Electrostimulation device

Abstract

An electrostimulation device according to the present invention comprises: an electrostimulation unit that is connected between a high-side reference line and a low-side reference line of a DC power supply unit and includes a pair of electrode parts to be brought into contact with the skin of a human body; a current detection unit 50 for detecting a current between the DC power supply unit and the electrostimulation unit; and a determination unit 34 for determining, on the basis of a result of the detection performed by the current detection unit 50, the state of the skin of the human body in contact with the pair of electrode parts.

Description

Electrical stimulation device

[0001] The present invention relates to an electrical stimulation device.

[0002] BACKGROUND ART Electrical stimulation devices that apply electrical stimulation to a user's muscles are known. Electrical stimulation devices can passively move muscles by passing a weak current through the muscles to tense and relax them.

[0003] Patent Document 1 discloses a low-frequency therapy device provided with a pair of positive and negative output electrodes. Patent Document 1 also discloses a technology for determining whether or not the output electrodes are attached to the human body, by utilizing the fact that if the output electrodes are not attached to the human body, a transistor is turned off and the state of the input port of a microcomputer becomes HIGH, and if the output electrodes are attached to the human body, a transistor is turned on and the state of the input port of the microcomputer becomes LOW.

[0004] Special Publication No. 6-57263

[0005] The low-frequency therapy device disclosed in Patent Document 1 determines whether or not the output electrode is attached to the human body based solely on binary information, namely, the on / off state of a transistor, so there is room for improvement in detecting the condition of the skin that comes into contact with the electrode, such as accurately detecting the attachment state and detecting the dryness of the skin.

[0006] The present invention has been made in light of this situation, and one exemplary purpose of one aspect thereof is to provide an electrical stimulation device that improves the accuracy of detecting the condition of the skin in contact with the electrode portion.

[0007] In order to solve the above problems, an electrical stimulation device of one embodiment of the present invention comprises an electrical stimulation unit including a pair of electrode units to be contacted with the skin of a human body, connected between a high-side reference line and a low-side reference line of a DC power supply unit, a current detection unit that detects the current between the DC power supply unit and the electrical stimulation unit, and a judgment unit that judges the condition of the skin in contact with the pair of electrode units based on the detection results by the current detection unit.

[0008] Any combination of the above components, or mutual substitution of the components or expressions of the present invention between methods, devices, systems, etc., are also valid aspects of the present invention.

[0009] According to the present invention, it is possible to provide an electrical stimulation device with improved accuracy in detecting the condition of the skin in contact with the electrode portion.

[0010] 1 is a diagram showing a basic circuit configuration of an electrical stimulation device according to an embodiment. FIG. 1 is a diagram for explaining an AC voltage waveform applied between a pair of first and second electrodes shown in FIG. 1. FIG. 2 is a diagram showing a first example circuit configuration of the electrical stimulation unit shown in FIG. 1. FIG. 3 is a diagram showing a second example circuit configuration of the electrical stimulation unit shown in FIG. 1. FIG. 4 is a diagram showing an example circuit configuration when the electrical stimulation device shown in FIG. 1 includes a skin detection unit according to a comparative example. FIG. 5 is a diagram showing an example circuit configuration when the electrical stimulation device shown in FIG. 1 includes a skin detection unit according to a first embodiment. FIG. 6 is a diagram showing an example circuit configuration of the skin detection unit shown in FIG. 7. FIG. 7 is a diagram showing an example of temporal changes in voltage at positions A to C in the example circuit configuration of the skin detection unit shown in FIG. 6. FIG. 8 is a diagram showing an example of an analog signal input to the A / D converter shown in FIG. 7 and a digital signal converted by the A / D converter based on this analog signal. FIG. 9 is a diagram showing a schematic relationship between an H-bridge voltage and a peak hold voltage due to differences in offset voltage. FIG. 10 is a diagram explaining an example of using a relative value as a criterion for determining skin condition. FIG. 11 is a diagram showing a schematic relationship between an H-bridge voltage and a peak hold voltage in an idling state. 7 is a diagram showing an example of a voltage waveform at a first position when the skin of a human body is in a dry state or a non-dry state. FIG. 8 is a diagram showing another example of time-varying voltage at positions A to C in the circuit configuration example shown in FIG. 7 of the skin detection unit shown in FIG. 6. FIG. 9 is a diagram showing an example of a circuit configuration when the electrical stimulation device shown in FIG. 1 is equipped with a skin detection unit according to a second embodiment.

[0011] The present invention will be described below based on preferred embodiments with reference to the drawings. The embodiments are illustrative and do not limit the invention, and all features and combinations described in the embodiments are not necessarily essential to the invention. In the embodiments and modifications, the same or equivalent components and members are designated by the same reference numerals, and redundant descriptions will be omitted where appropriate.

[0012] (Basic Circuit Configuration of Electrical Stimulation Device 1) FIG. 1 is a diagram showing the basic circuit configuration of electrical stimulation device 1 according to an embodiment. Electrical stimulation device 1 is an EMS (Electrical Muscle Stimulation) device that electrically stimulates the muscles of a user. Electrical stimulation device 1 includes an electrical stimulation unit 10, a DC power supply unit 20, a control unit 30, and a first drive circuit Dr1 to a fourth drive circuit Dr4. Electrical stimulation unit 10 includes an H-bridge-connected first switching element Q1 to a fourth switching element Q4, and a pair of first and second electrode units P1 and P2. Note that electrical stimulation device 1 according to this embodiment also includes a skin detection unit 40 or a skin detection unit 40A, which will be described later, but is not shown in FIG. 1.

[0013] The electrical stimulation device 1 is used with a pair of first and second electrodes P1 and P2 in contact with any part of the human body Hd. By contacting the first electrode P1 with one part of the human body Hd and the second electrode P2 with another part of the human body Hd, a current path is formed with the human body Hd as a load.

[0014] The pair of first and second electrode portions P1 and P2 are electrodes that do not require consumable gel pads, specifically, cloth electrodes. Cloth electrodes are used while soaked in water. Cloth electrodes have a long lifespan, meaning they can be used many times before their lifespan expires. Furthermore, cloth electrodes are washable. The pair of first and second electrode portions P1 and P2 may be electrodes other than cloth electrodes, such as metal. The pair of first and second electrode portions P1 and P2 may also be electrodes that require gel pads. The pair of first and second electrode portions P1 and P2 may be rubber electrodes made of EPDM (Ethylene Propylene Diene Monomer) rubber, conductive polyurethane, or the like. Rubber electrodes can be used without soaking in water.

