Month: December 2019

Brushless-dc motors are taking center stage in medical-equipment design because they last twice as long a competing technologies.

It used to be that brushless-dc (BLDC) motors just weren’t an option for most medical applications. But that situation is changing as the cost of BLDC drive electronics falls. Furthermore, a quest for more-efficient, compact, and reliable medical equipment has put BLDC motors on the prescription list for a variety of applications.

Treating sleep apnea
The treatment of sleep apnea requires the use of Positive Airway Pressure (PAP) respirators. The patient dons a special breathing mask attached to the PAP respirator. A blower fan within the respirator pressurizes the air in the mask to create positive airway pressure that helps the patient breathe while asleep. The blower fan must raise or lower the patient’s airway pressure in response to their breathing pattern.

Power density and reliability
There’s no question that recent events have put a strain on the world’s medical analysis and testing services. Reason’s include the continuing development and improvement of medical technologies in the areas of disease detection, prevention, and treatment. Moreover, there’s been a double-digit increase in the number of people needing medical care over the last decade. The growing worldwide demand for medical analysis and testing services has created a niche for equipment with greater throughput and high reliability.

Medical analyzers
Medical analyzers are multifunction machines that test human bodily fluids such as blood and urine. Fluid samples within the analyzers move from station to station for various tests. Generally, medical analyzers are totally enclosed. The temperature within them will rise to well above ambient temperature during periods of peak operation. Medical analyzers are designed to test thousands of samples annually and to run a minimum of 8 hr daily.

All in all, a need for high throughput and reliability in medical machines will continue to challenge the capabilities of brushed-dc motors. In addition, the trend toward squeezing more equipment functions into less volume promotes the use of smaller motors able to dissipate heat in small spaces. BLDC motors can meet these demands now and should continue to do so into the future.

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Stroke Length

In determining the right stepper motor linear actuator for a specific application it is necessary to understand stroke length. The stroke length allows the device to handle short or long operational distances. Most, but not all, stepper actuators have a stroke length that allows the actuator to move a specific amount. For example, a small actuator could move a curtain for a window, while a large actuator could move a curtain for a movie screen. As a result, a longer stroke length will increase the price of a linear actuator. Extra length is rarely required, so users should select stepper actuators that exactly fit the application.

Duty Cycle

Understanding the duty cycle, the elapsed time between operations, will provide a reasonable approximation of the expected lifetime of a stepper actuator. The duty cycle can be based on units of hours per day, minutes per hour, or strokes per minute. By managing the duty cycle one can increase the lifetime and the necessary maintenance required for the stepper actuator.

Load

One of the criteria for selecting a stepper actuator is to identify the amount of force required of the application. Defining the load required for the application can help identify the proper size and capabilities of the stepper actuator. The orientation also plays a key role in selecting the proper stepper actuator.

IMPORTANT NOTE: With a stepper actuator in a horizontal position, the overall load capabilities must compensate for the frictional force. With a stepper actuator in a vertical position, the load necessary is that of the weight due to the gravitational force.

Power Factor

Mechanical Power: The necessary requirement in calculating mechanical power is based on the linear force required to move the load multiplied by the speed at which the load will be moved.

Electrical Power: The electrical power is obtained through performance graphs illustrating force vs. speed and force vs. current, both of which are good representations of the performance of a stepper linear actuator. The performance graphs are specific to each specific stepper actuator model.

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1. Introduction
Currently, major therapeutic methods in the treatment of open, complicated and unstable fractures in traumatology, orthopaedics and surgery (limbs, joints, the pelvis, jaws, etc.) include external fixators. This therapeutic method provides the advantage of simple application of the external fixator with perfect stabilisation of the fracture,allowing for timely rehabilitation of the patient. External fixators can also be used to extend limbs or to correct axial deformities. However, no fixator has been made until now that would provide motor control of joint movement – advisable and desired for therapy associated with rehabilitation in unconscious patients or patients with complicated joint fractures. VSB-TU Ostrava has gained practical experience in this field in cooperation with University Hospital in Ostrava; fixator prototypes which are equipped with an electric stepper motor to control joint bending in patients exist.There are currently two solution variants that can be considered for the electric actuation, in principle.

