DESC:Technical Field of the Invention

The present invention relates to the field of prosthetic and bionic hands, more particularly to the usage of EMG sensors to sense the muscle signals and control the prosthetics accordingly.

Background of the Invention

The EMG sensors are well known for their use in prosthetic devices. An individual or amputee can wear the EMG sensor on his body contacting some part of tissue and can issue commands to prosthetic or similar system. These commands can be generated by voluntarily sending muscular signals to EMG. These signals are amplified and processed by EMG sensor to provide meaningful signal to control system. The control system interprets the signal and accordingly performs the desired or assigned action. Examples of such EMG sensors or electrodes is the Ossur Brand EMG Electrode (Electrodes compact 50Hz 300mm), part number PL091050A.

The Existing EMG sensors used in controlling prosthetic or bionic hands suffer from problems like leads off and lack of power consumption optimization. A lead off condition can be defined as one or more of the three contact points of EMG sensor that are not in contact with human tissue. The disconnected electrode will adversely affect the EMG signal. The control system may interpret saturated signal as input and as a result the system may malfunction. Also, when there is no input being taken from EMG Sensor, keeping it powered will consume power. This makes high demands on addressing these issues the device provide error free and power optimized input control system.

The main problems associated with biopotential measurements are 1. Movement Artefacts, 2. Instability of Sensor skin interface, 3. Sensor and Equipment Noise, 4. Common mode interference mainly from 50/60 Hz mains, 5. Noise from power supply, 6. ESD strikes and 7. Leads off error.

Therefore, there are many prosthetic or orthotic device (POD) based on electromyography (EMG) signals. The prior art W.O Patent No: 2016172057A1, discloses Systems, devices, and methods for control of a prosthetic or orthotic device (POD) based on electromyography (EMG) signals are described. The POD may be a lower or upper limb POD having one or more joints. One or more EMG sensors may detect the EMG signals. The EMG sensors may be external, subcutaneous, intraperitoneal, epimysial, intramuscular, or other types. Control of the POD may be based on EMG and non-EMG signals, such as velocity, acceleration, position, force, etc. Voluntary and/or automatic control may be implemented, for example with voluntary muscle contractions and/or data based on velocity, acceleration, position, force, etc.

The other prior art US4209860A discloses a method for controlling the operation of an electrically powered prosthesis appliance that replaces an amputee's missing limb which method includes calibration steps of picking up electromyographic (EMG) signals from the stump of or from at least one muscle close to the point of amputation of the missing limb, and processing the signals thus collected to drive the motors.

The other prior art US20190374352A1 A control system for control of a prosthetic device having a plurality of actuators receives an orientation signal indicative of a desired movement. Alternatively, in some embodiments, the sensors 18 may be EMG electrodes. In some embodiments, EMG electrode signals may be used in various controls, for example, but not limited to, turn on shoulder control, grip change control or movement control. The sensor CPU 19 inputs data from the one or more sensors 18 and filters and/or converts the data to generate user input signals. The user input signals are then sent to the device module 17 by the sensor module communicator 20. The sensor module communicator 20 may be hard wired to the device module 17 or may transmit the user input signals wirelessly, for example, but not limited to, through a radio transmitter, Bluetooth® or the like.

The other prior art RU2627818C1 discloses a method of bionic control of a technical device, including forming a control action by recording an electrophysiological signal from a contracting muscle, processing it, applying a signal to a control unit and then to an actuator, characterized in that the electrical impedance from antagonist muscles is recorded as an electrophysiological signal when performing a natural movement of these muscles. This invention discloses about the synchronous recording of an electrophysiological signal — an electrical impedance and an electromyogram (EMG) signal from electrodes located on the surface of the skin above the muscle.

The other prior art US20170340459A1 This invention generally relates to a system and method for fine motor control of fingers on a prosthetic hand. In particular, the present disclosure describes a system and method for controlling the flexion or extension of one or more fingers of a prosthetic hand to reproduce a natural stroke such as for, e.g., writing, painting, brushing teeth, or eating. The systems and methods described herein use electromyographic (EMG) signals and, more particularly, combinations of electromyographic signals, from muscles in the forearm to activate one or more motors of the prosthetic hand that control the motion of the prosthetic fingers.

