WO2001086801A1

WO2001086801A1 - Arrangement for controlling a unit that can be aimed, preferably a weapon sight, by means of a three-phase brushless direct-current motor

Info

Publication number: WO2001086801A1
Application number: PCT/SE2001/001009
Authority: WO
Inventors: Stefan LINDSTRÖM; Ulf Nilsson
Original assignee: Saab Ab
Priority date: 2000-05-11
Filing date: 2001-05-09
Publication date: 2001-11-15
Also published as: EP1303906A2; WO2001086801A8; SE0001734D0; AU5896901A; SE0001734L

Abstract

In an arrangement a three-phase brushless direct-current motor (MOT) is utilized for controlling a weapon sight (VP), using electrical signals. The arrangement comprises an analogue or digital motor amplifier for sinusoidal commutation, to which the electrical signals can be fed. The windings or phases of the motor are connected to individual pairs of drive transistors incorporated in a transistor bridge. The motor amplifier is arranged to generate pulse-width-modulated signals (PWM-R, PWM-S and PWM-T) and using these to control the drive transistors in the bridge and thereby cause generation of the phase drive currents in the motor's windings. Galvanically-isolated circuits (HE, HS and HE', HS' respectively) effect current feedback from the motor to the inpuT of the amplifier.

Description

Arrangement for controlling a unit that can be aimed, preferably a weapon sight, by means of a three-phase brushless direct-current motor.

This invention relates to an arrangement for controlling a unit that can be aimed, preferably in the form of a weapon sight, by means of a three-phase brushless direct-current motor, using electrical signals (commands) and comprising a motor amplifier for sinusoidal commutation, to which the signals can be fed. The arrangement can thereby be of the type that operates with analogue or digital electrical signals and analogue or digital motor amplifier.

When controlling weapon sights by means of brushless direct-current motors, there is a need to avoid to the greatest possible extent moment variations during .the respective motor revolutions. Such variations have an adverse effect on the setting of the sight. It is generally already known that the said disadvantage can be avoided by the use of so-called sinusoidal commutation.

Proposals for solutions are also already known, for example, by U.S. 5 194786, that utilize sinusoidal commutation in connection with linear amplification circuits that are arranged in parallel and are each allocated a motor winding. Special measures must thereby be taken in order to achieve the linear amplification and in order to avoid interference from and within the equipment.

Reference can also be made in general to the articles "Motor Commutation Techniques; Circuit Cellare INK ®", November 1998 (Chuck Levin) and "Motion Processor-Based Sinusoidal Commutation; Intelligent Motion", of September 1994 (Chuck Levin), both of which discuss in general sinusoidal commutation and the use of Hall elements as position sensors in connection with brushless direct-current motors. In particular with the use of three-phase brushless direct-current motors, there is a desire that the construction of the motor application arrangement can be kept technically simple, while at the same time retaining the requirement for equal moment throughout the whole respective motor revolution. Galvanic isolation must be able to be carried out, while at the same time there must be small current losses. In addition, conventional and well-proven technical components must be able to be used. If so required, there must be no need for special logic for commutation and current feedback. The output stage must be able to cope with temperature ranges of -40° to +85°C and the supply voltage to the direct-current motor must be able to be selected within the range 18-40 V, for example. The amplifier must also be able to drive a direct-current motor with 16 poles with angular velocities of up to 1 rad/sec or more. In addition, the motor amplifier should be able to be constructed from components that provide small external dimensions of the equipment as such.

The object of the invention is to solve all or parts of the abovementioned problem.

The principle characteristic of an arrangement according to the invention is that the windings of the motor are Y-connect'ed and each is connected to a separate pair of drive transistors comprised in a transistor bridge and that the motor amplifier is arranged to generate pulse-width-modulated signals and to control the drive transistors in the bridge using these pulse-width-modulated signals and thereby cause the generation of phase drive currents in the windings of the motor. In^' addition, the invention can be characterised in that galvanically-isolated circuits effect current feedback from the motor to the input of the amplifier.

