DE4229610A1 - Absolute position sensor for multi-turn angular detection - has shaft located rotatably in stator for determining exact angular position of transmitter during complete revolution and includes buffer battery - Google Patents

Abstract

The position sensor includes a mechanical closing switching element and a rotatable operating part for this element, connected to the sensor shaft (5). A buffer battery provides power upon failure of an external power supply. The circuit has at least one very high resistance (31), in series with the closed switching element (17), to limit the current in this circuit. A logic circuit (24,25), a counter(26), the switching element(15,17), and the buffer battery (21) are completely integrated in the rotation transmitter to form a compact unit. ADVANTAGE - Retains information without external power supply.

Description

The invention relates to a rotary encoder Absolute value position detection according to the generic term of Claim 1.

Encoder with an absolute value position detection usually with an angle encoder and corresponding optical scanning devices (with e.g. LEDs, photodiodes etc.). With the help of one Disc can be the absolute angular position with this one Encoder shaft connected within a disc Angular intervals from 0 ° to 360 ° can be detected. A Angular range over several revolutions is with one single disc is not measurable since its coding is based on Repeatedly going through one revolution.

Encoder with an absolute position value acquisition via several turns, so-called multi-turn encoders, are consequently in different embodiments known.

For example, several angle encoders were used a reduction gear connected to each other for use  brought. The reduction gear causes the Downstream angle encoder in each case complete rotation of the upstream Angle encoder by one, its resolving power corresponding unit is rotated. How it works of such a multi-turn encoder is with a conventional one Analog clock comparable with different hands. At a However, such an encoder multiplies accordingly Number of coding disks also the number of optical Scanning systems. This fact, as well as the effort involved the high precision required for that Reduction gears are caused by this Solution of great disadvantage.

Furthermore, multi-turn encoders have been developed only with an angle measuring device to detect a Angular range between 0 ° and 360 ° are provided, however to record the complete revolutions have a counting unit. This combination enables an extension of the measuring range of the encoder the maximum number of Revolutions, on the other hand, requires a constant Power supply to the counting unit and the scanning device the encoder disk. If the Power supply to the counting unit goes the contained therein Information lost. Switching off the power supply for the scanning device of the encoder also that the counting unit is new or no longer register reversed revolutions can. So there is a rotation of the encoder shaft also in this case the information about the absolute Lost position.

In order to remedy this disadvantage, in the following the The encoder is powered by a battery or buffered by an accumulator. For example  with the European application EP 04 66 209 A2 Multi-rotary encoders become known, the one Angle coding disk with the corresponding optical Detection device for recording the absolute angle within one revolution and also one separate magnetic signal generator and a counting unit for detecting revolutions that have been completed. The named encoder is used in the event of a power failure external battery buffered.

Such a device has the disadvantage that it is constantly be connected at least to the auxiliary power supply in order not to lose the stored information. In many cases, for example when using a Multi-rotary encoder in a robot, however, it is desirable that the encoder its information at Disconnecting external leads does not lose and furthermore the movements of the encoder shaft continue detected. This is particularly necessary if a Robot is set up for test purposes, then for the delivery is broken down into individual components will. In such a case there are multiturn encoders desirable even after or during the disassembly of the Robot's movements and positions of each Capture components so that the system according to their Reassembling is not new in its parts needs to be adjusted.

The invention is therefore based on the object propose inexpensive multi-turn encoders without external power supply its information reliable receives and the absolute position of the encoder shaft recorded a large number of revolutions. Buffering in In the event of a suspended external power supply, this should  very generous, d. H. over a period of several Years.

This task is characterized by the characteristics of the Claim 1 solved.

Accordingly, in an encoder according to the invention at least one mechanically closing switching element in Connection with a rotatable actuator that is fixed is connected to the encoder shaft. The current, which in the closed state via this switching element flows through a series connection with a very limited high resistance. In addition, the Logic circuit for pulse shaping and pulse selection, the from the signal of the switching element when spinning Actuator a logical signal per revolution of the Encoder shaft generated as well as the counting unit with the help of at least one integrated circuit also very much designed with high impedance. Because of the extreme in this way the buffer battery or the accumulator should be chosen so small that it is the same like the electronic circuits mentioned in the Encoder unit can be integrated. Such a, with the Components provided encoder forms one compact structural unit and is without external Power supply works for years.

By the measures mentioned in the subclaims advantageous designs and developments of Invention possible.

A simple and robust embodiment of the invention is included a mechanically acting actuator. A such actuator can be used as a cam on the encoder shaft be formed of the two contact tongues with the Revolutions of the encoder shaft opens or closes.  