1.1 Hybrid Actuators with Stepper Motors
Hybrid linear actuator stepper motor transfer the rotation movement of the stepper to the movement of a linear screw with the help of a special patented nut. The actuator contains a hybrid stepper motor, which utilizes both the advantages of a reluctance motor and a motor with permanent magnets. The construction is based on a reluctance motor and ensures a small step angle (up to 0.9°) and fine resolution. The use of permanent magnets on the other hand increases the turning moment and provides a stronger motor. The composition of these two technologies together with the movement nut into a single case creates an affordable compact linear drive  a hybrid stepper actuator.

Hybrid actuators represent an affordable solution for all application requiring small and exact control of a linear movement. Actuators create large forces in small spaces.The actuator contains a standard stepper motor, which may be simply controlled in the same way as stepper motors. The core of the hybrid actuator is an exact trapezoidal movement screw and nut shaped for the corresponding load. Integration of the movement screw in the motor provides a compact and precise drive unit which simplifies the construction of the resulting machine. Actuators find applications in medicine, measuring technology, handling technology and in other areas.

1.2 Stepper Motor Combined with a Linear Lead
The other possibility is offered by using a linear lead in connection with a standard two-phase stepper motor. The Kuroda linear lead used to convert rotational linearmovement can be mentioned as an example.The lead is equipped with a ball screw for positioning medium- up to heavy-weight
loads. The lead converts rotational movement of the stepper motor to the linear movement of the positioned load. An optimum configuration of the linear drive is obtained by combining the stepper motor and linear lead.

Which is Better for Cnc? Servo or Stepper Motors?

Torque and Speed Considerations Of Stepper Motor

A brushless DC motor consists of a rotor in form of a permanent magnet and stator in form of polyphase armature windings. It differs from conventional dc motor in such that it doesn’t contains brushes and the commutation is done using electrically, using a electronic drive to feed the stator windings.

4 Pole 2 Phase Motor Operation
The brushless DC motor is driven by an electronic drive which switches the supply voltage between the stator windings as the rotor turns. The rotor position is monitored by the transducer (optical or magnetic) which supplies information to the electronic controller and based on this position, the stator winding to be energized is determined. This electronic drive consists of transistors (2 for each phase) which are operated via a microprocessor.

7 Advantages of Brushless DC Motors
Better speed versus torque characteristics
High dynamic response
High efficiency
Long operating life due to a lack of electrical and friction losses
Noiseless operation
Higher speed ranges

Applications:
The cost of the Brushless DC Motor for sale has declined since its presentation, because of progressions in materials and design. This decrease in cost, coupled with the numerous focal points it has over the Brush DC Motor, makes the Brushless DC Motor a popular component in numerous distinctive applications. Applications that use the BLDC Motor include, yet are not constrained to:

Consumer electronics
Transport
Heating and ventilation
Industrial engineering
Model engineering
Principle of Working

The principles for the working of a BLDC motors are the same as for a brushed DC motor, i.e., the internal shaft position feedback. In case of a brushed DC motor, feedback is implemented using a mechanical commutator and brushes. Within BLDC motor, it is achieved using multiple feedback sensors. In BLDC motors we mostly use Hall-effect sensor, whenever rotor magnetic poles pass near the hall sensor, they generate a HIGH or LOW level signal, which can be used to determine the position of the shaft. If the direction of the magnetic field is reversed, the voltage developed will reverse too.

What are Brushless DC Motors Used For?

Brush DC Motor VS Brushless DC Motor

Step motors are widely used in automation due to their high resolution, precision positioning, minimal control electronics, and low cost. As an open loop system, traditional step motors are driven without the need for sensors to feed information back to a controller; however, the open loop configuration of step motors has challenges.