[0015] A first switching element Q1 and a second switching element Q2 connected in series, and a third switching element Q3 and a fourth switching element Q4 connected in series, are connected in parallel between a high-side reference line and a low-side reference line of the DC power supply unit 20. A first connection point N1 between the first switching element Q1 and the second switching element Q2 is connected to a first electrode portion P1. A second connection point N2 between the third switching element Q3 and the fourth switching element Q4 is connected to a second electrode portion P2.

[0016] The first switching element Q1 to the fourth switching element Q4 may be semiconductor switching elements such as bipolar transistors, MOSFETs (Metal-Oxide-Semiconductor Field-Effect Transistors), IGBTs (Insulated Gate Bipolar Transistors), etc. In the following, an example will be assumed in which PNP bipolar transistors (hereinafter simply referred to as PNP transistors) are used for the first switching element Q1 and the third switching element Q3, and NPN bipolar transistors (hereinafter simply referred to as NPN transistors) are used for the second switching element Q2 and the fourth switching element Q4.

[0017] In this case, the emitter terminal of the first switching element Q1 is connected to the high-side reference line, the emitter terminal of the second switching element Q2 is connected to the low-side reference line, and the connection point between the collector terminal of the first switching element Q1 and the collector terminal of the second switching element Q2 is the first connection point N1. Similarly, the emitter terminal of the third switching element Q3 is connected to the high-side reference line, the emitter terminal of the fourth switching element Q4 is connected to the low-side reference line, and the connection point between the collector terminal of the third switching element Q3 and the collector terminal of the fourth switching element Q4 is the second connection point N2.

[0018] The control unit 30 controls the entire electrostimulation device 1. The control unit 30 is provided in a microcontroller. The first drive circuit Dr1 to the fourth drive circuit Dr4 generate drive signals for the first switching element Q1 to the fourth switching element Q4 based on control signals for the first switching element Q1 to the fourth switching element Q4 input from the control unit 30, respectively, to drive the first switching element Q1 to the fourth switching element Q4.

[0019] In this embodiment, since bipolar transistors are used for the first switching element Q1 to the fourth switching element Q4, the first drive circuit Dr1 to the fourth drive circuit Dr4 are circuits that generate base currents to be supplied to the base terminals of the first switching element Q1 to the fourth switching element Q4, respectively. Note that if MOSFETs are used for the first switching element Q1 to the fourth switching element Q4, the first drive circuit Dr1 to the fourth drive circuit Dr4 are circuits that generate gate voltages to be supplied to the gate terminals of the first switching element Q1 to the fourth switching element Q4, respectively.

[0020] The control unit 30 controls the first switching element Q1 and the fourth switching element Q4 to an ON state and the second switching element Q2 and the third switching element Q3 to an OFF state, thereby applying a positive voltage between the first electrode portion P1 and the second electrode portion P2. The control unit 30 controls the first switching element Q1 and the fourth switching element Q4 to an OFF state and the second switching element Q2 and the third switching element Q3 to an ON state, thereby applying a negative voltage between the first electrode portion P1 and the second electrode portion P2.

[0021] In the present embodiment, control unit 30 controls electrostimulation unit 10 as follows. In one cycle, control unit 30 applies a positive pulse voltage and a negative pulse voltage alternately multiple times between first electrode P1 and second electrode P2, followed by an interval period. More specifically, in one cycle, control unit 30 applies a positive pulse voltage and a negative pulse voltage alternately an odd number of times between first electrode P1 and second electrode P2, followed by an interval period. In the next cycle, control unit 30 applies an odd number of pulse voltages with the phases of the odd number of pulse voltages inverted, followed by an interval period.

[0022] 2 is a diagram illustrating the AC voltage waveform applied between the pair of first electrode portion P1 and second electrode portion P2. The voltage waveform shown in FIG. 2 is composed of a combination of positive and negative basic pulses with a time width t1. A positive basic pulse causes a current to flow in a positive direction from one of the pair of first electrode portion P1 and second electrode portion P2 to the other, and a negative basic pulse causes a current to flow in a negative direction from the other electrode portion to the one.

[0023] A pause period of time width t2 is provided between positive and negative basic pulses. The applied voltage during this pause period is zero. In this waveform, a basic pulse group having a time width t3 (= 5 x t1 + 5 x t2) including five basic pulses and five pause periods is formed. This basic pulse group, together with the interval period of time width t4 provided after it, forms a basic waveform of one cycle (time width) t5 (= t3 + t4).

[0024] For example, if the time width t1 is set to 100 us and the time width t2 is set to 100 us, the time width t3 will be 1 ms. In this embodiment, the user can select between Mode A (20 Hz mode) and Mode B (4 Hz mode). When Mode A is selected, the time width t5 will be 50 ms (= 20 Hz) and the time width t4 (interval period) will be 49 ms. When Mode B is selected, the time width t5 will be 250 ms (= 4 Hz) and the time width t4 (interval period) will be 249 ms.

[0025] 2, the voltage polarity of the basic pulse is reversed for each waveform group. That is, if a positive pulse voltage is output three times and a negative pulse voltage is output twice in a given waveform group, the positive pulse voltage is output two times and the negative pulse voltage is output three times in the next waveform group, and these are alternately repeated. This makes it possible to suppress uneven charging of the first electrode portion P1 and the second electrode portion P2 by pairing the two waveform groups, thereby suppressing corrosion of the first electrode portion P1 and the second electrode portion P2.

[0026] The circuit configuration of the electrical stimulation unit 10 may be the following circuit configuration instead of the basic circuit configuration described above.

[0027] (Circuit Configuration Example 1 of Electrical Stimulation Unit 10) Fig. 3 is a diagram showing Circuit Configuration Example 1 of Electrical Stimulation Unit 10. In Circuit Configuration Example 1 of Electrical Stimulation Unit 10 shown in Fig. 3, a first coupling capacitor Cc1 and a second coupling capacitor Cc2 are added to the basic circuit of Electrical Stimulation Unit 10 shown in Fig. 1.