Recommended for a contactless operating part the use of a magnetic ring that over part of its circumference from a permanent magnetic and the other part is made of non-magnetic material, the switching element being designed as a reed switch, the one at a turn of this ring once is opened or closed.

By using two switching elements under one Angle of, for example, α = 45 ° to the zero crossing of the Angle measuring device are arranged, and two corresponding logic circuits for generating pulses and two counters, the current meter reading can be used synchronize the zero crossing of the angle measuring device. The counter with the one in front of the respective direction of rotation switching the zero crossing of the angle measuring device Switching element is coupled at the time of Zero crossing always the correct value. Depending on The direction of rotation must therefore be at the data output between the two Counters can be switched back and forth.

In the case of a logic circuit which is used both for the rising as well as on the falling edge of the switching signal Generated impulse, the closing should be effective Angular range of the actuating part larger than that of the both switching elements included angles α and α ′ be. With such an angular range, for example The switching state of the one switching element can be 180 ° used to switch from the other switching element associated pulses one pulse per revolution suppress. This gives you the exit at the Logic circuit for each switching element exactly per revolution a signal.  

A square wave signal can be found on one edge of a Switching state of a switching element, for example with With the help of a time delay element and a logical one Generate antivalence gates. The time delay of the Time delay element gives exactly the width of the Impulse.

In this way it only lies on every second flank of the original switching signal a logical pulse behind before the logic circuit, so the fact of whether there is is a rising or falling edge, the necessary information about the direction of rotation.

The above-mentioned suppression of every second one a switching element returning pulse using the Signals of the other switching element can in turn with a Logic gates are performed.

Switching back and forth between the two counters is preferably done with the help of a multiplexer that the current counter content in time with the most significant bit of that from the angle measuring device read binary number on the data output of the Encoder switches through. In this way the Encoder output data value with the Zero crossing of the angle measuring device during rotation the encoder shaft synchronized.

The implementation of the above is particularly advantageous Logic circuits for pulse shaping and pulse selection a so-called application-specific integrated Circuit (ASIC). This makes the circuit special be designed with high impedance and at the same time extremely be designed to save space. This is especially true in Considering that all of the above components are complete  be integrated into the encoder unit, of great Advantage.

The angle measuring device can be an optical one capacitive or an inductive scanning device. An angle coding part adapted to the scanning device, that rotates with the encoder shaft, for example one Angle coding disk for an optical scanning device, is to be provided here.

An embodiment of the invention is in the drawing shown and is in the description below explained in more detail.

Show it

Fig. 1 shows a longitudinal section through an inventive encoder,

Fig. 2 is a schematic plan view of a magnetic transducer, such as is used in an inventive encoder,

Fig. 3 is a block diagram of the signal processing,

Fig. 4 is a circuit diagram of the signal processing electronic circuit and

Fig. 5 is a diagram showing the timing of different voltage levels in the circuit of Fig. 4 during the operation of the encoder.

Fig. 1 shows a rotary encoder 1 with a rotary encoder housing 2 , which consists of a stator 3 and a housing cover 4 . An encoder shaft 5 , which is rotatably supported by ball bearings 6 , passes through the stator 3 from below. The inside of the housing 2 is divided by a shielding plate 7 into an upper 8 and a lower part 9 . In the lower part 9 there are the components of the rotary encoder 1 , which are provided for detecting the angular position within one revolution (single-turn encoder). In detail, these are an angle coding disk 10 , which is illuminated from below by an optical transmitter unit 11 . A receiver circuit board 12 , which has optical sensors (not shown) and a receiver circuit, is located above the angle encoder disk 10 .

In the upper part 8 of the rotary encoder 1 there is a magnet holder 13 which is plugged onto the encoder shaft 5 . The part 14 of the magnet holder 13 inserted over the encoder shaft 5 passes through the shielding plate and projects into the lower part 9 of the rotary encoder 1 . A magnetic ring 15 is attached to the magnet holder 13 at the top. A screw 16 fixes the magnet holder 13 on the encoder shaft 5 . Above the magnetic ring there are two reed switches 17 a, b within their shield caps 18 a, 18 b. The two reed switches 17 a, 17 b are attached to a circuit board 19 on which the circuits for signal shaping and selection, not shown, and the counters are constructed. At the top of the circuit board 19 there is a circuit board 20 with a DC voltage source and a battery 21 .

The components in the lower part 9 of the rotary encoder work in the manner known from conventional angular rotary encoders for angular resolution within one revolution of the encoder shaft 5 .

