CN112050684A - Accurate target practice device and system of electromagnetic gun - Google Patents
Accurate target practice device and system of electromagnetic gun Download PDFInfo
- Publication number
- CN112050684A CN112050684A CN202010968038.3A CN202010968038A CN112050684A CN 112050684 A CN112050684 A CN 112050684A CN 202010968038 A CN202010968038 A CN 202010968038A CN 112050684 A CN112050684 A CN 112050684A
- Authority
- CN
- China
- Prior art keywords
- relay
- circuit
- electrically connected
- electromagnetic gun
- electromagnetic
- Prior art date
- Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
- Pending
Links
- 230000033001 locomotion Effects 0.000 claims abstract description 59
- 239000003990 capacitor Substances 0.000 claims abstract description 58
- 238000007599 discharging Methods 0.000 claims abstract description 30
- 238000004146 energy storage Methods 0.000 claims description 58
- 230000005669 field effect Effects 0.000 claims description 26
- 238000012545 processing Methods 0.000 claims description 17
- 230000008685 targeting Effects 0.000 claims description 6
- 230000005291 magnetic effect Effects 0.000 description 10
- 238000010586 diagram Methods 0.000 description 9
- 238000000034 method Methods 0.000 description 8
- 238000006073 displacement reaction Methods 0.000 description 7
- 238000004458 analytical method Methods 0.000 description 6
- 238000004364 calculation method Methods 0.000 description 5
- 239000008188 pellet Substances 0.000 description 5
- 230000008569 process Effects 0.000 description 4
- 238000012360 testing method Methods 0.000 description 4
- 230000000694 effects Effects 0.000 description 3
- 239000003550 marker Substances 0.000 description 3
- XEEYBQQBJWHFJM-UHFFFAOYSA-N Iron Chemical compound [Fe] XEEYBQQBJWHFJM-UHFFFAOYSA-N 0.000 description 2
- PXHVJJICTQNCMI-UHFFFAOYSA-N Nickel Chemical compound [Ni] PXHVJJICTQNCMI-UHFFFAOYSA-N 0.000 description 2
- 230000001133 acceleration Effects 0.000 description 2
- 238000004422 calculation algorithm Methods 0.000 description 2
- 230000008859 change Effects 0.000 description 2
- 238000006243 chemical reaction Methods 0.000 description 2
- 238000011161 development Methods 0.000 description 2
- 238000003708 edge detection Methods 0.000 description 2
- 238000005516 engineering process Methods 0.000 description 2
- 238000001914 filtration Methods 0.000 description 2
- 230000005484 gravity Effects 0.000 description 2
- 239000003721 gunpowder Substances 0.000 description 2
- 238000005259 measurement Methods 0.000 description 2
- 239000002184 metal Substances 0.000 description 2
- 229910052751 metal Inorganic materials 0.000 description 2
- 230000004044 response Effects 0.000 description 2
- XUIMIQQOPSSXEZ-UHFFFAOYSA-N Silicon Chemical compound [Si] XUIMIQQOPSSXEZ-UHFFFAOYSA-N 0.000 description 1
- 230000009471 action Effects 0.000 description 1
- 230000009286 beneficial effect Effects 0.000 description 1
- 230000033228 biological regulation Effects 0.000 description 1
- 229910017052 cobalt Inorganic materials 0.000 description 1
- 239000010941 cobalt Substances 0.000 description 1
- GUTLYIVDDKVIGB-UHFFFAOYSA-N cobalt atom Chemical compound [Co] GUTLYIVDDKVIGB-UHFFFAOYSA-N 0.000 description 1
- 238000004891 communication Methods 0.000 description 1
- 238000000354 decomposition reaction Methods 0.000 description 1
- 238000012217 deletion Methods 0.000 description 1
- 230000037430 deletion Effects 0.000 description 1
- 238000001514 detection method Methods 0.000 description 1
- 230000005672 electromagnetic field Effects 0.000 description 1
- 238000005265 energy consumption Methods 0.000 description 1
- 239000003302 ferromagnetic material Substances 0.000 description 1
- 238000010304 firing Methods 0.000 description 1
- 230000010354 integration Effects 0.000 description 1
- 229910052742 iron Inorganic materials 0.000 description 1
- 229910052759 nickel Inorganic materials 0.000 description 1
- 230000003071 parasitic effect Effects 0.000 description 1
- 239000002245 particle Substances 0.000 description 1
- 238000003909 pattern recognition Methods 0.000 description 1
- 230000002093 peripheral effect Effects 0.000 description 1
- 238000009417 prefabrication Methods 0.000 description 1
- 239000004576 sand Substances 0.000 description 1
- 239000004065 semiconductor Substances 0.000 description 1
- 229910052710 silicon Inorganic materials 0.000 description 1
- 239000010703 silicon Substances 0.000 description 1
- 238000004088 simulation Methods 0.000 description 1
- 230000001629 suppression Effects 0.000 description 1
Images
Classifications
-
- F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
- F41—WEAPONS
- F41B—WEAPONS FOR PROJECTING MISSILES WITHOUT USE OF EXPLOSIVE OR COMBUSTIBLE PROPELLANT CHARGE; WEAPONS NOT OTHERWISE PROVIDED FOR
- F41B6/00—Electromagnetic launchers ; Plasma-actuated launchers
- F41B6/003—Electromagnetic launchers ; Plasma-actuated launchers using at least one driving coil for accelerating the projectile, e.g. an annular coil
Landscapes
- Engineering & Computer Science (AREA)
- Physics & Mathematics (AREA)
- Electromagnetism (AREA)
- Plasma & Fusion (AREA)
- General Engineering & Computer Science (AREA)
- Control Of Position Or Direction (AREA)
Abstract
The invention discloses an accurate target shooting device and system for an electromagnetic gun, wherein the device comprises: the device comprises a cradle head, a camera unit, a single chip microcomputer, a first driving motor, a second driving motor, an electromagnetic gun barrel, a control circuit, a second driving motor, a third driving motor, a fourth driving motor, a fifth driving motor and a sixth driving motor, wherein the cradle head is horizontally arranged, the camera unit is fixed on the cradle head through a vertically arranged support rod, the single chip microcomputer is electrically connected with the camera unit and used for receiving positioning and distance data and sending a motion instruction, the first driving motor is fixedly connected below the cradle head, the second driving motor is fixedly connected to the upper side of the cradle head, and the electromagnetic gun barrel electrically connected with; the invention has high precision which is more than 90% in 2-3m, and the invention can output larger current than the traditional mode under the same charging voltage by charging the multi-stage capacitors in parallel and discharging in series, thereby generating larger Lorentz force and effectively improving the power of the electromagnetic gun.
