Stepper Motor

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Information about Stepper Motor
Science-Technology

Published on June 2, 2008

Author: LSMguru

Source: authorstream.com

Stepper Motors :  Stepper Motors What is a Stepper Motor?:  What is a Stepper Motor? The stepper motor is a motor which takes input pulses and then takes proportional steps to input these signals. You can use for positioning and/or speed control for most any applications. The stepper motor needs a power circuit and a sequence circuit for changing phase. What is a Stepper Motor? <Stepper with Peripheral Construction>:  What is a Stepper Motor? <Stepper with Peripheral Construction> Sequencer Power Tr. CPU or Motion- Control-Chip Vm (Motor Power) <Driver> <Controller> <Motor> Vcc (Logic power) What is a Stepper Motor? <Applications>:  What is a Stepper Motor? <Applications> Medical: Infusion Pump, Brad Test, X-ray, Dialysis, DNA Extraction, Pump Semiconductor: Masking, Etching, Wafer Handling, Test-equipment, Die-Bonder FA: Pick & Place, NC Machine, X-Y-Z stage OA: Printer, Fax, Scanner HA: HVAC, Cleaner Robot Other: Vending machine Stepper and Synchronous Motors:  Stepper and Synchronous Motors Movement Generation Step Mode Torque Generation Characteristics Reduced Duty Cycle Synchronous Motor Movement Generation:  for the next step invert magnetic field in the other coil one step  invert magnetic field in 1 coil rotor follows the stator field Movement Generation A stepper motor always needs electronic control. step angle depends on number of poles -> fixed by construction Movement Generation Unipolar Principle:  Movement Generation Unipolar Principle every coil end has only one polarity (”+” or ”ground (-)”) motor coils are unipolar Movement Generation Bipolar Principle:  Movement Generation Bipolar Principle every coil end will be positive (”+”) or ground (”-”) motor coils are bipolar Movement Generation Unipolar Drive:  Movement Generation Unipolar Drive low side switches 4 switches for the whole motor Movement Generation Bipolar Drive:  Movement Generation Bipolar Drive 2 full bridges (or H-bridges) are needed = 8 switches switches in bridge configuration Movement Generation Tin Can Motor:  Movement Generation Tin Can Motor Movement Generation Tin Can Motor - Step Generation:  Movement Generation Tin Can Motor - Step Generation front side teeth back side teeth if there is only 1 magnetic system... Slide13:  Coil Stator Core Shaft Permanent Magnet Bobbin Movement Generation Tin Can Motor Movement Generation Tin Can Motor - Step Generation:  Movement Generation Tin Can Motor - Step Generation Slide15:  Old Technology, No Longer Used Movement Generation VR - Step Generation Slide16:  Hybrid Motor Bobbin Teeth Coil Shaft P.M. Rotor Stator B.B. P.M. Coil Stator Flame Rotor Bracket Movement Generation Hybrid - Step Generation Movement Generation Step Loss:  Rotor follows the stator field Rotor reaches the end stop  noise Rotor is not able to follow the stator field Rotor swings back Movement Generation Step Loss Motor will always loose n·4 steps Movement Generation Step Loss:  Rotor follows the stator field Rotor reaches the end stop  noise Rotor is not able to follow the stator field Rotor swings back Movement Generation Step Loss Motor will always loose n·4 steps Stepper and Synchronous Motors:  Stepper and Synchronous Motors Movement Generation Step Mode Torque Generation Characteristics Reduced Duty Cycle Synchronous Motor Step Mode Full Step Mode:  Step Mode Full Step Mode Step angle = catalogue value 0 -1 1 I1 / I1max I2 / I2max 1 0 -1 coil current in a bipolar motor Step Mode Half Step Mode:  Step Mode Half Step Mode Step angle = half catalogue value coil current in a bipolar motor Step Mode Half Step vs. Compensated Half Step:  Step Mode Half Step vs. Compensated Half Step 1/2 1/2 -1/2 -1/2 Stepper and Synchronous Motors:  Stepper and Synchronous Motors Movement Generation Step Mode Torque Generation Characteristics Reduced Duty Cycle Synchronous Motor Torque Generation Torque vs. Angle:  Torque Generation Torque vs. Angle Mel (torque) 1 2 3 -1 -2 4 MH (holding torque) -MH Torque Generation Positioning