Source: http://www.google.com/patents/US5497083?dq=4393663
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Patent US5497083 - Rod axial position detector including a first scale having equidistant ... - Google PatentsSearch Images Maps Play YouTube News Gmail Drive More »Sign in<nobr>Advanced Patent Search</nobr>PatentsA first magnetic scale consisting of a plurality of non-magnetic parts are arranged axially at equidistant intervals, and a second magnetic scale consisting of a plurality of non-magnetic parts arranged axially at unequal intervals, are formed parallel to each other on a rod consisting of a magnetic...http://www.google.com/patents/US5497083?utm_source=gb-gplus-sharePatent US5497083 - Rod axial position detector including a first scale having equidistant magnetic parts and a second scale having unequally distant parts and differing field strengthsAdvanced Patent SearchPublication numberUS5497083 APublication typeGrantApplication numberUS 08/168,096Publication dateMar 5, 1996Filing dateDec 15, 1993Priority dateDec 24, 1992Fee statusLapsedAlso published asDE4344290A1, DE4344290C2Publication number08168096, 168096, US 5497083 A, US 5497083A, US-A-5497083, US5497083 A, US5497083AInventorsMasakazu Nakazato, Youichi Shimoura, Masamichi SugiharaOriginal AssigneeKayaba Kogyo Kabushiki KaishaExport CitationBiBTeX, EndNote, RefManPatent Citations (8), Referenced by (13), Classifications (14), Legal Events (5) External Links: USPTO, USPTO Assignment, EspacenetRod axial position detector including a first scale having equidistant magnetic parts and a second scale having unequally distant parts and differing field strengthsUS 5497083 AAbstract A first magnetic scale consisting of a plurality of non-magnetic parts are arranged axially at equidistant intervals, and a second magnetic scale consisting of a plurality of non-magnetic parts arranged axially at unequal intervals, are formed parallel to each other on a rod consisting of a magnetic material which can be displaced in the axial direction. The non-magnetic parts of the second scale are symmetrically disposed on both side of a predetermined position on the rod. First and second magnetic sensors are disposed in fixed positions facing the scales. A memory which individually memorizes the absolute position of each non-magnetic part on the second magnetic scale in advance, a mechanism which detects the interval between non-magnetic parts passing the second sensor, and a mechanism for distinguishing on which side the second sensor is situated with reference to the aforesaid predetermined position are provided, together with a mechanism for identifying a non-magnetic part which has passed based on the distinguishing result of the distinguishing mechanism and the detected interval, a mechanism for calculating the displacement amount of the rod from the identified magnetic part to its current position based on the output signal from the first sensor, and a mechanism for calculating the current position of the rod from the absolute position of the identified magnetic part and the calculated displacement. In this way, the displacement distance of the rod required to obtain absolute position information is reduced.
The subscale 6 is formed in parallel with the main scale 2 on the circumference of the piston rod 1. The subscale 6 consists of non-magnetic parts 7 having a predetermined width disposed symmetrically to the left and right of the middle of the piston rod 1. Reference points h1 -h12 are set in the center of each of the non-magnetic parts 7.
The pitch interval between the non-magnetic parts 7 at h6, h7 on either side of the center is L0, the other non-magnetic parts 7 being arranged at progressively increasing pitch intervals SL1 -L5 towards the outside. The width of the non-magnetic parts 7 is L0 /2. The depth of the non-magnetic parts 7 having the reference points h1 -h6 to the left of the middle of the rod 1 is D1, and the depth of those having the reference points h7 -h12 to the right of the middle of the rod 1, is D2. The value of D2 is larger than that of D1.
scale[A]=1/|peak value-cen[A]|
This normalization coefficient scale [A] is intended to correct the difference of amplitude for each pitch interval of the main scale to the same level, and is used for computing the fine displacement hereinafter described. If for example the normalized value of |peak value-cen [A]| is 1, and a measured value was twice this magnitude, the normalization coefficient is 1/2. When the measured value is multiplied by this coefficient, the amplitude is corrected to 1, and is thereby adjusted to be the same level as the normalized amplitude.
The normalized signals correct [A], correct [B] should have the relation correct2 [A]+correct2 [B]=1. If this value does not fall within a certain range around 1, it is determined that there is a fault, i.e. a wire break or short circuit in the magnetic sensor 4 (S74). This range may be decided by considering noise tolerance levels, and the permitted range for the phase difference between the output signals.
