GB1559484A - Apparatus for indicating angular measurement - Google Patents

Description

(54) IMPROVEMENTS RELATING TO APPARATUS FOR INDICATING ANGULAR MEASUREMENT (71) We, BRITISH AIRCRAFT CORP- ORATION LIMITED, a British Company, of l00 Pall Mall, London, S. W. l., do hereby declare the invention, for which we pray that a patent may be granted to us, and the method by which it is to be performed, to be particularly described in and by the following statement :- The invention relates to apparatus for indicating angular measurements in mil units, one mil unit being l/6400th part of a circle.

According to the invention apparatus for indicating the magnitude of an angular measurement in mil units, one mil unit being 1/6400th part of a circle, includes means for generating electrical binary logic signals comprising at least six binary digits representing the angular measurement, first logic means responsive to the six most significant binary digits for indicating the number of 26th parts of a circle, i. e. hundreds of mils, in the measured angle and second logic means responsive to the remaining binary digits for indicating the remaining part of the measurement.

An embodiment of the invention will now be described by way of example with reference to the accompanying drawings, in which: Figure I shows a block diagram of apparatus for indicating angular measurement in mil units having a visual display, Figure 2 shows a more detailed block diagram in which the measurement is initially converted to a 11-bit binary number, Figure 3 lists the weightings of the 11- bit binary number, Figure 4 shows a block diagram similar to Figure 2 using an N-bit binary number, Figure 5 shows a block diagram of indicating apparatus having an alternative form of visual display.

The apparatus of Figure 1 comprises a converter 1 which receives analogue electrical signals from an angle measuring device, in this embodiment an angle resolver (not shown), commonly referred to as a synchro, although as an alternative a shaft encoder producing a digital output could be used with an appropriate converter, if needed. The synchro generates three analogue output signals on lines S, Sa and S3 indicating the measured angle.

These signals are received by the converter 1, together with a synchro reference signal on lines R, and R.., and converted into a binary number representing the measured angle. The binary number is presented in parallel form at the output of converter 1 on parallel output lines indicated generally at 2.

The parallel output lines 2 are connected to corresponding parallel inputs to a binary to 6400 binary coded decimal converter 3 which converts the binary number to the corresponding binary coded decimal (hereinafter referred to as B. C. D.) number such that a full binary count is equal to 6400 decimal. For a full count of 6400, fifteen B. C. D. digits are required, that is four digits for each of the hundreds, tens, units, and three for the thousands since the maximum number of these is six. The output of the converter 3 therefore comprises fifteen parallel output lines, indicated generally at 4, which are connected in turn to the appropriate inputs of a four digit visual display indicated generally at 5.

Thus, in operation the three synchro output signals are converted by converter 1 to a binary number which is in turn scaled by converter 3 to mil units and then presented by the visual display 5.

Figure 2 shows a practical indicator, in which parts have like references. The synchro to binary converter 1 produces an 11-bit binary number output, thus effectively dividing a circle into 2'1, or 2048, equal parts. The binary to 6400 B. C. D. converter 3 therefore has to scale each binary digit according to various bit weightings in mils shown in Figure 3. Bit 6, it will be seen, has a weighting of exactly 100 mils so that bits 1 to 6 inclusive comprise a binary number count in 100 mil units, whereas, bits 7 to 11 inclusive are cyclic repeating every 100 mils. The task of converting the 11-bit binary number into a 15 bit B. C. D. number can therefore be broken down into two separate and simpler tasks. The first task to produce B. C. D. numbers of the hundreds and thousands of mil unts is accomplished by addressing an appropriately programmed programmable read only memory (P. R. O. M.) 6 with bits 1 to 6. The P. R. O. M. 6 is programmed to produce the appropriate seven digit B. C. D. number corresponding to each possible six digit binary address code, and thus requires a total of 2x7, or 64 x 7, memory locations.

However, when converting from binary to B. C. D. the least significant digit of corresponding numbers is always the same.

Therefore bit 6 of the binary number does not require converting and may form part of the B. C. D. directly bypassing P. R. O. M.

6. The number of memory locations is thus halved to 25 x 7 which conveniently permits use of a currently manufactured standard size 32 x 8 P. R. O. M.

The second task to produce B. C. D. numbers of the tens and units of mils is accomplished by addressing a second P. R. O. NI. 7, appropriately programmed with bits 7 to 11. Again, the standard sized 32 x 8 P. R. O. M. can be used but must be programmed to take into account the mil units scaling factor. Figure 3 shows that a 2048th part of a circle is 3.125 mils, represented by the least significant bit of the binary number, i. e. bit 11. The binary number thus has a scaling such that an increase in the binary count of 1 digit represents an increase of 3.125 mils. In the example being described the P. R. O. M.

