JPS6110707A - Optical-beat type length-measuring apparatus - Google Patents

Abstract

PURPOSE:To make the length-measuring speed quick, by splitting two polarized beams from a two-frequency laser, inputting the light beams into a movable reflecting mirror and a specified phase element, combining the beam, separating the result into two polarized light beams having two azimuths, detecting the light beams, and combining the detected signal and the detected combined signal of a part of the initial two polarized light beams. CONSTITUTION:Two polarized light beams having the phase difference of 90 deg. from a two-frequency laser oscillator 1 are split by a splitter 2. One light beam is inputted to a phase element 5 through a fixed reflecting mirror 4. The other light beam is inputted into a movable reflecting mirror 3. The beams are combined in a splitter 6. The result is split by a splitter 8 in the directions of a phase advancing axis and a phase delaying axis. The results are detected by detectors 10 and 11 and signals (x) and (y) are obtained. Part of the light from the oscillator 1 is detected by a detector 12 through a polarizer 9. The signal x' is made to be a signal y' through a 90 deg. electric- phase shifter 13. The signals (x) and (y) are supplied to a sign judging device 22. The signal (x) and (y) and the signals x' and y' are supplied to subtracting circuits 18 and 20 and adder circuits 19 and 21 through multiplier circuits 14-17. A signal, which is not related to the difference in frequencies of the two-frequency laser, is outputted through a signal switching circuit 23.

Description

【発明の詳細な説明】 本発明は光ビートを用いた干渉測長装置に関する。[Detailed description of the invention] The present invention relates to an interferometric length measuring device using optical beats.

二層波レーザを光源としｒツブラーシフトを光と一部を
用いて測定し測長を行なう、装置はすでに実用されてい
る（例えばＨＰ　−５５２６Ａ　）　、　　　　　’し
かし在米の装置においては三周波レーず光の周波数差Ｌ
！よる被測定物の移動速度の限界が存在した。すなわち
、三周波レーず光の角周波数をそれぞれωいω、としω
０の光が移動している被測定物上の反射鏡イ反射された
光のシフ１角周波数を八〇とするとこの光と周波数ω、
を有する光の間の光じ一部周波数はω、−の。±△ωと
なる。士は被測定物の移動方向によって決る符号である
。ω、〉ωＯで、この符号が正に対応した移動方向にお
いては移動速度に限界はない。しかし、その逆の移動方
向においてはω１−ωＯ−△ω〈０となる速度が存在す
る。つまり光じ一部周波数の値は負となる。Devices that use a double-wave laser as a light source to measure the r-Tubler shift using light and a portion of the length are already in use (for example, the HP-5526A); Frequency difference L of light
! There was a limit to the moving speed of the object to be measured. In other words, let the angular frequencies of the three-frequency laser beams be ω and ω, respectively.
If the shift 1 angular frequency of the reflected light from the reflecting mirror on the object to be measured is 80, then this light and the frequency ω,
The partial frequency of light between light with is ω, -. It becomes ±△ω. is a sign determined by the moving direction of the object to be measured. ω, >ωO, and there is no limit to the moving speed in the moving direction with a positive sign. However, in the opposite direction of movement, there is a speed at which ω1-ωO-Δω<0. In other words, the value of the light part frequency is negative.

在来の装置はこのような負の光に一部周波数と正の光じ
一１周波数を区別する機能を有しておらず、正の光じ一
部周波数領域でのみ処理が行なわれていたので、二周波
し−丁光の角周波数差ωＣ−ω。Conventional devices do not have the ability to distinguish between negative light frequencies and positive light frequencies, and processing is performed only in the positive light frequency range. Therefore, the angular frequency difference between the two frequencies is ωC - ω.

の値が速度に制限を与えると之になっていた。またこの
周波数差は任意に人為的に選ぶことができない量である
’、　（ＨＰ　−５５２６Ａは２πｘ２ｘｌｏ　ｒａｄ
／ｓｅｃである。） 一方、産業界に招いては測長の高速性に対する要求は高
まっており、以上の速度限界を超える必要が生じて来た
。The value of gives a limit to the speed. Also, this frequency difference is a quantity that cannot be arbitrarily chosen artificially', (HP-5526A is 2πx2xlo rad
/sec. ) On the other hand, in the industrial world, the demand for high-speed length measurement is increasing, and it has become necessary to exceed the above-mentioned speed limits.

