Linear Drive - Converting Rotation to Translation

A linear drive converts rotational movements to linear movements and vice versa. Linear actuators are key components for motion control in many mechanical systems and mechanical engineering. Often, this conversion is needed to convert power and motion generated by motors and other rotating equipment into translation (linear motion). The drive is industrially realized with motors or also by hand. The article introduces frequently used and common concepts and lists the design criteria. Lastly, we will discuss examples for mechanical engineering applications.

Linear Drive - Converting Rotary Motion to Linear Motion

Mechanical engineering relies on various concepts to convert a rotational motion to a linear motion. The efficiency of motors in industrial environments is high and can be converted into linear movements by various mechanisms. The rotation of the motor can be used both rotationally and translationally.

The most common principles are:

• Slider crank mechanism
• Lead screw drive
• Cam gear
• Eccentric mechanism

The slider crank mechanism consists of a driven crank, a coupling (also called connecting rod) for power transfer, and a linearly guided slider. The drive is powered by a rotational movement that rotates the crankshaft and thus the crank. The connecting rod has a rotary linkage on both ends. The slider can only be moved in a translational manner. The constrained motion of the crank and slider creates a transmission that generates translation from rotation.

• 1 Lead screw
• 2 Ball screw nut with flange
• 3 Bearing
• 4 Carriage
• 5 Motor with gear box
• 6 Trapezoidal lead screw
• 7 Lead screw nut (cross-section)

The lead screw drive is a screw gear consisting of a rotating lead screw and a linearly guided carriage. The lead screw is driven by a motor and the lead screw pitch causes the carriage to move translationally. The guided movement and defined, uniform translation permit very precise and easy-to-control motion.

Lead screw drives and other screw gears are often powered by hand to adjust objects.

Cam gears are non-uniform transmissions. The rotary motion is converted by a powered, defining transmission geometry (e.g., a cam disc) and a scanner. The scanner is guided linearly.

Cam gears are classified by locking method, among other things. They are distinguished into friction locking and interlocking.

• Friction-locking transmissions are easier and less expensive to manufacture, but are not as efficient to operate and can be destroyed by resonances.
• Interlocking engineered solutions are more expensive to manufacture due to the additional guide surface and accuracy. These transmissions therefore usually require more space.

The eccentric mechanism consists of a control disc constructed with an eccentricity (offset to the axis of rotation) and a connecting rod. The eccentric mechanism is a coupling gear and acts like the slider crank. The control disc is the crank. The design often allows for a smaller installation space and has smoother operating properties due to higher masses.

Other methods for converting rotation to translation

Drives with rotary movements can also follow other principles. In principle, belt conveyors and traction drives also transform rotation to translation. However, these implementations are not suited for translation into rotation and are therefore not considered further.

Linear drive design criteria

The design of linear actuators differs by the employed mechanisms. In principle, linear actuators are gears that convert a gear ratio from a rotary motion to a translation.

• Stroke: In addition to the drive, the translational range of motion is the main feature of a linear drive. The stroke results from the geometry of the gear ratio. The speed of translation and the uniformity of movement depend on the geometry and rotational speed of the drive. The synthesis of the linear drive is also influenced by weight and inertia, since linear motions usually work with directional changes at the end of the stroke.
• Drive: The drive is powered by a rotation, usually initiated in mechanical engineering by an electric motor, that provides torque and rotational speed. This operating point can be changed with a transmission or a rotary speed control. When selecting the drive, it must also be noted whether certain circumstances or the principle dictate that the drive must be able to change the direction of rotation. Changes in rotary speed due to various operating points or uneven movements during synthesis must be also observed by taking into account the mass inertia of the system.
• Boundary conditions: Environmental conditions should also be considered when selecting linear actuators. The installation space is determined by the environment and periphery and can rule out certain principles. Weight can also play a key role at this point.

Application examples for linear drives in mechanical engineering

The application of linear actuators in mechanical engineering is diverse and multiple embodiments can often be implemented for one application. Examples of linear motion in mechanical engineering are:

• Sorting systems: A thrust crank moves perpendicular to a conveyor belt and pushes components down from the conveyor belt to the side.
• 3D printers: Industrial 3D printers user linear actuators for positioning.
• Mill: The motion control system of a CNC machine is formed by one lead screw per axis.
• Labeling: Cam gears or sliders crank mechanisms label bottles in medical engineering or general packaging engineering.
• Robotics: Robots in industrial environments use ball screws to achieve precise and low-friction motion with large acting forces.
• Adjustment: Screw transmissions, such as lead screw drives, are used to lock components into fixtures.

When synthesizing a linear drive, such as a slider crank, the MISUMI shop has the right connectors, such as hinge bolts and hinge bearing blocks, for supporting rotational movements, as well as articulated arms, connecting rods and spherical bearings for designing the gear ratio.

The components that cannot be replaced by standardized parts and purchased parts can be ordered on meviy. The meviy page is a contract manufacturing form where you can use CAD models to place an order - all without drawing derivation. The page will detect from the uploaded model whether it is a sheet metal part, turned part, or milled part and will calculate your price and lead time.