JP5005331B2 - Muscle force sensor - Google Patents

Description

  The present invention relates to a muscle force sensor, and more particularly to a muscle force sensor for detecting a weak myoelectric signal generated from a muscle of a human body.

  The muscle force sensor is a sensor for making a weak myoelectric signal generated from the muscle when a person moves the body visible from the skin surface above the muscle. The myoelectric signal changes in proportion to the magnitude of the muscle force.

  The above-described muscle force sensor can be applied to, for example, a wearable robot. When a human wears the wearable robot, one person can easily perform a tough work, and the burden on an aging nurse can be reduced and the number of caregivers can be reduced. A muscle sensor is an indispensable basic device for performing daily life support and social participation support for the elderly and the physically disabled by this wearable robot. That is, the muscle force state is grasped by the muscle force sensor, and information necessary for the wearable robot is generated based on the obtained myoelectric signal.

  FIG. 7 shows a needle electrode of a muscle force sensor that has been widely used in the past. These are so-called electromyogram recording electrodes. As shown in the figure, there are a single-core concentric electrode (a), a two-core concentric electrode (b), and a monopolar needle electrode (c). The single-core concentric electrode 82 is sealed with one sealing needle 84, and the two-core concentric needle electrode 86 is sealed with two sealing needles 88 and 90. The monopolar needle electrode 92 is obtained by coating a stainless needle 94 with Teflon (registered trademark). These needle electrodes 82, 86, and 92 were pierced into the skin to obtain weak myoelectric signals of the muscles. In addition, since the myoelectric signal is weak, it is usually performed to amplify to a necessary level and remove noise.

  Here, patent document 1 can be mentioned as an example which controls a control object using a myoelectric signal. According to this patent document 1, the myoelectric signal is detected and amplified by the myoelectric signal detecting device including the signal detecting unit and the signal amplifying unit. Based on the amplified myoelectric signal, the motion detection unit detects a finger motion, while the force detection unit detects a hand gripping force. The control unit controls the controlled object in accordance with a command recognized based on the detected finger movement and hand gripping force. In this way, by detecting the movement of a part of the body based on the myoelectric signal and the tension of the muscle in the other part, a complex command is assigned to the combination of finger movement and hand gripping force, Even a user who is not familiar with the keyboard operation can easily control the controlled object only by hand gestures regardless of the keyboard.

  Further, in Patent Document 2, in an information transmission system that transmits data from an information transmission device that can be worn on a human body to an information processing device, a change in capacitance around the human body or exercise of muscles by a sensor equipped with the information transmission device Alternatively, a configuration is disclosed in which a communication start signal is output from the information transmission apparatus to the information processing apparatus when a change in vibration is detected.

  That is, the sensor of Patent Document 2 detects a change in capacitance around the human body on which the information transmission device is mounted, and a pair of electrodes that are in electrical contact with the human body at a predetermined interval, and the pair of electrodes And a detection circuit for generating a detection signal in response to the change in the capacitance obtained by the above.

JP-A-7-248873 JP 2005-192699 A

  In a conventional muscular force sensor using a needle electrode, the needle electrode must be pierced into the skin, which causes a burden and discomfort to a person who supports care, and causes a sense of resistance to use. In addition, in the method of detecting a weak voltage with a needle electrode, in principle, it is easily affected by noise, and it is extremely difficult to obtain a stable output voltage.

  The signal detection part of the myoelectric signal detection apparatus of patent document 1 detects a weak myoelectric signal with a skin surface electrode. Accordingly, as described above, it is easily affected by noise and it is difficult to obtain a stable output voltage.

  The sensor for detecting a change in capacitance around the human body and a change in muscle movement or vibration in Patent Document 2 is provided on a surface where a pair of metal electrodes are in contact with the human body at a predetermined interval. Thus, a capacitance capacitor is configured, and a change in capacitance when a human body touches another object is detected. That is, Patent Document 2 detects changes in capacitance using electrodes, but in this case, it does not correspond to changes in muscular strength, and constitutes a circuit that enables only on / off digital control. ing.