The other prior art US9037530B2 discloses a “Wearable Electromyography-Based Controller” includes a plurality of Electromyography (EMG) sensors and provides a wired or wireless human-computer interface (HCI) for interacting with computing systems and attached devices via electrical signals generated by specific movement of the user's muscles. Examples of Wearable Electromyography-Based Controllers include articles of manufacture, such as an armband, wristwatch, or article of clothing having a plurality of integrated EMG-based sensor nodes and associated electronics. Above invention comprising a calibration phase that automatically identifies one or more specific user muscles that generate the electrical signals measured by one or more specific EMG sensors, and wherein the user performs one or more specific gestures as part of a training phase for the calibration. wherein a subset of the EMG sensors is identified by an automated multiplexing process which determines which EMG sensors are sufficient to measure the muscle generated electrical signals that are associated with one or more of the specific user gestures. comprising a module for automatically disabling all EMG sensors not included in the subset of EMG sensors.

Above prior art invention involve a wearable controller system that calibrates and finds the subset of required sensors to capture muscle activities and disables all other sensors during operation to save power.
These above inventions disclose usage of EMG for control of prosthetic devices but none of them involve EMG sensors with leads off detection or EMG sensors with enable pin to turn off the sensor when prosthetic device is not in use.

Therefore, in order to overcome the above-mentioned problems associated with the existing EMG sensors, a sensor for biopotential measurement is developed that can be used in prosthetics or bionic hands that reduces the power consumption of overall prosthetic hand.

Brief Summary of the Invention
The present invention relates to the field of prosthetic and bionic hands. More specifically the present invention is directed to EMG sensors used in bionic hands.

It is therefore an object of the present invention to develop an EMG sensor that senses muscle signals and controls the movement of fingers accordingly.

It is an object of the present invention to develop an EMG sensor that has three conductive contact plates which will be in contact with human tissue to sense the EMG Signals.

It is an object of the present invention to develop an EMG sensor provided with an electronic circuit that converts EMG signals to a format which is readable by the Microprocessor or Micro-controller or any signal converters.

It is an object of the present invention to provide a gain adjustment knob that helps in amplifying the EMG signals to a desired level.

Another object of the present invention is to provide a multi wire cable that connects the EMG sensor to process PCB or any other9 circuitry.

Another object of the present invention is to develop an EMG sensor with Leads OFF detection that enables the control system to know that the EMG sensor is not in proper contact with the Human tissue and to notify the user to take corrective action. The notification can be through a LED indication.

Another object of the present invention is to develop an EMG sensor with Enable input pin that ensures the sensor to be turned ON only when EMG signal input is required.
It is an object of the present invention to develop an EMG sensor that has electronic circuitry to avoid movement artefacts, to reject common mode voltages, to eliminate noise and to protect itself from ESD strikes.

In accordance with the aspect of the present invention, the EMG sensor is designed to acquire biopotentials from the surface of the skin and process the signal to get the meaningful data.

In accordance with the aspect of the present invention, lack of leads off detection is common problem in existing prosthetic hands which leads to wrong interpretation of the EMG signal. Leads OFF detection feature for proposed EMG sensor mitigates the risk of device malfunctioning due to wrong interpretation of EMG signal as high when the high EMG signal is actually generated because of Leads OFF of EMG Sensor inputs.

In accordance with the aspect of the present invention, high power consumption is also a major drawback in most of the existing prosthetic hands. The Enable input pin for proposed EMG sensor is provided so as to turn ON the EMG sensors only when the EMG signal is required, this reduces the overall power consumption of the device.

From the description above it is clear that various changes could be done to the preferred EMG sensor without departing from the scope of the invention.

From a reading of the description above of the preferred frameworks of the present invention, modifications and variations thereto may occur to those skilled in the art. Therefore, the scope of the present invention is to be limited only by the claims of this invention.

Brief Description of the Drawings

The present invention is illustrated by accompanying drawings, wherein:

Fig. 1 illustrates an improved EMG sensor depicting the arrangement of EMG sensors to the prosthetic socket according to the present invention.

Fig. 2 illustrates an improved EMG sensor depicting the fabrication of EMG sensors to the prosthetic socket and is connected to the amputee hand according to the present invention.

Fig. 3 illustrates an improved EMG sensor depicting the arrangement of electrode plates according to the present invention.

Fig. 4 illustrates an exploded view depicting the components and arrangement of improved EMG sensor according to the present invention.

