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New Hall generator applications
Solid-State Electronics Pergamon Press 1966. Vol. 9, pp. 567-570.
Printed in Great Britain
N E W HALL G E N E R A T O R A P P L I C A T I O N S F. KUHRT Siemens-Schuckertwerke A.G., Erlangen, Germany A b s t r a c t - - T h r e e novel types of contactless signal transmission by the Hall generator are presented, which have been developed in the laboratories of the Siemens-Schuckertwerke and of late have reached the stage of a certain maturity. Two of these developments, a control for the repetition of motion steps in machine tools and a small brushless d.c. motor can he considered to be related to
positioning information whereas a remote reading cyclometer register comes under the heading of contactless information transmission by the Hall generator. R6sutn6--Trois nouveaux types de transmission de signaux sans contact employant le g6n~rateur Hall sont pr~sent~s; ceux-ei ont 6t6 d6velopp6s dans les laboratoires de la Siemens-Schuckertwerke et ont derni~rement atteint un stage avanc& Deux de ces d6veloppements, un contr61e pour la r~p6tition des 6tapes de mouvement darts les machines-outils et un petit moteur h courant continu sans balais peuvent ~tre consid~r6s comme &ant reli~s aux informations de position cependant qu'un registre cyclom~tre lecteur assez 61oign6 tombe sous l'ent&e des transmissions d'information sans contact par g~n6rateur Hall. Z u s a m m e n f a s s u n g - - E s wird tiber drei neuartige Anwendungender berfihrungs- und kontaktlosen Signalgabe mit Hallgeneratoren berichtet. Dabei handelt es sich um Entwicklungsarbeiten,die in den Laboratorien der Siemens-Schuckertwerke A.G. durchgeftihrt wurden und gerade in den letzten Wochen und Monaten zu einem gewissen Abschluss gekommen sind. Zwei dieser Neuentwicklungen, niimlich eine Repetiersteuerung fiir Werkzeugmaschinen und ein btirstenloser Gleichstrommotor fallen in den Bereich der Positionsmeldung, w~ihrend ein fernabfragbares Ziffernrollenwerk dem Bereich der beriihrungs- und kontaktlosen Informationstibertragung mit Hallgeneratoren zuzuordnen ist. THE RECEPTION of signals from moving objects position of movable objects and that of transas well as the transmission of signals to them are mitting information of a more complex nature to among the most common applications of the Hall or from moving objects. Positioning information is generator because neither mechanical nor electrical required for the control of definite motions as for contact will be required. T h e short distance instance in the case of machine tools, automated separating transmitter and receiver can con- production equipment, or transfer lines. With the veniently be covered by a magnetic field. Either advent of electronic engineering in this field the small permanent magnets or magnetized foils way was paved also for the growing use of Hall fixed to the moving part are normally serving as generators as contactless position indicators. sources for the magnetic flux. T h e flux lines Hall generators operate with a h!gh degree of picked up by the receiver act on a Hall generator accuracy, are reliable, and are not subject to wear. which for its excitation is supplied with constant As an example of how binary coded information control current or constant control voltage. T h u s can be transmitted across short distances we should the signal given by the magnetic flux can in a like to m e n t i o n the marking of individual goods in simple way be transformed into a voltage which a transport line for the destinations to which they is approximately proportional to the flux intensity are to travel. I n a simple case pieces of magnetizand independent from the speed of the moving able foil will be attached to the cars or tables of the object. conveyor. As the cars are passing by a despatching T h i s method of signal transmission provides a station the information referring to the target or solution for two fundamentally different engin- an identification mark will be impressed on the eering problems, namely that of ascertaining the magnetic foil. T h i s can be done by means of a set 567
568
F. K U H R T