[0028] The first coupling capacitor Cc1 is inserted between the first connection point N1 and the first electrode P1 of the H-bridge circuit to provide DC insulation between the first connection point N1 and the first electrode P1. The second coupling capacitor Cc2 is inserted between the second connection point N2 and the second electrode P2 of the H-bridge circuit to provide DC insulation between the second connection point N2 and the second electrode P2.

[0029] By adding a first coupling capacitor Cc1 in series between the H-bridge circuit and the first electrode P1 and a second coupling capacitor Cc2 in series between the H-bridge circuit and the second electrode P2, it is possible to cut off the DC current flowing into the human body Hd from the electrical stimulation device 1. As described above, the EMS current supplied to the human body Hd from the electrical stimulation device 1 is an AC pulse, and therefore passes through the first coupling capacitor Cc1 and the second coupling capacitor Cc2 and does not affect steady-state operation.

[0030] (Circuit Configuration Example 2 of Electrical Stimulation Unit 10) Figure 4 is a diagram showing Circuit Configuration Example 2 of Electrical Stimulation Unit 10. In Circuit Configuration Example 2 of Electrical Stimulation Unit 10 shown in Figure 4, a first discharge switching element Qd1 and a second discharge switching element Qd2 are further added as discharge circuits to Circuit Configuration Example 1 of Electrical Stimulation Unit 10 shown in Figure 3.

[0031] The first discharge switching element Qd1 is connected between the wiring connecting the first coupling capacitor Cc1 and the first electrode portion P1 and the low-side reference line. The second discharge switching element Qd2 is connected between the wiring connecting the second coupling capacitor Cc2 and the second electrode portion P2 and the low-side reference line. NPN transistors are used for the first discharge switching element Qd1 and the second discharge switching element Qd2. When NPN transistors are used, base current flows, so there is no need to connect discharge resistors in series to the first discharge switching element Qd1 and the second discharge switching element Qd2. When MOSFETs are used, it is necessary to connect discharge resistors in series to each.

[0032] In circuit configuration example 2, a fifth drive circuit Dr5 is added to the electrical stimulation device 1. The fifth drive circuit Dr5 generates drive signals for the first discharge switching element Qd1 and the second discharge switching element Qd2 based on control signals for the first discharge switching element Qd1 and the second discharge switching element Qd2 input from the control unit 30, thereby driving the first discharge switching element Qd1 and the second discharge switching element Qd2. The fifth drive circuit Dr5 generates base currents supplied to the base terminals of the first discharge switching element Qd1 and the second discharge switching element Qd2.

[0033] The control unit 30 controls the on / off of the first discharge switching element Qd1 and the second discharge switching element Qd2 in synchronization with each other. Therefore, as shown in Fig. 4, the first discharge switching element Qd1 and the second discharge switching element Qd2 can share a drive circuit. However, separate drive circuits may be provided for the first discharge switching element Qd1 and the second discharge switching element Qd2.

[0034] The control unit 30 applies a positive pulse voltage and a negative pulse voltage alternately multiple times between the first electrode portion P1 and the second electrode portion P2 in one cycle, and inserts a discharge period (a period during which the first discharge switching element Qd1 and the second discharge switching element Qd2 are in the ON state) in the interval period thereafter. By simultaneously turning on the first discharge switching element Qd1 and the second discharge switching element Qd2 in the interval period, the first electrode portion P1 and the second electrode portion P2 become at the same potential via the ground potential of the low-side reference line, and any charge remaining in the human body Hd can be discharged.

[0035] (Skin detection unit 90 according to the comparative example) In the electrical stimulation device 1, if the pair of first and second electrodes P1 and P2 are not in proper contact with the skin of the human body Hd, sufficient electrical stimulation cannot be provided to the human body Hd. Furthermore, the electrical stimulation device 1 may gradually increase the voltage applied between the pair of first and second electrodes P1 and P2 to a target level for safety reasons. However, if at least one of the pair of first and second electrodes P1 and P2 is removed from the skin of the human body Hd after the applied voltage has increased to a certain level and then re-contacts the skin, a sudden large current may flow through the human body Hd. Therefore, it is preferable that the electrical stimulation device 1 have a function (hereinafter simply referred to as a "skin detection function") for detecting the condition of the skin of the human body Hd in contact with the pair of first and second electrodes P1 and P2. Here, the condition of the skin of the human body Hd in contact with the pair of first electrode parts P1 and second electrode parts P2 includes information on the degree of contact between the pair of first electrode parts P1 and second electrode parts P2 and the skin of the human body Hd, information on the degree of dryness or non-dryness of the skin of the human body Hd, etc.

[0036] Fig. 5 is a diagram showing an example of a circuit configuration when the electrical stimulation device 1 includes a skin detection unit 90 according to a comparative example. In the comparative example shown in Fig. 5, a Zener diode ZD is connected in series between the low-side reference line of the DC power supply unit 20 and the electrical stimulation unit 10. The Zener diode ZD is connected so that its forward direction faces the electrical stimulation unit 10. A resistor R0 may also be connected in parallel with the Zener diode ZD. The Zener diode ZD may also be connected in series between the high-side reference line of the DC power supply unit 20 and the electrical stimulation unit 10.

[0037] When the pair of first electrode portion P1 and second electrode portion P2 are in proper contact with the skin of the human body Hd, a current path is formed with the human body Hd as a load. At this time, the voltage applied in the reverse direction to the Zener diode ZD reaches the Zener voltage, and current flows through the Zener diode ZD. On the other hand, when at least one of the pair of first electrode portion P1 and second electrode portion P2 is not in proper contact with the skin of the human body Hd, a current path with the human body Hd as a load is not formed. At this time, the voltage applied in the reverse direction to the Zener diode ZD does not reach the Zener voltage, and no current flows through the Zener diode ZD.