Fig. 5 shows improved EMG sensor electronic chip depicting various pins of the improved EMG sensor according to the present invention.

Fig. 6 illustrates the block diagram depicting the electrode of improved EMG sensor according to the present invention.

Fig. 7 shows pinout of Analog Front End of the electrode of improved EMG sensor according to the present invention.

Fig. 8 shows the circuit diagram depicting the connections of electrode plates to Analog Front End according to the present invention.

Fig. 9 shows a circuit configuration for Leads off detection according to the present invention.

Fig. 10 shows configuration of right leg drive circuit according to the present invention.

Detailed Description of the Invention

The description that follows is presented to enable one skilled in the art to make and use the present invention and is provided in the context of a particular application and its requirements. Various modifications to the disclosed embodiments will be apparent to those skilled in the art, and the general principles discussed below may be applied to other embodiments and applications without departing from the scope and spirit of the invention. Therefore, the invention is not intended to be limited to the embodiments disclosed, but the invention is to be given the largest possible scope which is consistent with the principles and features described herein.

The terminology used herein is to describe particular example embodiments only and is not intended to be limiting. As used herein, the singular forms "a," "an" and "the" "said" may be intended to include the plural forms as well, unless the context indicates otherwise. The terms "comprises," "comprising," "including," and "having," are inclusive and therefore specify the presence of stated features, steps, operations, elements, and/or components, but do not preclude the presence or addition of one or more other features, steps, operations, elements, and components thereof.

According to an exemplary embodiment of the present invention, the usage of EMG sensors to sense the muscle signals and controlling of the prosthetics is disclosed. The improved EMG sensor system for a myoelectric controlled prosthetic device, wherein the prosthetic device includes a forearm portion, a battery component, a control unit, and at least one motor/actuator.
In accordance with the exemplary embodiment of the present invention, the control unit converts the received signals into useful patterns and drives the actuators to close and open fingers of the prosthetic device.

In accordance with the exemplary embodiment of the present invention, the said EMG sensor system adapted to be placed in contact with the subject’s skin at muscle mid and end positions of a residual limb, comprises of conductive electrode contact plates 1, 2, 3 connected with EMG sensor connectors (J1, J2, J3).

In accordance with the exemplary embodiment of the present invention, the said EMG sensor connector J1 is connected to the skin contact electrode plate 1, J3 connected to skin contact electrode plate 2, and J2 connected to skin contact electrode plate 3 which in turn connected to output of a Right Leg Drive (RLD) amplifier.

In accordance with the exemplary embodiment of the present invention, the said electrode contact plates 1, 2, 3 along with EMG sensors are housed in an enclosure wherein the said enclosure comprises of top cover, a rubber sealing, an electronic circuit and an enclosure bottom cover.

In accordance with the exemplary embodiment of the present invention, the said electrode plates of the said system are fixed to the said top cover and the electronic circuit is arranged inside the said bottom cover.

In accordance with the exemplary embodiment of the present invention, the control system checks current state of the prosthetic device (Leads OFF condition) and notifies the user to remove the bionic hand and put it on again so that all the electrode plates are in contact with the skin.

In accordance with the exemplary embodiment of the present invention, the electronic circuitry includes ESD diodes on signal Input and signal Output ports for protection from contact discharge and air discharges. The current limiting resistors added on a Drive right leg output pin to limit a patient leakage current to 10uA. The LDO regulator to reduce power consumption and eliminates power supply noise. An integrated analog front end to extract, amplify and filter small biopotential signals in the presence of noisy conditions.

In accordance with the exemplary embodiment of the present invention, the analog front end of the system designed to extract, amplify and filter small biopotential signals in the presence of noisy conditions, such as those created by motion or remote electrode placement.

In accordance with the exemplary embodiment of the present invention, integrated analog front end of the system comprises a pre-amplifier block to apply gain and to filter out near dc signals simultaneously, a two-pole high-pass filter for eliminating motion artifacts and the electrode half-cell potential, a right leg drive amplifier to improve common-mode rejection of the line frequencies in the system and other undesired interferences, a sallen-key LPF filter to attenuate electrode and equipment noise associated with surface Electromyography measurements, a mid-supply reference buffer to create a virtual ground between the supply voltage and the system ground, a Leads off detection circuitry (30) detects which of the two input leads are disconnected from the subject or patient.