Description
Technical Field
The invention belongs to the field of electromagnetic guns, and particularly relates to an accurate target shooting device and an accurate target shooting system for an electromagnetic gun.
Background
The electromagnetic gun is an advanced kinetic energy weapon for killing and killing by utilizing electromagnetic emission technology. It is very important to accurately control the striking point of the electromagnetic gun. With the development of science and technology, electromagnetic guns gradually become novel weapons. Different from the traditional cannon which applies gunpowder gas pressure to the projectile, the electromagnetic cannon accelerates the metal cannonball by utilizing the Lorentz force generated by an electromagnetic field in an electromagnetic system to enable the metal cannonball to reach the kinetic energy required by striking the target, and compared with the traditional cannon which is pushed by gunpowder, the electromagnetic cannon can greatly improve the speed and the range of the projectile. The pellet has the advantages of large electromagnetic driving force, high pellet speed, good pellet stability, good concealment, adjustable pellet emission energy and the like, and is outstanding in the field of military at present, so that the pellet attracts attention of military families in various countries in the world. Electromagnetic guns have become an increasingly important part of future weapon development programs since the early 80 s.
The electromagnetic gun in the prior art charges the energy storage element, outputs instantaneous high current through the discharge of the energy storage element and accelerates through the Lorentz force generated by the coil, but is limited by the charging voltage and the discharging current, the power is limited, and the accuracy of the electromagnetic gun is limited due to the traditional aiming mode.
Disclosure of Invention
The invention aims to provide a device and a system for accurately shooting a target by an electromagnetic gun, which can improve the accuracy of the electromagnetic gun.
The invention adopts the following technical scheme: an accurate target practice device of electromagnetic cannon, comprising:
the cradle head is horizontally arranged,
the camera unit is fixed on the holder through a vertically arranged support rod and is used for positioning and measuring the distance of the target and sending positioning and distance data in real time,
the singlechip is electrically connected with the camera unit and used for receiving positioning and distance data and sending a motion instruction,
the first driving motor is fixedly connected below the holder and used for receiving the motion command and controlling the course angle of the holder according to the motion command,
the second driving motor is fixedly connected to the upper side of the holder, an electromagnetic gun barrel electrically connected with the single chip microcomputer is fixed on the second driving motor and used for receiving the motion command and controlling the pitch angle of the electromagnetic gun barrel according to the motion command so that the electromagnetic gun barrel is aligned to the target,
the single chip microcomputer controls charging and discharging of the charging and discharging circuit through the control circuit, so that the electromagnetic gun can accurately hit a target, the control circuit is connected with the single chip microcomputer, and the charging and discharging circuit is connected with the electromagnetic gun barrel.
Furthermore, the control circuit comprises a conducting circuit and a selecting circuit, the conducting circuit conducts the selecting circuit after receiving the high level signal, the selecting circuit conducts the charging and discharging circuit after receiving the high level signal, and then the capacitor is charged or discharged, so that the emission of the electromagnetic cannon is controlled.
Furthermore, the conduction circuit comprises a first field effect tube, a third relay and a seventh relay, wherein the drain electrode of the first field effect tube is electrically connected with the input end of the seventh relay, the output end of the seventh relay is electrically connected with the input end of the third relay, and the output end of the third relay is connected with the power supply.
Further, the first field effect transistor is electrically connected with the seventh relay through the normally closed contact of the fifth relay.
Further, the selection circuit comprises a second field effect transistor, a sixth relay, a fifth relay and a fourth relay, wherein the drain electrode of the second field effect transistor is electrically connected with the input end of the sixth relay, the output end of the sixth relay is electrically connected with the input end of the fifth relay, the output end of the fifth relay is electrically connected with the input end of the fourth relay, and the output end of the fourth relay is connected with the power supply.
Further, the discharge circuit includes: the first energy storage capacitor, the second energy storage capacitor and the third energy storage capacitor are sequentially connected in series.
Furthermore, the charging circuit consists of a switching circuit and a first energy storage capacitor, a second energy storage capacitor and a third energy storage capacitor which are sequentially connected in parallel;
the switching circuit includes: the input ends of the first relay and the second relay are electrically connected with the output end of the fourth relay, and the output ends of the first relay and the second relay are electrically connected, so that the control signal sent by the selection circuit controls the closing and the opening of the first relay and the second relay to realize the series-parallel switching of the first energy storage capacitor, the second energy storage capacitor and the third energy storage capacitor.
Furthermore, the first field effect tube and the second field effect tube are also electrically connected with a current limiting circuit, and the current limiting is used for protecting the circuit; and the charging circuit and the discharging circuit are electrically connected with rectifier diodes.
An accurate targeting system of an electromagnetic gun, comprising:
the cradle head is horizontally arranged,
the machine vision module is used for positioning and ranging the target and transmitting positioning and distance data in real time,
the processing module is used for receiving positioning and distance data, sending a motion instruction, receiving a starting instruction, controlling the charging and discharging of the capacitor charging and discharging circuit through the power supply control circuit, enabling the electromagnetic gun to accurately hit a target,
the first driving module is fixedly connected below the holder and used for receiving the motion command and controlling the course angle of the holder according to the motion command,
the second driving module is fixedly connected to the upper side of the holder, is fixedly provided with an electromagnetic gun barrel electrically connected with the processing module and is used for receiving the motion command and controlling the pitch angle of the electromagnetic gun barrel according to the motion command so as to enable the electromagnetic gun barrel to align the target and send an alignment signal,
and the starting module is used for receiving the alignment signal and sending a starting instruction to the processing module.
The invention has the beneficial effects that: the invention has high precision which is more than 90% in 2-3m, and the invention can output larger current than the traditional mode under the same charging voltage by charging the multi-stage capacitors in parallel and discharging in series, thereby generating larger Lorentz force and effectively improving the power of the electromagnetic gun.