ENCODER FUNCTIONALITIES
Figure 1.< By adding an inexpensive encoder to a step motor system, the drive/controller can monitor the motor’s actual position, closing the feedback loop and avoiding many of the limitations traditionally associated with stepper systems.

The addition of an stepper motor encoder to the step motor system (Figure 1) adds functionality to detect and even prevent stalls by providing feedback to the drive. Depending upon how an operator programs the controller, encoder feedback can verify motor position, immediately detect motor stall, prevent motor stall, and create a closed loop servo system.

Position Verification — When pushed beyond its limits, a step motor will stall before reaching the endpoint. This event typically occurs when motors are not adequately specified for high-cycle applications. An encoder can provide position feedback at the end of the motion profile, indicating if the step motor stopped before reaching the end position

Stall Detection — Stall detection notifies the user/system/machine as soon as a motor stall occurs, eliminating the uncertainty of whether or not the motor reached its target position. A more advanced function than position verification, stall detection (Figure 2) enables the controller to compare the registers of the encoder counts and target motor position on a continuous basis instead of just at the end of the move.

Stall Prevention— While greatly increasing system functionality, stall detection does not inherently improve step motor performance; it still requires the operator to perform a corrective move and re-reference the axis to the home position. Stall prevention, on the other hand, dynamically and automatically adjusts the move profile to prevent a stall, enabling the motor to operate with constant torque to get into an accurate end position without stalling.

Servo Control and Increased Motor Torque — Using encoder feedback to servo-control, a step motor increases motor torque for greater dynamic performance. With peak torques up to 50% higher than the rated holding torque of the motor, the servo-controlled step motor system can operate at higher acceleration rates and with higher throughput for faster machine cycles.

When working as part of a fully closed loop stepper motor system, step motors run cooler, more efficiently, quieter, and with faster settling times than their open loop counterparts. Unlike the other encoder applications described here, servo control applies a peak torque that enables the motor to get past stall conditions without sacrificing speed. Some manufacturers offer motors (Figure 3) already preconfigured with a high-resolution incremental encoder and closed-loop servo control firmware.

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Some (Brushless DC) BLDC motors for sale are equipped with three internal hall-effect sensors that provide feedback to external circuits that facilitate precise control of the magnetic coils in the stator. Some types of BLDC controllers use the motor’s intrinsic Back EMF leaving the hall-effect sensors unused. In either case, the hall sensors can also be used for accurate position sensing.

BLDC Anatomy
The BLDC hub motor used in this experiment utilizes 27 electro-magnetic stator coils and 30 permanent magnets (also referred to as 15 pole pairs) (Figure 2). Many diagrams show the Hall effect sensors labeled as U, V, and W spaced equidistant (120 degrees) around the stator coils. Sensors are located equidistant from each other, but most are located on one side of the stator (Figure 3).

Note: The sensor labels (U, V, W) are assigned based on internal wire color code. For this experiment, sensor labeling is arbitrary.

The magic of 3 in BLDCs

As seen in Figure 3, the Hall sensors are centered in the coil faces. The center-to-center span between any two sensors is three coils, which results in 40 degrees of separation.

2 full coils + 2 half coils = 3 coil span

360 degrees / 27 coils * 3 coil span = 40 degrees

This configuration yields the same output values as if the sensors were physically 120 degrees apart. One third of the magnets will pass by each of the sensors resulting in 10 pulses from each sensor. Together, the sensors will deliver 30 pulses per 120 degrees or 90 pulses in one complete revolution.

9/27 (Coils) = 10/30 (Magnets) = 120/360 (degrees) = 30/90 (pulses) = 1/3 (of one rotation). Neat!

Summary

No matter which single sensor output square wave is examined following a transition, one of the remaining sensors is trailing while the other is leading (one is high while the other is low). It is for this reason that it does not matter which arrangement of sensor outputs you use when reading values. The only effected calculation is direction of rotation.

The animated illustration shows the sensor output at each transition and the relationship between the ten permanent magnets and the three sensored coils. Non-sensored, intermediate coils are omitted for visual clarity.