The arrangement of the two reed switches 17 a, 17 b in the upper part 8 of the rotary encoder is shown in the schematic plan view of FIG. 2. You are at an angle of α or α'≈45 ° to line 22 , which corresponds to the zero crossing of the encoder 10 . The magnetic ring 15 is composed of a magnetic 23 a and a non-magnetic part 23 b, so that the reed switches are open when the magnetic part 23 a of the magnetic ring is below them, and are closed in the other case.

The signals generated in this way by the different switching states of the reed switches 17 a, 17 b are further processed in accordance with the block diagram shown in FIG. 3. The signals generated by the reed switches as pulse generators 17 a, 17 b enter an electronic circuit for pulse shaping 24 , which forms a logic square pulse from each edge of its input signal. Subsequently, these square-wave pulses are selected in a circuit 25 for pulse selection in such a way that one square-wave pulse per revolution of the encoder shaft 5 is present at the output of this circuit. These impulses processed in this way are finally counted and stored in two counters. Since the two reed switches are at an angle .alpha. Or .alpha. 'To the zero crossing 22 , the current counter reading of one counter runs ahead of the actual value in a certain direction of rotation, while the counter reading of the other counter lags behind. Via a circuit for data selection 27 , the counter with the respectively correct data stock is selected and switched through synchronously with the zero crossing of the angle coding disk 10 to its output.

FIG. 4 shows a possible circuit for signal processing according to FIG. 3. An external power supply 28 and a lithium battery 29 supply the operating voltage for the following circuit as required. Depending on the switching state, the two reed switches 17 a, 17 b switch the two power lines 30 a, 30 b against the circuit ground via two very high-impedance and thus current-limiting resistors 31 a, 31 b. As a result, depending on the switching state, the voltages Va, Vb which are present in the signal lines 32 a, 32 b vary. By using a time delay element 33 a, 33 b and an Anitvalenzgates 34 a, 34 b, a rectangular pulse A or B is generated at the output of the antivalence gates 34 a, 34 b. With the help of AND gates 34 a, 34 b and the voltages Va, Vb of the signal lines 32 a, 32 b assigned to the respective other data channel, exactly one square-wave pulse A 'or B' is selected per revolution of the encoder shaft. The signals are counted and stored in the counters 26 a, 26 b. A multiplexer 36 selects the current data channel and switches its counter reading through to its output.

The time course of the various signals during the rotation of the encoder shaft is shown in FIG. 5. The top diagram shows the most significant bit MSB at the output of the single-turn encoder located in the lower part 9 of the encoder 1 . This bit is set exactly with the zero crossing of the encoder shaft at time t _o and switched to "Low" at 180 °. The two diagrams following below reflect the voltage curve Va, Vb in the signal lines 32 a, 32 b. The signal curve corresponds to that of the most significant bit MSB, but is offset by a time tα, tα ', in which the encoder shaft 5 rotates by the angles α and α'. The following two diagrams represent the pulses A, B at the output of the antivalence gates 34 a, 34 b. The width of the rectangular pulses A, B corresponds exactly to the time delay of the time delay elements 33 a, 33 b. The two diagrams below make it clear that only every second square-wave signal A ', B' are selected at the output of the AND gate 35 . Accordingly, the lowest data bits, Da, Db of the two counters 26 a, 26 b are switched with the input of these square-wave signals A ', B'. The lowest diagram shows, based on the lowest data bit Da, Db, how the current counter reading in accordance with the direction of rotation, in this case Db, is output in synchronism with the most significant bit of the angle coding disk MSB at the output of multiplexer 27 as data bit Dm.

An encoder according to the invention comes through measures described with buffer flows that are smaller than 10 µA. When using a small one Lithium battery with 0.95 Ah results in one secured function in the event of an external power failure of approx. 10 Years.

Claims (10)