In accordance with the exemplary embodiment of the present invention, the EMG sensor system with Leads OFF detection enables the control system to know that the EMG sensor contact plates are in proper contact with the human tissue and to take corrective action. It mitigates the risk of device malfunctioning due to wrong interpretation of EMG signal.

In accordance with the exemplary embodiment of the present invention, the EMG sensor system is provided with an inbuilt electronic circuitry that converts EMG signals to a format which is readable by the control unit or like, signal converters.

In accordance with the exemplary embodiment of the present invention, the electronic circuitry avoids movement artefacts, reject common mode voltages, eliminate noise and protects itself from ESD strikes.

In accordance with the exemplary embodiment of the present invention, the electronic circuitry includes a passive high pass filter to reduce the base line drifts in the output signal, a notch filter block is to reject the mains frequency noise which is a major source of noise for EMG related measurements, a precision rectifier is implemented to rectify the small signals to positive polarity signals, an operational amplifier removes reference voltage from signal, a passive low pass filter to estimate amplitude of EMG signal that need to be taken as envelop of the signal, a non-inverting amplifier is implemented to amplify the signal that is readable by the control unit that process the EMG signal.

In accordance with the aspect of the present invention, The EMG sensor system enable input pin, to turn ON the EMG sensors only when the EMG signal is required, this reduces the overall power consumption of the device.

Referring to the drawings, Fig. 1 illustrates an improved EMG sensor depicting the arrangement of EMG sensors to the prosthetic socket according to the present invention. The arrangement of EMG sensors (2) to the prosthetic device (23) comprises a forearm portion (1), a battery component (3), a control unit (4), and at least one motor/actuator (5), an EMG sensor system (2) adapted to be placed in contact with the subject’s skin at muscle mid and end positions of a residual limb. The sensor (2) sends information to a control system (4), which translates the data into commands for the electric motors (5) and moves the fingers. The prosthetic hands are battery (4) operated devices and they work based on electromyography signals.

Fig. 2 illustrates an improved EMG sensor depicting the fabrication of EMG sensors to the prosthetic socket and is connected to the amputee hand according to the present invention. The EMG sensor system (2) adapted to be placed in contact with the subject’s skin at muscle mid and end positions of a residual limb (6). The EMG sensors (2) with electrode contact plates 1, 2, 3 (7, 8 & 9) connected with EMG sensor connectors (J1, J2, J3). The EMG sensors (2) capture the muscle signals of the user, filters them, and passes them to control system unit (4). The control system unit (4) converts the received signals into useful patterns and drives the actuators (5) that close and open the fingers.

Fig. 3 illustrates an improved EMG sensor depicting the arrangement of electrode plates according to the present invention. The electrode contact plates 1, 2, 3 (7, 8 & 9) are fixed to the top cover. The contact plates (7, 8 & 9) of the system (2) that are connected with contact points on PCB (J1, J2, J3) are conductive plates to sense EMG signals from human tissue.

Fig. 4 illustrates an exploded view depicting the components and arrangement of improved EMG sensor according to the present invention. The electrode contact plates 1, 2, 3 (7, 8 & 9) along with EMG sensors (2) comprises of top cover (10), a rubber sealing (11), an electronic circuit (12), and an enclosure bottom cover (13). The electrode plates (7, 8 & 9) of the system (2) (7, 8 & 9) are fixed to the top cover (10), and the electronic circuit (12) is arranged inside the said bottom cover (13). The contact plates (7, 8 & 9) of the system (2) that are connected with contact points on PCB (J1, J2, J3) are conductive plates to sense EMG signals from human tissue.

Fig. 5 shows improved EMG sensor electronic chip depicting various pins of the improved EMG sensor according to the present invention. The connector J1 is connected to the skin contact electrode plate 1 (7), J3 connected to skin contact electrode plate 2 (8), and J2 connected to skin contact electrode plate 3 (9) which in turn connected to output of a Right Leg Drive (RLD) amplifier. The EMG sensor is provided with an inbuilt electronic circuitry (12) that converts EMG signals to a format which is readable by the control unit (4) or like, signal converters. The inbuilt electronic circuitry (12) avoids movement artefacts, reject common mode voltages, eliminate noise and protects itself from ESD strikes.