of individually switchable electromagnets which have no mechanical contact with the foil. The magnetic information on the foil which is available in the binary coded form can be picked up by Hall generators when the car is passing a readout station. During the last years installations of this kind with sometimes minor or major modifications have found extensive use, especially in the German automobile industry. Detailed descriptions of them have already been published elsewhere. When machine tools are to be operated automatically the information determining the dimensions and contours of the workpiece and the automatic sequence of machining operations has to be available in stored form. If this information is in numerical form represented by a binary code and stored, for instance, on punched tape, we used to call it a numerical control. Automatic machine tool control could, however, be much simplified, if the information relating to translatory displacement would be stored in analog form. It is possible to achieve this by setting on a magnetizable scale, which is arranged parallel to the workpiece, magnetic positioning marks through appropriable magnetization of the scale material. These position marks can subsequently be read very accurately and quite independently from the speed of travel. The only effort required for setting a position mark consists in the pressing down of a pushbutton and this can easily be done by a skilled worker as he operates the machine for making the prototype of a batch. Pressing down of a pushbutton in the beginning of each machining operation will feed the necessary switching information, such as cutting speed and rate of tool feed into the magnetic storage device. In the same way the position of the tool will be stored at the end of the operation after the workpiece has been machined to the desired dimensions. Once the first piece has been completed and found satisfactory the entire sequence of production operations can be repeated any number of times on the basis of the information stored. All the machine operator has to do for the following workpieces is to put the blank into the machine and to take down the finished work. This type of machine tool control has been termed repetitive motion control. It is distinguished by the very easy and quick way in which the programming can be done. This isj
of special advantage in the production of small and medium-sized lots. The way of recording position marks on a magnetic scale is shown on the left of Fig. 1, and the read-out process on the right. The magnetic scale consists of a tape of magnetic material of high coercivity which is supported on a soft iron base. The high coercivity material will be magnetized in a vertical direction as the scale which is shown in cross-section, is moving under the recording head in a direction perpendicular to the picture plane. As long as there is no signal the scale will be magnetized homogenously, the central track in the direction from top to bottom, the two outer tracks in opposite direction. By setting a position mark on a small spot of the scale with very limited longitudinal extension, the previous magnetization will be altered locally to form a narrow area of similar, but inversely oriented magnetization. In this way small bundles of magnetic flux lines originating from the central track will form tiny stray fields in the longitudinal direction of the scale. These stray flux lines are shown in red in the perspective view of the lower left-hand corner. They will act on the pick-up head as it travels along the control track in the manner shown in the upper right-hand part of the figure. The signal voltage induced in the pick-up head can be represented by a curve intersecting the abscissa at a very steep angle with a rate of rise of approximately 1.5 V/mm. Its passing through zero serves as position mark. The location of the mark is within wide limits unaffected by temperature changes of the ambient and by distance variations between pick-up head and magnetic scale. Figure 2 (top) shows a vertical milling machine, the work table of which was equipped with repetitive motion control for the longitudinal travel. The information contained in the magnetic storage device and relating to switching and translatory motion operations is fed into an electronics cabinet standing beside the machine and is there processed to form adequate switching instructions for the control of the respective drives. The magnetic scale is designed as a cylindrical drum having on its circumference 20 magnetic tracks parallel to the axis. Each track is intended for storing the information required for one translatory motion operation. After the tool has reached its final position for a certain operation a ratchet
FIG. 1. Position fixing by recording with magnetic and reading out by Hall effect.
FIG. 3. Brushless
d.c. motor controlled
FIG. 5. Principle
of pick-up head register.
marks
by Hall generators.
for
remote
readable
Fro.
2. Programme
repeater control machine tools.
system
for
FIG. 4. Circuit diagram of brushless d.c. motor controlled by Hall generators.
FIG. 6. Remote
readable register.