[0038] The skin detection unit 90 detects the current flowing through the Zener diode ZD. The skin detection unit 90 includes a switching element such as an NPN transistor. When the skin detection unit 90 detects a current, it determines that the pair of first and second electrodes P1 and P2 are in proper contact with the skin of the human body Hd. On the other hand, when the skin detection unit 90 does not detect a current, it determines that at least one of the pair of first and second electrodes P1 and P2 is not in proper contact with the skin of the human body Hd. In this way, the skin detection unit 90 according to the comparative example determines whether the pair of first and second electrodes P1 and P2 are in proper contact with the skin of the human body Hd based on binary information indicating whether or not a current flows through the Zener diode ZD. Therefore, the skin detection unit 90 according to the comparative example can perform a two-stage determination of whether the pair of first and second electrodes P1 and P2 are in contact with the skin of the human body Hd, but cannot perform more detailed determinations such as the degree of contact.

[0039] (Skin detection unit 40 according to the first embodiment) Figure 6 is a diagram showing an example of a circuit configuration when electrostimulation device 1 includes skin detection unit 40 according to the first embodiment. In the example shown in Figure 6, shunt resistor R1 is connected in series between the low-side reference line of DC power supply unit 20 and electrostimulation unit 10. A detection circuit 42 is connected to shunt resistor R1. Shunt resistor R1 and detection circuit 42 together constitute skin detection unit 40. In other words, shunt resistor R1 is one of the components of skin detection unit 40. Furthermore, detection circuit 42 is the portion of skin detection unit 40 other than shunt resistor R1. Details of skin detection unit 40 will be described later.

[0040] According to Ohm's law, the voltage drop across the shunt resistor R1 is proportional to the current flowing through it. In other words, the shunt resistor R1 is an element that converts the current in the current path with the human body Hd as a load into a voltage. That is, the skin detection unit 40 can detect the current in the current path with the human body Hd as a load by detecting the voltage drop across the shunt resistor R1. The shunt resistor R1 preferably has a low resistance, for example, between 1 Ω and 10 Ω, to avoid limiting the current or consuming energy as a load. The shunt resistor R1 may be connected in series between the high-side reference line of the DC power supply unit 20 and the electrical stimulation unit 10. In this case, the skin detection unit 40 detects the current between the high-side reference line of the DC power supply unit 20 and the electrical stimulation unit 10.

[0041] Fig. 7 is a diagram showing an example of the circuit configuration of skin detection unit 40. As shown in Fig. 7, skin detection unit 40 includes a current detection unit 50, a gain switching unit 60, a peak hold unit 70, and a discharge unit 80. In addition to the control unit 30 described above, skin detection unit 40 also includes an A / D converter 32 and a determination unit 34 as components of a microcontroller 38.

[0042] The main components of the current detection unit 50 include a shunt resistor R1 connected between the DC power supply unit 20 and the electrical stimulation unit 10, an operational amplifier OP1, a second resistor R2, and a third resistor R3. The connection point between the electrical stimulation unit 10 and the shunt resistor R1 is connected to the non-inverting input terminal of the operational amplifier OP1. The output terminal of the operational amplifier OP1 is connected to the second resistor R2. The second resistor R2 and the third resistor R3 are connected in series. The end of the third resistor R3 opposite to the side where the second resistor R2 is located is connected to the connection point between the shunt resistor R1 and the low-side reference line of the DC power supply unit 20. The connection point between the second resistor R2 and the third resistor R3 is connected to the inverting input terminal of the operational amplifier OP1.

[0043] The operational amplifier OP1, the second resistor R2, and the third resistor R3 function as a sense amplifier that amplifies the voltage drop across the shunt resistor R1. ｉｎ , the voltage output at the connection point between the output terminal of the operational amplifier OP1 and the second resistor R2 is V ｏｕｔ Then, V ｏｕｔ =(1+R2 / R3)×V ｉｎ Here, however, the influence of the gain switching unit 60 is ignored. An example is assumed in which the second resistor R2 is set to 270 kΩ and the third resistor R3 is set to 30 kΩ. The input voltage V ｉｎ is 0.2V, the output voltage V ｏｕｔ becomes 10 times, 2 V. That is, the gain of the sense amplifier becomes 20 dB.

[0044] In this way, the current detection unit 50 converts the current flowing through the electrical stimulation unit 10 into a voltage, and then outputs the amplified output voltage V ｏｕｔ Therefore, the current detection unit 50 can output the current value that continuously changes depending on the state of the skin of the human body Hd that is in contact with the pair of first electrode portion P1 and second electrode portion P2 as an output voltage V ｏｕｔ can be converted to the value and output.

[0045] The gain switching unit 60 mainly includes a gain-switching switching element Qs, a fourth resistor R4, and a fifth resistor R5. In the example shown in FIG. 7 , the gain-switching switching element Qs is an NPN transistor. The collector terminal of the gain-switching switching element Qs is connected to the low-side reference line of the DC power supply unit 20. The emitter terminal of the gain-switching switching element Qs is connected to the connection point between the second resistor R2 and the third resistor R3 via the fourth resistor R4. The base terminal of the gain-switching switching element Qs is connected to the control unit 30 via the fifth resistor R5.

[0046] The control unit 30 switches whether or not to output an ON signal to the base terminal of the gain switching switching element Qs. When the control unit 30 outputs an ON signal, the gain switching switching element Qs is turned ON, and the third resistor R3 and the fourth resistor R4 are connected in parallel to form a combined resistance. On the other hand, when the control unit 30 does not output an ON signal, the gain switching switching element Qs is turned OFF, and no current flows through the fourth resistor R4. In other words, when the control unit 30 does not output an ON signal, the input voltage V of the operational amplifier OP1, which was described above assuming that the influence of the gain switching unit 60 is ignored, ｉｎ and output voltage V ｏｕｔ The following relationship holds, and the gain of the sense amplifier is 20 dB.

[0047] Assume an example in which the second resistor R2 is set to 270 kΩ, the third resistor R3 is set to 30 kΩ, and the fourth resistor R4 is set to 3 kΩ. When the control unit 30 outputs an ON signal, the input voltage V ｉｎ In contrast, the output voltage V of the operational amplifier OP1 ｏｕｔ is multiplied by 100. That is, the gain of the sense amplifier is 40 dB.

