JP2016200400A - Method for calibrating measured value of load sensor - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a method for calibrating the measured value of a load sensor that makes it possible to easily calibrate the measured value of a load sensor that measures a load that the sole of a user receives from the ground surface.SOLUTION: A method for calibrating the measured value of a load sensor 22 that measures a load that the sole S of a user receives from the ground surface while walking, the method which is executed by a walking auxiliary device 1 that assists a user in walking involving: determining whether or not the sold S is separate from the ground surface on the basis of whether or not the measured value of the load sensor 22 is less than or equal to a prescribed value; calculating the time mean value of measured values when the sold S is separate from the ground surface and thereby calculating an offset value; and subtracting the offset value from the measured values and thereby calibrating the measured values.SELECTED DRAWING: Figure 1

Description

  The present invention relates to a method for calibrating a measurement value of a load sensor, which is executed by a walking assistance device that assists a user's walking, and that measures a load that a user's sole receives from the ground.

  A technology for a robot (walking assisting device) for assisting a user's walking is disclosed.

  For example, the walking assistance device according to Patent Document 1 is a measurement value of a load sensor attached to the left and right soles of a user (a measurement value of a ground reaction force that is an upward force received from the ground as a reaction of a user's load). ), The assist force for the left and right knees is determined. Here, when the seating portion of the walking assist device pushes the user upward, the ground reaction force may decrease, and the correct assist force may not be determined. In order to prevent this, the walking assist device according to Patent Literature 1 distributes the seating surface reaction force that the seating portion gives to the user to the measurement values of the left and right foot load sensors. As a result, the walking assistance device performs control to correct the detected ground reaction force to make the assist force more accurate.

JP 2014-184086 A

  In the walking assist device, a predetermined offset value is added to the load value due to the ground reaction force to the measurement value of the load sensor attached to the sole of the user. This offset value occurs not only due to the above-described seating surface reaction force but also due to the deflection of the mechanism to which the load sensor is attached, the change in the electrical characteristics of the load sensor, and the like. In the walking assist device according to Patent Document 1 described above, the grounding reaction force is corrected based on the seating surface reaction force given to the user by the seating unit. However, as described above, the factor of the offset value is other than the seating surface reaction force. Is also possible. Therefore, the walking assist device according to Patent Document 1 may not be able to accurately calibrate the measurement value of the load sensor.

  The method for calibrating the measurement value of the load sensor according to the present invention makes it possible to accurately calibrate the measurement value of the load sensor that measures the load that the user's sole receives from the ground.

According to the present invention, a walking assist device for assisting a user's walking executes a calibration method of a measurement value of a load sensor that measures a load that a user's sole receives from the ground during walking.
Based on whether or not the measurement value of the load sensor is equal to or less than a predetermined value, it is determined whether the sole is away from the ground,
Calculate the offset value by calculating the time average value of the measured value when the sole is away from the ground,
The measured value is calibrated by subtracting the offset value from the measured value.

  With this method, the walking assistance device calibrates the measurement value by calculating the offset value based on the measurement value when the sole is away from the ground. Therefore, an accurate offset value during walking can be calculated, and the measured value is calibrated with the offset value. Therefore, the measured value of the load sensor can be calibrated accurately.

  According to the present invention, it is possible to accurately calibrate a measurement value of a load sensor that measures a load that a user's sole receives from the ground.

It is the schematic of the walking assistance apparatus concerning embodiment. It is the schematic of a load sensor unit. It is a block diagram of a load sensor unit and control ECU. It is a flowchart which shows the calculation method of the offset value of a calibration part. It is a flowchart which shows the calibration method of the measured value of a calibration part. It is a flowchart which shows the control processing of a control part. It is a graph which shows an example of the relationship between an ideal measurement value and an actual measurement value.

  Embodiments of the present invention will be described below with reference to the drawings. As shown in FIG. 1, the walking assist device 1 according to the embodiment includes a load sensor unit 11, ankle joints 12a and 12b, lower links 13a and 13b, a lower connecting bar 14, and upper links 15a and 15b. The upper connecting bar 16, the motor / encoder unit 17, and a control ECU (Electronic Control Unit) 18 are provided. The walking assist device 1 is attached to the user's right leg F, and assists the user's walking motion by applying torque to the user's knee joint. Hereinafter, each part of the walking assist device 1 will be described.

