Computer control of measuring equipment mechanisms. Scheme, description

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ENCYCLOPEDIA OF RADIO ELECTRONICS AND ELECTRICAL ENGINEERING
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Computer control of measuring equipment mechanisms. Encyclopedia of radio electronics and electrical engineering

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Encyclopedia of radio electronics and electrical engineering / Measuring technology

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A hardware-software device for controlling stepper motors, designed to provide measurements of the parameters of electroacoustic equipment using software tools of the measuring complex.

When measuring the spatial characteristics (building radiation patterns) of acoustoelectric and electroacoustic transducers using the previously described real-time computer measuring complex [1], accurate remote positioning by the angle of the acoustic receiver and emitter is necessary. This task is most effectively solved with the help of stepper motors. The advantage of stepper motors is that they allow you to convert an electrical control signal into an angular movement of the rotor with fixing it in a given position without any feedback devices. This circumstance greatly simplifies the design of the respective units and the measuring setup as a whole.

The proposed hardware-software device is designed for interactive, independent and simultaneous control of two stepper motors. The device allows you to set in digital form the magnitude and direction of rotation of the rotors of stepper motors. The main area of application is the control of mechanical units of measuring equipment and experimental installations.

The device consists of a hardware interface unit and an original computer control program. The maximum rotation speed of the motor rotors is 100 steps per second. The hardware interface unit is connected to the computer through a standard parallel (printer) interface port. The control program is designed to work in the Windows 95/98/Me/NT/2000/2003/XR operating system and has a size of only 320 KB. It should be noted that administrator rights are required to run the program under Windows NT/2000/2003/XP.

The interface unit is designed with the greatest possible simplicity on the cheapest and most common domestic components. This makes it possible to repeat it. To simplify the device, the entire control algorithm is implemented in software. Only the functions of electrical matching of the computer and the engine are assigned to the hardware.

Computer control of measuring equipment mechanisms
Fig. 1

The block diagram of the hardware interface of stepper motors with a computer is shown in fig. 1. The DD1 chip simultaneously performs the functions of a buffer memory and a preamplifier. The information supplied from the parallel port of the computer [2] is written to the storage register of the DD1 microcircuit by a negative pulse generated by the software at the CS1 input (pin 1). The final amplification of the signal for supplying the control winding of the stepper motor is performed by the node on transistors 1VT1 and 1VT2 (only one of the eight is shown in the circuit diagram, highlighted by a dash-dotted line; the remaining seven are connected, respectively, to the outputs Q2-Q8 of the DD1 register). Such a switching scheme allows all powerful transistors to be located on a common heat sink without the use of additional electrical insulation of their cases, usually connected to the transistor collector. This makes it possible to significantly simplify the mechanical design of the interface unit. In the absence of forced ventilation, the heat sink area should be approximately 50 cm2 for each of the eight high-power output transistors.

Diode 1VD1 performs the functions of damping parasitic oscillations that occur when switching current in the control winding of a stepper motor.

This interface unit is designed to work with four-phase stepper motors DShI200-3(1) with a nominal step of 1,8±0,05° (the step is indicated without the use of a gearbox). Other engines can be used; to work with three-phase in the control program, a corresponding switch is provided. Alternate switching on and off of the motor windings, necessary for their rotation, is carried out by software. Winding switching diagrams are selected when setting up the program based on the type of motor and the requirements for the operating mode. Voltage pulses are alternately applied either to single stator windings or to their adjacent pairs with an offset of one during each step. These modes are selected in the program settings window, and they are designated "1-1-1-1" and "2-2-2-2" respectively. In the second case, the torque and holding torques of the motor increase (at least for DShI200), but the power consumed by the device and the heating of the electric motors increase accordingly.

The main menu of the program is called by pressing the right mouse button on the title of the program window. The program settings window is opened by the "Motor Settings" menu item.

There are two switchable motor stop modes in the motor control program. In the first variant, the voltage is removed from the motor windings after a set time interval (0...99 s) after stopping. This greatly facilitates the thermal regime of the electric motor and the interface unit, but can subsequently lead to spontaneous movement of the mechanism associated with the rotor. In the second mode, after stopping, the voltage from the motor winding is not removed - this is the so-called fixation mode. Such a mode can lead to excessive heating of the electric motor, but after stopping it ensures reliable immobility of the rotor and the mechanical device associated with it. The required engine stop mode is selected based on the conditions of the problem. For example, if a worm gear is used to transmit rotation, the immobility of the device at rest, as a rule, will be ensured even without electromagnetic fixation of the stepper motor rotor. These modes are selected in the program settings window with the Auto Release button.

The program provides for the introduction of scale factors (Rate in the settings window) and the initial offset separately for each of the electric motors. This allows you to set and display on the computer screen the real values of the adjustable parameters of devices mechanically connected to stepper motors. For example, the angle of rotation directly in degrees, or the movement in millimeters. To set the required initial displacement, move the mechanical device to the required position using a stepper motor or in another way (for example, manually). Then you need to enter the calibration mode by pressing the appropriate button (exclamation point in a triangle) on the control panel. The color of the digital movement indicator will turn red. After that, you should set the true value of the corresponding parameter on the displacement indicator and press the "Calibration" button again, then close the window. The scaling factors are determined based on the design (taking into account the possible presence of a gearbox) of the serviced device and the nominal step of the electric motor.

The settings window provides the ability to edit the name and dimension of the parameters of specific devices regulated by stepper motors displayed in the program.

