# Ball Screw Actuator

### Overview

Ball screw linear actuators are typically used for medium duty applications that require higher load capacity and precision. Supported at each end by an angular ball bearing embedded within a plate and linked by two Vention 45 x 90 mm extrusions, the assembly can accomodate any of Vention’s Nema 34 stepper motors and comes in three different lengths.

### Compatible Guides

The ball screw linear actuator can drive a variety of gantries that are in turn supported by both Eccentric and Concentric V-shaped rollers (MO-LM-001-0027/0028) or linear bearings on shafts (MO-LM-014-XXXX). Both configurations can be seen below.

### Applications

There are several application for ball screw linear actuators, including a High Precision UR10 7th Axis or a 2-Axis High Precision Linear Actuator.

### Technical Specifications

Available Lengths |
585mm, 855mm and 1530mm Net displacements are 405mm, 675mm and 1350mm respectively |

Displacement Ratio (mm/turn) |
10 |

Linear Force / Torque Ratio (N/Nm) |
565.5 |

Linear Force Capacity (N) |
3500 @ 50mm/s |

Repeatability (mm) |
±0.023 per 300mm length |

Back Drive Resistance |
High |

Motor Compatibility |
NEMA 34, 14mm shaft, 5mm keyway |

Sensor Compatibility |
Compatible with all M18 sensors using the sensor bracket (CE-HW-001-0001) |

The figure below demonstrates the linear force output in function of the linear speed of the ball screw linear actuator. This was calculated using Vention’s NEMA 34 stepper motors.

Observing the figure above, the force sharply decreases as the linear velocity increases, making the ball screw ideal for high force, low speed applications.

#### Buckling Calculations

The Vention ballscrew actuator is designed with one end of the ballscrew fully fixed and the other end of the screw supported. The fully fixed end is on the side where the motor is mounted which can be an important consideration when designing. Buckling can occur when a long rod collapses due to compressive loads. In most use cases, the Vention ballscrew is not susceptible to buckling, however in the longest option and at max load it does pose a risk if the screw is in compression. In these cases, the ballscrew should be oriented with the motor at the top so that the screw is always in tension while lifting loads. The following calculation can be used to calculate bucking force:

- Cbkl corresponds to a coefficient called the fixity factor. In this case, a fixity factor of 2 is used because one end is fully fixed and one is supported.
- d1 is the root diameter of the screw in mm. The Vention ballscrew has a root diameter of 13mm.
- A safety factor of 1.25 is recomended when performing bucking calculations.

Knowing these constants, the buckling formula can be simplified as:

In the case of Vention’s longest ballscrew, a maximum possible unsupported length of 1440mm is possible. This leads to a critical buckling force of 2135N. This means that if this configuration is possible in your design, the motor must be mounted facing up so that the screw is in tension instead of compression, thereby avoiding the possibility of exceeding 2135N compressive loads and buckling the screw.

### Assembly Instructions

#### Support Plate

1. Insert a 12mm ID angular ball bearing into the opening of a ball screw end plate.

2. Secure the bearing in place using a ball screw end cap and 4 X M4 X 10mm screws

3. Repeat steps 1 and 2 for the second side of the ball screw

#### Ball Nut Housing

4. Slide the ball nut housing onto ballscrew up to the ball nut, making sure the ball nut is properly housed within its housing.

5. Secure the ball nut to the housing using the 4 outside mounting holes and 4 x M5 x 20mm screws.

#### Structure

6. Insert the ball screw ends through both bearings housed in the end plates

7. Tap both holes at each end of both 45 x 90mm extrusions (if required)

8. With the ball screw properly inserted in both end bearings, secure each end plate to the extrusions using 4 x M8 x 55mm fasteners.

#### Motor Support

9. Fasten the threaded end of the screw using the bearing locknut. The ball screw should now be contained and unable to move axially.

10. Insert the 3mm machine key into the ball screw’s keyway.

11. Insert the end of the ball screw into the smaller side of the 14mm to 10mm flexible shaft coupling. Secure the ball screw by tightening the small side clamping screw of the coupling.

12. Secure the motor mount to the ball screw end plate where the coupling is located using 4 x M8 x 20mm screws

13. To mount one of Vention’s 3 motors, simply insert the shaft through the mount and into the larger side of the coupling, properly aligning the machine key. Tighten the coupling and fasten the motor to the support block.