本発明は光に一部周波数が負の周波数になることを認め
ることにより二層波レーザ光の周波数差に基づく速度限
界を取り除いたもので、本発明により光じ一部を用いた
レーザ千渉潤長が高速で行なわれることとなワた。The present invention removes the speed limit based on the frequency difference of dual-layer laser light by recognizing that a part of the frequency of light becomes a negative frequency. I hope Juncho is done at high speed.

以下図面を用いて本発明の説明を行なう。The present invention will be explained below using the drawings.

第１図は本発明の実施例である。第１図に詔いて二層波
レーザ発振器１から出たレープ光のうち一方の偏光、例
えば方位が９０°の偏光は偏光に−へ分離器２を通過し
、さらにじ−Δ分割器６を通過して移動反射鏡３で反射
されてど−ム分割器６に返される。また、レープ光のう
ち他方の偏光例えば方位０°の偏光は偏光じ−ム分１器
２イ反射された後、固定反射ｆｉ４ｆ反射され方位が４
５°リターデーシヨンが９０°の位相子５を通過し、ど
−ム分割器６に入り、先の移動鏡で反、射された光と重
ねられた後、必要な場合には旋光子７で旋光し偏光に一
Δ分１１１ａ８により前記の位相子の進相軸の方向に対
応した偏光成分と遅相軸の方向に対応した偏光成分に分
離され、それぞれの偏光成分がそれぞれ別個の検知器１
１ど１２で検知される。FIG. 1 shows an embodiment of the invention. As shown in FIG. 1, one polarized light of the rape light emitted from the double-layer wave laser oscillator 1, for example, polarized light with an azimuth of 90°, passes through the separator 2 into polarized light, and then passes through the -Δ splitter 6. The light passes through, is reflected by the movable reflecting mirror 3, and is returned to the beam divider 6. In addition, the other polarized light of the rape light, for example, polarized light with an azimuth of 0°, is reflected by the polarization beam, then fixed reflection fi4f is reflected, and the azimuth is 4
The 5° retardation passes through the 90° retarder 5, enters the dome splitter 6, is superimposed with the light reflected and reflected by the previous moving mirror, and then is transferred to the optical rotator 7 if necessary. The polarized light is rotated by 1 Δ minute 111a8 and separated into a polarized light component corresponding to the direction of the fast axis of the retarder and a polarized light component corresponding to the direction of the slow axis of the retarder, and each polarized light component is sent to a separate detector. 1
1 to 12 are detected.

今二周波し−ず光のうち、方位９０°の偏光の角周波数
をω。、方位ｏ０の偏光の角周波数をω１、移動反射鏡
の運動による角周波数シフトを△ωとし、検知器コ−１
、１２で検知される光ご一１信号をそれぞれχ考とする
と Ｘ　＝Ｃ０９＜　ＣＬ）Ｉ　　（ωＯ士△ｗ）ｉｔ　　
　　　　　−１）ンヒ＝　ｓｉｎ　　（Ｃ＋）１−　（
ω。±／〉ωンＦ、　　　　　　　　−２）となる。そ
の理由の説明を第３図によって行なう。Of the two-frequency static light, the angular frequency of polarized light with an azimuth of 90° is ω. , the angular frequency of the polarized light in the direction o0 is ω1, the angular frequency shift due to the movement of the moving reflector is Δω, and the detector code 1 is
, 12, if each optical signal detected by 12 is considered as χ, then
-1) Nhi = sin (C+)1- (
ω. ±/〉ωnF, -2). The reason for this will be explained with reference to FIG.

