Premier Control Technologies Flow, pressure, level and temperature solutions
Tuesday, May 23, 2023
If you have selected a peristaltic pump head that meets your flow requirements, you now want to select a drive system that suits your control needs as well. There are many electric motor choices such as stepper, servo, brush or brushless DC, synchronous or asynchronous AC that can be used with or without a gearbox. Below you can see an example of a brushless DC model:
Torque requirements across the full pump performance envelope is essential. The critical part is the worst-case scenario – e.g., highest back pressure, “hardest” tubing to occlude, highest speed. As with any engineering design it's always good to have a safety margin built in.
Once you select the stepper motor with enough torque you need a driver to drive it. Not all stepper motor drives “unleash” full potential of the stepper motor. It’s like having a great car engine but if the rest of the car is badly designed most of its potential is going to be wasted.
It is important to review and understand the torque curve of the stepper motor because unlike traditional dc motors, higher stepper motor RPM usually results in less available torque.
Stepper motors are an ideal choice for peristaltic pumps because they can provide precise and controlled rotation, which in turn is essential for accurate fluid transfer or dispensing. The stepper motor's natural ability to move in micro, precise steps is perfect for peristaltic pumps. Other drive technologies often must be adapted, for example adding encoders and gearboxes to achieve the same effect.
In addition, stepper motors can maintain a constant speed and torque at low speeds which is the most common operation mode for peristaltic pumps.
Stepper motors also have a high holding torque, which means they can hold a rotor position which is essential for peristaltic pumps. Other motors often need to design a braking system to achieve the same.
Another advantage of stepper motors is how popular they are within 3D printing and how industry standardised. Making them cost competitive and readily available minimising any problems with the supply chain issues.
The precise and repeatable control of the pump's operation, making it suitable for use in a wide range of applications, such as in medical devices, laboratory equipment, and chemical processing.
As their name suggests, stepper motors don’t rotate in the manner of a traditional motor. Instead, they step. Steppers make repeated movements of small, fixed increments, appearing to the naked eye as continuous motor rotation.
This is perfect for peristaltic pumps, because the volume dispensed is proportional to number of steps of the motor.
Stepper drives form part of the OEM Peristaltic Pump category.
The stepper motors can be classified as unipolar, bipolar, and hybrid.
The number of connection wires in a stepper motor can also vary and this is one of the downsides because it can be off putting as well as too complex.
Common stepper motors have 4, 5, 6, 8, or more wires. The number of wires determines the number of coils in the motor and how they are connected. Simplifying, more wires means more precise control of the motor's movement but this in turn increases the cost.
The 4-wire Hybrid Bipolar motor now appears to be the stepper of choice due to its widespread use and availability. The evolution of high-quality sophisticated drivers during the last decade has made these motors suitable for more applications than ever before.
For some applications a dc gearmotor is still going to be a preferred choice. Applications where accuracy, noise, motor life are secondary conditions, and the torque is most important are good examples. Another instance where dc gearmotors should be considered is when multiple pump heads are mounted to a single drive. Another alternative could be a brushless gear motor which is the most common example because there are no brushes which extends the motor life considerably.
Otherwise, if noise, motor life, precision is important therefore you shouldn't use the standard dc gearmotor.
Steppers rated voltages is the minimum voltage required to operate at the rated torque. The driver selected needs to operate at any voltage above that, but not exceeding the insulation rated voltage The maximum current is the most important factor. The driver must operate at the rated current and then configure the driver to match that current.
The reason for the stepper motor losing steps is essentially the incorrect choice of the stepper motor driver. Choosing the correct and appropriate stepper motor driver enables the stepper motor to exert precise control.
Generally speaking, any application that requires highly accurate positioning, speed control, and low speed torque can benefit from the use of stepper motors.
Stepper motors do get hot. Their cases can get up to 100-110℃. This is because the drive is supplying the motor with full current the whole time to keep the motor in position. This is different than a servo where the drive only gives the servo motor as much current needed to maintain its position. The servo has feedback for this purpose where the stepper does not. Most stepper motor drivers provide current adjustment that allows for a lower current setting or holding current when the motor is not spinning. This can result in significant heat reduction.
Stepper motors are known for producing a characteristic sound during operation, which is often described as “signing”, “high-pitched”, “whine”,” hum”. This sound is created by the interaction of the motor's magnetic fields.
When electricity is applied to the coils in the stator, they generate magnetic fields that interact with the magnetic fields of the rotor.
This causes violent changes in the magnetic field, which in turn generates a voltage and a corresponding sound wave.
At certain frequencies due to the resonate frequency effect sounds are amplified.
Although all stepper motors have a natural frequency where audible noise and vibration occur, a well-designed and tuned driver can help minimize the undesirable effects. Our specially designed board minimises the effect thanks to the top of the range controller we use. Click the link below to learn more:
Common stepper motors have 4, 5, 6, 8, or more wires on the harness. The number of wires determines the number of coils in the motor and how they are connected. Simplifying, more wires means more precise control of the motor's movement or electrical configuration options that allows customizing motor performance, depending on the particular motor. but this in turn increases cost.
(for instance, 8 wire motor can be wired in series or parallel)
Generally speaking the top speed of a stepper motor is approximately 1000rpm. For example, if you have a stepper motor with a step angle of 1.8 degrees and a maximum step rate of 1000 steps per second, the maximum speed would be:
Max speed (RPM) = (1000 * 1.8) / 360 = 5 RPM
On average the figure given by manufactures is 10,000 operating hours for stepper motors (approximately 4.8 years, running one eight-hour shift per workday). This is a safe estimate and the motors can lost many hours more and will.
When using stepper motors with peristaltic pumps you do not need the gearbox, which reduces the cost and increases reliability. A typical spur gearbox is often rated for 5000 hours or less.
Here are just some of the other benefits that can reduce the overall cost of using stepper motors:
We have extensive knowledge and experience in stepper motors/drives and the role in which they play in the larger application. Do contact us if you have any questions at all about your application and we will do our best to help.
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