Fig. 6 illustrates the block diagram depicting the electrode of improved EMG sensor according to the present invention. The enclosure material used for improved EMG sensor is PA12, which is a biocompatible material, and the skin contact electrode plates are made from medical grade stainless steel 316L. The distance between these electrode plates is selected based on SENIAM recommendations and the dimensions are selected based on the target sensor dimensions. The EMG Sensor (2) include an ESD diodes (14) on signal Input and signal Output ports that protects electronic circuit from contact discharge and air discharge, a current limiting resistors (15) added on a Drive right leg output pin to limit a patient leakage current to 10uA, LDO regulator (24) to reduce power consumption and eliminates power supply noise and an integrated analog front end (16) to extract, amplify and filter small biopotential signals in the presence of noisy conditions.

The electrode includes a passive high pass filter (22) to reduce the base line drifts in the output signal, a notch filter (21) block to reject the mains frequency noise which is a major source of noise for EMG related measurements, a precision rectifier (20) is implemented to rectify the small signals to positive polarity signals, an operational amplifier (19) removes reference voltage from signal, a passive low pass filter (18) to estimate amplitude of EMG signal that need to be taken as envelop of the signal and a non-inverting amplifier (17) is implemented to amplify the signal that is readable by the control unit (4) that processes the EMG signal.

The integrated analog front end (16) comprises a pre-amplifier (25) block to apply gain and to filter out near dc signals simultaneously, a two-pole high-pass filter (26) for eliminating motion artifacts and the electrode half-cell potential, a right leg drive amplifier (27) to improve common-mode rejection of the line frequencies in the system and other undesired interferences, a sallen-key LPF filter (28) to attenuate electrode and equipment noise associated with surface Electromyography measurements, a mid-supply reference buffer (29) to create a virtual ground between the supply voltage and the system ground and a Leads off detection circuitry (30) detects which of the two input leads are disconnected from the subject or patient. The control system (4) ensures the input pin to turn ON only when the EMG signal input is required, to reduce the overall power consumption of the device.

Fig. 7 shows pinout of Analog Front End used in the improved EMG sensor according to the present invention. An integrated analog front end (16) extracts, amplifies and filters small biopotential signals in the presence of noisy conditions such as those created by motion or remote electrode placement (muscle mid and end positions of a residual limb).

Fig. 8 shows the circuit diagram depicting the connections of electrode plates to the Analog Front End according to the present invention. The +IN, -IN pins of AD8232 are connected to J1 (electrode plate 1), J3(electrode plate 2) respectively. J2(electrode plate 3) is connected to output of RLD (right leg drive amplifier). Whenever subject/patient wears the bionic hand, all the three electrodes of improved EMG sensor are in contact with the subject’s skin.

Fig. 9 shows a circuit configuration for Leads off detection according to the present invention. The Leads off detection circuitry (30) detects which of the two input leads are disconnected from the subject or patient. The Leads OFF detection (30) enables the control system (4) to know that the EMG sensor contact plates are in proper contact with the human tissue and notifies the user to take corrective action, the leads off detection (30) mitigates the risk of device malfunctioning due to wrong interpretation of EMG signal.

Fig. 10 shows configuration of right leg drive circuit according to the present invention. The Leads Off detection works by sensing when either instrumentation amplifier input voltage is within 0.5 V from the positive rail. A 10 M? pull-up resistor is added on each input of instrumentation amplifier. When the EMG signal potential is inside the common-mode range of the instrumentation amplifier then the voltage on the input pin will be greater than 0.5V due to the presence of pull-up resistor. This voltage will be compared with internal comparator of AFE and a logic high will be set on LOD+ or LOD- pins. The logic high on LOD+ and LOD- pins indicates that IN+ and IN- pins are disconnected. Control system present in the bionic hand can read the status of LOD+ and LOD- pins and whenever there is a logic high on these pins it means that leads-off is detected and control system can notify the user using LED indications so that user can take corrective action.