Ａは移動反射＃Ｉ！テ反射して返された方位が９０°の
偏光である。一方方位が００の偏光が、方位が４ダリ４
−チーショシが９０″の位相子を通過することにより、
方位が　４５　’でそれぞれの間で位相差が９０°であ
る二つの偏光に分解される。分解されたニつの偏光Ｂ、
Ｃと先の偏光Ａが方位が　４５°の偏光こ−ム分離器に
より重ねられると、偏光Ａの偏光Ｂの方向成分の干渉に
よる光じ一部と、偏光Ａの偏光Ｃの方向成分の光じ−１
が分離して検出されることになり、しかも、位相子によ
る９０°のリターデーションのため、二つの光に一部の
開に９０°の位相差が存在するので、光ｊ−１信号とし
て９０６の位相差を有する二つの信号として正弦。A is moving reflex #I! The reflected light is polarized light whose direction is 90°. On the other hand, polarized light whose direction is 00 is 4dari4
- By passing through a 90″ retarder,
It is resolved into two polarized lights with an azimuth of 45' and a phase difference of 90° between them. Two decomposed polarized lights B,
When C and the previous polarized light A are superimposed by a polarization beam separator with an azimuth of 45°, a part of the light beam due to interference of the direction component of polarized light B of polarized light A and a light beam of the direction component of polarized light C of polarized light A are separated. J-1
will be detected separately, and because there is a 90° phase difference between the two lights due to the 90° retardation caused by the phase shifter, the light j-1 signal will be 906 sine as two signals with a phase difference of.

余弦の信号が得られるわけである。以上の信号は光じ一
部信号の正負の判定に用いる。This results in a cosine signal. The above signals are used to determine whether the optical signal is positive or negative.

再び第１図の説明を続ける。三周波レーず１のレープ光
の一部を方位４５°の偏光子９を通して検知器１２で検
知するとω１−ω。なる角周波数を有する光に一部信号
が検出される。三周波レー＋！１が周波数安定化レーザ
であると、ω、−ω。二００の値は一定であるので、電
気的位相シフ５１３により９０゜位相のシフトを行なう
ことにより二つの信号工′＝Ｃ０５Ｄ、。ｔ　　　　　
　　　　　　　−３）’ｊ’＝　ｓｉｎΩ。ｔ　　　　
　　　　　−４）をつくることができる。前記の光に−
ト角周波数゛ω自−（ω。±　ΔｃＡ３　）　＝Ｑ は移動反射鏡の移動方向が帖）ｕｏ、でΔωが十のとき
、移動反射鏡の移動速度が大となるとΩくＯとなる。つ
まり移動速度が大となると光に一部嘉周波数立は正から
負に変る。しかし光ビートを観測するだけではこの正負
の判定はできない。つまりわれわれは周波数ｎの絶対値
Ｕしか知ることが出来ない。そこで本発明においては次
のような手続きを採る。１）、２）式は χ＝　ｃｏｓ　ｊρＩｔ　　　　　　　　　　　　１′
）’ｌ＝ｓ″、ｎ１Ｑｌ七　　　　　　　　　　　　　
２′）と書かれるが、χは検知器１０の出力、１は検知
器１１の出力信号であるとみなす。（現実は直流成分を
持っているが後述の、方法で直流成分は除去する。）さ
らにに′は検知器１２の出力信号、）′はＸ′の信号を
電気的に９０°位相シフトを行なったものである。ここ
イｘ４．χ′、ν′という４つの信号が得られたわけで
あるが、これらの４つの信号について４個の掛算回路１
４．１５．１６．１７と２個の加算回路１９．２１と２
個の減算回路１８．２０を図の実施例のごとく結ぶこと
により次のような演算を行なうことができる。The explanation of FIG. 1 will be continued again. When a part of the laser beam from the three-frequency laser beam 1 is detected by the detector 12 through the polarizer 9 with an azimuth of 45°, ω1-ω. Some signals are detected in light having an angular frequency of Three-frequency Ray+! 1 is a frequency stabilized laser, ω, −ω. Since the value of 200 is constant, by shifting the phase by 90° by the electrical phase shift 513, the two signal generators'=C05D. t
-3) 'j' = sinΩ. t
-4) can be created. To the light mentioned above-
The angular frequency ゛ωself-(ω.±ΔcA3)=Q is the moving direction of the moving reflecting mirror)uo, and when Δω is 0, when the moving speed of the moving reflecting mirror increases, Ω decreases to O. In other words, as the moving speed increases, the part of the light's frequency changes from positive to negative. However, it is not possible to determine whether the light is positive or negative just by observing the optical beats. In other words, we can only know the absolute value U of frequency n. Therefore, in the present invention, the following procedure is adopted. 1), 2) Equations are χ= cos jρIt 1'
)'l=s'', n1Ql7
2'), where χ is the output of the detector 10 and 1 is the output signal of the detector 11. (In reality, it has a DC component, but the DC component is removed using the method described later.) Furthermore, '' is the output signal of the detector 12, and ')' is the signal of X', which is electrically phase-shifted by 90 degrees. It is something that Kokoi x4. Four signals, χ' and ν', were obtained, and four multiplication circuits 1 were used for these four signals.
4.15.16.17 and two adder circuits 19.21 and 2
By connecting the subtracting circuits 18 and 20 as in the embodiment shown, the following calculation can be performed.