  As shown in FIG. 2, the load sensor unit 11 includes a sole unit 21 and a vertical load sensor 22. The sole unit 21 is attached to the sole S of the right leg F of the user, has a role as a shoe sole in direct contact with the sole S of the user, and corresponds to the shape of the sole S of the user. Have a different shape. The vertical load sensor 22 is a sensor provided in the sole unit 21 and detects the magnitude of the load applied in the direction perpendicular to the sole unit 21 as a measurement value, so that the sole S is grounded during walking. Measure the load received from. In FIG. 2, four vertical load sensors 22 are provided on the sole unit 21. The two vertical load sensors 22A are provided at the front part of the sole part S, and the two vertical load sensors 22B are provided at the rear part of the sole part S. Thereby, the vertical load sensor 22A can measure the load that the front part of the sole S receives from the ground, and the vertical load sensor 22B can measure the load that the rear of the sole S receives from the ground.

  Returning to FIG. 1, the description of the walking assist device 1 is continued. The ankle joints 12a and 12b are positioned so as to sandwich the ankle of the right leg F from both sides, and are positioned coaxially with the pitch axis of the ankle (the axis in the left-right direction of the right leg F). The ankle joint 12a connects the load sensor unit 11 and the lower link 13a, and the ankle joint 12b connects the load sensor unit 11 and the lower link 13b. The ankle joints 12a and 12b connect the load sensor unit 11 to the lower links 13a and 13b so as to be swingable.

  The lower links 13a and 13b are located on both sides of the right leg F in the pitch axis direction of the lower leg. The lower link 13a connects the ankle joint 12a, the lower connecting bar 14, and the upper link 15a, and the lower link 13b connects the ankle joint 12b, the lower connecting bar 14, and the upper link 15b.

  The lower connecting bar 14 is in the vicinity of the knee K of the right leg F, and connects the lower links 13a and 13b and connects the upper links 15a and 15b. The upper links 15 a and 15 b are located on both sides of the right leg F in the pitch axis direction of the upper leg, and are connected by the upper connecting bar 16 at the upper part thereof.

  The motor / encoder unit 17 is attached to the upper link 15 a and is located outside the right leg F. The motor / encoder unit 17 includes a motor and an encoder (not shown). The motor is driven under the control of the control ECU 18 described later, and swings the lower links 13a and 13b around the pitch axis. Thereby, the walking assistance apparatus 1 can apply a torque to a user's knee joint and can assist walking operation. For example, when the right leg F is in the free leg state, the walking assist device 1 drives the motor so that the user assists in the operation of bending the knee (performs the bending assist operation). In addition, when the right leg F is in the standing state, the motor is driven so as to maintain the standing state. The encoder of the motor / encoder unit 17 can detect the rotation angle and rotation angular velocity of the motor.

  As shown in FIG. 3, the control ECU 18 includes a calibration unit 31 and a control unit 32. The calibration unit 31 and the control unit 32 can be configured by a circuit such as a memory or other IC (Integrated Circuit) in hardware, and are realized by a program loaded in the memory in software. . For example, a CPU (Central Processing Unit) in a computer reads a program loaded in a memory in the computer, thereby realizing the following processing.

  The calibration unit 31 acquires the measurement value of the total vertical load sensor 22. For example, in FIG. 3, the measurement value A of the vertical load sensor 22A and the measurement value B of the vertical load sensor 22B are acquired by the calibration unit 31. When determining that the load from the ground is not applied to the sole S, the calibration unit 31 calculates an offset value in the acquired measurement data. This calculation method will be described with reference to the flowchart of FIG.

  First, the calibration unit 31 acquires measurement data of all the vertical load sensors 22 and determines whether or not all the acquired measurement values are equal to or less than a predetermined value, whereby the load from the ground is applied to the sole S. It is determined whether it is not applied (that is, whether the sole S is not grounded) (step S11). This is because when all the vertical load sensors 22 are not loaded from the ground, their measured values are all equal to or less than a specific predetermined value.

  When a load from the ground is applied to the sole S (No in Step S11), at least some of the vertical load sensors 22 do not measure the offset value. Therefore, the calibration unit 31 does not execute (ends) the offset value calculation process.