@cing
p. 568
NEW H A L L G E N E R A T O R A P P L I C A T I O N S mechanism will rotate the cylinder by a given angle. In this way a new track is selected on which the information for the next following machining operation is stored. The recording and pick-up heads are mounted on the stationary base of the machine; they are adjusted to coincide in their respective position exactly with the axial position of the cylindrical scale. The cylindrical drum, however, is attached to the moving work table. T h e control information required for each machining step, such as sense of motion, rate of feed, etc. is stored at the right end of the scale drum on its respective track. This control information enables the machine to repeat the stored programme with an accuracy of - ~ mm. Another new application where Hall generators prove useful is with d.c. motors for batteryoperated magnetic tape recorders. There is a good prospect already that in the near future brushless d.c. motors will be used extensively for that purpose. The purpose of the commutator in an ordinary d.c. motor is to switch over the armature current according to the angular position assumed by the rotor as it revolves. Therefore the commutator has the function of both a sensing device for angular position and of an electrical switch. I f we are going to replace the commutator by a contactless electronic device, the transistor is coming readily to the mind as an ideal device for the switching functions. As a sensor for the angular position of the rotor the Hall generator is an obvious suggestion, as it operates without mechanical or electrical contact. Figure 3 shows the design of a brushless d.c. motor with Hall generator control. The rotor consists of a cylindrically shaped permanent magnet which is magnetized across one diameter. T h e stator winding is composed of 4 coils which are housed in pairs in the 2 winding compartments of a coil former. Two diametrically opposite quadrants belong to the same winding compartment. T h e 2 winding compartments are perpendicular to each other, so that the motor has 2 pole pairs under a right angle. T h e return path for the flux lines is constituted by a stack of annular, slotless laminations which can be slid over the wound-up coil former. T h e angular position of the rotor at any moment is sensed by 2 Hall generators which are housed
569
in two small recesses of the laminated stator core at the periphery of the winding. T h e 2 recesses are set under an angle of 90 ° with respect to each other. As can be seen on the right of Fig. 3 the magnetic flux vector of the stator, which is dependent on the rotor position, revolves by jumps of 90 ° every time. T h e necessary switching is brought about by the red part of the circuit in Fig. 4. One pole pair is formed by coils 1 and 2, the other perpendicular pair, by coils 3 and 4. T h e coils 1 and 2 are wound in opposite sense as are the coils 3 and 4. For any 90 ° of rotor revolution there will be a different path for the current through the coils. These four possibilities are: current passing through coils 1 and 3, 1 and 4, 2 and 4, and 2 and 3. The method of always connecting the coils of 2 different pole pairs in series limits the dips in the counter-electromotive force (counter-e.m.f.) so that they will not exceed 30 per cent. This makes for a low content of harmonics in the stator current and results in good efficiency. By providing a coupling resistor between the 2 Hall generators it is ensured that the current through the base of the transistor will be proportional to the Hall voltage. The temperature dependency of the transistor threshold voltage can thus be disregarded. A small oscillator supplies constant voltage for the control current of the Hall generators. In this way the temperature drift of the Hall voltage will be smaller than 0"3 per cent/°C. T h e described motor has a speed of 5500 rev/min when being operated on a 9 V battery at no load, and an efficiency of 56 per cent with a mechanical power output of 0.5 W. An important problem of data transmission in the field of remote reading and control is the remote reading out of cyclometer registers. I f Hall generators are to be employed for that purpose the digit rolls have to carry their information on magnetic material in coded form. One method which has the merit of facilitating production of the digit rolls consists in inserting small pieces of soft magnetic sheet into the mould before injecting the plastic material. The magnetic flux required for reading out such digit rolls can be provided by two small permanent-magnets which are incorporated in the pick-up head. Figure 5 shows in principle, how the contactless reading out of cyclometer register rolls can be effected. As long
570
F. K U H R T
as the pole faces of the pick-up head are not bridged by a piece of soft iron the total magnetic flux through the Hall generator will be zero. However, when a small piece of iron lies across the left and the central legs of the pick-up, the magnetic flux originating from the left magnet will be greater than that of the right magnet and will induce a voltage signal which we consider to be positive. In an analogous way a piece of iron across the right-hand part of the pick-up would induce a negative signal. Figure 6 shows how this arrangement can serve for the remote reading out of cyclometer registers.
Upon a given starting impulse the pick-up head mounted on a small carriage will be moved by a small synchronous motor with worm gear to travel in axial direction across the surface of the digit rolls. After having picked up the information from all the cyclometer rolls the head with its carriage is returned to its initial position. The reading out of 10 cyclometer rolls and hence of a 10-digit number will take approximately 2 see. The information stored in the individual digit rolls will be transformed by the reading-out process into a sequence of binary coded signals and can thus be transmitted directly on a teleprinter line.
