KEVOS® MAKEOS · Springs
Lid Counterbalance with Torsion Springs (Balance, Handle Force, Spring Stress)
Will these torsion springs counterbalance my hinged lid so it is easy to lift and stays open, and are the springs within stress when wound up?
Check of a hinged lid, hatch or guard balanced by torsion springs at the hinge: the lid’s weight torque as it opens, each spring’s rate from its wire, coil and turns (as the helical torsion spring tool), the spring torque from the wind-up at the closed position, the out-of-balance torque over the whole opening and the largest force at the handle, whether the lid stays open and shut, and the spring stress at full wind-up against your allowable.
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How this tool works
Inputs, units and where to find them
| Input | Unit | Typical source |
|---|---|---|
| Lid mass | kg | Mass of the lid. |
| Hinge to lid centre of gravity | mm | Distance from the hinge axis to the lid’s centre of gravity, with the lid closed and horizontal. |
| Opening angle | ° | Angle the lid opens to from horizontal. |
| Number of springs | Number of identical springs sharing the load. | |
| Each spring | ||
| Wire diameter | mm | Wire diameter of each spring. |
| Mean coil diameter | mm | Mean coil diameter. |
| Body turns | turns | Number of body turns. |
| Elastic modulus | GPa | Elastic modulus of the spring wire. |
| Wind-up at the closed position | ° | Angle the springs are wound up when the lid is closed (they unwind as it opens). |
| Allowable bending stress | MPa | Allowable bending stress of the spring wire. |
| Handle | ||
| Hinge to handle | mm | Distance from the hinge to the handle. |
| Largest handle force | N | Largest force you accept at the handle anywhere in the swing. |
Method and formulas
- Spring rate k = E d⁴ ÷ (64 D N_b) per radian; stress = K_i 32 M ÷ π d³ with K_i = (4C² − C − 1) ÷ [4C (C − 1)] (as the helical torsion spring tool).
- Lid torque = m g r cos θ; spring torque = n k (θ₀ − θ) at opening angle θ.
- Out-of-balance torque scanned over the opening; handle force = largest out-of-balance ÷ handle distance.
- Example: each spring has 7,896.4 N·mm/rad; the worst handle force is 9.9979 N at 40°; spring stress 1,143.8 MPa.
Limitations
- Lid centre of gravity on the line through the hinge when closed; offsets change the torque curve.
- Friction in the hinge ignored; it helps hold positions.
- Example values are illustrations. Replace them with values for your actual task.
Typical uses
- Balance a machine guard or hatch
- Check handle force on a heavy lid
- Choose torsion springs for a hinge
Who it is for
- Machine designers
- Product designers
- Design engineers
What you get
- Spring rate and torque
- Out-of-balance torque and handle force
- Spring stress at full wind-up
Interpreting the result
- A linear spring cannot match the cosine weight curve exactly: balance near the middle of the swing to keep handle forces low at both ends.
References
- Machinery’s Handbook, 29th edition (Industrial Press, 2012), printed pp. 333–343. Topic reference; no source tables or recommended settings are reproduced.
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Open the Lid Counterbalance with Torsion Springs (Balance, Handle Force, Spring Stress) calculator