7 is programmed such that the angle in mils is rounded to the nearest 5 mils, for example the memory locations addressed by the binary numbers corresponding to 53.125 mils and 56.25 mils are both programmed to generate the B. C. D. number 55.

Figure 4 shows a generalised block diagram of apparatus having the same operating principles as that of Figures 1 and 2 with bit 6 of the synchro to binary converter 1 output bypassing P. R. O. M. 6. The remaining bits 7 to N, where N is any number determined by the required resolution of the apparatus, are shown addressing P. R. O. M. 7 which has 8 outputs and 2 ('-') inputs.

Figure 5 shows a block diagram of apparatus operating according to the same principe but employing an alternative form of visual displav in which the indicated angle is a deviation from a datum direction. The maximum value of the angle is thus 3200 mils but it may have a positive or negative value indicating the direction of measurement.

In a complete revolution of the angle measuring synchro the binary number output from converter 1, except for the most significant bit, is repeated in each semicircle. The most significant bit therefore will indicate within which of the two semicircles the measured angle lies, whilst the remaining binary bits will indicate a clockwise angIe in the first semicircle and their complements an anti-clockwise angle in the second semicircle. However, since In the example of Figure 5 the most significant bit of the synchro-to-digital converter 1, bit 1, is connected via a gate 8 to control an additional display 9 to show a minus sign whenever the measured angle lies between 0 and-3200 mils, (i. e. between +3200 and +6400 mils). The remaining bits are now connected to P. R. O. M.'s 6 and 7, through exclusive OR a full binary count occurs in the same position as a zero count the complementary binary number contains an error of one least significant bit. Unless the one bit error can be tolerated the means for producing the complementary binary number must also include error correcting means. gates, generally indicated at 10, each of which is also connected to bit 1. Thus when bit 1 is'0'the binary bits from converter I are supplied unchanged to the P. R. O. M. inputs, but when bit 1 is'1'the binary bits are inverted so that the P. R. O. M.'s are addressed by the binary coded complement of the measured angle.

The apparatus just described may utilise commercially made exclusive OR gates normally available only in standard packages containing four gates. Thus, since nine of the eleven bits of the synchro to digital converter 1 must be inverted an extra three standard packages are required.

However, an alternative method employs only two extra P. R. O. M.'s, the two normal P. R. O. M.'s programmed for straight-forward conversion from binary to B. C. D. in the 0 to +3200 mils range, and two additional P. R. O. M.'s programmed for the inverse conversion for the range 0 to-3200 mils. The state of the most significant bit is now used to select the appropriate pair of P. R. O. M.'s and the one bit error does not occur.

Claims (8)

1. WHAT WE CLAIM IS :- 1. Apparatus for indicating the magnitude of an angular measurement in mil units, one mil unit being 1/6400th part of a circle, including means for generating electrical binary logic signals comprising at least six binary digits representing the angular measurement, first logic means responsive to the six most sig- nificant binary digits for indicating the number of 26th parts of a circle, i. e. hundreds of mils, in the measured angle and second logic means responsive to the remaining binary digits for indicating the remaining part of the measurement.
2. 2. Apparatus according to claim 1 wherein the first logic means comprises binary to binary-coded-decimal converting means for converting the six most significant binary digits to a seven digit binarycoded-decimal number indicating the hundreds of mils in the measured angle.
3. 3. Apparatus according to claim 2 wherein the binary to binary-coded-decimal converting means comprises programmable read-only memory means arranged to be addressed by the five most significant binary digits and programmed to produce in response to each address code the corresponding six digit binarycoded-decimal number, which together with the sixth most significant binary digit forms the required seven digit binary coded decmal number,
4. 4. Apparatus according to any preceding claim wherein the measured angle is indicated as any part of a fuli circle measured with respect to a reference position.
5. 5. Apparatus according to any of claims 1, 2 or 3 wherein the measured angle is indicated as any part of a half circle measured with respect to a reference position in either a first direction or a second and opposite direction.
6. 6. Apparatus according to claim 5 wherein the direction, with respect to the reference position, of the indicated angular measurement is indicated by means responsive to the most significant binary digit and the first logic means indicates the measured angle directly when the most significant digit occupies a first binary state and indicates the reciprocal angle when the digit occupies the alternative binary state.
7. 7. Apparatus according to any preceding claim further including visual display means responsive to the indication of the angular measurement for providing a visual indication of the measured display.
8. 8. Apparatus substantially as described herein with reference to the accompanying drawings.