Printed in Great Britain
N E W HALL G E N E R A T O R A P P L I C A T I O N S F. KUHRT Siemens-Schuckertwerke A.G., Erlangen, Germany A b s t r a c t - - T h r e e novel types of contactless signal transmission by the Hall generator are presented, which have been developed in the laboratories of the Siemens-Schuckertwerke and of late have reached the stage of a certain maturity. Two of these developments, a control for the repetition of motion steps in machine tools and a small brushless d.c. motor can he considered to be related to
positioning information whereas a remote reading cyclometer register comes under the heading of contactless information transmission by the Hall generator. R6sutn6--Trois nouveaux types de transmission de signaux sans contact employant le g6n~rateur Hall sont pr~sent~s; ceux-ei ont 6t6 d6velopp6s dans les laboratoires de la Siemens-Schuckertwerke et ont derni~rement atteint un stage avanc& Deux de ces d6veloppements, un contr61e pour la r~p6tition des 6tapes de mouvement darts les machines-outils et un petit moteur h courant continu sans balais peuvent ~tre consid~r6s comme &ant reli~s aux informations de position cependant qu'un registre cyclom~tre lecteur assez 61oign6 tombe sous l'ent&e des transmissions d'information sans contact par g~n6rateur Hall. Z u s a m m e n f a s s u n g - - E s wird tiber drei neuartige Anwendungender berfihrungs- und kontaktlosen Signalgabe mit Hallgeneratoren berichtet. Dabei handelt es sich um Entwicklungsarbeiten,die in den Laboratorien der Siemens-Schuckertwerke A.G. durchgeftihrt wurden und gerade in den letzten Wochen und Monaten zu einem gewissen Abschluss gekommen sind. Zwei dieser Neuentwicklungen, niimlich eine Repetiersteuerung fiir Werkzeugmaschinen und ein btirstenloser Gleichstrommotor fallen in den Bereich der Positionsmeldung, w~ihrend ein fernabfragbares Ziffernrollenwerk dem Bereich der beriihrungs- und kontaktlosen Informationstibertragung mit Hallgeneratoren zuzuordnen ist. THE RECEPTION of signals from moving objects position of movable objects and that of transas well as the transmission of signals to them are mitting information of a more complex nature to among the most common applications of the Hall or from moving objects. Positioning information is generator because neither mechanical nor electrical required for the control of definite motions as for contact will be required. T h e short distance instance in the case of machine tools, automated separating transmitter and receiver can con- production equipment, or transfer lines. With the veniently be covered by a magnetic field. Either advent of electronic engineering in this field the small permanent magnets or magnetized foils way was paved also for the growing use of Hall fixed to the moving part are normally serving as generators as contactless position indicators. sources for the magnetic flux. T h e flux lines Hall generators operate with a h!gh degree of picked up by the receiver act on a Hall generator accuracy, are reliable, and are not subject to wear. which for its excitation is supplied with constant As an example of how binary coded information control current or constant control voltage. T h u s can be transmitted across short distances we should the signal given by the magnetic flux can in a like to m e n t i o n the marking of individual goods in simple way be transformed into a voltage which a transport line for the destinations to which they is approximately proportional to the flux intensity are to travel. I n a simple case pieces of magnetizand independent from the speed of the moving able foil will be attached to the cars or tables of the object. conveyor. As the cars are passing by a despatching T h i s method of signal transmission provides a station the information referring to the target or solution for two fundamentally different engin- an identification mark will be impressed on the eering problems, namely that of ascertaining the magnetic foil. T h i s can be done by means of a set 567
568
F. K U H R T
