 1 to close. An auxiliary base 6 is provided on the side of the fixed base 5 near the drive frame 3. The auxiliary base 6 is fixed to the guide rod 51, and the two ends of the driver are respectively mounted on the fixed base 5 and the auxiliary base 6. The driver can be mounted using bolts, mortise and tenon joints, and other methods, depending on the driver installation standards. This embodiment will not be further described.

[0076] During operation, if the gripping mechanism is able to effectively wrap around the object, the load can be directly offset by the positive force. However, if the gripping mechanism is unable to effectively wrap around the object, a greater gripping force is required to meet the operational requirements. Therefore, when the gripping mechanism is opened and closed, the gripping force should be greater at a larger opening angle. Therefore, a linear actuator 7 is preferably used as the actuator.

[0077] The ultrasonic sensor 8 is also mounted on the fixing base 5, and the hose 81 extends through the auxiliary base 6 and the drive frame 3 to the gripper finger 1, providing the gripper finger 1 with a sense of touch. Furthermore, the hose 81 located on the auxiliary base 6 and the drive frame 3 can be covered with a rigid sheath to prevent errors.

[0078] The manipulator of the present invention, the bionic Venus flytrap, adopts repeated attempts to grasp, such as Figure 4 The specific working process is as follows:

[0079] 1. The robot arm searches for the object by attempting to grasp it.

[0080] 2. Use the tactile sensor to determine whether the object touches the gripper finger 1;

[0081] 3. If no object touches gripper finger 1, move the manipulator and continue trying to grasp it;

[0082] 4. If an object touches gripper finger 1, close gripper finger 1;

[0083] 5. Obtain the number of gripper fingers 1 in contact with the object to determine whether the object is grasped stably;

[0084] 6. If the grip is unstable, continue to close the gripper finger 1, or release the gripper finger 1 and try to grip again.

[0085] It will be understood that the present invention is described by way of some embodiments, and it will be appreciated by those skilled in the art that various changes or equivalent substitutions may be made to these features and embodiments without departing from the spirit and scope of the present invention. In addition, under the teachings of the present invention, these features and embodiments may be modified to adapt to specific circumstances and materials without departing from the spirit and scope of the present invention. Therefore, the present invention is not limited to the specific embodiments disclosed herein, and all embodiments falling within the scope of the claims of this application are intended to be protected by the present invention.

Claims

1. A robot, characterized in that: The tactile sensor includes an ultrasonic sensor, which is provided with a probe connected to a hose, so that ultrasonic waves generated by the ultrasonic sensor are transmitted along the inner cavity of the hose; a contact portion is formed on the side wall of the hose, and the contact portion is contacted by an object, so that the contact portion is deformed to reflect the ultrasonic waves in the inner cavity of the hose to obtain a tactile signal; The manipulator also includes centrally symmetrical gripper fingers that close to grasp an object; a hose is provided on the inner wall of the gripper fingers to detect the gripping status of the object by the gripper fingers; The gripper finger includes a straight end, the end of which is formed with an inwardly curved arc segment so that the arc segment can cover the grasped object; The invention also includes a mounting frame and a driving frame that can move coaxially relative to the mounting frame; the end of the gripper finger is hinged to the mounting frame; a connecting rod is provided on the driving frame, one end of the connecting rod is hinged to the driving frame, and the other end of the connecting rod is hinged to the gripper finger, so that the gripper finger, the connecting rod and the driving frame form a crank rocker mechanism; The fixed seat is also provided with a guide rod fixedly connected to the fixed seat in the axial direction. The end of the guide rod away from the fixed seat passes through the driving frame and is fixed to the mounting frame, so that the driving frame can slide along the guide rod. An auxiliary seat is provided on one side of the fixed seat close to the driving frame, and the auxiliary seat is fixed to the guide rod; a driver is installed between the fixed seat and the auxiliary seat, and the driver drives the driving frame to slide; When the hose is pressed and closed by contact with an object, the ultrasonic waves propagating along the hose are reflected back to the ultrasonic sensor. The ultrasonic sensor is encapsulated at one end of the hose, limiting the ultrasonic sensing volume to the propagation path, thereby concentrating the ultrasonic pulses emitted by the ultrasonic sensor and guiding the ultrasonic waves along the hose. The ultrasonic sensor is installed on a fixed seat, and a hose passes through the auxiliary seat, the driving frame and extends to the gripper fingers to enable the gripper fingers to form a tactile sense.

2. The manipulator according to claim 1, characterized in that: The ultrasonic sensor uses PW output mode to output ultrasonic waves.

3. The manipulator according to claim 1, characterized in that: The hose is provided with a first failure end at one end close to the ultrasonic sensor and a second failure end at one end away from the ultrasonic sensor, and the contact portion is located between the first failure end and the second failure end.

4. The manipulator according to claim 1, characterized in that: The diameter of the hose is less than or equal to half the wavelength of the ultrasonic wave.

5. The manipulator according to claim 1 or 4, characterized in that: The diameter of the hose is larger than the acoustic boundary layer on the inside wall of the hose.

6. The robot according to claim 1, characterized in that: An adapter is provided between the ultrasonic sensor and the probe; a first socket is formed at one end of the adapter and is sleeved outside the probe, and a second socket is formed at the other end of the adapter and is sleeved outside the hose.

7. The robot according to claim 1, characterized in that: An embedding groove extending along the length direction is provided on the inner wall of the gripper finger, and the side surface of the hose is fixed on the embedding groove.

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