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en:examples:motor:stepper [2013/03/26 21:15] – external edit 127.0.0.1en:examples:motor:stepper [2020/07/20 09:00] (current) – external edit 127.0.0.1
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 ====== Stepper motor ====== ====== Stepper motor ======
  
-//Necessary knowledge: [HW] [[en:hardware:homelab:motor]], [AVR] [[en:avr:io]], [LIB] [[en:software:homelab:library:module:motor]]//+//Necessary knowledge:  
 +[HW] [[en:hardware:homelab:combo]],  
 +[AVR] [[en:avr:io]],  
 +[LIB] [[en:software:homelab:library:module:motor]], \\ 
 +[LIB] [[en:software:homelab:library:delay]]//
  
 ===== Theory ===== ===== Theory =====
  
 [{{  :examples:motor:stepper:stepper.jpg?220|Stepper-motor}}] [{{  :examples:motor:stepper:stepper.jpg?220|Stepper-motor}}]
- 
-Stepper motors can generally be divided into unipolar and bipolar steppers. 
-Unipolar stepper motors are characterized by their centre-tapped windings, which 
-divide two coils into four. Stepper motors have neither built-in brushes nor internal 
-electronics, meaning all commutation must be performed externally. The most 
-common commutation type is the open-loop mode: the motor driver energizes the 
-coils following a certain pattern, but uses no feedback. Steps can be missed in case of 
-motor shaft torque overload. Missed steps cause inaccurate positioning. Bipolar 
-stepper motors usually have four wires and two separate coils inside; they have many 
-features similar to those of unipolar steppers. Unipolar stepper motors can be run as 
-bipolar stepper motors, but not vice versa. 
  
 Stepper-motors are widely used in applications which demand accuracy. Unlike DC motors, stepper motors do not have brushes nor commutator – they have several independent coils, which are commutated with exterior electronics (drivers). Rotating the rotor is done by commutating coils step by step, without feedback. This is one of the faults in stepper motors – in case of mechanical overloading, when the rotor is not rotating, the steps will be mixed up and movement becomes inaccurate. Two types of stepper motors are distinguished by coils: unipolar and bipolar stepper motors. By construction three additional segments are considered: Stepper-motors are widely used in applications which demand accuracy. Unlike DC motors, stepper motors do not have brushes nor commutator – they have several independent coils, which are commutated with exterior electronics (drivers). Rotating the rotor is done by commutating coils step by step, without feedback. This is one of the faults in stepper motors – in case of mechanical overloading, when the rotor is not rotating, the steps will be mixed up and movement becomes inaccurate. Two types of stepper motors are distinguished by coils: unipolar and bipolar stepper motors. By construction three additional segments are considered:
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 Depending on the model of stepper motor, performing one full rotation (360 degrees) of the rotor, demands hundredths of steps of commutations. For stable and smooth movement, appropriate control electronics are used which control the motor according to its parameters (inertia of the rotor, torque, resonance etc.). In addition to control electronics different commutating methods may be applied.  Commutating one winding in a row is called Full Step Drive and if the drive is alternated between one and two windings it is called Half Stepping. Cosine micro stepping is also used, allowing specially accurate and smooth controlling.  Depending on the model of stepper motor, performing one full rotation (360 degrees) of the rotor, demands hundredths of steps of commutations. For stable and smooth movement, appropriate control electronics are used which control the motor according to its parameters (inertia of the rotor, torque, resonance etc.). In addition to control electronics different commutating methods may be applied.  Commutating one winding in a row is called Full Step Drive and if the drive is alternated between one and two windings it is called Half Stepping. Cosine micro stepping is also used, allowing specially accurate and smooth controlling. 
- 
- 
-~~PB~~ 
  
 **Unipolar stepper-motor ** **Unipolar stepper-motor **
  
-[{{  :examples:motor:stepper:motor_stepper_unipolar.png?250|The windings of an unipolar-stepper motor}}] +Unipolar-stepper motor has 5 or 6 leads. According to the scheme of the motor only ¼ of the windings is activated. //Vcc// lines are usually connected to the positive power supply. During commutation the ends of windings 1a, 1b, 2a and 2b are connected through transistors only to the ground and that makes their control electronics fairly simple.  
- +
-Unipolar-stepper motor has 5 or 6 leads. According to the scheme of the motor only ¼ of the windings is activated. //Vcc// lines are usually connected to the positive power supply. During commutation the ends of windings 1a, 1b, 2a and 2b are connected through transistors (transistor array of the motor board ULN2803) only to the ground and that makes their control electronics fairly simple.  +
  
 **Bipolar stepper-motor** **Bipolar stepper-motor**
  
 +[{{  :examples:motor:stepper:motor_stepper_unipolar.png?250|The windings of an unipolar-stepper motor}}]
 [{{  :examples:motor:stepper:motor_stepper_bipolar.png?250|The windings of a bipolar stepper-motor.}}] [{{  :examples:motor:stepper:motor_stepper_bipolar.png?250|The windings of a bipolar stepper-motor.}}]
  
-Bipolar stepper motor differs from unipolar stepper motor by having the polarity of the windings altered during the commutation. Half of the windings are activated together, this allows to gain higher efficiency than unipolar stepper motors. Bipolar stepper motors have four leads, each connected to a different half-bridge (driver L293 on the board of motors). During commutation half-bridges are applying either positive or negative voltage to the ends of the windings. Unipolar motors can be started using bipolar driver: just connect lines 1a, 1b, 2a and 2b of the windings (//Vcc// will be not connected).+Bipolar stepper motor differs from unipolar stepper motor by having the polarity of the windings altered during the commutation. Half of the windings are activated together, this allows to gain higher efficiency than unipolar stepper motors. Bipolar stepper motors have four leads, each connected to a different half-bridge. During commutation half-bridges are applying either positive or negative voltage to the ends of the windings. Unipolar motors can be started using bipolar driver: just connect lines 1a, 1b, 2a and 2b of the windings (//Vcc// will be not connected).
  