of individually switchable electromagnets which have no mechanical contact with the foil. The magnetic information on the foil which is available in the binary coded form can be picked up by Hall generators when the car is passing a readout station. During the last years installations of this kind with sometimes minor or major modifications have found extensive use, especially in the German automobile industry. Detailed descriptions of them have already been published elsewhere. When machine tools are to be operated automatically the information determining the dimensions and contours of the workpiece and the automatic sequence of machining operations has to be available in stored form. If this information is in numerical form represented by a binary code and stored, for instance, on punched tape, we used to call it a numerical control. Automatic machine tool control could, however, be much simplified, if the information relating to translatory displacement would be stored in analog form. It is possible to achieve this by setting on a magnetizable scale, which is arranged parallel to the workpiece, magnetic positioning marks through appropriable magnetization of the scale material. These position marks can subsequently be read very accurately and quite independently from the speed of travel. The only effort required for setting a position mark consists in the pressing down of a pushbutton and this can easily be done by a skilled worker as he operates the machine for making the prototype of a batch. Pressing down of a pushbutton in the beginning of each machining operation will feed the necessary switching information, such as cutting speed and rate of tool feed into the magnetic storage device. In the same way the position of the tool will be stored at the end of the operation after the workpiece has been machined to the desired dimensions. Once the first piece has been completed and found satisfactory the entire sequence of production operations can be repeated any number of times on the basis of the information stored. All the machine operator has to do for the following workpieces is to put the blank into the machine and to take down the finished work. This type of machine tool control has been termed repetitive motion control. It is distinguished by the very easy and quick way in which the programming can be done. This isj
of special advantage in the production of small and medium-sized lots. The way of recording position marks on a magnetic scale is shown on the left of Fig. 1, and the read-out process on the right. The magnetic scale consists of a tape of magnetic material of high coercivity which is supported on a soft iron base. The high coercivity material will be magnetized in a vertical direction as the scale which is shown in cross-section, is moving under the recording head in a direction perpendicular to the picture plane. As long as there is no signal the scale will be magnetized homogenously, the central track in the direction from top to bottom, the two outer tracks in opposite direction. By setting a position mark on a small spot of the scale with very limited longitudinal extension, the previous magnetization will be altered locally to form a narrow area of similar, but inversely oriented magnetization. In this way small bundles of magnetic flux lines originating from the central track will form tiny stray fields in the longitudinal direction of the scale. These stray flux lines are shown in red in the perspective view of the lower left-hand corner. They will act on the pick-up head as it travels along the control track in the manner shown in the upper right-hand part of the figure. The signal voltage induced in the pick-up head can be represented by a curve intersecting the abscissa at a very steep angle with a rate of rise of approximately 1.5 V/mm. Its passing through zero serves as position mark. The location of the mark is within wide limits unaffected by temperature changes of the ambient and by distance variations between pick-up head and magnetic scale. Figure 2 (top) shows a vertical milling machine, the work table of which was equipped with repetitive motion control for the longitudinal travel. The information contained in the magnetic storage device and relating to switching and translatory motion operations is fed into an electronics cabinet standing beside the machine and is there processed to form adequate switching instructions for the control of the respective drives. The magnetic scale is designed as a cylindrical drum having on its circumference 20 magnetic tracks parallel to the axis. Each track is intended for storing the information required for one translatory motion operation. After the tool has reached its final position for a certain operation a ratchet
FIG. 1. Position fixing by recording with magnetic and reading out by Hall effect.
FIG. 3. Brushless
d.c. motor controlled
FIG. 5. Principle
of pick-up head register.
marks
by Hall generators.
for
remote
readable
Fro.
2. Programme
repeater control machine tools.
system
for
FIG. 4. Circuit diagram of brushless d.c. motor controlled by Hall generators.
FIG. 6. Remote
readable register.