Accurancy:  Mel (torque) 1 2 3 -1 -2 4 MH (holding torque) -MH Mel Torque Generation Positioning Accurancy Torque Generation Micro Step Modus:  Torque Generation Micro Step Modus micro step only for smoother travel at low frequencies with tin can motor: Current in coils increases/decreases in small increments Stepper and Synchronous Motors:  Stepper and Synchronous Motors Movement Generation Step Mode Torque Generation Characteristics Reduced Duty Cycle Synchronous Motor Characteristics Torque:  Characteristics Torque with chopper (pull out graph) reduced duty cycle = increased power consumption (pull out graph) Resonances may influence application! Characteristics Influence of Inertia:  Characteristics Influence of Inertia Inertia Factor FI = JROTOR JLOAD + JROTOR Characteristics Output Power:  Characteristics Output Power torque frequency power Motor output power : P = M ·  with M...torque ...angular velocity f...step frequency z...steps per revolution Slide31:  Characteristics Resonance Step motors are resonant because in short their rotors behave much like a classic “mass on a spring”. Slide32:  When a step motor takes a step, the rotor reacts to the changing stator field in the same way a mass on a spring reacts to a change in position. Characteristics Resonance Slide33:  Just like the mass on a spring, the motion of the rotor settles into position after each step. This settling can last as long as a second or more in worst cases! Characteristics Resonance Slide34:  If the settling doesn’t occur rapidly, or the ringing of the rotor gets worse, the motor can become unstable and lose position (stall). Characteristics Resonance Slide35:  There are two major, negative side effects of resonance. Rough motion When step motors resonate they generally vibrate excessively. This can be bad for sensitive equipment. Loss of torque, which can lead to loss of position When step motors resonate much of the torque available in the motor is used up in keeping the rotor synchronized with the stator field, and in worst cases the motor will not have enough torque to move the load. Loss of torque often leads to stalling. Characteristics Resonance Stepper and Synchronous Motors:  Stepper and Synchronous Motors Movement Generation Step Mode Torque Generation Characteristics Reduced Duty Cycle Synchronous Motor Reduced Duty Cycle:  higher output power requires higher input power -> power losses increase -> duty cycle needs to be reduced, otherwise motor becomes too hot Reduced Duty Cycle Otherwise you get a motor with reduced coil resistance. But the winding is changed so that it will have the same maximum power dissipation, same duty cycle and therefore the same output torque. “We need more torque!“ Reduced Duty Cycle Independence from Resistance:  Reduced Duty Cycle Independence from Resistance lm j a Q RM n I S PCu  average length of a copper wire magnetic flux angle current linkage magnetic resistance no. turns (winding) current current density consumed energy temperature Reduced Duty Cycle Operations:  Duty cycle is based on 5 minutes cycle time (unless otherwise specified). Reduced Duty Cycle Operations t T t T tS tB t T tS tB continuous operation operation with reduced duty cycle tB...ON-time tS...cycle time Duty Cycle Reduced Duty Cycle A Simplified Calculation:  Reduced Duty Cycle A Simplified Calculation input power at 100% duty cycle: UK...supply voltage from catalogue Rph..coil resistance real duty cycle: PED100 ... Power for 100% duty cycle US ... supply voltage in application RED100... coil resistance for 100% duty cycle Stepper and Synchronous Motors:  Stepper and Synchronous Motors Movement Generation Step Mode Torque Generation Characteristics Reduced Duty Cycle Synchronous Motor Synchronous Motor Schematic:  Synchronous Motor Schematic construction is similar to bipolar stepper motor Synchronous Motor Frequencies:  Synchronous Motor Frequencies clock i1 i2 i1 i2 t t t t t bipolar stepper motor f = 200Hz synchronous motor f = 50Hz f = step frequency = fs f = frequency of coil current = fi Synchronous Motor Operation Area:  Synchronous Motor Operation Area C U Resonance thermal overload minimum voltage to