Drawings
FIG. 1 is a schematic view of the apparatus of the present invention;
FIG. 2 is a schematic diagram of a STM32C8T6 minimum system in the invention;
FIG. 3 is a schematic diagram of an A4988 stepping motor driving module according to the present invention;
FIG. 4 is a schematic diagram of a coil-type electromagnetic transmitter according to the present invention;
FIG. 5 is a relationship between the throw angle θ and the throw angle x when there is air resistance in the present invention;
FIG. 6 is a circuit diagram of a charging circuit and a discharging circuit in accordance with the present invention;
FIG. 7 is a circuit diagram of a control circuit according to the present invention;
FIG. 8 is a block diagram of the targeting system of the present invention.
Wherein: 1. a first drive motor; 2. an electromagnetic gun barrel; 3. a holder; 4. a camera unit; 5. a strut; 6. a second drive motor; 7. a machine vision module; 8. a processing module; 9. a first driving module; 10. a second driving module; and 11, starting a module.
Detailed Description
The present invention will be described in detail below with reference to the accompanying drawings and specific embodiments.
The invention discloses an accurate target practice device of an electromagnetic gun, as shown in figure 1, comprising: the device comprises a cloud deck 3, a camera unit 4, a single chip microcomputer, a first driving motor 1 and a second driving motor 6, wherein the cloud deck 3 is horizontally arranged, the camera unit 4 is fixed on the cloud deck 3 through a support rod 5 which is vertically arranged, the camera unit 4 is used for positioning and ranging targets and sending positioning and distance data in real time, the single chip microcomputer is electrically connected with the camera unit 4 and is used for receiving the positioning and distance data and sending motion instructions, the first driving motor 1 is fixedly connected below the cloud deck 3, the first driving motor 1 is used for receiving the motion instructions and controlling the course angle of the cloud deck 3 according to the motion instructions, the second driving motor 6 is fixedly connected on the upper side of the cloud deck 3, an electromagnetic gun barrel 2 which is electrically connected with the single chip microcomputer is fixed on the second driving motor 6, the second driving motor 6 is used for receiving the motion instructions and controlling the pitch angle of the electromagnetic gun barrel 2 according to the motion instructions, the target is aimed at by the electromagnetic gun barrel 2, wherein the single chip microcomputer controls charging and discharging of the charging and discharging circuit through the control circuit, so that the electromagnetic gun can accurately hit the target, the control circuit is connected with the single chip microcomputer, and the charging and discharging circuit is electrically connected with the electromagnetic gun barrel 2.
The control circuit comprises a conduction circuit and a selection circuit, the conduction circuit conducts the selection circuit after receiving the high level signal, the selection circuit conducts the charge-discharge circuit after receiving the high level signal, and then the capacitor is charged or discharged, so that the emission of the electromagnetic gun is controlled. The conduction selection bit of the conduction circuit is connected with the single-chip IO port PD8, and the charge and discharge selection bit of the charge and discharge circuit is connected with the single-chip IO port PD 9.
The conduction circuit comprises a first field effect transistor, a third relay and a seventh relay, the drain electrode of the first field effect transistor is electrically connected with the public end of the fifth relay, the output end of the seventh relay is electrically connected with the input end of the third relay, and the output end of the third relay is connected with the power supply. The control signal controls the on-resistance of the first field effect transistor, and further controls the on-off of the third relay and the seventh relay so as to control the on-off of the circuit.
The selection circuit comprises a second field effect transistor, a sixth relay, a fifth relay and a fourth relay, wherein the drain electrode of the second field effect transistor is electrically connected with the input end of the sixth relay, the output end of the sixth relay is electrically connected with the input end of the fifth relay, the output end of the fifth relay is electrically connected with the input end of the fourth relay, and the output end of the fourth relay is connected with the power supply. The control signal controls the on-resistance of the second field effect transistor, further controls the on-off of the fifth relay and the sixth relay to switch between the charging circuit and the discharging circuit, and controls the on-off of the fourth relay to send a control signal to the capacitor charging and discharging circuit.
The drain electrode of the second field effect transistor is electrically connected with the input end of the fifth relay, the normally closed contact of the fifth relay is electrically connected with the public end of the seventh relay, and the normally open contact of the fifth relay is electrically connected with the public end of the third relay. And the on-resistance of the second field effect transistor is controlled to control the on-off of the fifth relay so as to connect the circuit current to the common end of the third relay or the seventh relay.
The discharge circuit includes: the first energy storage capacitor, the second energy storage capacitor and the third energy storage capacitor are sequentially connected in series. The charging circuit consists of a switching circuit and a first energy storage capacitor, a second energy storage capacitor and a third energy storage capacitor which are sequentially connected in parallel; the switching circuit includes: the input ends of the first relay and the second relay are electrically connected with the output end of the fourth relay, and the output ends of the first relay and the second relay are electrically connected, so that the control signal sent by the selection circuit controls the closing and the breaking of the first relay and the second relay to realize the series-parallel switching of the first energy storage capacitor, the second energy storage capacitor and the third energy storage capacitor. The positive poles of the first relay and the second relay are electrically connected with the fourth relay, the negative poles of the first relay and the second relay are connected with the negative pole of the control circuit, and the control signal sent by the control circuit controls the closing and the opening of the first relay and the second relay so as to realize the switching of the discharging circuit and the charging circuit.
The first field effect transistor and the second field effect transistor are also electrically connected with a current limiting circuit, the anode of the first current limiting resistor is electrically connected with the grid electrode of the first field effect transistor, the anode of the second current limiting resistor is electrically connected with the grid electrode of the second field effect transistor, and the current limiting circuit is used for protecting the circuit.
The charging circuit and the discharging circuit are respectively electrically connected with rectifier diodes, namely a first energy storage capacitor, a second energy storage capacitor and a third energy storage capacitor which are sequentially connected in series form three energy storage circuits respectively with a first rectifier diode, a second rectifier diode and a third rectifier diode, wherein the anode of the first energy storage capacitor is electrically connected with the cathode of the first rectifier diode, the cathode of the first energy storage capacitor is electrically connected with the normally closed contact of the first relay, the anode of the second energy storage capacitor is electrically connected with the cathode of the second rectifier diode, the cathode of the second energy storage capacitor is electrically connected with the normally closed contact of the second relay, the anode of the third energy storage capacitor is electrically connected with the cathode of the third rectifier diode, the cathode of the third energy storage capacitor is electrically connected with the common end of the second relay, and a control signal sent by the control circuit controls the first relay and the second relay to be closed and opened so as to realize the series-parallel connection of the first energy storage circuit, the second energy storage circuit and the third energy storage circuit And (4) performing combined switching.