In further developments of the invention concept, the said analogue or digital input signals or control command signals comprise first and second signals that correspond to two of the phases' sinusoidal moments with 120°^'displacement. The motor amplifier must also be able to operate with a third input signal calculated from the said first and second signals. The current feedback is effected in two phases and the current feedback for the third phase is extrapolated from the abovementioned two first phases. In a preferred embodiment, the motor amplifier must be able to effect pulse-width-modulated signals by means of natural sampling of triangular waves. The motor amplifier thereby generates a pulse-width-modulated signal for the respective phase. A drive circuit connected to the amplifier or belonging to the amplifier, converts the three pulse-width-modulated signals into six pulse-width-modulated signals, each of which controls a drive transistor in the said drive transistor bridge. The drive circuit thereby continually supplies the six pulse- width-modulated signals to the drive transistors in the transistor bridge in accordance with a selected pattern, which can constitute a pre-selected pattern. The pattern can thereby be obtained automatically by means of the natural sampling.

The galvanically-isolated circuits for the current feedback are located on semiconductor-technology components that detect the phase currents. An adjusting function is thereby arranged in order to eliminate or counteract the components' deviations. In addition, the adjustment function can work with three adjusting signals, where a first adjusting signal indicates the phase that is to be controlled at the present time, a second adjusting signal indicates whether the adjustment is to take place upwards or downwards and a third adjustment signal effects the change by increments. The deviation adjustment can thereby be initiated upon starting up and is essentially the same as long as the supply voltage is connected. Alternatively, the adjustment function can work with a storage function, whereby the stored adjustment function can assume the same value until it is changed, whereupon storage takes place of the changed value, and so on.

In an embodiment, the two analogue or digital signals mentioned above form the desired moment for the two first phases. The motor amplifier can thereby effect a comparison between the said two input signals and signals from the current feedback. The latter signals can be adjusted for deviations before the comparison. The amplifier creates fault indication signals between the desired value and the actual value and amplifies the fault indication signals and transmits these to comparators which compare the amplified fault indication signals with a triangular wave and create the pulse-width-modulated signals. ln the respective pairs of transistors concerned, the first transistor can open when a relevant pulse-width, signal goes high. In the same way, the second transistor in the pair of transistors can open when the pulse-width signal goes low. The driving of the transistors in the respective pairs is also arranged to prevent the first and second transistors in the pair conducting at the same time, in order to avoid shorting between the transistors. The driving is also arranged to ensure that the distance between the activations of the first and second transistors in the respective pairs of transistors is small, in order to prevent overtones occurring. Additional characteristics of the invention can be that the arrangement works without commutation logic and/or that it works without current feedback logic.

A number of advantages are obtained by means of the abovementioned. The output stage can handle currents of up to 10 A and is easily modified to handle currents of different sizes. The current-feedback output stage can be implemented in such a way that the moment is proportional to the appropriate input signal or signals. By means of the invention, a. relatively complex six-stage commutation does not need to be used. By means of the invention, it is also possible to arrange for sinusoidal commutation and to control the current or currents in each winding, which paves the way for being able to obtain an even moment. The system can be constructed as a data-processing card with a digital signal processor, for example of the type TMS 320. Low order harmonics and hysteresis can also be eliminated.

DESCRIPTION OF THE FIGURES

A currently preferred embodiment of an arrangement with the significant characteristics of the invention will be described below with reference to the attached figures in which:

Figure 1 shows in outline and in block diagram form the construction of parts of the new motor amplifier, Figure 2 shows in outline and in block diagram form other parts of the new motor amplifier, which in the figure is connected to a direct-current motor that drives a symbolically indicated weapon sight,

Figure 3 shows in schematic form a constructive version of a drive circuit that is incorporated in the. motor amplifier according to Figure 2,

Figure 4 shows in outline schematic form the windings of the direct-current motor connected to a drive transistor bridge, and

Figure 5 shows in diagrammatic form pulse-width-modulated signals for controlling the drive transistors in the bridge according to Figure 4.

In order to control the new amplifier, two input signals are required in accordance with Figure 1 , which are indicated by REF_R and REF_S, which correspond to the desired moment for two first phases in the direct-current motor in question. These input signals are compared with signals IR and IS that are obtained from a current feedback that is described below. Before the said signals are compared with each other, the signals IR and IS are offset. A fault indication between the desired value and the actual value is created from this comparison. The fault indication is amplified and is forwarded to a comparator Kfor each. In the respective comparators the amplified fault indication is compared with a triangular wave Tl and pulse-width-modulated signals PWM_R, PWM_S and PWM_T are formed. The third desired value that is required to drive the third phase is calculated from the abovementioned input signals REF_R and REF_S. In the same way, in connection with the abovementioned' current feedback, the current can be measured of the two first phases IR and IS and the third phase can be calculated. These calculations of the said third phases can be carried out in a known way.