start minimum capacity operation area UN±10% CN±10% Competitors for Stepper Motor:  Competitors for Stepper Motor Rotary: Portescap (Danaher) HSI (Haydon Switch & Instrument) Hybrid: Lin Engineering Portescap (Danaher) Oriental Motor Sanyo Denki, Shinano Linear: HSI (Haydon Switch & Instrument) Lin Engineering NPM/NPA Products:  NPM/NPA Products Tin-Can Rotary <PF/PFC Series> PF20, PF25, PF25C, PF35, PF35T, PF42, PF42T, PF42H PF55, PF55H Tin-Can Linear: <PFL/PFCL Series> PFCL25, PFL35T Hybrid: <PJB Series> PJB42S, PJB56H <PR Series> (Only for North America ) PR20, PR28, PR35, PR42, PR57 Designation – PF/PF Series:  Designation – PF/PF Series PF C 42 H – 48 C 1 Magnet Material 1: Ferrite Anisotropic 2: Ferrite Isotropic 4: Neodymium Winding Code Unipolar> B:24V, C:12V, D:5V Bipolar> P:12V, Q:5V Step/Rev 24: 15deg/step 48: 7.5deg/step 96: 3.75deg/step Connector Version Motor Size Dia. (mm) 25, 35, 42, 55 Motor Length or High Torque Version Blank: Standard T: Thin stack (Avail. In 35 and 42) H: High Torque (Avail. 42 and 55) Designation – PF/PF Series:  Designation – PF/PF Series PFC42H–48C1 G 1/10 Gear Ratio G: w/ gear head Designation – PR Series:  Designation – PR Series PR 42 H -25 – 04 04 J A A: Shingle Shaft B: Double Shaft Step Angle J: 1.8deg/step (=200step/rev) M:0.9deg/step (=400step/step) Step/Rev 24: 15deg/step 48: 7.5deg/step 96: 3.75deg/step Size (mm) Stack Length (mm) H: High Torque S: Standard Motor Current 04: 0.4Amp/phase 10:1.0Amp/phase Weakness and Settlements :  Weakness and Settlements Mis-step -> 1. Taking Care Margin (Chose Best) 2. Closed loop (Add Encoder) 3. Use/Change Higher Current Resonance -> 1. Use High Resolution Motor 2. Use Microstep Driver 3. Adjustment (reduce) Current Stepper VS Servo (Brushless):  Stepper VS Servo (Brushless) Stepper Servo Cost √ Speed (600rpm) √ (3000rpm) Power/Torque √ Response √ Silence √ Easy to Use √ Glossary -1:  Glossary -1 Holding Torque The holding torque is the maximum torque the stepping motor has when rated current is being supplied but the motor is not rotating (with consideration given to the permissible strength of the gear when applicable). If you are setting "automatic current down (Idle Current)" function at motor standstill, the holding torque should be less than setting rated current. Pullout Torque Pullout torque is the maximum torque that can be output at given speed. When selecting a motor, be sure the required torque falls within this curve. Rotor Inertia This refers to the inertia of rotor inside the motor. This is necessary when the required torque (acceleration torque) for the motor needs is calculated. Glossary -2:  Glossary -2 Rated Current The rated current is determined by motor temperature rise. It is the current value that can flow to the motor coils continuously at motor standstill. As a general rule, the current must be set to the rated current. Step Angle The step angle is the angular distance (in degrees) that the motor moves at the input of one pulse from the driver. It differs depending on the motor structure and excitation system. Gear Ratio This is the ratio in rotation speed between the input speed from the motor and the speed of the ear output shaft. For example, the gear ratio 10:1 is that when the input speed from the motor is 10rpm, the gear output shaft is 1rpm. Glossary -3:  Glossary -3 Allowable (Permissible) Torque The allowable torque represents the torque value limited by the mechanical strength of the gear. Backlash The play of gear output shaft when the motor shaft is fixed. When positioning in bi-direction, the positioning accuracy is affected. Maximum Starting Frequency (fs) This is the maximum pulse speed at which the motor can start or stop instantly (without an acceleration or deceleration period) when the functional load and inertial load of the stepper motor are 0. Driving the motor at greater than this pulse speed requires gradual acceleration or deceleration. This frequency drops when there is load inertia on the motor. Glossary -4:  Speed Torque Glossary -4 Pull-Output Torque Pull-in Torque Max. Starting Frequency Holding Torque

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