# US 2013/0154610 A1 · Powder sensor

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- Number: US 2013/0154610 A1
- Document ID: US20130154610A1
- Status: Published application
- Kind: A1
- Application number: 13/710,554
- Filed: 2012-12-11
- Published: 2013-06-20
- Earliest claimed: 2011-12-19
- Assignees: TDK Corporation
- Inventors: Nobuo Furukawa
- Web page: https://patentgrep.com/patent/US20130154610A1

## CPC

- G03G 15/0849: {Detection or control means for the developer concentration}
- G03G 15/086: {the level being measured by electro-magnetic means}
- G03G: ELECTROGRAPHY; ELECTROPHOTOGRAPHY; MAGNETOGRAPHY

## Abstract

A powder sensor includes a piezoelectric element, an oscillator circuit, a first square wave signal generator, a second square wave signal generator, and a phase judgment circuit. The oscillator circuit applies to the piezoelectric element an output signal having a frequency equal to or near a resonance frequency of the piezoelectric element. The first square wave signal generator generates a first square wave signal by converting a terminal voltage of the piezoelectric element. The second square wave signal generator generates a second square wave signal that transits from an initial level to a detection level when the first square wave signal rises or falls in a detection period and that does not transit outside of the detection period. The detection period is a part of each cycle of the output signal of the oscillator circuit. The phase judgment circuit determines phase of the second square wave signal.

## Claims

### Claim 1

A powder sensor comprising:
a piezoelectric element;
an oscillator circuit that applies to the piezoelectric element an output signal having a frequency equal to or near a resonance frequency of the piezoelectric element;
a first square wave signal generator that generates a first square wave signal by converting a terminal voltage of the piezoelectric element into the first square wave signal;
a second square wave signal generator that generates a second square wave signal that transits from an initial level to a detection level when the first square wave signal rises or falls in a detection period and that does not transit from the initial level to the detection level when the first square wave signal rises or falls in a period outside of the detection period, wherein the detection period is a part of each cycle of the output signal of the oscillator circuit; and
a phase judgment circuit that determines phase of the second square wave signal.

### Claim 2 (depends on 1)

The powder sensor according to claim 1 comprising a clear signal generator that generates a clear signal and inputs the clear signal to the second square wave signal generator to set the second square wave signal to the initial level before beginning of the detection period of a subsequent cycle.

### Claim 3 (depends on 1)

The powder sensor according to claim 1, wherein the second square wave signal generator comprises an edge trigger flip-flop having a clock input receiving the first square wave signal.

### Claim 4 (depends on 3)

The powder sensor according to claim 3, wherein the flip-flop has a D-input receiving a detection period limiting signal that has a first level in the detection period and a second level outside the detection period.

### Claim 5 (depends on 4)

The powder sensor according to claim 4, wherein the output signal of the oscillator circuit applied to the piezoelectric element is the detection period limiting signal.

### Claim 6 (depends on 1)

The powder sensor according to claim 1 comprising a powder presence/absence judgment circuit that determines whether powder is present or absent based on the phase determined by the phase judgment circuit, wherein the powder presence/absence judgment circuit makes a determination that powder is absent if the phase judgment circuit detects, n consecutive times (where “n” is an integer and n≧2), that the phase of the second square wave signal satisfies a predetermined phase condition.

### Claim 7 (depends on 6)

The powder sensor according to claim 6, wherein
the phase judgment circuit comprises an n-stage shift register, and
the powder presence/absence judgment circuit comprises a logic gate that receives, as an input, output signals from the n-stage shift register.

### Claim 8 (depends on 1)

The powder sensor according to claim 1, wherein the oscillator circuit is a sweep oscillator circuit that sweeps the frequency of the output signal through a frequency range inclusive of a resonance frequency of the piezoelectric element.