1. Encoder ( 1 ) for absolute value position detection, with a stator ( 3 ) and a rotatably mounted encoder shaft ( 5 ), the encoder ( 1 ) an angle measuring device for detecting the exact position of the encoder shaft ( 5 ) during a complete revolution in one Angle interval of 0 ° -360 ° and an output unit for outputting the detected position of the encoder shaft as an angle indication on a data output, wherein the angle measuring device and the output unit are fed by an external power supply and the encoder also a device for detecting the number of completely passed Revolutions with a non-rotatably arranged first part ( 17 ) and a second part ( 15 ) fastened to the encoder shaft ( 5 ) and rotating therewith, and the rotary encoder ( 1 ) with a logic circuit for forming and selecting ( 24 , 25 ) a logical one Impulse from the output signal of the device for detecting the rev The encoder shaft ( 5 ) and for detecting the direction of rotation is provided and has a counting unit ( 26 ) which is dependent on the direction of rotation and which, depending on the direction of rotation, sums up or subtracts the logic pulses generated in this way from the respective counter reading and whose current counter reading can be read on the data output, and wherein a battery ( 21 ) or an accumulator for maintaining the power supply is provided for the device for the detection of complete revolutions, the logic circuit ( 24 , 25 ) and the counting unit ( 26 ) in the event of an interruption of the otherwise supplied external power supply, characterized in that the device for detecting complete revolutions has a mechanically closing switching element and a rotatable actuating part for the switching element, which is connected to the encoder shaft ( 5 ) and which reduces the size of the battery ( 21 ) or the accumulator for buffering the rotary encoder ( 1 ) in the event of failure the external power supply ( 28 ) there is a circuit ( 24 ) which has a resistor ( 31 ) in series with it, at least when the switching element ( 17 ) is closed, so that the current in this circuit is limited so that the logic circuit ( 24 , 25 ) for pulse shaping and selection with at least one integrated circuit and, like the counting unit ( 26 ), is designed with high resistance and that the logic circuit ( 24 , 25 ), the counting unit ( 26 ), the switching element ( 15 , 17 ) and the Backup battery ( 21 ) or accumulator are fully integrated in the encoder unit ( 2 ), so that the encoder ( 1 ) forms a compact structural unit with the components mentioned. 2. Encoder according to one of the preceding claims characterized in that a mechanically acting Actuating part for actuating the mechanically closing Switching element is provided. 3. Encoder according to claim 1 or 2, characterized in that a magnetic ring ( 15 ) is mounted on the encoder shaft ( 5 ) as an actuating part, which consists of a magnetically active part ( 23 a) and a magnetically inactive region ( 23 b) and that the mechanically closing switching element is a reed contact ( 17 ) which, when the magnetic ring ( 15 ) rotates, depends on whether a magnetically active ( 23 a) or ineffective ( 23 b) part of the magnetic ring ( 15 ) passes alternately open or closed in its vicinity. 4. Encoder according to one of the preceding claims, characterized in that the magnetic ring ( 15 ) from a magnetic part ( 23 a) and a non-magnetic part ( 23 b) is composed. 5. Encoder according to one of the preceding claims, characterized in that it has two switching elements ( 17 a, 17 b) which are arranged at an angle of 45 ° to the zero crossing ( 22 ) of the encoder shaft ( 5 ), two logic circuits ( 24 a, 24 b, 25 a, 25 b) for generating pulses and two counters ( 26 a, 26 b) and that the closing part ( 23 a) and the non-closing part ( 23 b) of the actuating part ( 15 ) so are designed so that the switching elements ( 17 ) are switched every 180 ° during the rotation of the encoder shaft ( 5 ). 6. Encoder according to one of the preceding claims, characterized in that a pulse is generated from the different switching states (Va, Vb) of the switching elements ( 17 a, 17 b) by means of a time delay element ( 33 ) and a logic gate ( 34 ) the direction of the edge of the switching element ( 17 a, 17 b) outgoing signal (Va, Vb) can be used to switch the counting mode of the counter between addition or subtraction and that the signal line ( 32 a, 32 b) of the one switching element ( 17 a , 17 b) with a logic gate ( 35 a, 35 b) and the signal line ( 32 a, 32 b) of the other switching element ( 17 a, 17 b) is connected so that every second pulse is suppressed and per complete revolution of the encoder shaft ( 5 ) only one pulse is generated. 7. Encoder according to one of the preceding claims, characterized in that a multiplexer ( 27 ) is provided which, depending on the direction of rotation, the counter content of each counter ( 26 a, 26 b) of the encoder ( 1 ) in time with the most significant bit (MSB ) of the code read by the angle measuring device ( 10 ) is switched through to the data output of the rotary encoder ( 1 ) in such a way that the data value of the rotary encoder ( 1 ) present at the output with the zero crossing ( 22 ) of the angle coding part ( 10 ) of the angle measuring device on the encoder shaft ( 5 ) while their rotation can be synchronized. 8. Encoder according to one of the preceding claims characterized in that the angle measuring device with an optical scanner and a corresponding one Angle coding part is provided. 9. Encoder according to one of the preceding claims characterized in that the angle measuring device with a capacitive sensing device and one corresponding angle coding part is provided. 10. Encoder according to one of the preceding claims characterized in that the angle measuring device with an inductive scanning device and a corresponding one Angle coding part is provided.