）′×Ｘ＋χ’ｘ　）　＝　５ｉｎ（ｎｏ旧（１１）（
：　　−５））′ｘχ−χ′Ｘ″ｌ＝　５ｉｎ（１１，
−１ｎｌ　）ｔ−６）χ′×χ−）’Ｘ　）　＝　ｃｏ
ｓ（ｎ、＋ｌユＩ）ｔ　　　−７）χ’ＸＸ　＋　）’
Ｘ　）　＝　ｃｏｓ（ｎ、−１０７）ｔ　　　−８）こ
のようにして得られた信号は信号切換回路２３の２組の
入力端子ｆ、ｎおよび省、ｒにそれぞれ５ｉｎ（ｊ’ｌ
ｏ　　ＩＪＬＩ）ｔ　　、　ｃｏｓ（ｎｏ−１ｆｌｌ　
）ｔ　の組詔よび５ｉｎ（ｆｌａ＋１Ｑｌ）ｔ、　ｃｏ
ｓ（几＋１ΩＩ）ｔの組として入力される。一方、前記
の信号χを横軸、信号）を縦軸にとってリュージュを求
めると（第４図）立が正から負に変るとりサージュの回
転方向は逆転する。との逆転を後述する符号判定回路２
２で検知して、角周波数ｑの正負の判定を行ないΩが正
のときには信号切換回路のＪＬ、ｖａの信号すなわち　
　５ｉｎ（ｆｌ、　　　ｌΩｌ）ｔ　、ｃｏｓ（Ω。−
１Ω１）七　を　１．Ω。)'×X+χ'x) = 5in(no old(11)(
: -5))′xχ−χ′X″l= 5in(11,
-1nl)t-6)χ'×χ-)'X) = co
s(n, +lyuI)t -7)χ'XX + )'
X ) = cos (n, -107) t -8) The signal thus obtained is sent to two sets of input terminals f, n and r of the signal switching circuit 23 at 5 inches (j'l), respectively.
o IJLI)t, cos(no-1fll
)t and 5in(fla+1Ql)t, co
It is input as a set of s(几+1ΩI)t. On the other hand, if the luge is calculated with the signal χ on the horizontal axis and the signal (signal) on the vertical axis (see FIG. 4), as the vertical changes from positive to negative, the direction of rotation of the luge is reversed. The sign determination circuit 2 will be described later.
2, and determines whether the angular frequency q is positive or negative. If Ω is positive, the JL and va signals of the signal switching circuit, that is,
5in(fl, lΩl)t, cos(Ω.-
1Ω1) Seven 1. Ω.

する。このようにして得られた例えば ｃｏｓ（Ｌ　　Ｉｆｌｌ）ｔ　　、　ｃｏｓ（Ω。刊Ｑ
ｔ　）ｔは実質的には絶対値１１の除かれた　Ｃ０５（
０，４）ｔ　　（但シΩは正から負に変化）と同じであ
り　ｃｏｓｃＱｅ　　Ｑ）４−の周波数あるいは位相を
測定することにより二周波し−ずの周波数差Ω。の大小
には無関係に高速での測長が可能となる。本実施例にお
いては信号切換回路の出力　ｃｏｓ（Ｑ、　−Ｑ　）ｔ
　、　５ｉｎ（Ａ。一旦）Ｌを用い符号判定回路２２と
同様な他の符号判定回路２４を用い、移動反射鏡の移動
方向の判定を行なっており、例えば　ｃｏｓ（Ω。−Ω
）ｔをカウシ５２５の計数端子に入力すると共に加減端
子に符号判定回路２４の出力を入力せしめている。do. For example, cos(L Ifll)t, cos(Ω.Published Q
t ) t is essentially C05(
0, 4) t (however, Ω changes from positive to negative) coscQe Q) By measuring the frequency or phase of 4-, the frequency difference Ω between two frequencies. High-speed length measurement is possible regardless of the size of the object. In this embodiment, the output of the signal switching circuit cos(Q, -Q)t
, 5in (A. Once) L is used to determine the moving direction of the movable reflecting mirror using another sign determining circuit 24 similar to the sign determining circuit 22. For example, cos(Ω.-Ω
)t is input to the counting terminal of the counter 525, and the output of the sign determination circuit 24 is input to the addition/subtraction terminal.

