Motion Control Basics: A Glossary of Terms

Motion control plays a major role in modern product design. Many high-end products use innovative hinge mechanisms to stand out from the crowd.

Building a product with heavy-duty industrial hinges can be complex, so we created a glossary of motion control basics (which also serves as a basic ergonomics glossary).

Reviewing these terms will help you communicate more effectively with your vendor:

Motion Control Basics

• 3-bar hinge/mechanism: A hinge or mechanism with three links to provide nonparallel motion up and down.
• 4-bar hinge/mechanism: A hinge or mechanism with four links connected by a pivot. This mechanism can provide parallel or nonparallel motion.
• 6-bar hinge/mechanism: A hinge or mechanism with six links and pivots. The higher the number of bars and the more complex the design, the higher the cost.
• Articulating hinge: Has complex movement falling under the “kinematic motion” category in that it features both translation and rotation. May also be called a multilink hinge.
• Balance angle: The number of degrees at which the center of gravity is directly above a pivot.
• Balance point: The location where the center of gravity lines up directly over the top of the pivot. At the balance point, a lid or door will stay put and not swing in either direction.
• Center of gravity: A point that represents the average location of the weight of an object. Click here to learn more.
• Center of mass: The same measurement as the center of gravity.
• Coast close: The lid will tend to move toward the closed position because the lid torque is greater than the spring plus friction torque.
• Coast open: The lid will tend to move toward the open position as a result of the lid torque being less than the spring minus friction torque.
• Compression spring: Stores mechanical energy in the wire of the spring. The force is generated by compression.
• Concealed hinge: A hinge purposely hidden in the product’s design. This is typically done for aesthetic reasons, but can also help consolidate product footprint and avoid high heat and other sensitive areas of the product.
• Counterbalance hinge: A complex hinge that incorporates various types of springs. Mitigates the force felt by users so they can easily open heavy lids and doors. Click here to learn more.
• Damping: Restraint of vibration (mechanical, noise, etc.) by dissipation of energy. Click here to learn more.
• Ergonomics: The study of people and their working conditions in relation to motion and comfort. The end goal is to improve mental and physical health through more efficient equipment, posture, etc.
• Extension spring: A spring that stores energy or provides force when you stretch it (i.e. a screen door spring).
• Force: The resulting push or pull from an interaction between two objects (including air). Click here to learn more.
• Gas cylinder: An energy storage device that relies on gas and oil to provide a controlled force.
• Gas spring: Another name for a gas cylinder.
• Gravity lock: A feature common in ergonomic products. With this feature, as users tilt a keyboard mechanism or similar product, they unlock the links and can move it up and down as needed. When the user lets go, the device locks in place. 
• Handle force: The amount of force you need to exert on a handle for the attached object to move.
• Kinematics: A branch of physics that focuses on the motion of objects (velocity, acceleration, etc.). The object’s mass is not taken into account.
• Kinetics: A branch of physics that focuses on kinematics while also describing what forces or torques are influencing the kinematic motion. This branch takes the object’s mass into account.
• Lid torque: A function of the lid’s weight multiplied by the horizontal distance between the object’s center of gravity and the pivot axis.
• Mechanical spring: Allows controlled application of force, as well as storage of energy. The spring returns an equivalent amount of energy when released.
• Motion control: The process of having an object move through a desired path. To get there, a component can use linkages, pivots, mechanisms, etc. Click here to learn more.
• Multilink hinge: A complex hinge that can have more than four links. Also known as an articulating hinge.
• Negative tilt: When the axis makes a negative angle along the lines of longitude. An angle used when positioning an ergonomic keyboard tray or similar device for posture. The tray is tilted down and away from the user to allow for a more neutral, low-stress posture. Negative tilt is recommended for an upright position.
• Pivot hinge: A mechanism that rotates around a pin. Allows full turning of the attached assembly.
• Pop-up: A slight rise of a few degrees from the closed position due to the spring torque being greater than the lid torque. This can be advantageous when a latch is used, as it creates a gap for opening the lid.
• Positive tilt: When the axis makes a positive angle along the lines of longitude, toward the user. An angle used when positioning an ergonomic keyboard tray or similar device. This is recommended for a reclined position.
• Simple hinge: A 2-bar hinge with two members of a single pivot.
• Slam: Undesirable, violent closing resulting in a negative user experience. Lack of a properly counterbalanced unit can create noise, an abrupt stop, damage to the product, and even injury to the user.
• Soft close: The rate of final closing controlled by the use of a counterbalance that limits the closing torque. Excess energy is absorbed to prevent a sudden slam.
• Soft open: The rate of final opening controlled by the use of a counterbalance that limits opening torque. Excess energy is absorbed to prevent a sudden stop.
• Spring assist: Force that offsets the heavy feel of a lid. The lid will coast open and/or closed from wherever the engineer desires. This is different from a counterbalance in that it won’t stay put when released; it will either drift open or closed based on your design.
• Spring torque: Used to counteract the torque caused by gravity. At angles where spring torque is higher than lid torque, a lid will self-open. When the spring torque is lower, the lid will self-close.
• Tension spring: Another term for extension spring.
• Torsion spring:  Stores mechanical energy in the wire of the spring.
• Translation: Movement that’s in and out (or vice versa) or left and right (or vice versa).
• True counterbalance: When a lid stays exactly at the desired angle. This occurs when the lid torque (force times distance) is matched by spring torque and controlled friction. This balance improves safety and ease of use.