@cing
p. 568
NEW H A L L G E N E R A T O R A P P L I C A T I O N S mechanism will rotate the cylinder by a given angle. In this way a new track is selected on which the information for the next following machining operation is stored. The recording and pick-up heads are mounted on the stationary base of the machine; they are adjusted to coincide in their respective position exactly with the axial position of the cylindrical scale. The cylindrical drum, however, is attached to the moving work table. T h e control information required for each machining step, such as sense of motion, rate of feed, etc. is stored at the right end of the scale drum on its respective track. This control information enables the machine to repeat the stored programme with an accuracy of - ~ mm. Another new application where Hall generators prove useful is with d.c. motors for batteryoperated magnetic tape recorders. There is a good prospect already that in the near future brushless d.c. motors will be used extensively for that purpose. The purpose of the commutator in an ordinary d.c. motor is to switch over the armature current according to the angular position assumed by the rotor as it revolves. Therefore the commutator has the function of both a sensing device for angular position and of an electrical switch. I f we are going to replace the commutator by a contactless electronic device, the transistor is coming readily to the mind as an ideal device for the switching functions. As a sensor for the angular position of the rotor the Hall generator is an obvious suggestion, as it operates without mechanical or electrical contact. Figure 3 shows the design of a brushless d.c. motor with Hall generator control. The rotor consists of a cylindrically shaped permanent magnet which is magnetized across one diameter. T h e stator winding is composed of 4 coils which are housed in pairs in the 2 winding compartments of a coil former. Two diametrically opposite quadrants belong to the same winding compartment. T h e 2 winding compartments are perpendicular to each other, so that the motor has 2 pole pairs under a right angle. T h e return path for the flux lines is constituted by a stack of annular, slotless laminations which can be slid over the wound-up coil former. T h e angular position of the rotor at any moment is sensed by 2 Hall generators which are housed
569
in two small recesses of the laminated stator core at the periphery of the winding. T h e 2 recesses are set under an angle of 90 ° with respect to each other. As can be seen on the right of Fig. 3 the magnetic flux vector of the stator, which is dependent on the rotor position, revolves by jumps of 90 ° every time. T h e necessary switching is brought about by the red part of the circuit in Fig. 4. One pole pair is formed by coils 1 and 2, the other perpendicular pair, by coils 3 and 4. T h e coils 1 and 2 are wound in opposite sense as are the coils 3 and 4. For any 90 ° of rotor revolution there will be a different path for the current through the coils. These four possibilities are: current passing through coils 1 and 3, 1 and 4, 2 and 4, and 2 and 3. The method of always connecting the coils of 2 different pole pairs in series limits the dips in the counter-electromotive force (counter-e.m.f.) so that they will not exceed 30 per cent. This makes for a low content of harmonics in the stator current and results in good efficiency. By providing a coupling resistor between the 2 Hall generators it is ensured that the current through the base of the transistor will be proportional to the Hall voltage. The temperature dependency of the transistor threshold voltage can thus be disregarded. A small oscillator supplies constant voltage for the control current of the Hall generators. In this way the temperature drift of the Hall voltage will be smaller than 0"3 per cent/°C. T h e described motor has a speed of 5500 rev/min when being operated on a 9 V battery at no load, and an efficiency of 56 per cent with a mechanical power output of 0.5 W. An important problem of data transmission in the field of remote reading and control is the remote reading out of cyclometer registers. I f Hall generators are to be employed for that purpose the digit rolls have to carry their information on magnetic material in coded form. One method which has the merit of facilitating production of the digit rolls consists in inserting small pieces of soft magnetic sheet into the mould before injecting the plastic material. The magnetic flux required for reading out such digit rolls can be provided by two small permanent-magnets which are incorporated in the pick-up head. Figure 5 shows in principle, how the contactless reading out of cyclometer register rolls can be effected. As long
570
F. K U H R T
as the pole faces of the pick-up head are not bridged by a piece of soft iron the total magnetic flux through the Hall generator will be zero. However, when a small piece of iron lies across the left and the central legs of the pick-up, the magnetic flux originating from the left magnet will be greater than that of the right magnet and will induce a voltage signal which we consider to be positive. In an analogous way a piece of iron across the right-hand part of the pick-up would induce a negative signal. Figure 6 shows how this arrangement can serve for the remote reading out of cyclometer registers.
Upon a given starting impulse the pick-up head mounted on a small carriage will be moved by a small synchronous motor with worm gear to travel in axial direction across the surface of the digit rolls. After having picked up the information from all the cyclometer rolls the head with its carriage is returned to its initial position. The reading out of 10 cyclometer rolls and hence of a 10-digit number will take approximately 2 see. The information stored in the individual digit rolls will be transformed by the reading-out process into a sequence of binary coded signals and can thus be transmitted directly on a teleprinter line.