From the description above it is clear that various changes could be done to the preferred EMG sensor system without departing from the scope of the invention.
,CLAIMS:1. An improved EMG sensor system (2) for a myoelectric controlled prosthetic device (23), wherein the prosthetic device (23) includes:
a forearm portion (1), a battery component (3), a control system (4), and at least one motor/actuator (5);
the control system (4) converts the received signals into useful patterns and drives the actuators (5) to close and open fingers of the prosthetic device (23);
the said EMG sensor system (2) adapted to be placed in contact with the subject’s skin at muscle mid and end positions of a residual limb, comprises of conductive electrode plates 1, 2, 3 (7, 8 & 9) connected to contact points on PCB (J1, J2, J3);
the said EMG sensor connector J1 is connected to the skin contact electrode plate 1 (7), J3 connected to skin contact electrode plate 2 (8), and J2 connected to skin contact electrode plate 3 (9) which in turn connected to Analog Front End.
the electronic circuit along with electrode plates is housed in an enclosure wherein the said enclosure comprises of top cover (10), a rubber sealing (11), an electronic circuit (12), and an enclosure bottom cover (13);
Characterized in that:
the EMG sensor system (2) having an inbuilt electronic circuitry (12) checks the Leads Off condition and the control system turns OFF the EMG sensors to save the power, wherein the electronic circuitry includes:
ESD diodes (14) to protect from contact discharge and air discharge that are added on signal Input and signal Output ports;
current limiting resistors (15) added on a Drive right leg output pin to limit a patient leakage current to 10uA;
a LDO regulator (24) to reduce power consumption and eliminates power supply noise;
an integrated analog front end (16) to extract, amplify and filter small biopotential signals in the presence of noisy conditions, wherein the integrated analog front end (16) comprises:
a pre-amplifier (25) block to apply gain and to filter out near dc signals simultaneously;
a two-pole high-pass filter (26) for eliminating motion artifacts and the electrode half-cell potential;
a right leg drive amplifier (27) to improve common-mode rejection of the line frequencies in the system and other undesired interferences;
a sallen-key LPF filter (28) to attenuate electrode and equipment noise associated with surface Electromyography measurements;
a mid-supply reference buffer (29) to create a virtual ground between the supply voltage and the system ground; and
a Leads off detection circuitry (30) detects which of the two input leads are disconnected from the subject or patient.
a passive high pass filter (22) is implemented to reduce the base line drifts in the output signal;
a notch filter (21) block is to reject the mains frequency noise which is a major source of noise for EMG related measurements;
a precision rectifier (20) is implemented to rectify the small signals to positive polarity signals;
an operational amplifier (19) removes reference voltage from signal;
a passive low pass filter (18) to estimate amplitude of EMG signal that need to be taken as envelop of the signal; and
a non-inverting amplifier (17) is implemented to amplify the signal that is readable by the control unit (4) that processes the EMG signal.
2. The system (2) as claimed in claim 1, wherein the said contact plates (7, 8 & 9) of the said system (2) that are connected with contact points on PCB (J1, J2, J3) are made of conductive materials to sense EMG signals from human tissue.

3. The system (2) as claimed in claim 1, wherein the said electrode plates (7, 8 & 9) of the said system (2) fixed to the top cover (10), and the electronic circuit (12) is arranged inside the said bottom cover (13).

4. The system (2) as claimed in claim 1, wherein the analog front end of the system (2) is designed to extract, amplify and filter small biopotential signals in the presence of noisy conditions, such as those created by motion or remote electrode placement (muscle mid and end positions of a residual limb).

5. The system (2) as claimed in claim 1, wherein the said system (2) is provided with an inbuilt electronic circuitry (12) that converts EMG signals to a format which is readable by the control unit (4) or like, signal converters.

6. The system (2) as claimed in claim 1, wherein the said system (2) with Leads OFF detection (30) enables the control system (4) to know that the EMG sensor contact plates (7, 8 & 9) are in proper contact with the human tissue and to notify the user to take corrective action in case of leads OFF detection.

7. The system (2) as claimed in claim 1, wherein the said system (2) with inbuilt electronic circuitry (12) avoids movement artefacts, reject common mode voltages, eliminate noise and protects itself from ESD strikes.

8. The system (2) as claimed in claim 1, wherein the said system (2) acquires biopotentials from the surface of the skin and process the signal to get meaningful data.

9. The system (2) as claimed in claim 1, wherein the leads off detection (30) of the said system (2) mitigates the risk of device malfunctioning due to wrong interpretation of EMG signal.

10. The system (2) as claimed in claim 1, wherein the said system (2) ensures the input pin to turn ON only when the EMG signal input is required, to reduce the overall power consumption of the device.