  When the load from the ground is not applied to the sole S (Yes in Step S11), the calibration unit 31 stores the measurement value of each vertical load sensor 22 (Step S12). Then, the calibration unit 31 determines whether or not the measurement values can be stored for each vertical load sensor 22 for a predetermined time required for the offset value calculation process (step S13). This predetermined time is a time such that when the time average of the measurement values is calculated, the time average becomes a reliable value as the offset value.

  When the measured value cannot be stored for a predetermined time (No in step S13), the calibration unit 31 returns to step S11 and continues the process. When the measured value can be stored for a predetermined time (Yes in step S13), the calibration unit 31 calculates the time average of the measured values at the predetermined time of each vertical load sensor 22, thereby calculating the offset value of each vertical load sensor 22. calculate.

  Note that the calibration unit 31 may calculate an average of continuous measurement values in a predetermined time as the offset value. Alternatively, sampling data of measurement values may be taken intermittently within a predetermined time, and an average value of the sampling data may be calculated as an offset value.

  Next, a method for calibrating the measurement value of the calibration unit 31 will be described with reference to the flowchart of FIG. First, the calibration unit 31 determines whether or not the offset calculation shown in FIG. 4 has been completed (step S15). When the offset calculation is not completed (No in step S15), the calibration unit 31 does not calibrate the measurement value.

  When the offset calculation has been completed (Yes in step S15), the calibration unit 31 performs a process of subtracting the offset value corresponding to each vertical load sensor 22 from the original measurement value of each vertical load sensor 22 ( Step S16). The offset value corresponding to each vertical load sensor 22 is obtained in step S14 of FIG.

  The calibration unit 31 outputs the measurement data of each vertical load sensor 22 that has been calibrated as described above to the control unit 32. The control unit 32 executes walking control of the walking assist device 1 based on the measured value. Hereinafter, a processing example of walking control will be described with reference to the flowchart of FIG.

  First, the control unit 32 determines whether or not the right leg F is in the free leg state and the bending assist operation is performed (step S21). This determination may be performed based on the detection result of the encoder of the motor / encoder unit 17, for example.

  When the right leg F is in the free leg state and the bending assist operation is performed (No in step S21), the control unit 32 controls the motor to continue the bending assist operation (step S22).

  When the right leg F is not in the free leg state, that is, in the standing state (Yes in Step S21), the vertical load sensor 22 is in a state where a load is applied (that is, the load sensor unit 11 is grounded). State) and a state in which no load is applied (that is, a state in which the load sensor unit 11 is not grounded). In the following description, the former is defined as a load state, and the latter is defined as a heavy state. In the following flow, the control unit 32 performs processing for determining the state.

  First, the control unit 32 determines whether or not the previous state determination result is a load state (step S23).

  When the previous state determination result is a load state (Yes in step S23), the control unit 32 indicates that the total of all the measured values of the current vertical load sensor 22 (total load amount) is greater than a predetermined weight determination threshold value X. It is determined whether it is small (step S24).

  When the total load amount is smaller than the weight determination threshold value X (Yes in step S24), the control unit 32 determines that the current state is the weight removal state (step S25). On the other hand, when the total load amount is equal to or greater than the extraction determination threshold value X (No in step S24), the control unit 32 determines that the current state is the load state (step S26).

  In step S23, when the previous state determination result is in the heavy state (No in step S23), the control unit 32 determines whether or not the total load amount is larger than a predetermined load determination threshold Y (step S27). ). As an example, the magnitude relationship between X and Y is X ≦ Y.

  When the total load amount is larger than the load determination threshold Y (Yes in step S27), the control unit 32 determines that the current state is the load state (step S26). On the other hand, when the total load amount is equal to or less than the load determination threshold Y (No in step S27), the control unit 32 determines that the current state is the heavy load state (step S25). The state determination results shown above are stored in the memory in the control ECU 18, and are used in the determination in step S28 described later and the determination in the next step S23.

  The control unit 32 compares the current state determination result with the previous state determination result, and determines whether or not the current state is the state in which the load state has changed to the heavy load state (step S28).

  When it is the state which changed from the load state to the heavy weight state (Yes of step S28), it determines with the control part 32 having changed to the state which left | separated from the state which the right leg part F grounded with the user's walk. To do. In this case, the control unit 32 controls the motor to start the bending assist operation (step S29).

