The present disclosure relates to a vehicle seat, and particularly relates to a vehicle seat that performs a function of measuring the heart rate of a seated passenger.
In recent years, for the purpose of promptly reporting, to a driver, that the driver's physical condition has been changed while a vehicle is running, various vehicle seats capable of displaying a change in physical condition by detecting various parameters indicating the state of the driver have been proposed.
For example, Japanese Patent Publication JP 2009-050679 discloses an electrocardiogram measurement device including first and second electrodes serving as two sensors optionally arranged at a seat back and a ground electrode disposed at a seat cushion and configured to determine a reference potential. In this electrocardiogram measurement device, an electric signal associated with an electrocardiogram detected from a driver by two sensors is efficiently sensed in such a manner that the electric signal is amplified by a two-stage amplifier, and therefore, a driver's health condition can be determined.
Japanese Patent Publication JP 2007-301175 discloses a measurement device including planar electrodes serving as a plurality of sensors arranged respectively at the positions contacting the back of a driver, the region extending from the waist to the hip of the driver, and the thighs of the driver. In this measurement device, one of the sensors is provided for obtaining the neutral-point potential of an amplifier. Thus, abnormality can be determined in such a manner that a electrocardiographic signal and a respiration signal from the driver are suitably detected.
Sheet-shaped sensors have been broadly used, such as the sensors of Japanese Patent Publication JP 2009-050679 and Japanese Patent Publication JP 2007-301175. Each sensor generally includes a conductive line forming a sensor body, and a conductive sheet fixing the conductive line. These sensors are arranged at part of the seat back supporting the back of the seated passenger. When the seated passenger leans on the seat back, the sheet-shaped sensors of this type obtain voltage from the contact portion between the back of the seated passenger and the seat to measure the heart rate.
However, static electricity is caused by slight vibration while the vehicle is running, friction between clothes and the seat back when the seated passenger leans on the seat back, or contact between the seated passenger and, e.g., a steering wheel or a footrest due to movement of the seated passenger in operation. Such static electricity is, as noise, contained in an electrocardiographic waveform. In the vehicle seat including the electrocardiogram measurement device as described in Japanese Patent Publication JP 2009-050679 and Japanese Patent Publication JP 2007-301175, removal and reduction of such static electricity are not taken into consideration. Due to the noise caused by the static electricity, it is difficult to stably detect a bioelectric signal such as an electrocardiographic signal of the seated passenger. For this reason, vital information such as the heart rate might not be able to be accurately measured.