Ball Screw Stepper Motor - Applications
Working Principle of Stepper Motor
The motor converts electrical energy into mechanical energy, and it converts the electrical pulse into a specific rotating motion.
The motion generated by each pulse is accurate and can be repeated.That's why the stepper motor is so effective in positioning applications.
The motion generated by each pulse is accurate and can be repeated.That's why the stepper motor is so effective in positioning applications.
Single-Phase Power On
Typical stepping sequence for the two-phase stepper motor
showed by diagram below:
Step 1: Phase A is electrically connected in the two-phase stator, and its magnetic field fixes the rotor in the position shown in the figure since the opposite-pole attraction.
Step 2: When phase A powered off and phase B powered on, the rotor rotates clockwise by 90°.
Step 3: Phase B is powered off, and A is connected to electricity, but because the polarity is opposite to the first step, the rotor is rotated 90°.
Step 4: Phase A is powered off, phase B is re-powered, and the polarity is opposite to the second step. Repeat the sequence so that the rotor follows 90. The Angle of clockwise rotation, the power mode is one-way power.
showed by diagram below:
Step 1: Phase A is electrically connected in the two-phase stator, and its magnetic field fixes the rotor in the position shown in the figure since the opposite-pole attraction.
Step 2: When phase A powered off and phase B powered on, the rotor rotates clockwise by 90°.
Step 3: Phase B is powered off, and A is connected to electricity, but because the polarity is opposite to the first step, the rotor is rotated 90°.
Step 4: Phase A is powered off, phase B is re-powered, and the polarity is opposite to the second step. Repeat the sequence so that the rotor follows 90. The Angle of clockwise rotation, the power mode is one-way power.
Two-Phase Power On
"The common power mode is two-phase power on, that is, two phases of the motor have been powered on. However, the polarity can be converted for only one phase at one time.
As shown in the figure below, when the two-phase stepping, two phases of between the rotor and the stator at the direction 45° is sucked. Since two phases are energized all the time, this method provides 41.4% more torque than the single phase energized method, but the input power is twice than that of original."
As shown in the figure below, when the two-phase stepping, two phases of between the rotor and the stator at the direction 45° is sucked. Since two phases are energized all the time, this method provides 41.4% more torque than the single phase energized method, but the input power is twice than that of original."
Stepping Sequence when Single-Phase Power On
Stepping Sequence when Two-Phase Power On
Unipolar Winding
Unipolar winding has two windings on each pole. When one winding is energized, the north magnetic field is generated; The other winding is energized, creating a south magnetic field. The current from the driver to the coil does not reverse, so it is called a unipolar winding. This method is designed to simplify the driver, but its torque is about 30% smaller than that of bipolar, since the excitation coil is only half utilized.
Wiring Scheme and Excitation Sequence for Unipolar Motor
| Unipolar Stepping |
Q1 | Q2 | Q3 | Q4 |
| 1 | ON | OFF | ON | OFF |
| 2 | OFF | ON | ON | OFF |
| 3 | OFF | ON | OFF | ON |
| 4 | ON | OFF | OFF | ON |
| 1 | ON | OFF | ON | OFF |
Bipolar Winding
The stepping sequence of the two-phase power on which was described before is adopted the bipolar windings. Each polar has one winding. The electromagnetic polarity will be changed by changing the current direction in the windings.
Wiring Scheme and Excitation Sequence for Bipolar Motor
The following is the wiring diagram
and excitation sequence of a typical two-phase bipolar drive:
and excitation sequence of a typical two-phase bipolar drive:
| Bipolar Stepping |
Q2-Q3 | Q1-Q4 | Q6-Q7 | Q5-Q8 |
| 1 | ON | OFF | ON | OFF |
| 2 | OFF | ON | ON | OFF |
| 3 | OFF | ON | OFF | ON |
| 4 | ON | OFF | OFF | ON |
| 1 | ON | OFF | ON | OFF |
L/R Drive Mode
L/R Drive Mode means constant voltage drive. Most of these drivers in the market can be configured to bipolar and unipolar stepper motors running. L/R reprents the electrical relations between inductance (L) and resistance (R). The ratio of the motor coil impedance to the stepping rate is determined by these parameters. The driver should match the output voltage of the power supply with the rated voltage of the motor to adapt to continuous load operation. The power supply output voltage level must be set high to compensate for the voltage drop inside the driver circuit for optimal continuous operation.
Chopper Drive Mode
LThe chopper drive mode allows the stepper motor to maintain a greater torque at a higher speed than the L/R drive mode. The chopper driver is a constant current driver, which is the bipolar type. It controls the motor's current by quickly powering it on and off. For this drive mode, a low impedance motor coil and a maximum supply voltage can be used, and the driver will deliver the best performance. In order to achieve the best performance, we recommend the ratio of 8:1 between the supply voltage and the rated voltage of the motor.