  When the load state has not changed to the depressing state (No in step S28), the control unit 32 determines that the right leg portion F has not shifted to the state away from the state where the right leg portion F has reached the ground. In this case, the control unit 32 performs the control to maintain the standing state without performing the bending assist operation, and drives the motor (step S30).

  As described above, the control ECU 18 includes a motor built in the motor / encoder unit 17 so as to assist the user's walking motion based on all the measured values of the vertical load sensor 22 attached to the load sensor unit 11. Drive. The control ECU 18 can also control the drive of the motor in the motor / encoder unit 17 based on the detection result of the encoder in the motor / encoder unit 17.

  In the walking assist device, the measured value of the load sensor attached to the user's sole is a value obtained by adding a predetermined offset value to the load value due to the reaction force from the ground. FIG. 7 is a graph showing an example of a relationship between an ideal measurement value (a load value due to a reaction force from the ground) and an actual measurement value (a value obtained by adding a predetermined offset value to a load value due to a reaction force from the ground) It is. As shown in FIG. 7, even if the leg to be measured by the load sensor is in a state of being pulled, the measured value of the load sensor does not become 0 but becomes a predetermined offset value.

  If the control of the walking assist device is executed based on the measurement value of the load sensor without correcting the offset value, even if the leg to be measured by the load sensor is a free leg, the walking assist device has a ground reaction force. There is a possibility of misrecognizing that it is on the leg. For this reason, the walking assist device may not be able to perform accurate control of itself. Therefore, it is necessary to calibrate the measurement data so as to cancel the offset value.

  Here, it may be time-consuming for the user to execute calibration that cancels the offset value of the load sensor before using the walking assistance device. For example, during calibration, in order to prevent a load from being applied to the load sensor, it may be necessary for the user to fix the walking assist device to a jig or the like so that the load sensor is not grounded.

  The offset value changes due to a change in the deflection of the mechanism to which the load sensor is attached, a change in the electrical characteristics of the load sensor, and the like. Therefore, even while the user is using the walking assistance device, the offset value may change due to the progress of walking or the change of the walking assistance device over time. For this reason, even if the offset value is calibrated before using the walking assistance device, the offset value may deviate from the value at the time of calibration while the user is walking. In this case, even if the leg to be measured by the load sensor is a free leg, the measurement value of the load sensor may not be accurately calibrated, and the walking assistance device may not be able to accurately control itself. There is.

  However, in the embodiment, the walking assist device 1 calibrates the measurement value by calculating the offset value based on the measurement value when the user's sole S is away from the ground. Therefore, it is not necessary for the user to calibrate the offset value, and the walking assist device 1 automatically calibrates the offset value, so that the user's trouble in using the walking assist device 1 is reduced.

  In addition, an accurate offset value during walking can be calculated, and the measured value is calibrated with the offset value. Therefore, the measured value of the load sensor can be calibrated accurately. Furthermore, by repeating the flow shown in FIGS. 4 to 5 while the user is walking, the measured value can be accurately calibrated even if the offset value of the load sensor changes.

  Note that the present invention is not limited to the above-described embodiment, and can be changed as appropriate without departing from the spirit of the present invention. For example, the number of vertical load sensors 22 provided in the load sensor unit 11 may be a number other than four. In other words, the number of the vertical load sensors 22 may be any number as long as it is one or more. Further, the load sensor unit 11 may be attached to the sole of the left leg (or both the left and right legs) instead of the user's right leg.

  The present invention can be similarly applied not only to the load sensor unit 11 provided in the walking assistance device but also to the load sensor provided in the leg portion of the robot that performs the bipedal walking independently. Here, the robot performs a walking motion based on the measurement value of the load sensor.

1 walking assist device 11 load sensor unit 17 motor / encoder unit 18 control ECU
21 Sole unit 22 Vertical load sensor 31 Calibration unit 32 Control unit

Claims (1)

A method for calibrating a measurement value of a load sensor that measures a load that a user's sole receives from the ground during walking, executed by a walking assist device that assists the user's walking,
Based on whether or not the measurement value of the load sensor is equal to or less than a predetermined value, it is determined whether the sole is away from the ground,
Calculate the offset value by calculating the time average value of the measured value when the sole is away from the ground,
Calibrating the measurement value by subtracting the offset value from the measurement value;
Calibration method for load sensor measurements.

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