What are Ball Screw Actuators?

Medical applications have some of the most stringent requirements in terms of precision and reliability. This means that the components used in these applications must also meet the same high standards. One such component that meets the linear motion requirements of the industry is a ball screw actuator. Ball screw actuators are a type of linear actuators that utilize a ball screw to impart motion. The ball screw is a cylindrical shaft with helical grooves around the circumference. Balls travel up and down the grooves, which converts rotational motion into linear motion.

Factors to Consider When Selecting Ball Screw Actuators for Medical Applications

When it comes to selecting ball screw actuators for medical applications, there are a few factors you will need to take into account. First, you need to make sure the actuator is compatible with the type of medical devices used. Second, you need to find an actuator that can handle the required force and speed. The size and weight of the actuator will also need to be taken into account. Moreover, you need to make sure the actuator is safe and reliable. Let us look into these factors briefly.

• Speed: Speed is how quickly the actuator can move the load. Ball screw actuators can achieve both high speeds and high precision, making them a good choice for many medical applications.
• Load Capacity: The other most important is the load capacity of the actuator. Load capacity is the amount of weight or force that the actuator can handle. The actuator must be able to handle the weight of the object being moved, as well as any additional forces that may be exerted on it. It is important to select an actuator that is strong enough to handle the load without becoming overloaded.
• Accuracy: Another important factor is accuracy. Ball screw actuators must be able to move the object with great accuracy. Accuracy is how closely the actuator can move the load to the desired position – in order to ensure the safety and well-being of the patient.
• Wear/Tear: In addition, the actuator must be able to withstand the high levels of wear and tear that can occur in medical settings.
• Cost: You need to consider the cost of the actuator. Not all actuators are created equal, and some are more expensive than others. It’s important to find an actuator that fits your budget.
• Miscellaneous: Other factors to consider include the type of motion required, the size and weight of the actuator, and the environmental conditions in which it will be used.

When selecting ball screw actuators for medical applications, it is also important to consider the following factors:

• Force and torque requirements
• Enclosure and mounting considerations
• Environmental conditions
• Power requirements
  
  Learn more on this topic in our related blog – 5 Popular Medical Actuator Applications

When looking for the best actuators for medical applications, ensure to partner with a manufacturer who has been designing for the healthcare and medical industry. This is because they understand the stringent requirements of this industry and would help you find the best solution for your needs. Many experienced manufacturers can also provide customized linear motion solutions for medical applications, as they understand one-size-fits approach doesn’t work for everyone. 

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A Brief Explanation on Acme Screw Actuators & Ball Screw Actuators

The most basic difference between these two types of actuators lies in their mechanics.

• Acme screws are distinguished by their trapezoidal thread, which rolls on the lead screw to create a motion. In Acme screw actuators, linear force is transmitted to the nut by the rotating shaft. Efficiency of the linear motion depends on various factors such as lead screw, nut material, and lubrication. Most times, nuts are made from materials such as polymers, self-lubricating plastics, and metals like bronze, or brass. Nonmetallic nuts require no lubrication, and have low coefficient of friction. Both these characteristics contribute to their higher efficiencies. Metallic nuts are well-known for their load bearing properties, but they require lubrication, and high frictional forces.
• Ball screws are distinguishable due to their circular threads on the nut and the screw. These circular threads serve as helical raceway for ball bearings. The ball bearings roll through circular threads when the nut or screw moves. This rolling movement creates a linear motion.

Uses and Advantages of Acme Screw Linear Actuators and Ball Screw Linear Actuators

Firstly, let’s understand the advantages of Acme screw linear actuators.

• Acme screw linear actuators produce no noise because there are no rolling components.
• These actuators are ideal choice for vertical, as well as light load applications.
• The preloaded nut assembly in these actuators help reduce or completely eliminate backlash. This boosts application scope of these actuators.
• These actuators are safe to operate when the unit has a static load to hold.
• Lead screws are self-locking, which means there is no need to apply brakes, even in situations of power outage.
• Acme screw actuators are extremely affordable because they have low manufacturing costs.

Ball screw linear actuators are valued for their following advantages:

• Ball screws can carry heavy loads than Acme screw actuators.
• In these actuators, the screw thread and the nut don’t make a direct contact, but they always move along the rolling ball bearings. Hence, the low friction helps improve its speed, force, and duty cycle rating. Also, the low friction aids to its longer life cycle, and less motor power is required to drive them.
• The most common applications of these actuators include robots, aircraft, power steering, and semiconductors.
• These actuators can turn rotational motion into straight motion, and vice-versa.

As seen, both these variants have their own benefits. Thus, the choice will entirely depend on your application requirements.

Learn more on this topic in our related blog: Acme Screw DC Actuators: Why Are They Suited For Your Industrial Applications

Most linear actuator manufacturers in USA provide either of these two actuators in various specifications. However, your applications may have special requirements. In such cases, it is always better to opt for custom designed ball screws or Acme lead screws. There are very few linear actuator manufacturers who can provide you customized actuation solutions. Venture Mfg. Co. is one such Acme lead screw and ball screw linear actuators manufacturer who specialize in customized solutions.

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The center of gravity of the load that is moved keeps changing as it moves across the axes. For every position, the center of gravity with respect to the datum (home) point on the different axes needs to be calculated. As the load/ object travels across the system in accelerated or decelerated movements, its center of gravity relative to a coordinate will keep changing. So, when mounting the linear systems, the different positions and calculations of center of gravity of the object at various points with respect to all the axes will need to be calculated.

Calculating the center of gravity at various positions, in the application and averaging the calculations will assist you in employing the right mounting methods.

2. Load Bearing Capacity

Calculating the mass or geometry of the load at various points on the axes with respect to the coordinates will help determine the load bearing capacity of the system. Stationary loading factors, and rapid moment loads, are other factors to be considered when determining the load capacity. The integrated linear systems, engines, and gearboxes act as overhung loads. This is also a determinant in calculating the load capacity.

3. Stroke Lengths

The stroke length of the actuator for each axis needs to be determined to provide the right direction and magnitude of movement. The extent of movement is largely dependent on the type of actuator used. For example, when using heavy duty ball screw actuators, the ball screw will determine the length of stroke. The stroke length cannot exceed the length of the ball screw. On the other hand, linear actuators utilizing belt drives have no limit on the stroke length. Theoretically, the stroke length can be infinite but in practical application, the length rarely exceeds 10 meters.

Learn more on this topic in our related blog: Positioning System Guide to Choosing the Correct Linear Actuator in 12 Steps – Part IV

4. Precision & Repeatability

Most applications that require movement have definite needs for precision and repeatability. These are two important factors during the design and conception stages. The repeatability and accuracy of every linear actuator is defined upon production. You will need to speak to your manufacturer or supplier and purchase an actuator that fits your specific requirements. Generally, linear actuators with ball screws are more precise compared to those with belt drives.

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