The displacement of the piston rod is computed from the normalized signals correct [A], correct [B] using the graph in FIG. 9. Describing this in simple terms, if for example the pitch interval of the non-magnetic parts 3 of the main scale 2 is 2 mm, counting is performed in 1mm units. If this unit is divided into 100 parts, a fine displ for the current point C1 in FIG. 9 is obtained from the relation θ:π=fine displ:100. This relation is rewritten as:
tan &#952;=|correct[B]|/|correct[A]|
&#952;=tan-1 |correct[B]|/|correct[A]|
As a result, the fine dspl is expressed as follows:
fine displ=(100/π)*tan-1 (|correct[B]|/|correct[A]|)
From this equation, using the normalized signals correct [A], correct [B], the displacement from the center of the non-magnetic part 3 at the point C1 is calculated. The displacement of the piston rod 1 may thus be found by adding the fine displacement calculated by the above inverse trigonometric function, to the coarse displacement found from the count number (S86) using the following relation:
The actual fine displacement is different according to which of the eight zones divided by the vertical axis, horizontal axis and 45 degrees lines shown in FIG. 9, it comprises the current point. At the points C2, C3, C4, it may be calculated by the relations:
Fine displacement at C2 =-fine displacement
Fine displacement at C3 =50-fine displacement
Fine displacement at C4 =50+fine displacement
A distinction is therefore made according to the zone of FIG. 9 in which the Z current point lies, and depending on the result, the equations giving the fine displacement at the points C1 -C4 are used selectively (S78-80, S83-85).
In the region where |correct[B]|≦|correct[A]|, the counter value count [A] is entered in a parameter coarse displ, which indicates the coarse displacement; in the region where |correct[B]|>|correct[A]|, the counter value count [B] is entered in the parameter coarse displ (S75, 76 and S75, 81).
The above level basZ may be found, using the center level cen [ZB] and the amplitude level lev 1 when the depth of the non-magnetic parts is D1, from the equation:
When an interruption signal is output at the center crossover point for the output signal sig [ZA], the CPU 14 checks the output of the comparator 30, and if an "L" level is output, the software determines that this point is the reference point. It also determines whether the amplitude level at the center crossover point for the output signal sig [ZA] corresponds to the depth D1 or D2 of the non-magnetic parts 7. The set value corresponding to the depth D1 is lev 1, the set value corresponding to the depth D2 is lev 2, and lev 1<lev 2. For example, if the amplitude level of the output signal sig [ZB] exceeds (lev 1+lev 2)/2, it is determined to be lev 2, and if it is less than this value, it is determined to be lev 1.
From this amplitude determining level basL and the magnitude of the output signal sig [ZB], the amplitude may be determined as lev 2 when basL>sig [ZB], and lev 1 in other cases. Moreover, this determining may be performed using hardware as shown in FIG. 16. In this case, a digital/analog converter 41 for analog detection of basL, and a comparator 42 for comparing the converter output with the output signal level sig [ZB], are provided. Whether software or hardware is used, however, the determining of amplitude level must be performed at the center crossover point of the output signal sig [ZA], i.e. when the reference point is detected.
First, a first reference point is detected by giving the piston rod 1 a movement in either direction, and the displacement at that time is computed based on the output signals sig [A], sig [B] from the main scale 2. The updated value of the displacement data (displ calculated in the step 86 of FIG. 8) is then entered in a parameter X1, and the amplitude level of the output signal sig [ZB] is entered in a parameter AZ1, (S92, 93).
When a second reference point is detected, the updated value of the displacement data (displ calculated in the step 86 of FIG. 8) is entered in a parameter X2, and the amplitude level of the output signal sig [ZB] is entered in the parameter AZ2 (S94, 95). The interval between the reference points is then calculated from the two parameters X1, X2 (=X2 -X1)(S96).
Next, it is determined whether the value of the parameter AZ2 corresponds to either the amplitude level lev 1 or lev 2, and whether the sign of the reference point interval L is positive or negative (S99, 100, 101).
(i) AZ2 =lev 2 and L>0
(ii) AZ2 =lev 1 and L>0
(iii) AZ2 =lev 1 and L<0
(iv) AZ2 =lev 2 and L<0
The case |L|<L0 corresponds to crossing the same reference point twice in succession. In this case, it is determined that the reference point interval cannot be accurately calculated, the value of X2 is entered in X1, the value of AZ2 is shifted to AZ1, and the program returns to the step S94 so that zone determining is not performed.
If it is known which zone comprises the current point, the following calculations may be performed from the absolute value |L| of the reference point interval for each of the zones (S100, 102, 103 or S101, 104, 105):
In zone (i), AD=|L|* m+base 1
In zone (ii), AD=|L|* m+base 3
In zone (iii), AD=|L|* m+base 4
In zone (iv), AD=|L|* m+base 2
AD indicates a storage address in the RAM 31 containing absolute value positions of the second reference point (i.e. the one detected later). As shown by the memory map of FIG. 13, for example, the second reference point in zone (i) (AZ2 =lev 2 and L<0 ) is h7, h8, h9, h10, h11 or h12, i.e. there are six cases. Absolute position data corresponding to these cases are stored in advance in the same number of storage locations in the RAM 31.