Microstepping Drive Mode
Many bipolar drivers have the microstepping function, which electronically subdivides one full step into smaller steps. Microstepping can effectively reduce the step of the motor. But compared with the full step, the accuracy has a larger percentage relative error, which is non-cumulative. In most cases, microstepping drive can effectively weaken or eliminate the low-frequency vibration of the stepper motor.
Lifetime
The life of the linear motor is the number of cycles in which the motor can run under a specified load and maintain step accuracy. The life of the rotary is determined by the working hours. Normally, the linear motor can achieve 5 million running cycles, while the rotary motor can provide up to 20,000 hours running life. The ultimate fatigue and overall life of the motor is determined by the specific application of each user. The failure of the normal use of the motor is generally caused by the screw nut meshing working place and bearing, the working torque or the thrust load and the working environment will affect the life of these parts, and then affect the service life of the whole machine.
Working Pinciple of the Lead Screw Stepper Motor
In order to make the stepper motor from rotary motion to linear motion, the simplest design is to integrate the screw nut into the stepper motor. The entire linear transformation is realized inside the motor. This method greatly simplifies the design of the whole structure. In many applications, linear motors can be directly used for precise linear transmission without installing external mechanical linkage. The basic principle is to install a nut in the center of the rotor of the linear motor, and a screw and the nut are engaged accordingly. In order to make the screw forward and back move, it is necessary to prevent the screw and the rotor assembly from rotating together in some way. When the rotor rotates, the screw will achieve linear movement due to the screw rotation is constrained.
Section View of the Captive Lead Screw Stepper Motor
Lead screw motors based on hybrid stepper motors are familiar with many equipment designers. This kind of motors are highly durable and maintenance-free, which are widely used in precise linear motion designs field. With the trend of equipment miniaturization and modular design, the use of linear motors has gradually expanded in recent years, including medical device, laboratory device, communication, semiconductor, imaging equipment, valve control, printing equipment, XYZ platform, stage lighting and other fields.
Terminology
| Detent or Residual Torque | The torque required to rotate the motor's output shaft with no current applied to the windings. |
| Holding Torque | The torque required to rotate the motor's output shaft while the windings are energized with a steady state DC current. |
| Dynamic Torque | The torque generated by the motor at a given stepping rate. Dynamic torque can be represented by pull in torque or pull outtorque |
| Pull In Torque | The maximum torque the motor can deliver once the motor is running at constant speed. There is no inertial torque due to the speed is constant. Also, the kinetic energy stored in the rotor and load inertia help to increase the pull out torque. |
| Pull Out Torque | The torque required to accelerate the rotor inertia and any rigidly attached external load up to speed plus whatever friction torque must be overcome. Pull in torque, therefore, is always less than pull out torque. |
| Drive | The electrical controlled installation to run a stepper motor including power supplies, logic sequencers, switching components and a variable frequency pulse source to determine the stepping rate. |
| Inertia | The value is measured by the object's resistance to acceleration or deceleration. is used in reference to the inertia of the load to be moved by a motor or the inertia of a motor's rotor. |
| Step Angle | The rotation of the rotor caused by each step, measured in degrees. |
| Step | The linear travel movement generated by the lead screw with each single step of the rotor. |
| Pulse Rate | The number of pulses per second (pps) applied to the windings of the motor. The pulse rate is equivalent to the motor step rate. |
| Ramping | A drive technique to accelerate a given load from a low step rate, to a given maximum step rate and then to decelerate to the initial step rate without the loss of steps. |
| Lead Accuracy | The deviation between the actual distance traveled and the theoretical distance traveled based on the lead of the screw. |
| Repeatability | It means the consistency which the motor instructed to the same target position range under certain conditions. |
| Temperature Rise | Allowable increase in motor temperature by design. Motor temperature rise is caused by the internal power dissipation of the motor as a function of load. This power dissipation is the sum total from copper loss, iron (core) loss, and friction. The final motor temperature is the sum of the temperature rise and ambient temperature. |
| Resolution | It means the linear distance which is generated by the motor receiving each pulse. |