In accordance with what is described below, the current in the motor windings is measured in a known way by current sensors that are based on semiconductor technology and thereby are completely galvanically isolated. The sensors' measurement offset (deviation) can be adjusted by an adjusting function incorporated in the amplifier. The offset adjustment is controlled in accordance with Figure 1 by three signals INC, PHASE R/S and UP/DOWN. The signal PHASE R S controls which phase is to be adjusted, UP/DOWN controls whether the offset is to adjust upwards or downwards and the signal INC changes the offset by increments. The offset can thereby be adjusted at each start-up without being stored. The adjustment is then the same so long as the supply voltage is connected. When it is disconnected, followed by starting up, the same adjustment procedure must be repeated. In an alternative embodiment, a storage function can be utilized, whereby the adjustment is stored. The adjustment is then the same as the stored adjustment at each start up, until it is again changed and stored.

The figure shows filters F and F' for the two input signals. In addition, the said comparators are indicated by K for the creation of PWM_R, K' for the creation of PWM_S and K" for the creation of PWM_T. The triangular wave Tl is generated in a circuit OIK that is controlled by a digital signal SQ that can have a frequency of 19.2 kHz. Figure 1 also contains reception circuits EEPOT and EEPOT, of which the latter is connected at its input to an inverter

INV for the signal PHASE R/S. The circuit also includes summation nodes of a known type. As the functions of such are completely apparent from the above and from the figure, the said nodes will not be described here in greater detail.

In accordance with Figure 2, the signals PWM_R, PWM_S and PWM_T are connected to optocouplers OP, OP', OP" of a known type which galvanically isolate the circuit components according to Figure 1 from the circuit components according to Figure 2. In addition, an actuation signal ENABLE can be connected to the circuit according to Figure 2 via an optocoupler OP"'. The said three pulse-width- modulated signals are applied to a drive circuit DK, which drives the transistors in accordance with what is described below. In the drive circuit DK the said three pulse-width-modulated signals are converted into six pulse-width-modulated signals in accordance with what is described below. The latter six signals are supplied to six drive transistors described below, which are required to drive the motor MOT in the weapon sight VP. The said six transistors are arranged in a drive step DS and signal transmission from the drive circuit DK to the drive step DS is symbolised by the arrow DP. Figure 2 shows symbolically two Hall elements HE, HE' arranged to detect the currents in two of the motor's MOT phases. The Hall elements are connected to current sensors HS and HS' respectively which effect the said signals IR and IS respectively.

In accordance with Figure 3, the drive circuit DS can consist of a known drive circuit, for example a drive circuit HIP 4086, which can handle voltages up to 80 V. Of course, the drive circuit can consist of a different type of drive circuit. The drive circuit drives the control inputs (the gates) on the transistors in each bridge in order to avoid shorting. When a PWM signal goes high, a lower transistor in the phase concerned opens. However, if the PWM signal goes low, the upper transistor in the pair opens. As the function and construction of the circuit as such is already well known, it will not be described here in greater detail, but reference is made to the outline drawing Figure 4. The six transistors shown in Figure 3 (the MOSFET transistors) correspond to the pairs of transistors Q1 and Q4, Q2 and Q5, Q3 and Q6. The said transistors Q1-Q6 are arranged in a bridge connection that has a supply voltage of +28 V. The transistors' gates are indicated by 1 , 2, 3, 4, 5 and 6 respectively. The other ends of the Y-connected motor windings are connected to connection points 7, 8, and 9 respectively between the pairs of transistors Q1 , Q4 and Q2, Q5 and Q3, Q6 respectively. Thus the R-phase is connected to the connection point 7, the S-phase is connected to the connection point 8 and the T- phase is connected to the point 9. Depending upon how the drive circuit is affected by the abovementioned six pulse-width-modulated signals that are supplied to the gates 1 , 2, 3, 4, 5, and 6 respectively, drive or phase currents IRS, 1ST, ITR are obtained, which drive or phase currents are co-ordinated and aligned so that they drive the direct-current motor. The six transistors Q1-Q6 are controlled so that all are continually pulse-width modulated. When the moment is zero, all pulse with 50% pulse ratio and no current passes through the windings.