  The present invention has been made in view of the above problems, and an object of the present invention is to provide a muscle force sensor that is not affected by noise, can obtain a stable output voltage, and can obtain a signal linearly corresponding to a change in muscle strength. It is to provide.

  In order to achieve the above-mentioned determination, the inventors have intensively studied, and by changing the muscle strength, the ionic composition in the skin changes, and by detecting the change in the dielectric constant accompanying the change in the ionic composition, We thought that the relationship with muscle strength would become clear.

That is, in order to achieve the above object, the muscle force sensor according to claim 1 includes a pair of electrodes attached to the body surface, and a detection circuit that detects a change in dielectric constant between the pair of electrodes, the change in muscle strength under the surface, in the muscle force sensor you measured as a change in dielectric constant detected by said detection circuit, a change in the dielectric constant is detected as a change in capacitance, of the pair of electrodes An auxiliary electrode is inserted between the pair of electrodes to reduce the capacitance between the pair of electrodes.

  As described above, since a change in muscle strength can be measured as a change in dielectric constant, a signal corresponding to the change in muscle strength can be obtained stably without being affected by noise. The detection circuit may have any internal circuit configuration as long as it can measure a change in dielectric constant.

In addition, since the change in the dielectric constant is detected as a change in capacitance, a circuit for detection can be easily configured, and the influence of noise can be suppressed to a low level.
Furthermore, since the auxiliary electrode is inserted between the pair of electrodes, the capacitance value between the pair of electrodes can be lowered. In this case, since the amount of change in capacitance due to a change in muscle strength is not drastically reduced, detection sensitivity can be improved. That is, the capacitance between the pair of electrodes is represented by C ± ΔC, but the capacitance C is reduced without sacrificing the capacitance change ΔC, so that the capacitance change amount ΔC is It becomes relatively large and the detection sensitivity is improved. Note that the size and number of auxiliary electrodes can be appropriately determined depending on the part where the sensor electrode is attached, the size of the sensor electrode, and the like.

According to a second aspect of the present invention, the detection circuit is a capacitance-voltage conversion circuit, and the muscle strength is measured by converting the change in capacitance into a change in voltage, so that the myoelectric signal is easier to handle. It will be obtained in the form.

As described in claim 3 , since the capacitance- voltage conversion circuit is configured by a ring detection circuit, a myoelectric signal can be obtained with high accuracy with a simple differential amplifier circuit. is there.

  The muscle force sensor of the present invention includes a pair of electrodes attached to the body surface, and a detection circuit that detects a change in dielectric constant between the pair of electrodes, and the change in muscle strength under the body surface is Since it is characterized by measuring the change in dielectric constant detected by the detection circuit, the change in muscle strength can be measured as a change in dielectric constant, and the signal corresponding to the change in muscle strength is not affected by noise, and It became possible to obtain stably.

  Embodiments of the present invention will be described with reference to the drawings. FIG. 1 is a schematic configuration diagram of a muscle force sensor of the present invention. The muscle force sensor 10 includes a sensor unit 12, a capacitance-voltage conversion circuit 14, a low-pass filtering circuit, and an amplification circuit 16.

  The sensor unit 12 is configured by inserting an auxiliary electrode 12c between a pair of electrodes 12a and 12b. The size of the pair of electrodes 12a and 12b was a circle having a diameter of 10 mm, and the distance between the electrodes was about 20 mm. In the present embodiment, the pair of electrodes 12a and 12b is attached to the biceps region. One auxiliary electrode 12c is inserted approximately at the center of the pair of electrodes 12a and 12b. The shape of the auxiliary electrode 12c is a rectangular shape having a length of 5 mm and a width of 5 mm. However, the size of the auxiliary electrode 12c can be determined as appropriate depending on the portion where the pair of electrodes 12a and 12b are attached and the size of the pair of electrodes 12a and 12b. Also, the number of auxiliary electrodes 12c can be appropriately selected in relation to the detection sensitivity described below.