| Resonance | Since the motor is an elastomer system, the stepper motor has an inherent resonant frequency. Resonance will occur when the stepping rate is equal to the inherent frequency of the motor, and the motor may produce audible noise changes meanwhile vibration increases. The resonance point will vary from the application and load, but the resonance point is usually around 200PPS. In severe cases, the motor may be out of step near the oscillation point. Changing the step rate is the easiest way to avoid many problems associated with resonance in the system. In addition, half-step or micro-step drives can often reduce resonance problems. When accelerating and decelerating, cross the resonance zone as soon as possible. |
Wiring of the Hybrid Linear Stepper Motor
Stepping Sequence of the Hybrid Linear Stepper Motor
| Bipolar Stepping |
Q2-Q3 | Q1-Q4 | Q6-Q7 | Q5-Q8 |
| Unipolar Stepping |
Q1 | Q2 | Q3 | Q4 |
| 1 | ON | OFF | ON | OFF |
| 2 | OFF | ON | ON | OFF |
| 3 | OFF | ON | OFF | ON |
| 4 | ON | OFF | OFF | ON |
| 1 | ON | OFF | ON | OFF |
Insert an off state in the phase sequence transition to achieve a half-step
Conventional Drive Connection
General Technical Parameter
| Lead Screw Material | SUS303 precision cold rolled stainless steel |
| Screw Coating | Standard lead screws are coated with a thin layer of grease. Teflon coating is optional. |
| Standard Screw Accuracy (Lead Accuracy) |
0.06mm/100mm, if lead screw length over 100mm, the result will be multiply 0.0006mm/mm |
| Screw Straightnes | 0.05mm/100mm, if lead screw length over 100mm, the result will be multiply 0.0005mm/mm. |
| Screw Efficiency | From 26% to 87%, dependent on lead. It also depends on the usage of the anti-backlash nut with screw. The larger lead, the higher efficient the screw will be.. |
| Axial Clearance(Screw & Nut) | 0.02mm |
| Radial Clearance(Screw & Nut) | 0.1mm ~ 0.25mm |
| Nut Material | POM/PBT with self-Lubricating material |
| Wear Life of Screw and Nut | Depending on the load, speed, and environment, it is typically 5 millions of cycles. |
| Operating Temperature | -20℃ ~ 50℃ |
| Storage Conditions | Normal temperature, keep in dry, humidity less than 75%, clean without corrosion |
Warning
- No disassembling the motor in any case.
- No applying radial load to the lead screw while taking or mounting the motor.
- No applying any grease except from THINKERMOTION to the nut or lead screw. Meanwhile, protect the grease from being wiped off when mounting. Measures should be taken to protect the lead screw surface from dust.
- No dropping the motor or the lead screw. At the same time, no pulling or hitting the lead wires to avoid short circuit or open circuit.
- When using a chopper driver, please set its current (RMS current) at proximate the motor's rated current. No making input current overload, otherwise, it will bring the motor overheat even burnout.
- Motors operate should in such an ambient temperature from -20℃ to +50℃. In order to avoid the motor out of step or stuck, the actual load of the motor should be lower than 50% of the the motor's maximum thrust at the running speed. For the Captive lead screw stepper motor, it should be limited to the linear motion within the stroke range, and should not be used beyond the range, otherwise, it will cause internal nut damage and stuck. To maximize motor's life, the shock load, sudden stop and sudden start during the use of the motor are not permitted. For any assistance, please contact our sales engineer.
- Storage conditions: Normal temperature, keep in dry, humidity less than 75%, clean without corrosion.
Problems and Solutions
| Problems | Analysis | Solutions |
|---|---|---|
| Motor Does Not Work | Power indicator is off | Check the power supply circuit for normal power supply |
| Motor shaft is locked | Pulse signal is weak; increase the signal current | |
| Speed is too low | Select the right micro-stepping | |
| Drive's protected | Re-power | |
| Enable signal's problem | Pull up or disconnect the enable signal | |
| Wrong command pluse | Check whether IPC has pulse output | |
| Wrong Rotary Direction | Rotary direction is reverse | Replace the wiring sequence or adjust command direction |
| Open circuit in motor wires | Check the wires connection | |
| Only one rotation direction | Pulse mode error or DlR port damaged | |
| Alarm Indicator On | Wrong wiring | Check the wiring |
| Voltage is too high or too low | Check the power | |
| Motor or drive broke down | Replace the motor or the drive | |
| Wrong Position or Speed | Signal is interfered | Eliminate interference for reliable grounding |
| Wrong command input | Check whether IPC instructions to ensure the output is correct | |
| Setting of pulse per revolution is wrong | Check the DlP switch status and correctly connect the switches | |
| Out of step | Check whether the command speed is high or whether the motor size is small | |
| Drive Terminals Burned Out | Short circuit between terminals | Check power polarity or external short circuit |
| Internal resistance between terminals is too high | Check whether there is any solder ball due to excessive addition of solder on the wire connections | |
| Locked-rotor | Acceleration and deceleration is too short | Decrease command acceleration or increase drive filtering parameters |
| Motor torque is too small | Select the motor with big torque | |
| Load is too heavy | Check the weight and the mass of the motor to adjust the mechanical structure | |
| Current is too small | Check the DlP switch to increase the output current |
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