[0048] The control unit 30 controls the output voltage of the DC power supply unit 20 (hereinafter referred to as the "H-bridge voltage V ＨＢThe control unit 30 controls the DC power supply unit 20 to output a first voltage for applying electrical stimulation to the human body Hd, and a second mode for controlling the DC power supply unit 20 to output a second voltage for detecting contact of the pair of first electrode unit P1 and second electrode unit P2 with the skin of the human body Hd. The second mode is a mode for detecting skin and is set before driving in the first mode. The skin detection function in this embodiment can also be executed while the first mode is set. While the first mode requires applying electrical stimulation to the human body Hd, the second mode applies a voltage that places as little strain on the human body Hd as possible. Therefore, the second voltage is smaller than the first voltage. For example, the first voltage is several hundred mV, while the second voltage is several mV.

[0049] As described above, the output voltage of the DC power supply unit 20 differs greatly between the first mode and the second mode. Therefore, the control unit 30 controls the gain switching unit 60 to switch the gain of the sense amplifier between when the first mode is set and when the second mode is set. Specifically, when the first mode is set, the output voltage V ｏｕｔ In order to prevent erroneous detection due to excessive amplification of the output voltage V, the control unit 30 does not output an ON signal and keeps the gain switching element Qs in an OFF state. ｏｕｔ In order to sufficiently amplify the signal, the control unit 30 outputs an ON signal to turn on the gain switching element Qs.

[0050] The gain switching unit 60 is not limited to the above configuration as long as it can switch the gain of the operational amplifier OP1. For example, the gain switching unit 60 may be capable of switching the gain of the operational amplifier OP1 in three or more stages, or may be a variable resistor that can be switched continuously.

[0051] As a result, the gain switching unit 60 switches the gain of the operational amplifier OP1 so that it is higher in the second mode than in the first mode. For example, when the second mode is set and the control unit 30 outputs an ON signal, the input voltage V ｉｎWhen is 0.02V, the output voltage V of the operational amplifier OP1 ｏｕｔ When the first mode is set and the control unit 30 does not output an ON signal, the input voltage V of the operational amplifier OP1 is 100 times as large as the input voltage V of the operational amplifier OP1. ｉｎ When is 0.2V, the output voltage V of the operational amplifier OP1 ｏｕｔ becomes 10 times as much, or 2V.

[0052] The peak hold unit 70 is a peak hold circuit including, as its main components, a diode D1 and a capacitor C1. The anode terminal of the diode D1 is connected to the connection point between the output terminal of the operational amplifier OP1 and the second resistor R2 via a seventh resistor R7. The seventh resistor R7 is not necessarily connected. One end of the capacitor C1 is connected to the cathode terminal of the diode D1, and the other end is connected to the low-side reference line of the DC power supply unit 20. In the peak hold unit 70, the charge stored in the capacitor C1 is prevented from flowing back by the diode D1 and is accumulated in the capacitor C1. As a result, the peak hold unit 70 holds the peak level of the voltage amplified by the operational amplifier OP1. Therefore, even if the duration of the pulse voltage applied between the first electrode P1 and the second electrode P2 in the second mode is short, for example, the output voltage V ｏｕｔ The peak level of the output voltage V ｏｕｔ can be detected.

[0053] The discharge unit 80 is a discharge circuit including, as its main components, a discharge switching element Qd and a sixth resistor R6. In the example shown in FIG. 7 , the discharge switching element Qd is an NPN transistor. The emitter terminal of the discharge switching element Qd is connected to the connection point between the cathode terminal of the diode D1 and the capacitor C1. The collector terminal of the discharge switching element Qd is connected to the low-side reference line of the DC power supply unit 20. The base terminal of the discharge switching element Qd is connected to the control unit 30 via the sixth resistor R6. The connection point between the emitter terminal of the discharge switching element Qd and the capacitor C1 is connected to the A / D converter 32.

[0054] The control unit 30 outputs an ON signal to the base terminal of the discharge switching element Qd at a predetermined timing. When the control unit 30 outputs the ON signal, the discharge switching element Qd is turned ON, and the charge stored in the capacitor C1 is discharged via the discharge switching element Qd and the low-side reference line. This causes the discharge unit 80 to discharge the voltage held by the peak hold unit 70.

[0055] 8 is a diagram schematically illustrating an example of changes in voltage over time at positions A to C in the circuit configuration example of the skin detecting unit 40 shown in FIG. 7. In FIG. 8, the horizontal axis represents time, and the vertical axis represents voltage. The first position A is a position between the seventh resistor R7 and the diode D1. The second position B is a position between the A / D converter 32 and the connection point between the emitter terminal of the discharge switching element Qd and the capacitor C1. The third position C is a position between the control unit 30 and the sixth resistor R6.

[0056] The voltage at the first position A is the output voltage V from the operational amplifier OP1. ｏｕｔ As shown in Fig. 8, the voltage at the first position A rises at a timing corresponding to the pulse voltage applied between the first electrode portion P1 and the second electrode portion P2. This pulse voltage is, for example, the pulse voltage for skin detection in the second mode described above. The time width of each pulse voltage is, for example, approximately 50 µs.

[0057] The voltage at the second position B is the voltage at which the maximum voltage at the first position A is held by the peak hold unit 70 (hereinafter referred to as the "peak hold voltage V ＰＨ (See FIG. 10, etc.). The peak hold unit 70 can extend the holding time of the maximum voltage at the second position B to several hundred ms. This makes it easier for the determination unit 34, which will be described later, to make a determination based on the period during which the maximum voltage is held.

[0058] The voltage at the third position C is the voltage of the ON signal output from the control unit 30 to the base terminal of the discharge switching element Qd. The voltage held by the peak hold unit 70 at the second position B needs to be discharged before the next pulse voltage is applied. Therefore, the control unit 30 outputs an ON signal to the base terminal of the discharge switching element Qd at a timing just before the next pulse voltage is applied. As a result, the voltage at the second position B becomes almost zero before the next pulse voltage is applied.

[0059] Returning to FIG. 7 , the A / D converter 32 is an analog-to-digital converter that converts the analog voltage signal amplified by the operational amplifier OP1 and whose peak level is held by the peak hold unit 70 into a digital signal. The resolution of the A / D converter 32 is not particularly limited, but is 3 bits or more, for example, 12 bits. The sampling period of the A / D converter 32 is not particularly limited, but is, for example, 200 ksamples / second. The digital signal converted by the A / D converter 32 is input to the determination unit 34. The determination unit 34 determines the condition of the skin of the human body Hd in contact with the pair of first and second electrodes P1 and P2 based on the converted digital signal.