How to Use Hall Effect To Drive Brushless DC Motor

How Do Brushless BLDC Motors Work?

Stepper motor control circuit is a simple and low-cost circuit, mainly used in low power applications. The circuit is shown in figure, which consist 555 timers IC as stable multi-vibrator. The frequency is calculated by using below given relationship:

Frequency = 1/T = 1.45/(RA + 2RB)C Where RA = RB = R2 = R3 = 4.7 kilo-ohm and C = C2 = 100 µF.

The output of timer is used as clock for two 7474 dual ‘D’ flip-flops (U4 and U3) configured as a ring counter. When power is initially switched on, only the first flip-flop is set (i.e. Q output at pin 5 of U3 will be at logic ‘1’) and the other three flip-flops are reset (i.e. output of Q is at logic 0). On receipt of a clock pulse, the logic ‘1’ output of the first flip-flop gets shifted to the second flip-flop (pin 9 of U3). Thus logic 1 output keeps shifting in a circular manner with every clock pulse. Q outputs of all the four flip-flops are amplified by Darling-ton transistor arrays inside ULN2003 (U2) and connected to the stepper motor windings orange ,brown, yellow, black to 16, 15 ,14, 13 of ULN2003 and the red to +ve supply.

The common point of the winding is connected to +12V DC supply, which is also connected to pin 9 of ULN2003. The color code used for the windings is may vary form make to make. When the power is switched on, the control signal connected to SET pin of the first flip-flop and CLR pins of the other three flip-flops goes active ‘low’ (because of the power-on-reset circuit formed by R1-C1 combination) to set the first flip-flop and reset the remaining three flip-flops. On reset, Q1 of IC3 goes ‘high’ while all other Q outputs go ‘low’. External reset can be activated by pressing the reset switch. By pressing the reset switch, you can stop the stepper motor. The motor again starts rotating in the same direction by releasing the reset switch.

Now you have got an idea about the types of super motors and its applications if you have any queries on this topic or on the electrical and electronic projects leave the comments below.

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https://activerain.com/blogsview/5437527/how-to-choose-a-stepper-motor-and-power-supply-voltage

Selecting the appropriate linear actuator can be quite the ordeal – and selecting the wrong one could dramatically reduce the efficiency of your application, and shorten its lifespan. Learn about the different types of linear actuators, how to select the right one, and which services can help make the decision as simple as 1-2-3!

There are few different designs of linear actuators you need to consider when selecting an actuator for your design; each design has its advantages and disadvantages, and serves unique purpose, so let’s examine each design:

The maximum force this application can handle is also limited, meaning that you should carefully consider how much strength you’ll need before selecting the external nut configuration.

External Nut
The most popular design of linear stepper actuators, the external nut configuration is simple, compact, and offers a high level of design flexibility. In the external nut configuration, the shaft of the stepper motor is replaced with a lead screw. In a typical application, the motor is fixed in position and an apparatus is attached to the nut. As the lead screw rotates, the external nut travels along the length of the screw, providing linear motion.

Non-Captive
In non-captive configuration, the nut is incorporated into the motor’s rotor. As the rotor rotates, it creates linear motion by passing the leadscrew through the shaft. In this instance, your apparatus can be attached in one of two ways: directly to the motor, or to the leadscrew.

The mass of the motor can also limit the acceleration and maximum operating speed of your application, and certain power efficiency is sacrificed because more mass needs to be moved.

Another popular option is to attach an apparatus to the lead screw while keeping the motor fixed in position. This removes the need for long leads and lead tracking. Most of the benefits can be retained if the apparatus can be supported from both ends of the lead screw.

Captive

The third common configuration is the captive linear actuator. In this design, a screw is attached to a splined shaft. That shaft is prevented from spinning through the use of a splined socket attached to the face of the motor. Linear motion is achieved while each component is rotationally fixed and where no rotation is visible from outside. This is a good choice if your application lacks a mechanism which prevents either the lead screw or the nut from rotating.