  The auxiliary electrode 12c can reduce the capacitance C determined by the pair of electrodes 12a and 12b. Since it has been confirmed through experiments that the capacitance change ΔC does not decrease at the same rate, it is possible to improve detection sensitivity as a result. That is, physically, by inserting the auxiliary electrode 12c, the same effect as the series connection of the capacitors is produced. When applying each electrode to the skin, a gel is applied on the electrode in order to improve conductivity.

  When a pair of electrodes is attached to a specific part of the human body, the capacitance is determined between the electrodes according to the state of the muscle, that is, the change in the ionic composition in the skin. Here, when the muscle is moved, the ionic composition in the skin changes to change the dielectric constant, so that the detected capacitance changes. That is, the muscle force sensor of the present invention is characterized in that changes in the ionic composition in the skin are read as changes in the dielectric constant between the electrodes, in particular, changes in capacitance.

  FIG. 2 shows a detection circuit for converting a change in capacitance into a voltage. A kind of ring detection circuit is configured. The output voltage of the signal from the crystal oscillator 22 in FIG. 2 is adjusted by the variable resistor 23, and a sine wave voltage of several MHz is supplied to the detection circuit. Capacitors 24 and 26 are bridge-connected capacitors and are equal film capacitors having a small temperature coefficient.

  The diodes 28, 30, 32, and 34 are silicon diodes having the same capacitance, forward resistance, and temperature coefficient. The capacitor 36 is a capacitor to be measured, and this corresponds to the sensor unit 12. The capacitor 38 is a balancing capacitor for the bridge circuit, and has a capacitance that can be varied so that the circuit is balanced even if the capacitance of the capacitor to be measured 36 changes.

  When the high-frequency voltage is supplied to the conversion circuit, the impedance Z of the capacitor changes due to the change of the angular frequency ω (= 2πf, f: frequency) and the change of the capacitance C from the relationship of Z = 1 / (ωC). . Here, since the frequency f is constant, the impedance Z changes due to the change in the capacitance C. The change in the capacity C corresponds to the change in muscular strength as described above.

  FIG. 3 shows a low-pass filter circuit and an amplifier circuit. Since the output voltage from the capacitance-voltage conversion circuit 14 in FIG. 2 includes a high frequency of the oscillation frequency, it is removed by a constant K type low-pass filtering circuit composed of a capacitor and a resistor. At this time, the response frequency of the sensor unit 12 is determined by the characteristics of the low-pass filter circuit.

  The output voltage from the low-pass filtering circuit is as weak as several mV. In order to indicate or record the change in capacitance, the voltage must be amplified. A general OP amplifier 70 can be used as the amplifier. Since the OP amplifier 70 amplifies the difference between the two input voltages, when the outputs E1 and E2 from the capacitance-voltage conversion circuit shown in FIG. 2 are input to the input terminals 72 and 76 in FIG. The output voltage E0 is a voltage proportional to the capacitance change ΔC.

  FIG. 4 is a measurement example of the muscle force sensor of the present invention, and shows the relationship between muscle strength and output voltage. The horizontal axis is time (ms), and the vertical axis is voltage (mV). The detection waveform when holding the hand and bending the arm with force is shown. This waveform is a waveform obtained by the oscilloscope 18. The output voltage when reaching out without putting force was about 150 mV, which was a stable state. When force was applied and the arm was bent, the voltage gradually increased. When the arm was bent 90 °, the output voltage was about 190 mV. After that, when the arm was returned to a straight state, it returned to the same voltage as in the initial stage.

  FIG. 5 is a measurement example of the muscle force sensor of the present invention, and shows the relationship between the arm angle and the output voltage. A solid line indicates when no force is applied, and a broken line indicates when a force is applied. Regardless of the presence or absence of force, when both arms were bent, the output voltage increased in proportion to the angle of bending. However, when bending with force, the change was larger and the result was higher by about 15 to 20 mV.