[0060] 9 is a diagram schematically illustrating an example of an analog signal input to the A / D converter 32 and a digital signal converted by the A / D converter 32 based on this analog signal. In FIG. 9, the horizontal axis represents time. The analog signal is represented by a curve, and in this case the vertical axis represents the voltage value shown at the left end. The digital signal is represented by a black circle, and in this case the vertical axis represents the binary number shown at the right end. In the example shown in FIG. 9, for simplicity of explanation, the resolution of the A / D converter 32 will be described as 3 bits.

[0061] The A / D converter 32 converts the analog signal into a digital signal at each predetermined sampling period. Specifically, the A / D converter 32 pre-associates adjacent binary values ​​of the digital signal with a fixed range of the voltage value of the analog signal (0.47 V in the example shown in FIG. 9 ), and converts the digital signal into a binary value that is closest to the voltage value of each sampling period. The analog signal input to the A / D converter 32 can continuously change depending on the condition of the skin of the human body Hd in contact with the pair of first electrode portion P1 and second electrode portion P2. The A / D converter 32 converts such an analog signal into a multi-level digital signal, allowing the determination unit 34 to make a detailed determination. The conditions that the determination unit 34 can determine based on the digital signal include, for example, whether the entire or only a portion of the pair of first and second electrodes P1 and P2 is in contact with the skin of the human body Hd, the moisture content of the pair of first and second electrodes P1 and P2, and the degree of dryness or non-dryness of the skin of the human body Hd due to, for example, sweating. Furthermore, the information that the determination unit 34 can determine is not limited to the condition of the skin of the human body Hd that is in contact with the pair of first and second electrodes P1 and P2. For example, the determination unit 34 may detect whether an overcurrent is occurring in the circuit based on the digital signal.

[0062] In this way, the determination unit 34 determines the peak hold voltage V ＰＨ In order for the determination unit 34 to make a correct determination, the peak hold voltage V ＰＨ is the H-bridge voltage V ＨＢ However, the peak hold voltage V ＰＨ may contain unnecessary components resulting from offset voltage, circuit voltage, etc. The offset voltage is a characteristic value of the operational amplifier OP1. The circuit voltage may be generated by the base current from the H-bridge circuit flowing into the shunt resistor R1. Hereinafter, the peak hold voltage V ＰＨ Although an offset voltage will be taken as an example of an unwanted component that may be included in the signal, the same applies to the circuit voltage.

[0063] FIG. 10 shows the H-bridge voltage V ＨＢ and peak hold voltage V ＰＨ 10, the horizontal axis represents the H-bridge voltage V ＨＢ The vertical axis represents the peak hold voltage V ＰＨ 10 shows graphs for first to third products M1 to M3, which are examples of products to which electrical stimulation device 1 is applied. ＰＨ The threshold V Ｔｈ 1 and the threshold V Ｔｈ A threshold V greater than 1 Ｔｈ 2. In reality, the determination unit 34 determines the peak hold voltage V ＰＨ Although the determination is made based on the digital signal converted from, for the sake of simplicity, the above threshold will be used.

[0064] In the first product M1, the offset voltage is negligibly small. In the second product M2, the offset voltage is positive. In the third product M3, the offset voltage is negative. As shown in FIG. 10, the H-bridge voltage V ＨＢ Even if the peak hold voltage V is the same, the first product M1 to the third product M3 each have a different peak hold voltage V ＰＨ Therefore, each of the first product M1 to the third product M3 has a peak hold voltage V ＰＨ is the threshold V Ｔｈ 1 or threshold V Ｔｈ When the H-bridge voltage V is equal to 2, ＨＢ The value of the offset voltage may differ, resulting in a difference in the sensitivity of skin detection. Although it is conceivable to use a known offset cancellation circuit to reduce the offset voltage, this poses a problem in that it requires adjustment for each product.

[0065] The offset voltage is a value specific to the operational amplifier OP1 and can vary depending on the product. ＨＢ Similarly, the circuit voltage may vary depending on the product, but the H-bridge voltage V ＨＢ Therefore, the inventors came up with the idea of ​​using relative values ​​instead of absolute values ​​as the criteria for determining the skin condition.

[0066] 11 is a diagram illustrating an example in which a relative value is used as a criterion for determining the skin condition. Similar to FIG. 10, FIG. 11 shows the H-bridge voltage V ＨＢ and peak hold voltage V ＰＨ In the example shown in FIG. 11, the relationship between the H-bridge voltage V ＨＢ is a constant ΔV ＨＢ The peak hold voltage V for the first product M1 to the third product M3 when the ＰＨ The changes ΔV1 to ΔV3 in the H-bridge voltage V ＨＢ Peak hold voltage V when V = 0V ＰＨ The value of the H-bridge voltage V ＨＢ is increased, and the H-bridge voltage V ＨＢ = ΔV ＨＢ The peak hold voltage V ＰＨ The peak hold voltage V ＰＨ The determination unit 34 makes a determination based on a comparison of the differences ΔV1 to ΔV3 between the value of the peak hold voltage V and the predetermined reference value ΔV. ＰＨ This reduces the influence of unnecessary components such as offset voltage that may be included in the signal, thereby improving the accuracy of the determination.

[0067] Even when a relative value is used as the criterion for determining the skin condition, if the determination unit 34 determines different conditions based on the magnitude relationship with respect to a single threshold value, the peak hold voltage V ＰＨ The peak hold voltage V may change around the threshold value, causing the judgment state to frequently switch. Therefore, by providing hysteresis to the threshold value, the judgment accuracy can be further improved. As an example, a first threshold value and a second threshold value greater than the first threshold value are used as the two threshold values. ＰＨ If the peak hold voltage V increases, it is determined that the threshold value has been exceeded when the peak hold voltage V exceeds a second threshold value (for example, 300 mV). ＰＨ When the voltage V falls from a value higher than the second threshold, no determination is made even if the voltage V falls below the second threshold, but it is determined that the voltage V falls below the threshold when the voltage V falls below the first threshold (for example, 200 mV).