 The commutation necessary for controlling stepper-motors with windings at full step mode and half step mode is displayed in the table below. Since in drivers for uni-polar stepper motors only opening of the transistors takes place, the steps are marked by 0 and 1. Controlling of bipolar stepper motors may need more signals and therefore the steps are marked using the polarity of the driver outputs:   The commutation necessary for controlling stepper-motors with windings at full step mode and half step mode is displayed in the table below. Since in drivers for uni-polar stepper motors only opening of the transistors takes place, the steps are marked by 0 and 1. Controlling of bipolar stepper motors may need more signals and therefore the steps are marked using the polarity of the driver outputs:  
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 ===== Practice ===== ===== Practice =====
 +The Combo Module has a H-bridges to control bipolar stepper motors and the transistor matrix for unipolar stepper motor.
  
-The goal of this exercise is to start a bipolar stepper motor, which can be replaced by unipolar stepper motor using the above described method. There are drivers, on the board of motors, which must be controlled via four input pins by the microcontroller. Each pin represents the polarity of one end of a winding.  The voltage of the end of the winding is positive if the pin is high and negative if the pin is low. To the ends 1A, 1B, 2A and 2B correspond the pins of the microcontroller PB0, PB1, PB2 and PB3. +There are functions //bipolar_init// and //unipolar_init// in the library of the HomeLab which sets the pins as output and functions //bipolar_halfstep// and //unipolar_halfstep// executes revolving by determined half steps. The commutation is done by the table of half steps, but more complex bit operations are used. Unipolar stepper motor is connected to a separate connector //Unipolar Stepper//, bipolar stepper motor is connected to a DC motor connector, where one of the bipolar motor occupies driver pins of two DC motor. The following code section is HomeLab II (ATmega2561) library functions.
- +
-There is function //bipolar_init// in the library of the HomeLab for controlling the bipolar stepper motors setting the pins as output and function //bipolar_halfstep// executes revolving by determined half steps. The commutation is done by the table of half steps, but more complex bit operations are used.    +
  
 <code c> <code c>
-// +// Preparing for controlling the bipolar stepper motor
-// Preparing for controlling the bipolar stepper motor. +
-//+
 void bipolar_init(void) void bipolar_init(void)
 { {
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 } }
  
-// +// Moving the bipolar stepper motor by half steps
-// Moving the bipolar stepper motor by half steps. +
-//+
 void bipolar_halfstep(signed char dir, void bipolar_halfstep(signed char dir,
  unsigned short num_steps, unsigned char speed)  unsigned short num_steps, unsigned char speed)
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  state2 += dir;  state2 += dir;
  
- // Creating the pattern.+ // Creating the pattern
  pattern = (1 << ( (state1 % 8) >> 1) ) |  pattern = (1 << ( (state1 % 8) >> 1) ) |
            (1 << ( (state2 % 8) >> 1) );            (1 << ( (state2 % 8) >> 1) );
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  PORTB = (PORTB & 0xF0) | (pattern & 0x0F);  PORTB = (PORTB & 0xF0) | (pattern & 0x0F);
  
- // Taking a break to wait for executing the step.+ // Taking a break to wait for executing the step
  sw_delay_ms(speed);  sw_delay_ms(speed);
  }  }
  
- // Stopping the motor.+ // Stopping the motor
  PORTB &= 0xF0;  PORTB &= 0xF0;
 } }
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 <code c> <code c>
-// +// The test program for the stepper motor of the HomeLab
-// The test program for the bipolar stepper motor of the motor's +
-//module of the HomeLab. +
-//+
 #include <homelab/module/motors.h> #include <homelab/module/motors.h>
  
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 int main(void) int main(void)
 { {
- // Set up of the motor. + // Set up of the motor 
- bipolar_init();+ unipolar_init(0);
   
- // Endless loop.+ // Endless loop
  while (true)  while (true)
  {  {
  // Turning the rotor 200 half steps to one direction   // Turning the rotor 200 half steps to one direction 
  // at speed of 30 ms/step.  // at speed of 30 ms/step.
- bipolar_halfstep(+1, 200, 30);+ unipolar_halfstep(0,+1, 2000, 30);
  
  // Turning 200 half steps to the other direction   // Turning 200 half steps to the other direction 
  // at speed 30 ms/step.  // at speed 30 ms/step.
- bipolar_halfstep(-1, 200, 30);+ unipolar_halfstep(0,-1, 2000, 30);
  }  }
 } }
 </code> </code>
en/examples/motor/stepper.1364332537.txt.gz · Last modified: 2020/07/20 09:00 (external edit)
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