A first rectifying diode, a second rectifying diode, the positive pole of the third rectifier diode is connected with the normally closed end of the sixth relay, the negative pole of the first energy storage capacitor is connected with the normally closed end of the first relay, the negative pole of the first energy storage capacitor is electrically connected with the negative pole of the first rectifier diode and the normally opened end of the first relay, the positive pole of the second energy storage capacitor is electrically connected with the negative pole of the second rectifier diode, the negative pole of the second energy storage capacitor is electrically connected with the common end of the first relay and the normally closed end of the second relay, the negative pole of the third energy storage capacitor is connected with the common end of the second relay, the positive pole of the third energy storage capacitor is electrically connected with the negative pole of the third rectifier diode, the positive pole of the third energy storage capacitor is connected with the normally opened end of the sixth relay, the first relay is connected with the power supply of the second relay in parallel, and the negative pole of the first energy storage capacitor is connected.
When the charging circuit and the discharging circuit are switched, the first energy storage circuit, the second energy storage circuit and the third energy storage circuit are connected in series to discharge, and when the switching circuit is switched to be connected in parallel, the first energy storage circuit, the second energy storage circuit and the third energy storage circuit are connected in parallel to charge.
The invention also discloses an accurate target shooting system of the electromagnetic gun, as shown in fig. 8, comprising: the device comprises a machine vision module 7, a processing module 8, a first driving module 9, a second driving module 10 and a starting module 11, wherein the machine vision module 7 is used for positioning and ranging a target and sending positioning and distance data in real time, the processing module 8 is used for receiving the positioning and distance data and sending a motion instruction, the processing module 8 is also used for receiving the starting instruction and controlling the charging and discharging of a capacitor charging and discharging circuit through a power supply control circuit so that the electromagnetic gun can accurately hit a target, the first driving module 9 is fixedly connected below a tripod head 3, the first driving module 9 is used for receiving the motion instruction and controlling the course angle of the tripod head 3 according to the motion instruction, the second driving module 10 is fixedly connected to the upper side of the tripod head 3, an electromagnetic gun barrel 2 electrically connected with the processing module 8 is fixed on the second driving module 10, the second driving module 10 is used for receiving the motion instruction and controlling the pitch angle of the electromagnetic gun barrel 2 according to the motion instruction, so that the electromagnetic gun barrel 2 is aligned to the target and sends an alignment signal, and the starting module 11 is used for receiving the alignment signal and sending a starting instruction to the processing module 8.
The system is provided with an STM32C8T6 microcontroller, after the whole system is powered on, the single chip microcomputer is started to initialize a serial port, after prefabrication is finished, the single chip microcomputer sends a series of responses to the single chip microcomputer, then the single chip microcomputer reads memory data and sends the memory data to an LCD for display, then the single chip microcomputer enters key scanning, when the single chip microcomputer is effectively pressed down, the mode is switched, 4OpenMV data of a camera unit is read and sent to a started STM32C8T6 chip, a driving motor is controlled to rotate, a mark target is tracked and identified, charging energy storage of an electromagnetic gun is started at the same time, after the energy storage is finished, the STM32C8T6 chip controls a relay to be disconnected, and after the target is rightly.
For the selection of the single chip microcomputer, the STM32F103C8T6 single chip microcomputer is selected in the invention. The STM32F103xx enhanced family is designed by the mindset semiconductor group, uses a high performance arm port-M332 bit RISC core, operating frequency 72MHz, built-in high speed memory (high 128 kbyte flash and 20 kbyte SRAM), rich enhanced I/O ports and peripherals coupled to both APB buses. All models of devices contain 2 ADCs of 12 bits, 3 universal 16-bit timers and a PWM timer, and also contain standard and advanced communication interfaces: up to 2I 2C and SPI, 3 USART and 1 USB, 1 CAN. STM32F103ZET6 cost performance is higher, and the configuration is abundant nimble, and the biggest integration is integrated, and the real-time performance is excellent, easily develops and the low-power consumption. The single chip microcomputer has extremely strong calculation processing capacity and is suitable for an electromagnetic gun tracking system needing quick response. According to the invention, STM32F103ZET6 is used as a main control chip, the hardware requirement of the system is met, the method is closer to reality, the precision is greatly improved, and a minimum system schematic diagram is shown in FIG. 2.
For the selection of the camera unit 4, the invention selects the OpenMV camera for ranging, the camera has high-speed operation and high accuracy, is provided with an STM32F7 series processor, can process the obtained data in real time, sends the simplified data to the microcontroller, saves resources, is less interfered by the external environment, and can accurately measure the distance.
For the selection of the first driving motor 1 and the second driving motor 6, the stepping motor is selected for the present invention. The stepping motor is an open-loop control element motor which converts an electric pulse signal into angular displacement or linear displacement. In the case of non-overload, the rotation speed and the stop position of the motor only depend on the frequency and the pulse number of the pulse signal and are not influenced by load change. Its rotation is performed step by step at a fixed angle. The angular displacement can be controlled by controlling the number of pulses, so that the aim of accurate positioning is fulfilled; meanwhile, the rotating speed and the rotating acceleration of the motor can be controlled by controlling the pulse frequency, so that the purpose of speed regulation is achieved, the position angle can be accurately adjusted, and the device is suitable for an accurate system.
The motor driving module adopts an A4988 stepping motor driving module. A4988 is a DMOS micro-step driver with converter and overcurrent protection, which can operate bipolar stepping motor in full, half, 1/4, 1/8 and 1/16 stepping modes, and the output drive performance can reach 35V and +/-2V, and A4988 includes a constant off-time current regulator which can work in slow or mixed attenuation mode. The schematic diagram is shown in fig. 3.