[0068] The electrical stimulation device 1 can be in an idle state, such as a second mode that is not a first mode for applying electrical stimulation to the human body Hd, with the pair of first and second electrodes P1 and P2 in contact with the skin of the human body Hd. In this idle state, as the wearing time passes, sweat from the skin of the human body Hd that is in contact with the first and second electrodes P1 and P2 can cause current to flow more easily, making it easier for the user to feel the electrical stimulation. Therefore, in the idle state, the electrical stimulation device 1 sets a peak hold voltage V ＰＨ When the voltage V rises above a predetermined value, the H-bridge voltage V ＨＢ This can prevent unnecessary electrical stimulation from being given to the user.

[0069] FIG. 12 shows the H-bridge voltage V ＨＢ and peak hold voltage V ＰＨ 1 is a diagram showing a schematic diagram of the relationship between the H-bridge voltage V ＨＢ Even if the value is constant, the peak hold voltage V ＰＨ gradually increases, and V ＰＨ 1 (e.g. 300mV) to V ＰＨ In this case, the electrical stimulus to the user is large, so the peak hold voltage V ＰＨ On the condition that exceeds 1000mV, the H-bridge voltage V ＨＢ This reduces the peak hold voltage V ＰＨ is V ＰＨ V smaller than 2 ＰＨ It can be lowered to 3, reducing electrical stimulation to the user.

[0070] Even if the voltage applied between the pair of first and second electrodes P1 and P2 is the same, the intensity of the stimulation felt by the human body Hd may vary depending on the degree of dryness of the human body Hd's skin. This difference in the intensity of the stimulation felt by the human body Hd depending on the degree of dryness of the human body Hd's skin is particularly pronounced when the pair of first and second electrodes P1 and P2 are rubber electrodes. As mentioned above, rubber electrodes can be used without water, but unless the skin of the human body Hd is moistened to a certain extent, it is difficult to stably apply electrical stimulation to the human body Hd. Furthermore, the drier the skin of the human body Hd, the weaker the electrical stimulation felt by the human body Hd. Therefore, it is preferable to change the control of the electrical stimulation device 1 depending on the degree of dryness of the human body Hd's skin.

[0071] By determining the degree of dryness of the skin of the human body Hd, the electrical stimulation device 1 can perform, for example, the following processing. When the pair of first electrode P1 and second electrode P2 are rubber electrodes, the electrical stimulation device 1 may remain in a standby state and not apply a voltage between the pair of first electrode P1 and second electrode P2 during the period from when the pair of first electrode P1 and second electrode P2 are attached to the skin of the human body Hd until the skin of the human body Hd is determined to be dry. Then, when the electrical stimulation device 1 determines that the skin of the human body Hd has transitioned to a non-dry state due to sweating or the like, it may start applying a voltage between the pair of first electrode P1 and second electrode P2.

[0072] Furthermore, the electrical stimulation device 1 can perform the following processing, for example, by determining the degree of dryness of the skin of the human body Hd. As described above, the drier the skin of the human body Hd, the weaker the sensitivity of the human body Hd to electrical stimulation. If voltage application between the pair of first electrode P1 and second electrode P2 is initiated in such a state, and the skin of the human body Hd transitions to a non-dry state during application, the human body Hd may be more sensitive to the electrical stimulation, potentially resulting in an unnecessarily strong stimulation. Therefore, the electrical stimulation device 1 may set an upper limit on the output voltage of the DC power supply 20 depending on the dryness of the skin of the human body Hd. A method for determining the degree of dryness of the skin of the human body Hd will be described below.

[0073] 13 is a diagram showing an example of a voltage waveform at the first position A when the skin of the human body Hd is dry or wet. The voltage waveform shown in FIG. 13 shows the time change of voltage (hereinafter referred to as the "detection pulse voltage") corresponding to the pulse voltage applied between the first electrode portion P1 and the second electrode portion P2. As shown in FIG. 13, when the skin of the human body Hd is dry, such as immediately after the first electrode portion P1 and the second electrode portion P2 are attached to the pair of electrodes, the voltage shows a sharp peak at the start of the detection pulse voltage and a rapid decrease toward the end of the detection pulse voltage. On the other hand, when the skin of the human body Hd is wet due to sweating, such as several minutes after the first electrode portion P1 and the second electrode portion P2 are attached to the pair of electrodes, the voltage shows a sharp peak at the start of the detection pulse voltage and a gradual decrease toward the end of the detection pulse voltage.

[0074] That is, the voltage waveform at first position A may have a similar peak voltage value in both the dry and non-dry states at the timing of the start point of the detection pulse voltage, but the effective value is lower in the dry state than in the non-dry state. In other words, the voltage waveform at first position A has a smaller area in the dry state than in the non-dry state. Here, the impedance of the skin of the human body Hd (hereinafter referred to as "skin impedance Z") is the value obtained by dividing the output voltage value of the DC power supply unit 20 by the above-mentioned effective value. In other words, the skin impedance Z is lower in the non-dry state than in the dry state. The inventors have discovered that the degree of dryness of the skin of the human body Hd can be determined by measuring the skin impedance Z as follows.

[0075] FIG. 14 is a diagram schematically illustrating another example of the temporal change in voltage at positions A to C in the circuit configuration example of the skin detection unit 40 shown in FIG. 7 . The example shown in FIG. 14 differs from the example shown in FIG. 8 in the timing of the application of the ON signal from the control unit 30 at the third position C. Specifically, the control unit 30 sequentially switches the timing of turning off the ON signal directed to the base terminal of the discharge switching element Qd, i.e., the timing of the end of discharge by the discharge unit 80, during the application of each of the multiple detection pulse voltages at the first position A, so that the timing is different for each of the multiple detection pulse voltages. In the example shown in FIG. 14 , the control unit 30 sequentially switches the timing of turning off the ON signal so that the timing gradually shifts from the start point to the end point of the multiple detection pulse voltages at the first position A. As a result, the voltage at the second position B becomes a voltage obtained by holding the voltage at each point of one detection pulse voltage for a certain period of time. Therefore, if the A / D converter 32 converts the voltage values ​​at the second position B, which are held for a certain period of time, into digital signals, the microcontroller 38 can measure the skin impedance Z.