また検知ａ２６は検知６１０に入射する光と位相がｘａ
ｏ　０興なる光を検知しており、その出方を加算増幅器
２７によって検知器１０の出力に加算す号ならびに検知
器１１の出力信号と基準電位の差を求めることにより、
直流成分を除き正、負に変化するχ、′ｌ−信号１をつ
くり、前記のリサージュが原点を中心に回転するように
なされている。In addition, the detection a26 has a phase of xa with respect to the light incident on the detection 610.
0 is detected, and its output is added to the output of the detector 10 by the summing amplifier 27, and by calculating the difference between the output signal of the detector 11 and the reference potential,
Excluding the direct current component, a χ,'l-signal 1 which changes from positive to negative is created, and the Lissajous described above rotates around the origin.

なお、本実施例においては５）、６）、？）、８）式で
示される信号すべてを用いてｌ／′Ｉるが、必ずしもそ
の必要はなく、符号判定回路２４を省略し計数器に入力
する信号として、５）、６）式あるい、は？）、８）式
で示される信号だけを用いて測長装置を構成してもよい
。In addition, in this example, 5), 6), ? ), 8) All the signals shown in equations 5), 6) or teeth? ), 8) The length measuring device may be configured using only the signals shown in equations.

第２図は符号判定回路の一例である。前記の光じ＝ト信
号χ、）゛および信号Ｊが反転増幅器３１で反転された
信号がコシパレータ３２．３３、および３４に入力され
、コンパレータ３３とコンパレータ３２の出力がプンｒ
ゲート３６に、コシパレータ３２の出力がインバータ３
５で反転された出力とコンパレータ３４の出力がプシ「
ゲート３７に入力される。つまり、す９−シュが１′軸
を横切るごとにリサージュの回転方向がチェックされ、
回転方向が変化しなければプシｒゲー１３６．３７のど
ちらかからのみパルスが出ているが、回転方向が変化す
ればパルスを出すゲートが変化する。FIG. 2 is an example of a sign determination circuit. The optical signal χ,)'' and the signal J inverted by the inverting amplifier 31 are input to the cosciparators 32, 33, and 34, and the outputs of the comparators 33 and 32 are
The output of the cossiparator 32 is connected to the gate 36 of the inverter 3.
The output inverted by 5 and the output of comparator 34 are
The signal is input to gate 37. In other words, the rotation direction of Lissajous is checked every time the 9-sh crosses the 1' axis.
If the direction of rotation does not change, pulses are output from only one of the gates 136 and 37, but if the direction of rotation changes, the gate that outputs the pulse changes.

フリップフロツブ３日はパルスを出すゲートが変化した
ことを知ると同時に雑音によってリリ〜ジュが不必要に
χ軸を横切ったときそれに応答しないためにもうけたも
のである。The 3-day flip-flop was created to prevent Lilige from responding to the noise when it unnecessarily crosses the χ axis at the same time as it knows that the gate that outputs the pulse has changed.

【図面の簡単な説明】[Brief explanation of the drawing]

第１図は本発明の実施例、第２図は符号判定回路０゛例
、第３図は説明図、第４図は他の説明図である。 １・・・・・・・・・・二層波レーず ２．８・・・・・・偏光じ一ム分睡器 ３・・・・・・・・・・移動反射鏡 ４・・・・・・・・・・固定反射鏡 ５・・・・・・・・・・位相子 ６・・・・・・・・・・じ−ム分割器 ７・・・・・・・・・・旋光子 ９・・・・・・・・・・偏光子 １０．１１．１２．２６・・・・・検知器１３・・・・
・・・・電気的位相シフタ１４．１５．１６．１７・・
・・・掛算回路１８．２０・・・・・減算回路 １９．２１・・・・・加算回路 ２２．２４・・・・・符号判定回路 ２３・・・・・・・・信号切換回路 ２５・・・・・・・・カラシタFIG. 1 is an embodiment of the present invention, FIG. 2 is an example of a code determination circuit 0, FIG. 3 is an explanatory diagram, and FIG. 4 is another explanatory diagram. 1......Double-layer wave laser 2.8...Polarized light beam splitter 3...Moveable reflector 4... ...... Fixed reflector 5 ...... Phaser 6 ...... Dimension divider 7 ...... Optical rotator 9...Polarizer 10.11.12.26...Detector 13...
...Electrical phase shifter 14.15.16.17...
... Multiplication circuit 18.20 ... Subtraction circuit 19.21 ... Addition circuit 22.24 ... Sign determination circuit 23 ... Signal switching circuit 25 ...・・・・・・Karashita

