Method for measuring capacitance and capacitive sensor unit

• US 9,304,156 B2
• Filed: 08/08/2013
• Issued: 04/05/2016
• Est. Priority Date: 02/08/2011
• Status: Active Grant

• Current Assignee: Brose Fahrzeugteile GmbH & Company KG Hallstadt (Brose)
• Original Assignee: Brose Fahrzeugteile GmbH & Company KG Hallstadt (Brose)
• Inventors: Weingaertner, Thomas, Wuerstlein, Holger, Pohl, Florian
• Primary Examiner(s): Nguyen, Tung X
• Assistant Examiner(s): Frederiksen, David
• Application Number:
  US13/962,234
• Publication Number:
  US 20130321006A1
• Time in Patent Office: 971 Days
• US Class Current: 1/1
• CPC Class Codes: B60R 25/2054 by foot gestures
• CPC Class Codes: E05F 15/46 responsive to changes in electrical capacitance
• CPC Class Codes: E05F 15/73 responsive to movement or presence of persons or objects
• CPC Class Codes: E05Y 2400/852 Sensors
• CPC Class Codes: E05Y 2400/858 by body parts
• CPC Class Codes: E05Y 2900/50 for vehicles
• CPC Class Codes: E05Y 2900/546 Tailgates
• CPC Class Codes: G01R 27/2605 Measuring capacitance capacitive sensors G01D5/24
• CPC Class Codes: H03K 17/955 using a capacitive detector
• CPC Class Codes: H03K 2217/960715 Rc-timing; e.g. measurement of variation of charge time or discharge time of the sensor
• CPC Class Codes: H03K 2217/960725 Charge-transfer

Abstract

A method measures a capacitance. According to the method, a first detection measurement for the capacitance which is to be measured is detected by a first measurement method during a first measurement phase. In this case, a second measurement phase is started when the first detection measurement satisfies a transition criterion. A second detection measurement for the capacitance which is to be measured is detected during the second measurement phase by a second measurement method which differs from the first measurement method. The second measurement method has higher measurement accuracy than the first measurement method but also greater energy expenditure.

Claims

1. A method for measuring a capacitance, which comprises the steps of:

during a first measuring phase, detecting a first measured quantity of the capacitance via a first measuring method, the first measuring method includes performing one of the further steps for detecting the first measured quantity;

detecting a measurement of a charging speed of a sensor electrode;

detecting an amplitude of an alternating voltage present on a voltage divider containing a sensor electrode;

or

detecting a phase angle between the alternating voltage and a strength of a flow of current caused by the alternating voltage;

starting a second measuring phase when the first measured quantity satisfies a transition criterion; and

during the second measuring phase, detecting a second measured quantity of the capacitance to be measured via a second measuring method being different from the first measuring method, the second measuring method having a higher level of measuring accuracy compared to the first measuring method, and the first measuring method having a lower expenditure of energy compared to the second measuring method, the second measuring method includes performing one of the further steps of;

detecting a measurement of a charge quantity on the sensor electrode as the second measured quantity;

or

detecting a frequency of a voltage which is generated by an RC oscillator containing the sensor electrode.

2. The method according to claim 1, which further comprises:

defining the transition criterion to contain a threshold value comparison of the first measured quantity with a given threshold value; and

detecting an electrical voltage dropping across the sensor electrode or a charging resistor connected upstream as the first measured quantity and the transition criterion is met when the first measured quantity does not reach the given threshold value in a predefined time frame.

3. The method according to claim 1, which further comprises:

detecting, during the second measuring phase, a capacitor voltage present at a reference capacitor owing to a transfer of charge from the sensor electrode to the reference capacitor;

increasing a charge quantity at the reference capacitor incrementally until the capacitor voltage reaches a predefined limiting value; and

detecting a number of charge increasing increments as the second measured quantity.

4. The method according to claim 1, which further comprises:

during the second measuring phase, transferring charge incrementally from the sensor electrode to a reference capacitor and is accumulated at the reference capacitor; and

detecting, after a number of charge increasing increments, a capacitor voltage present at the reference capacitor, and the capacitor voltage is detected as the second measured quantity.

5. The method according to claim 1, wherein in order to determine a basic measurement of capacitance, alternating switching occurs between the first measuring phase and the second measuring phase in a timing pattern.

6. A detection method, which comprises the steps of:

detecting a door opening request of a motor vehicle user in a motor vehicle via a capacitive sensor unit which measures a capacitance, by the further steps of;

during a first measuring phase, detecting a first measured quantity of the capacitance to be measured via a first measuring method, the first measuring method includes performing one of the further steps for detecting the first measured quantity;

detecting a measurement of a charging speed of a sensor electrode;

detecting an amplitude of an alternating voltage present on a voltage divider containing a sensor electrode;

or

detecting a phase angle between the alternating voltage and a strength of a flow of current caused by the alternating voltage;

starting a second measuring phase when the first measured quantity satisfies a transition criterion; and

during the second measuring phase, detecting a second measured quantity of the capacitance to be measured via a second measuring method which is different from the first measuring method, the second measuring method having a higher level of measuring accuracy compared to the first measuring method, and the first measuring method having a lower expenditure of energy compared to the second measuring method, the second measuring method includes performing one of the further steps of;

detecting a measurement of a charge quantity on the sensor electrode as the second measured quantity;

or

detecting a frequency of a voltage which is generated by an RC oscillator containing the sensor electrode.

7. A capacitive sensor unit, comprising:

a sensor electrode;

an evaluation unit;

a charging resistor; and

a reference capacitor, said sensor electrode, said evaluation unit, said charging resistor and said reference capacitor coupled or can be coupled to each other via signaling technology;

said evaluation unit configured and programmed to measure a capacitance by the steps of;

during a first measuring phase, detecting a first measured quantity of the capacitance to be measured via a first measuring method, the first measuring method includes performing one of the further steps for detecting the first measured quantity;

detecting a measurement of a charging speed of said sensor electrode as the first measured quantity;

detecting an amplitude of an alternating voltage present on a voltage divider containing a sensor electrode;

or

detecting a phase angle between the alternating voltage and a strength of a flow of current caused by the alternating voltage;

starting a second measuring phase when the first measured quantity satisfies a transition criterion; and

during the second measuring phase, detecting a second measured quantity of the capacitance to be measured via a second measuring method which is different from the first measuring method, the second measuring method having a higher level of measuring accuracy compared to the first measuring method, and the first measuring method having a lower expenditure of energy compared to the second measuring method, the second measuring method includes performing one of the further steps of;

detecting a measurement of a charge quantity on the sensor electrode as the second measured quantity;

or

detecting a frequency of a voltage which is generated by an RC oscillator containing the sensor electrode.