The electromagnetic gun in the invention is a coil gun, the schematic diagram of which is shown in fig. 4, a plurality of driving coils are fixed and are respectively fed with current i1, the emitter coil carries current i2, i1 and i2 are opposite, and the two coils repel each other. Assuming that the self-inductance of each driving coil is L1, the self-inductance of the emitter coil is L2, and the mutual inductance between the driving coils and the emitter coil is M, the magnetic energy calculation of the single driving coil and the emitter coil is shown in formula (1):
calculation of the force exerted by a single drive coil on the emitter is shown in equation (2)
When M' (x) changes positive and negative (the two coils move away from each other from one another), the direction of the force changes, so that when i1, i2 are reversed and the emitter is located to the right of the center of drive coil 1, drive coil 2 is either not energized first, or its current is made to be in the same direction as i2, and when the emitter has just passed right over the center of drive coil 2, drive coil 2 is then energized with a current … … that is opposite to i1, whereupon the emitter is accelerated by the series of drive coils.
Energy analysis and parameter calculation
The electromagnetic gun barrel (2) is regarded as a load of a power supply, and because an armature and an emitter move in the emission process, an electromagnetic emitter of the electromagnetic gun barrel (2) can be regarded as the series connection of an inductor lg (x) and a resistor Rg (x) which change along with the position x of the emitter and an armature resistor Rs, so that the inductor and the resistor of the load are respectively
R in the formula (3)0，L0The parasitic resistance and the inductance of the loop connection line are small and can be ignored generally; l 'g (x), R' g (x) are the derivatives of coil inductance and resistance to x, i.e. inductance and resistance per unit length of track, respectively called the inductance gradient and resistance gradient of the track.
The voltage of the power circuit end is expressed by formula (4):
in the formula (4), t represents time, usIs the voltage drop across the armature; if u is ignoredsAnd track resistance and various energy losses, the power output is given by the equation (5)
Energy calculation of the electromagnetic transmitter system is shown in equation 6
Em is system magnetic energy, EkM and V are the kinetic energy, mass and speed of the accelerated components respectively, and the power output power of the power supply should be equal to the system energy increase rate dE/dt, so taking m to 5g, Vm to 5m/s (the exit speed that the electromagnetic gun tries to reach at present), I to 6A (amplifying the current available at present), L' g (X) to 1 μ H/m, t to 40ms, and X to 3 m.
Air resistance analysis
Air resistance is always present, sometimes negligible, and sometimes not negligible. Generally, the air resistance is considered to be proportional to the velocity to the power n, and is specified as follows:
in formula (7): c is the air resistance coefficient, which is usually an experimental value, and it is related to the characteristic area (windward area) of the object, the smoothness of the object, and the overall shape; rho is air density, and can be monitored in field; s is the characteristic area of the object; v is the relative movement velocity of the object and the air; n is an air resistance index (only the case where n is 2 is considered herein, which will be described shortly). As can be seen from the above, the magnitude of the air resistance is normally proportional to the air resistance coefficient and the windward area, and proportional to the velocity square.
Analysis of skew projectile motion
The oblique throwing motion is a motion of throwing the object at an initial speed of a certain magnitude from a direction at a certain angle (not 0) to the horizontal direction. The 'oblique projectile motion in the high school physics category' is that the motion trail is the parabolic uniform velocity curve motion under the action of gravity. According to the motion independence principle, the oblique projectile motion can be regarded as the combined motion of uniform linear motion in the horizontal direction and vertical projectile motion in the vertical direction, so that the processing is convenient.
Since the up-throw motion and the down-throw motion are similar, only the oblique up-throw motion is studied and processedThe oblique upward throwing motion is simply referred to as oblique throwing motion. By analyzing the oblique projectile motion process, the speed v in the horizontal direction can be known from Newton's second law1Velocity v in the vertical direction2The equation for the displacement x in the horizontal direction and the equation for the displacement y in the vertical direction are:
v1＝v0×cosθ；
v2＝v0×sinθ-gt；
x＝v0×t×cosθ；
y＝v0×t×sinθ-gt2/2 (8)
v from equation (8)2Can be obtained as v2When the ball reaches the highest point, t is equal to v0X sin theta/g, so the ball movement time is T2 x v0Xsin θ/g. The highest point that the small ball can reach is called shooting height, and the horizontal displacement from the throwing point to the landing point is called shooting range. Considering the inclined projectile motion with the initial height of 0, the decomposition speed, the maximum height equation and the horizontal range equation which can be reached by the inclined projectile motion are as follows:
h＝v0 2×sin2θ/(2g)
S＝v0 2×sin2θ/g (9)
wherein v is0In order to throw out the speed, theta is the included angle between the speed and the horizontal plane, and g is the gravity acceleration. As can be seen from equation (9), when θ is 45 °, 2 θ is 90 °, and sin2 θ has the maximum value, so that the throw distance is the farthest when the inclination angle of the skew motion is 45 °.
Inclined projectile motion considering air resistance
For objects reduced to particles, the skew motion is a common form of motion. The process of the movement of the mass center of the oblique projectile motion of the object is a main mechanical index. In a rectangular coordinate system, m represents the mass of the object, x, y represent displacements in2 directions, v, respectively, in consideration of air resistancex、vyRepresenting the velocity components in2 directions, Fx、FyRepresenting 2 components of the force, the discussion about the resolution of the force follows from newton's law:
Fx＝-Kvx 2
Fy＝-mg-Kvy 2 (10)
k in equation (10) is related to S, C and ρ in equations (3) to (7), and only the case where n is 2 is considered here because the air resistance is generally proportional to the square of the velocity in real life.
Simulation experiment under air resistance
x＝mv0cosθ/n(m-Ktv0cosθ)
In the formula (11), g is 10, K is 0.1, m is 1, v0Is 1 and t is 5. y is the height with landing time of 5 seconds, and data is ignored. As can be seen from the particular scenario in the formula depicted in fig. 5, when air resistance is considered, y has a maximum value, approaching 20, when taken around 0.95.
Therefore, when the initial height is 0 and the air resistance coefficient K is 0.1, the throw distance y is the largest when the throw angle is about 55 degrees (theta is 0.95).
From the above description, the electromagnetic gun is a simple electromagnetic driving structure, but it can be roughly regarded as the shell throwing, so the larger the launching angle is, the larger the force of instant push is, so the force effect when the inclination angle of the inclined throwing motion is about 45 ° in the ideal case is not necessarily the best, according to the above description, it can be obtained: when the muzzle angle is 35-45 degrees, the better the effect of shell launching, namely when the electromagnetic gun is at fixed launching height h, theta belongs to (35 degrees, 45 degrees), the firing range S is the largest, and the energy consumption is the smallest.