  FIG. 6 is a measurement example of the muscle force sensor of the present invention, and shows the relationship between the weight load and the output voltage. The figure shows the change in voltage when a weight is placed on the palm while the arm is stretched without bending. The voltage is higher in proportion to increasing the weight as a load little by little. When loaded up to 8 kg, the output voltage showed a change of about 35 mV. This result is considered to have changed due to the muscular strength when holding the weight because the arm is not bent unlike FIG. It was also found that when the weight was doubled, the voltage was also doubled and changed linearly.

  With the muscle force sensor of the present invention, changes in muscle strength can be converted into voltage and measured, and basic data of a wearable robot can be obtained. In addition, since the electrode is attached, the burden on the person can be reduced.

  The muscle force sensor of the present invention is not limited to the embodiments, and can be variously modified within the scope described in the claims. For example, it is possible to change the shape of the pair of electrodes from a circular shape to a substantially elliptical shape or polygonal shape, or to change the size thereof. The characteristics of the low-pass filter circuit and the amplifier circuit may be changed as necessary.

  The muscle force sensor of the present invention changes a change in muscle strength into a change in capacitance, and further changes a change in capacitance into a change in voltage. What has been measured by changing the muscle strength change of the present invention into a capacitance change has not been found so far, and many applications using this phenomenon are conceivable in the future.

  The application to wearable robots is as described above, and the contribution to social welfare is great if the burden on aging nurses can be reduced and the number of caregivers can be reduced. In addition, for example, a great number of applications are conceivable, such as a survey of muscle fatigue during muscle training of athletes, a monitoring of muscle status during surgery of hospital patients, and a survey of muscle fatigue status of various pilots.

It is a schematic block diagram of the muscle force sensor of this invention. 2 is a capacitance-voltage conversion circuit of the muscle force sensor of FIG. 1. It is the low-pass filter circuit and amplifier circuit of FIG. It is a measurement example of the muscular force sensor of the present invention, and shows a change in output voltage when a force is applied. It is a measurement example of the muscle force sensor of the present invention, and shows the relationship between the arm angle and the output voltage. It is a measurement example of the muscle force sensor of the present invention, and shows the relationship between the weight load and the output voltage. The needle electrode used for the conventional muscular force sensor is shown.

Explanation of symbols

DESCRIPTION OF SYMBOLS 10 Muscular force sensor 12 Sensor part 12a Sensor electrode 12b Sensor electrode 12c Auxiliary electrode 14 Capacitance-voltage conversion circuit 16 Low-pass filter circuit and amplification circuit 18 Oscilloscope 20 Body surface 22 Crystal oscillator 23 Variable resistance 24, 26 Capacitors 28, 30 , 32, 34 Diode 36 Capacitor to be measured 38 Capacitor for bridge circuit balancing 40 Ground terminal 42, 44 Output terminal 46, 48, 54, 56 Capacitor 50, 52, 58, 60, 62, 64 Resistor 66, 68 Feedback resistor 70 OP Amplifier 72, 76 Input terminal 78 Output terminal 74, 80 Ground terminal 82 Single-core concentric needle electrode 84, 88, 90 Encapsulated needle 86 Two-core concentric needle electrode 92 Monopolar needle electrode
94 Stainless needle

Claims (3)

A pair of electrodes attached to the body surface;
A detection circuit for detecting a change in dielectric constant between the pair of electrodes,
The change in muscle strength under the surface, in the muscle force sensor measured as a change in dielectric constant detected by said detection circuit,
The change in dielectric constant is detected as a change in capacitance,
A muscle force sensor characterized in that an auxiliary electrode is inserted between the pair of electrodes to reduce a capacitance between the pair of electrodes. 2. The muscle strength sensor according to claim 1 , wherein the detection circuit is a capacitance-voltage conversion circuit, and measures muscle strength by converting the change in capacitance into a change in voltage. The muscle force sensor according to claim 2 , wherein the capacitance- voltage conversion circuit is configured by a ring detection circuit.

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