Claims (1)

【特許請求の範囲】[Claims] 周波数の異なる直交した第１と第２の偏光を放出する二
周波レーザを光源とし、該第１の偏光と第２の偏光を偏
光分離器によって分離し、該第１の偏光を移動反射鏡に
入射せしめると共に該第２の偏光を、該第２の偏光の方
位に対しほぼ４５°の方位を有しかつほぼ９０°のリタ
ーデーションを有する位相子を通過せしめた後、前記第
１の偏光の前記移動反射鏡による反射光と重ね合わせ、
該重ねられた光を、前記位相子の進相軸ならびに遅相軸
の方向に対応した方位を有する２つの偏光に分離して、
該２つの偏光をそれぞれ別個に第１および第２の検知器
で検知して第１および第２の光ビート信号を得ると共に
、前記第１の偏光と第２の偏光を重ね合わせて第３の検
知器で検知して第３の光ビート信号を求めさらに該第３
の光ビート信号に対しほぼ９０°の位相差を持つ第４の
光ビート信号をつくり、第３の光ビート信号と第２の光
ビート信号の積と第４の光ビート信号と第１の光ビート
信号の積の和および差よりなる１組の和信号と差信号、
あるいは第４の光ビート信号と第２の光ビート信号の積
と第３の光ビート信号と第１の光ビート信号の積の和お
よび差よりなる他の１組の和信号と差信号、あるいは前
記の組すべてから成る２組の和信号と差信号をつくると
共に、前記第１の光ビート信号の値と前記第２の光ビー
ト信号の値の間の相対的な変化ならびに変化方向をしら
べ、該変化ならびに変化方向によって前記第１および第
２の光ビート周波数の正負信号を発生せしめ該正負信号
に応じて前記の１組あるいは２組の和信号と差信号のう
ち、和信号、差信号いづれを採るかの決定ならびに切換
を行ない、該切換えられた和信号あるいは差信号を計数
することを特徴とする光ビート測長装置。A dual-frequency laser that emits orthogonal first and second polarized light having different frequencies is used as a light source, the first polarized light and the second polarized light are separated by a polarization separator, and the first polarized light is transmitted to a moving reflecting mirror. After making the second polarized light incident and passing through a retarder having an orientation of approximately 45° with respect to the orientation of the second polarized light and having a retardation of approximately 90°, the polarized light of the first polarized light is Superimposing the light reflected by the moving reflector,
Separating the superimposed light into two polarized lights having orientations corresponding to the directions of the fast axis and slow axis of the retarder,
The two polarized lights are detected separately by first and second detectors to obtain first and second optical beat signals, and the first and second polarized lights are superimposed to obtain a third optical beat signal. A third optical beat signal is detected by a detector, and the third optical beat signal is detected by a detector.
A fourth optical beat signal having a phase difference of approximately 90° with respect to the optical beat signal is created, and the product of the third optical beat signal and the second optical beat signal, the fourth optical beat signal and the first optical a set of sum and difference signals consisting of the sum and difference of products of beat signals;
Alternatively, another set of sum and difference signals consisting of the sum and difference of the product of the fourth optical beat signal and the second optical beat signal and the product of the third optical beat signal and the first optical beat signal, or creating two sets of sum and difference signals consisting of all the sets, and examining the relative change and direction of change between the value of the first optical beat signal and the value of the second optical beat signal, Depending on the change and the direction of change, positive and negative signals of the first and second optical beat frequencies are generated, and depending on the positive and negative signals, one of the sum signal and the difference signal of the one or two sets of sum signal and difference signal is generated. What is claimed is: 1. An optical beat length measuring device, which determines and switches whether to take a signal, and counts the switched sum signal or difference signal.