[0076] (Skin detection unit 40A according to the second embodiment) Figure 15 is a diagram showing an example of the circuit configuration when electrical stimulation device 1 is equipped with skin detection unit 40A according to the second embodiment. In the drawings and explanation of the second embodiment, components and members that are the same as or equivalent to those in the first embodiment are given the same reference numerals. Explanations that overlap with the first embodiment will be omitted as appropriate, and the explanation will focus on the configuration that differs from the first embodiment.

[0077] Skin detecting unit 40A differs from skin detecting unit 40 in that it further includes an A / D converter 44. Skin detecting unit 40A also differs from skin detecting unit 40 in that it does not need to include peak hold unit 70 and discharge unit 80.

[0078] The A / D converter 44 is connected via a seventh resistor R7 to the connection point between the output terminal of the operational amplifier OP1 and the second resistor R2, and to the low-side reference line of the DC power supply unit 20. The A / D converter 44 is connected to the microcontroller 38 so as to be able to communicate with them via SPI (Serial Peripheral Interface) communication or the like.

[0079] The A / D converter 44 converts the analog signal of the voltage amplified by the operational amplifier OP1 into a digital signal. The A / D converter 44 performs conversion at multiple timings during application of one detection pulse voltage included in the voltage amplified by the operational amplifier OP1. That is, the A / D converter 44 has a sampling rate sufficient to enable conversion at multiple timings during application of one detection pulse voltage. This allows the microcontroller 38 to measure the skin impedance Z based on the digital signal converted by the A / D converter 44. Furthermore, the determination unit 34 determines the skin condition of the human body Hd in contact with the pair of first electrode portion P1 and second electrode portion P2 based on the digital signal converted by the A / D converter 44. In the above example, the A / D converter 44 is described as being external to the microcontroller 38, but the A / D converter 44 may also be built into the microcontroller 38.

[0080] As described above, electrical stimulation device 1 includes electrical stimulation unit 10 including a pair of electrodes P1, P2 connected between the high-side reference line and the low-side reference line of DC power supply unit 20 and to be in contact with the skin of human body Hd, current detection unit 50 detecting the current between DC power supply unit 20 and electrical stimulation unit 10, and determination unit 34 determining the condition of the skin of human body Hd in contact with the pair of electrodes P1, P2 based on the detection result by current detection unit 50. As a result, electrical stimulation device 1 can determine the condition of the skin of human body Hd in contact with the pair of electrodes P1, P2 based on the current value that continuously changes between DC power supply unit 20 and electrical stimulation unit 10, thereby improving the accuracy of detecting the contact state of the electrodes with the skin.

[0081] Current detection unit 50 may include a shunt resistor R1 connected between DC power supply unit 20 and electrical stimulation unit 10, and a sense amplifier that amplifies the voltage drop across shunt resistor R1. This allows electrical stimulation device 1 to convert the continuously changing current value between DC power supply unit 20 and electrical stimulation unit 10 into a voltage value, and determine the condition of the skin of human body Hd in contact with pair of electrodes P1, P2 based on this converted voltage value.

[0082] The electrical stimulation device 1 may further include a control unit 30 that controls the output voltage of the DC power supply unit 20. The control unit 30 may be capable of setting a first mode in which the DC power supply unit 20 outputs a first voltage for applying electrical stimulation to the human body Hd, and a second mode in which the DC power supply unit 20 outputs a second voltage that is smaller than the first voltage for detecting contact of the pair of electrodes P1, P2 with the skin. The electrical stimulation device 1 may further include a gain switching unit 60 that switches the gain of the sense amplifier so that it is higher in the second mode than in the first mode. This allows the gain of the sense amplifier to be switched to an appropriate amplification factor depending on the magnitude of the voltage.

[0083] The present invention has been described above based on an embodiment. This embodiment is merely an example, and it will be understood by those skilled in the art that various modifications are possible in the combination of the components and processing steps, and that such modifications are also within the scope of the present disclosure.

[0084] The present invention relates to an electrical stimulation device that applies electrical stimulation to the muscles of a user.

[0085] 1 Electrical stimulation device, OP1 operational amplifier, R1 shunt resistor, 10 electrical stimulation unit, 20 DC power supply unit, 30 control unit, 32 A / D converter, 34 determination unit, 40 skin detection unit, 50 current detection unit, 60 gain switching unit, 70 peak hold unit, 80 discharge unit.

Claims

1. An electrical stimulation device comprising: an electrical stimulation unit including a pair of electrodes connected between a high-side reference line and a low-side reference line of a DC power supply unit to be brought into contact with human skin; a current detection unit that detects the current between the DC power supply unit and the electrical stimulation unit; and a determination unit that determines the condition of the skin in contact with the pair of electrodes based on the detection results by the current detection unit.

2. The electrical stimulation device of claim 1, wherein the current detection unit comprises: a shunt resistor connected between the DC power supply unit and the electrical stimulation unit; and a sense amplifier that amplifies the voltage drop across the shunt resistor.

3. The electrical stimulation device of claim 2, further comprising a control unit that controls the output voltage of the DC power supply unit, wherein the control unit is capable of setting a first mode in which a first voltage for applying electrical stimulation to the human body is controlled to be output from the DC power supply unit, and a second mode in which a second voltage smaller than the first voltage for detecting contact of the pair of electrodes with the skin is controlled to be output from the DC power supply unit, and further comprising a gain switching unit that switches the gain of the sense amplifier so that it is higher in the second mode than in the first mode.

4. The electrical stimulation device according to claim 2, further comprising a peak hold unit that holds a peak level of the voltage amplified by the sense amplifier.

5. The electrical stimulation device according to claim 4, further comprising a discharge unit that discharges the voltage held by the peak hold unit.

6. The electrical stimulation device of claim 5, wherein the discharge unit sequentially switches the discharge end timing so that the timing is a different timing for each of the plurality of detection pulse voltages included in the voltage amplified by the sense amplifier during application of each of the plurality of detection pulse voltages.

7. The electrical stimulation device of claim 2, further comprising an analog-to-digital converter that converts the analog signal of the voltage amplified by the sense amplifier into a digital signal, wherein the analog-to-digital converter performs the conversion at multiple times during application of one detection pulse voltage included in the voltage amplified by the sense amplifier, and the determination unit performs determination based on the digital signal.

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