The invention pushes the cannonball by Lorentz force to achieve the effect of shooting the cannonball. From the lorentz force equation: the kinetic energy obtained by the cannonball is related to the magnetic field intensity and the current intensity according to the BIL, and the kinetic energy is represented by a capacitance electric energy formula: when W is 1/2CU and the law of conservation of energy, the higher the voltage, the larger the magnetic energy converted, and the larger the initial velocity obtained by the corresponding shell. Calculated from the formula of the magnitude of the magnetic field: H-nI in this equation, I is the current through the solenoid and n is the number of solenoid turns per unit length, it can be seen that the magnitude of the magnetic field is related to the number of coil turns and the current. But when the number of turns is increased, the resistance is also increased, and the current is reduced; so reasonable voltage and coil turn number size need to be selected.
Because the emission is controlled by the discharge of the capacitor, the instantaneous current is extremely large, and the maximum current borne by the silicon controlled switch is only 0.8A, so the loop switch selects a relay.
Under a certain number of turns of the coil, the analysis of the circuit is selected:
considering that the increasing voltage reaches the launching condition, the voltage needs more than 100v, the high-voltage operation has certain danger, the increasing voltage can proportionally increase the speed of the cannonball in a certain range, but the voltage can be expected to be increased to be very high under the condition that other parameters are not changed, and according to the capacitance discharge characteristic, after the cannonball passes through the middle point of the coil, the large current still passes through the coil, the serious reverse pull is generated, the speed of the cannonball is reduced, and the efficiency is influenced, so the scheme of increasing the circuit current is adopted.
Firstly, the number of turns of the coil is 500, namely n is 500, and the stress of the constant-voltage 15V discharge ferromagnetic material is shown as the formula (12):
and (3) converting the capacitance discharge formula I into U/Z into 2 pi fCU and a formula of the magnetic field magnitude: when H is substituted into formula (12), the current in the circuit is 5A or more, and the emission condition is calculated, so 8 polar capacitors with specification of 50V 4700 μ F are selected for charging and discharging.
Tracking procedure for marker targets
In image processing and pattern recognition, information of a mark target in a picture is often required to be acquired, the acquired picture is firstly subjected to graying processing, then edge detection, conversion into a binary image and other operations are performed, and the edge detection is required to perform the following steps:
1) and converting the color image into a gray image, and denoising the image by using Gaussian smooth filtering.
2) And filtering the image by using the first-order differential of Gaussian to obtain a better gradient edge.
3) And carrying out non-maximum suppression and hysteresis threshold processing on the gradient to obtain the edge of the image.
4) Edges are detected and connected using a double-threshold algorithm. Setting 2 thresholds for detecting strong edges and weak edges; and when the threshold value of the detected edge point is higher than the threshold value of the strong edge, outputting the edge point as the strong edge, when the threshold value of the detected edge point is between the threshold value of the strong edge and the threshold value of the weak edge, considering the detected edge point as the weak edge point, and when and only when the weak edge is connected with the strong edge, outputting the weak edge, and after the steps, detecting the edge of the image and outputting the edge.
The electromagnetic cannon is a device which generates extremely large current by capacitor instant discharge, and the current generates an ultra-strong magnetic field through a coil, so that the cannonball (iron, cobalt and nickel) is sucked out. Energy conversion: electric → magnetic → kinetic energy. In order to enable the cannonball to reach a designated position and require the Lorentz force F of the device to meet the condition, the invention selects a method for increasing current to meet the requirement of the theme, and the core transmitting part of the device is formed by connecting two same circuits in parallel. The idea of parallel charging and series discharging is adopted to provide charging efficiency and discharging current, the capacitors are connected in parallel and discharge instantly, the diodes are rectified, so that the current in the whole circuit can reach more than 5A instantly, and the current is supplied to a muzzle coil of an electromagnetic gun, so that the magnetic field of the muzzle coil reaches the transmitting condition.
The invention mainly comprises that a microcontroller judges whether an electromagnetic gun is fully charged or not by detecting a voltage value acquired by an ADC module, and simultaneously receives data transmitted by OpenMV to drive a stepping motor to enable a muzzle to be aligned with a target. And when the OpenMV finds the identification target, the distance from the target surface is obtained by detecting the area of the color block of the target surface through a series of algorithms and is transmitted to the microcontroller, and the microcontroller controls the electromagnetic relay to be switched on and off to emit the cannonball.
Example 1
OpenMV is detected within 2m to 3m, and the position of the marker target is varied within 2m to 3m, and tracking and ranging are performed using the position. For the electromagnetic gun, the voltage and the current of the capacitor are set by controlling the power-on and power-off time, so that the emission distance is controlled. And finally, transmitting the generated data to a single chip microcomputer, and calculating by the single chip microcomputer to obtain corresponding data, controlling the rotation angle of the cradle head 3 and transmitting the cannonball.
The camera ranging was tested by placing the marker targets 200cm, 225cm, 250cm, 275cm, 300cm from the initial position of the camera unit 4, respectively, and the test results are shown in the following table:
| number of measurements | Actual distance (cm) | Measuring distance (cm) | Deviation (cm) | Precision (%) |
| For the first time | 200 | 201 | 1 | 99.5 |
| For the second time | 225 | 227 | 2 | 99.1 |
| The third time | 250 | 255 | 5 | 98.0 |
| Fourth time | 275 | 283 | 8 | 97.1 |
| Fifth time | 300 | 313 | 13 | 95.7 |
And (4) conclusion: along with the distance becomes far away, the camera precision is lower and lower, but within 300cm the error almost maintains within 5%, can comparatively accurate record distance.
Distance measurement test
| Number of times | Input angular distance | Time of use | Actual angular distance | Deviation of | Whether it is qualified or not |
| 1 | 30°240cm | 12s | 29.7°231cm | 0.3°9cm | Qualified |
| 2 | 40°240cm | 15.4s | 40° |
0°13cm | Qualified |
| 3 | 40°270cm | 16.3s | 40.3°294cm | 0.3°24cm | Qualified |
| 4 | 50°270cm | 17.1s | 50.4°302cm | 0.4°32cm | Qualified |
And (4) conclusion: the angle control is more accurate, but the distance deviation is larger, and the method is basically qualified.