In accordance with Figure 5, the resultant pulse-width signal that is created between the different phases is completely different to the one that arrived at the drive step DS. Figure 5 shows the three pulse-width-modulated signals that are transmitted to the drive circuit DK. The figure also shows with the three lowest pulse formations how the potential differences arise between the different phases. The three bottom diagrams show here that the resulting signal is sinusoidal. It is hereby essential that the signals are synchronised with each other to some extent, which they are when the signal is created with a triangle wave in accordance with the above. The advantage of the invention is that no actual commutation logic is required. The only logic that is required is the logic for the offset adjustment, which does not need to be included in order for the output stage to work. Nor does the current feedback require any logic. The current sensors provide the correct sign straight away depending upon the direction in which the current passes through the windings.

The invention is not restricted to the embodiment described above for the purpose of exemplification, but can be modified within the scope of the following patent claims.

Claims

1. Arrangement for controlling a unit (VP) that can be aimed, preferably in the form of a weapon sight, by means of a three-phase brushless direct-current motor (MOT), using electrical signals (REF_R, REF_S) and comprising a motor amplifier for sinusoidal commutation, to which the electrical signals can be fed, characterized in that the windings of the motor (MOT) are Y-connected and each is connected to a pair (Q1 , Q4; Q2, Q5; and Q3, Q6 respectively) of drive transistors comprised in a transistor bridge, that the motor amplifier is arranged to generate pulse-width- modulated signals (PWM_R, PWM_S, PWM_T) and with these to control the drive transistors in the bridge and thereby cause the generation of phase drive currents (IRS, 1ST, ITR) in the windings of the motor, and that galvanically-isolated circuits (HE, HS and HE', HS', respectively) effect current feedback (IR, IS) to the input of the amplifier.

2. Arrangement according to Claim 1 , characterized in that the said signals comprise first and second signals that correspond to two of the phases' sinusoidal moments with 120° displacement, that the motor amplification also operates with a third input signal calculated from the first and second signals, and that the current feedback is effected in two phases and the current feedback for the third phase is extrapolated from the two first phases.

3. Arrangement according to Claim 1 or 2, characterized in that the motor amplifier effects pulse-width-modulated signals by means of natural sampling of triangular waves (Tl), that the motor amplifier thereby generates a pulse-width- modulated signal for the respective phase and that a drive circuit (DK) connected to the amplifier or belonging to the amplifier, converts the three pulse-width-modulated signals into six pulse-width-modulated signals that each control a drive transistor in the said drive transistor bridge.

4. Arrangement according to Claim 3, characterized in that the drive circuit (DK) continually supplies the six pulse-width-modulated signals to the drive transistors (Q1-Q6) in the drive transistor bridge in accordance with a selected pattern, for example a pattern automatically controlled by means of the natural sampling.

5. Arrangement according to any one of the preceding claims, characterized in that the galvanically-isolated circuits for the current feedback are based on Hall- technology components (HE, HE') that detect the phase currents, that an adjusting function is arranged to eliminate or counteract the components' deviations and that the adjustment function works with three adjusting signals, where a first adjusting signal indicates the phase that is to be controlled, a second adjusting signal indicates whether the adjustment is to take place upwards or downwards and a third adjustment signal effects the change by increments.

6. Arrangement according to Claim 5, characterized in that the deviation adjustment is initiated upon starting up and is the same as long as the supply voltage is connected.

7. Arrangement according to Claim 5, characterized in that the adjustment function works with a storage function, and that the stored adjustment function assumes the same value until it is changed, whereupon storage takes place of the changed value, and so on.

8. Arrangement according to any one of the preceding claims, characterized in that the two analogue or digital input signals (REF_R, REF_S) form the desired moment for two first phases, that the motor amplifier effects a comparison of the said two input signals with signals (IR and IS respectively) from the current feedback, that before the comparison the latter signals (IR, IS) are deviation-adjusted, that the amplifier creates fault indication signals between the desired value and the actual value and amplifies the fault indication signals and transmits these to comparators (K, K', K") which compare the amplified fault indication signals with a triangular wave and create the pulse-width-modulated signals.

9. Arrangement according to any one of the preceding claims, characterized in that the first transistor (Q1 , Q2 and Q3 respectively) in the pairs of transistors concerned (Q1 , Q4; Q", Q5 and Q3, Q6 respectively) opens when a relevant pulse- width signal goes high and the second transistor (Q4, Q5 and Q6 respectively) in the pair of transistors opens when the pulse-width signal goes low and that the driving of the drive transistors in the respective pair is also arranged to prevent the first and second transistors conducting at the same time in order to avoid shorting through the transistors, and also to keep the distance between the activations small in order to prevent overtones occurring.