There are two independent command streams in the engine control program: the control command input stream and the data output stream to the hardware interface unit. In the input stream, the position of the motor rotors is set and displayed in units reduced to the real values of the parameters of mechanically connected devices. In the output stream, the true (current) position of the motor rotors is continuously compared with the required value and an action is issued on the interface unit to parry a possible mismatch. This construction of the control program allows you to set a new value for the angle of rotation of the motor rotors, regardless of whether the previously entered value has been reached or not. In the latter case, the motor rotor will continue to rotate (possibly changing direction) to reach the newly set position.

To enter and display numerical named values in the program, the original control and indication element "Digital Panel" is used. Numeric values are entered bit by bit using the mouse. Place the cursor on the required indicator digit and set the required value by pressing the left or right mouse button. The left button decreases and the right button increases the number. The transfer to the highest rank occurs automatically.

If you hover over the dimension symbols, then by pressing the left or right mouse button, you can respectively decrease or increase the value on the indicator ten times. The sign of the number (if it is shown on the indicator) is changed by pressing the mouse buttons in the same way. When the button is held down for more than 0,5 s, the action is automatically repeated. If you move the cursor away from the indicator while holding down the mouse button, then auto-repeat will continue regardless of the further state of the mouse. To stop auto-repeat, move the cursor over the indicator again and click on any mouse button; if you use a mouse with a wheel, you can use it. Turning the wheel away from you increases the value of the indicator digit and vice versa - when turning it towards you. The auto-repeat mode in the least significant digits allows you to set the continuous rotation of stepper motors at a speed less than the nominal one.

For the functioning of the device as part of the software systems, external (from other programs) control of the operation of the engines is provided. Control commands are transmitted by sending special Windows operating system messages containing parameters from client programs to the server program that directly controls the operation of the engines.

During breaks between work sessions, the program automatically saves all the set parameters and the current state on the computer's hard disk for further use.

The hardware interface unit must be powered from a DC voltage source with a power sufficient to operate the applied stepper motors (at least 70 W for two DShI200-3 motors). It is unacceptable to use the power supply built into the control computer in order to avoid malfunctions of the latter. Chip DD1 must be powered by a stabilized source, preferably independent of the power supply of powerful output keys.

The connection of the hardware unit with the parallel (printer) port of the computer is carried out by an unshielded ribbon cable up to 3 m long with alternating signal and "ground" conductors. For longer cables, it is recommended to use a bundle of individual shielded wires.

If your computer does not have an unoccupied parallel port, you must install an additional card. At present, boards are commercially produced, usually containing two parallel ports. They are made for computers with a PCI bus, as well as for older computers with an ISA bus. These boards usually have switches to select the base addresses of the ports. For example, on the TS-020-EP board used by the author (for the ISA bus), each of the two parallel ports on it can be set to the following base addresses: ZVSN, 378H, 278H, 27CH, 26CH, or 268H. The control program provides for setting any of the above addresses as active. Support for additional ports from the BIOS or operating system is not required for the control program to work. You only need to configure the address of additional ports so that there is no conflict with all the ports already in the system (not just parallel ones).

Computer control of measuring equipment mechanisms
Fig. 2

The overall design of the device can be arbitrary. The author made a prototype on a printed circuit board made of foil fiberglass with a thickness of 2 mm. A drawing of a printed circuit board and the location of parts on it are shown in fig. 2 a b. Printed conductors should be as wide as possible.

The simplest heat sinks for output transistors can be made in the form of two duralumin plates 130x50x3 mm in size; they are fixed on the printed circuit board using duralumin corners through specially provided holes. The resulting design for the heat sinks is fixed in the device case.

On fig. 3 shows a photograph of one of the variants of this device, made by the author. On the ribbed heat sink (on the right), in addition to transistors, powerful diodes of the power supply rectifier are also fixed (through insulating mica spacers). On the left are the smoothing capacitors of the power supply.

Computer control of measuring equipment mechanisms

The input and output connectors can be fixed either on heat sinks or on the device case. The RPMM1-50SH1-V connector was used as an input (for connecting to a computer). Two output connectors (one for each motor) - RG1N-1-5, in each of which two adjacent outputs are connected in parallel to reduce the current load. In general, there may be other connectors with sufficiently powerful contacts. The connector contacts are connected to the corresponding conductors of the printed circuit board with a conventional flexible wire. For output circuits, the cross section of the wires must be at least 1 mm2.

Transistors KT815 and KT818 can be used with any letter indices or other powerful transistors of the corresponding structure can be used. Diodes of the KD213 series can be replaced with KD212 or other powerful pulse diodes. The type and power of the resistors used do not matter.

Instead of the K589IR12 register, it is possible to use the KR580IR82 with the correction of the printed circuit board. The pin numbering for this option is shown in fig. 1 in brackets. It should be noted that the recording of data supplied from the parallel port of the computer to the storage register KR580IR82 must be carried out according to the positive edge of the pulse at the STB input (pin 11). To change the polarity of the strobe pulse, the program provides a corresponding switch (menu item Slope Positive).

The described device does not require any adjustment. It is only necessary to make sure that the windings of the stepper motors are connected to the outputs of the powerful switches in the proper order. If this is not provided, then the rotor of the engine, instead of rotating, will most likely simply vibrate in place or turn in jerks.

Programs for the device can be downloaded hence.

Literature

Shmelev O. Computer measuring complex. - Radio, 2007, No. 3-7.
Guk M. Hardware IBM PC. Encyclopedia. - S.-Pb.: "Peter Cohn", 1999, p. 632-635.

Author: O. Shmelev, Moscow; Publication: radioradar.net

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