Basic requirement testing
Testing of exertion part
The exertion part is that a ring target is placed at any position in a specified range, after one key is started, the electromagnetic gun automatically searches for a target and shoots the ring target, the number of the shot ring target rings is counted, and the completion time is less than or equal to 30 s.
| Serial number | Distance of placing angle | Time taken(s) | Average score | Whether it is qualified or not |
| 1 | |
21 | 6.1 | Qualified |
| 2 | |
7 | 4.3 | Qualified |
And (4) conclusion: the system can basically complete the play part.
Error analysis
Through analysis, the main error of the system comes from the collection of the camera image, on one hand, the influence of the environment is large when the image is collected, so that the condition of edge deletion exists when the identification target is identified. On the other hand, because the camera is fixed, can not be all the time with directly facing the target surface, when cloud platform 3 rotated, the image of gathering was the ellipse for there is certain error in the position acquisition of target center.
Conclusion
Through experimental detection, the device can well finish various task indexes, and the precision is up to more than 90% within 2-3 m.
Claims (9)
1. The utility model provides an accurate device of shooing of electromagnetism big gun which characterized in that includes:
a cloud deck (3) which is arranged horizontally,
the camera unit (4) is fixed on the holder (3) through a support rod (5) which is vertically arranged and is used for positioning and ranging the target and sending positioning and distance data in real time,
the singlechip is electrically connected with the camera unit (4) and is used for receiving positioning and distance data and sending a motion instruction,
the first driving motor (1) is fixedly connected below the pan-tilt (3) and is used for receiving the motion instruction and controlling the course angle of the pan-tilt (3) according to the motion instruction,
a second driving motor (6) which is fixedly connected with the upper side of the holder (3), is fixedly provided with an electromagnetic gun barrel (2) which is electrically connected with the singlechip and is used for receiving the motion instruction and controlling the pitch angle of the electromagnetic gun barrel (2) according to the motion instruction so that the electromagnetic gun barrel (2) is aligned to the target,
the single chip microcomputer controls charging and discharging of the charging and discharging circuit through the control circuit, so that the electromagnetic gun can accurately hit a target, the control circuit is connected with the single chip microcomputer, and the charging and discharging circuit is connected with the electromagnetic gun barrel (2).
2. The accurate target practice device of an electromagnetic gun according to claim 1, wherein the control circuit comprises a conduction circuit and a selection circuit, the conduction circuit conducts the selection circuit after receiving the high level signal, and the selection circuit conducts the charge-discharge circuit after receiving the high level signal, so as to charge or discharge the capacitor, thereby controlling the emission of the electromagnetic gun.
3. The accurate target practice device of an electromagnetic cannon according to claim 2, wherein the conduction circuit comprises a first field effect transistor, a third relay, and a seventh relay, wherein a drain of the first field effect transistor is electrically connected with an input terminal of the seventh relay, an output terminal of the seventh relay is electrically connected with an input terminal of the third relay, and an output terminal of the third relay is connected with a power supply.
4. The accurate targeting device for an electromagnetic cannon according to claim 3, wherein the first field effect transistor is electrically connected with the seventh relay through a normally closed contact of the fifth relay.
5. An electromagnetic gun accurate targeting device according to any one of claims 2-4, characterized in that the selection circuit comprises a second field effect transistor, a sixth relay, a fifth relay, and a fourth relay, the drain of the second field effect transistor is electrically connected with the input terminal of the sixth relay, the output terminal of the sixth relay is electrically connected with the input terminal of the fifth relay, the output terminal of the fifth relay is electrically connected with the input terminal of the fourth relay, and the output terminal of the fourth relay is connected with the power supply.
6. An electromagnetic gun precision targeting device according to claim 5, characterized in that the discharge circuit comprises: the first energy storage capacitor, the second energy storage capacitor and the third energy storage capacitor are sequentially connected in series.
7. The accurate target practice device of an electromagnetic gun according to claim 6, wherein the charging circuit is composed of a switching circuit and a first energy storage capacitor, a second energy storage capacitor and a third energy storage capacitor which are connected in parallel in sequence;
the switching circuit includes: the input ends of the first relay and the second relay are electrically connected with the output end of the fourth relay, and the output ends of the first relay and the second relay are electrically connected, so that the control signal sent by the selection circuit controls the closing and the opening of the first relay and the second relay to realize the series-parallel switching of the first energy storage capacitor, the second energy storage capacitor and the third energy storage capacitor.
8. The accurate targeting device for the electromagnetic cannon according to claim 7, wherein the first field effect tube and the second field effect tube are electrically connected with a current limiting circuit, and the current limiting circuit is used for protecting the circuit; and the charging circuit and the discharging circuit are electrically connected with rectifier diodes.
9. The utility model provides an accurate target practice system of electromagnetism big gun which characterized in that includes:
a cloud deck (3) which is arranged horizontally,
a machine vision module (7) for positioning and ranging the target and transmitting the positioning and distance data in real time,
the processing module (8) is used for receiving positioning and distance data, sending a motion instruction, receiving a starting instruction, controlling the charging and discharging of the capacitor charging and discharging circuit through the power supply control circuit, enabling the electromagnetic gun to accurately hit a target,
the first driving module (9) is fixedly connected below the pan-tilt (3) and used for receiving the motion instruction and controlling the course angle of the pan-tilt (3) according to the motion instruction,
the second driving module (10) is fixedly connected to the upper side of the holder (3), is fixedly provided with an electromagnetic gun barrel (2) which is electrically connected with the processing module (8) and is used for receiving the motion instruction and controlling the pitch angle of the electromagnetic gun barrel (2) according to the motion instruction so that the electromagnetic gun barrel (2) is aligned with the target and sends an alignment signal,
and the starting module (11) is used for receiving the alignment signal and sending a starting instruction to the processing module (8).