Further, if for example the second reference point is h8, the absolute position data for h8 are found in the storage location for the address AD which is calculated from L1, i.e. AD=L1 * m+base 1. In other words, the values of the constant m and base 1-4, are matched in advance to the addresses AD which store the absolute positions of the reference points.
When the first reference point h1 is detected in this process, the displacement of the piston rod 1 detected from the main scale 2 at that time is stored in the parameter X1, and the amplitude level of sig [ZB] is stored in the parameter AZ1 (S113).
While the piston rod 1 is elongating from its most compressed state to its middle position, L>0 and the amplitude level of sig [ZB]=lev 1. After detecting the reference point h2, therefore, the address AD is computed in a step S124 every time a new reference point is detected. The contents of the parameter X2 are then shifted to the storage location indicated by this address (S126), X2 is shifted to X1, and the value of AZ2 is shifted to AZ1 (S127). Also, processing after detection of the second reference point is repeated (S114-127).
Therefore, when the piston rod 1 reaches the middle position, absolute value data for each of the reference points h2 to h6 are stored in 5 addresses based on base 3 in FIG. 13.
Likewise, from when the piston rod 1 is in the middle to when it reaches its most elongated position, L>0 and the amplitude level of sig [ZB]=lev 2, so the address AD is calculated in a step S122. When the piston rod 1 returns from its most elongated position to the middle position, L<0 and the amplitude level of sig [ZB]=lev 2, so the address AD is calculated in a step 123. When the piston rod returns from its middle position to its most compressed position, L<0 and the amplitude level of sig [ZB]=lev 1, so the address AD is calculated in a step S125. The contents of the parameter X2 at each of these times are respectively stored in storage locations indicated by the address AD.
Therefore, when the piston rod 1 executes one complete cycle between its most compressed position and its most elongated position, absolute position data for h1 -h12 are stored in all the addresses shown in FIG. 13.
In FIG. 1, there is only one minimum reference point interval L0, but it is possible to provide two as shown in FIG. 2. Further, if there are three or more different depths of the non-magnetic parts 7, the same number of reference point intervals as the number of depths may be provided.
As the calculation of the reference point interval L uses high precision displacement data (calculated in 0.01 mm units), based on the output signal from the magnetic sensor 5, the difference between reference point intervals (e.g. L2 -L1) can be made small. It is sufficient that the difference between reference point intervals be larger than the minimum unit displacement (i.e. the unit of fine displacement) detected from the main scale 2.
To prevent the piston rod 1 from reaching its most elongated position or its most compressed position, provision may be made for an alarm to be emitted when the reference points h1 and h12 which are closest to these positions are detected. For example, from the sign of two adjacent reference points and the amplitude level of sig [ZB], it can be detected whether the piston rod 1 is moving past h1 toward the most compressed position, or whether it is moving past h12 toward the most elongated position, this information then being sent to external devices.
In FIG. 1, six different reference intervals (L0 -L5) were symmetrically arranged to the left and right of the middle of the piston rod 1 as center, and the reference point interval was made to progressively increase from the center toward the outside. The reference intervals may however be unsymmetrically arranged (so that they become progressively smaller towards the left of the figure from the center of the full stroke), or alternatively they may be arranged without any order, i.e. L0, L5, L2, L1 . . .
Further, the non-magnetic parts 7 of the subscale 6 were all given the same width L0 /2, however this width may be greater or lesser than L0 /2 provided the minimum reference interval L0 call be identified, or each of the parts 7 may have a different width. L0 can be set independently from the pitch interval P of the main scale 2.
According to this embodiment, the non-magnetic parts 3 of the main scale 2 are formed with a depth M1 from the furthest end to the middle, and with a greater depth M2 over the remaining half of the piston rod 1. Between the non-magnetic parts 3, there are magnetic parts 4 consisting of the magnetic material of which the rod 1 is made, the non-magnetic parts 3 and magnetic parts 4 being alternately disposed at a pitch interval of 1/2 P.
The non-magnetic parts 7 of the subscale 6 are symmetrically disposed to the left and right of the middle of the piston rod 1 as in the first embodiment, reference points h1 -h12 being set in the center of each of these non-magnetic parts 7. The non-magnetic parts 7 all have the same depth D and width L0 /2.