Priority Applications (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| CN202010968038.3A CN112050684A (en) | 2020-09-15 | 2020-09-15 | Accurate target practice device and system of electromagnetic gun |
Applications Claiming Priority (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| CN202010968038.3A CN112050684A (en) | 2020-09-15 | 2020-09-15 | Accurate target practice device and system of electromagnetic gun |
Publications (1)
| Publication Number | Publication Date |
|---|---|
| CN112050684A true CN112050684A (en) | 2020-12-08 |
Family
ID=73602945
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| CN202010968038.3A Pending CN112050684A (en) | 2020-09-15 | 2020-09-15 | Accurate target practice device and system of electromagnetic gun |
Country Status (1)
| Country | Link |
|---|---|
| CN (1) | CN112050684A (en) |
Cited By (2)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| CN113899243A (en) * | 2021-10-13 | 2022-01-07 | 广东海洋大学 | Intelligent electromagnetic propulsion device and method |
| CN113932649A (en) * | 2021-09-30 | 2022-01-14 | 北京化工大学 | Automatic aiming system based on CV and AI algorithm and electromagnetic gun |
Citations (6)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| US4934243A (en) * | 1986-10-03 | 1990-06-19 | The Secretary Of State For Defence In Her Britannic Majesty's Government Of The United Kingdom Of Great Britain And Northern Ireland | Electromagentic projectile launcher |
| US5458043A (en) * | 1994-07-28 | 1995-10-17 | The United States Of America As Represented By The Secretary Of The Air Force | Battery charging capacitors electromagnetic launcher |
| US20160245613A1 (en) * | 2014-05-20 | 2016-08-25 | The Boeing Company | Electromagnetic Muzzle Velocity Controller and Booster for Guns |
| CN110631414A (en) * | 2019-09-26 | 2019-12-31 | 南京大学 | Simulated electromagnetic gun control device for accurate guidance of shells |
| CN110631415A (en) * | 2019-10-25 | 2019-12-31 | 南京邮电大学 | Automatic target shooting control system of electromagnetic gun based on voltage detection |
| CN110763081A (en) * | 2019-11-29 | 2020-02-07 | 湖北工业大学 | Electromagnetic curved shooting gun device capable of accurately controlling striking position |
-
2020
- 2020-09-15 CN CN202010968038.3A patent/CN112050684A/en active Pending
Patent Citations (6)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| US4934243A (en) * | 1986-10-03 | 1990-06-19 | The Secretary Of State For Defence In Her Britannic Majesty's Government Of The United Kingdom Of Great Britain And Northern Ireland | Electromagentic projectile launcher |
| US5458043A (en) * | 1994-07-28 | 1995-10-17 | The United States Of America As Represented By The Secretary Of The Air Force | Battery charging capacitors electromagnetic launcher |
| US20160245613A1 (en) * | 2014-05-20 | 2016-08-25 | The Boeing Company | Electromagnetic Muzzle Velocity Controller and Booster for Guns |
| CN110631414A (en) * | 2019-09-26 | 2019-12-31 | 南京大学 | Simulated electromagnetic gun control device for accurate guidance of shells |
| CN110631415A (en) * | 2019-10-25 | 2019-12-31 | 南京邮电大学 | Automatic target shooting control system of electromagnetic gun based on voltage detection |
| CN110763081A (en) * | 2019-11-29 | 2020-02-07 | 湖北工业大学 | Electromagnetic curved shooting gun device capable of accurately controlling striking position |
Non-Patent Citations (2)
| Title |
|---|
| 宫瑶等: "基于STM32的模拟电磁曲射炮设计", 《软件》 * |
| 龚浩岳等: "基于串并联切换的超级电容充电法", 《华北电力技术》 * |
Cited By (2)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| CN113932649A (en) * | 2021-09-30 | 2022-01-14 | 北京化工大学 | Automatic aiming system based on CV and AI algorithm and electromagnetic gun |
| CN113899243A (en) * | 2021-10-13 | 2022-01-07 | 广东海洋大学 | Intelligent electromagnetic propulsion device and method |
Similar Documents
| Publication | Publication Date | Title |
|---|---|---|
| CN112050684A (en) | Accurate target practice device and system of electromagnetic gun | |
| CN110314349B (en) | Badminton picking robot and control method thereof | |
| CN111475958A (en) | Electromagnetic curved fire gun design method based on machine vision | |
| CN203829610U (en) | Electromagnetic type ball pitching machine | |
| CN105185208A (en) | Electromagnetic cannon experiment device | |
| CN102489007A (en) | Intelligent golf, terminal system and data acquisition and analysis method | |
| CN109737805A (en) | It is a kind of that magnetic artillery experimental provision is accelerated based on the multistage of STM32 control | |
| CN204594329U (en) | Small ball electromagnetic ejection system | |
| CN110631414A (en) | Simulated electromagnetic gun control device for accurate guidance of shells | |
| CN210321396U (en) | Man-machine confrontation training device based on artificial intelligence | |
| CN206601068U (en) | A kind of bow and arrow training aids | |
| CN110763081A (en) | Electromagnetic curved shooting gun device capable of accurately controlling striking position | |
| CN111912289A (en) | Self-propelled electromagnetic gun control system, method and device | |
| CN109633202A (en) | A kind of double net target projectile-velotity detecting systems and its test method | |
| CN205028552U (en) | Novel magnetic artillery experiment device | |
| CN206688193U (en) | A kind of solar powered basketball shooting counts score detection means automatically | |
| CN211626251U (en) | Automatic simulation electromagnetism of aiming shooting curved cannon circuit | |
| CN112923790A (en) | Intelligent mobile target shooting electromagnetic device based on computer vision and control method | |
| CN209726919U (en) | It is a kind of that magnetic artillery experimental provision is accelerated based on the multistage of STM32 control | |
| CN208238634U (en) | Laser ranging night sight and anti-unmanned plane catch rifle with net | |
| CN110533995A (en) | A kind of applied mathematics probability statistics compiling device | |
| CN113368488B (en) | Virtual table tennis bat and force feedback method and system thereof | |
| CN110470178B (en) | Real-bullet-free target aiming training system and training method based on simulated recoil | |
| CN113008073B (en) | High-precision shooting training guidance system | |
| CN204614318U (en) | A kind of electromagnetic launch experimental provision and electromagnetic induction thereof produce circuit |
Legal Events
| Date | Code | Title | Description |
|---|---|---|---|
| PB01 | Publication | ||
| PB01 | Publication | ||
| SE01 | Entry into force of request for substantive examination | ||
| SE01 | Entry into force of request for substantive examination | ||
| RJ01 | Rejection of invention patent application after publication | ||
| RJ01 | Rejection of invention patent application after publication |
Application publication date: 20201208 |