If one of these output signals is considered to be a sine curve, the other signal may be considered to be a cosine curve. The corrected signals y1 and y2 in one pitch interval (0-2π) of the magnetic scale 2 are:
y1 =V1 *sin &#952;
y2 =V2 *cos &#952;
V1 =peak voltage value
V2 =peak voltage value
If the gain is adjusted so that V1 =V2 :
tan &#952;=sin &#952;/cos &#952;=y1 /y2 The angle θ between the corrected signals y1, y2 is therefore:
&#952;�tan-1 (y1 /y2)
The coarse displacement of the piston rod 1, i.e. the displacement of the piston rod 1 in 1/2 pitch interval units, is found by counting the peak values or center values of the corrected signals y1, y2. The displacement of the piston rod 1 may therefore be found with good precision by adding this fine displacement to the coarse displacement.
As shown in FIG. 19, the amplitudes of the signals sig [A], sig [B] are lev 1 when the depth of the non-magnetic parts 3 is M1, and lev 2 when this depth is M2. From the magnitude of this amplitude, it can be determined on which side the detected reference point lies with respect to the middle of the piston rod 1. In a step S203, the average of preset standard values of lev 1 and lev 2 are compared with the amplitude amp. If the amplitude amp is the larger, the amplitude level is set to 2 in a step S204, and if it is the smaller, the amplitude level is set to 1 in a step S205. In FIG. 19, the amplitude level 1 is on the left of the middle position, while the amplitude level 2 is on the right.
When the piston rod 1 is moved (S210), it is determined whether or not the output signal sig [ZA] of the magnetic sensor 9 is the center value cen [ZA], and whether the output signal sig [ZB] does not exceed basZ (S211). The first reference point is detected according to this determining. When the first reference point is detected, in a step S212, the displacement of the piston rod 1 at that time, i.e. a relative position computed according to the hereintofore described method based on the output signals sig [A], sig [B] of the magnetic sensor 5, is stored in the memory as a parameter X1. The amplitude level of the output signal sig [B] is also stored in the memory as a parameter A1.
When the second reference point is detected, a relative position is stored in the memory as a parameter X2, and an amplitude level of the output signal sig [B] is stored in the memory as a parameter A2 in a step S214 in the same way as in the step S212.
In a step S215, the interval between the first and second reference points is calculated from these parameters X2, X1.
In a step S216, the absolute value of the interval L and the minimum interval L0 of the subscale 6 are compared. If the interval L is greater than L0, the program proceeds to a step S218, while if the interval L is less than L0, the values of the parameters A1, X1 are updated in a step S217, and the second reference point is detected again.
If the detection result of the step S216 is affirmative, it is determined in the step S218, whether or not the amplitude level A2 of the second reference point is lev 1. It can therefore be determined whether the second reference point lies in the range h1 -h6, or the range h7 -h12.
If the result of this determining is affirmative, i.e. the second reference point lies the range h1 -h6, the program proceeds to a step S220, while if it is negative, i.e. the second reference point lies in the range h7 -h12, the program proceeds to a step S219.
All the absolute positions of the reference points h1 -h12 are therefore stored in advance in memories. The addresses of these memories in which these absolute positions h1 -h12 are stored, are obtained by adding processing by the preset constants base 1-base 4 and m obtained in the steps S221-224, to the absolute value of the interval L obtained in the step S215. The addresses of the memories in which the absolute positions h1 -h12 are stored, are therefore preset as shown in FIG. 23. The absolute value of the interval L found in the step S215 is equal to one of the values L0 -L5, so if the above four cases can be distinguished, the addresses of the memories can be identified from the absolute value of the interval L and the amplitude level of sig [B]. The base 1-base 4 and m are constants for converting absolute values of the interval L to addresses.
Even if the absolute value of the interval L is the same, the values of base 1-base 4 are set according to whether sign of the interval L is positive or negative and to the amplitude level of sig [B], so that the indicated addresses are different. As shown in FIG. 23, the absolute position of each reference point is stored in different addresses. The values stored for the same reference point are not necessarily identical, because the detection position of the reference point, i.e. the position at which the signal sig [ZA] is equal to the center value cen [ZA], may slightly differ depending on the displacement direction of the piston rod 1. In order to store the precise position of reference points h1 -h12, therefore, different addresses are prodded for the same reference point according to the displacement direction of the piston rod 1
Insofar as concerns the subscale 6, the reference points h1 -h5 and h7 -h11 may also be disposed at intervals L0 -L4 respectively to the left and right of a reference point in the middle of the piston rod 1 as shown in FIG. 24. Further, instead of having the interval between reference points on the subscale 6 progressively increase from the middle towards the outside, they may for example be arranged in a random fashion such as L0, L5, L3, L1.