Screw Drive Basics Design 1 Screw, directly implemented in the gearhead 2 Radial bearing 3 Axial bearing 4 Planetary gearhead 0–4 stages 5 Motor 6 Encoder
Technical Data
Explanation
7 Max. efficiency The given efficiency is a maximum value that applies when loaded with maximum feed force. Efficiency falls sharply with very small loads. The stated value refers to the complete screw drive (gearhead and screw). 20 Max. feed velocity Specifies the maximum permissible feed velocity. 21 Max. feed force (continuous) Is the maximum permissible feed force which may be continuously applied. Exceeding this value Is the maximum permissible feed force which may be intermittently applied. “Intermittently” is defined as follows: − during max. 1 second − during max. 10% of operation Exceeding these values results in a reduced service life. 23 Mechanical positioning accuracy In this value, following factors are taken into consideration: − backlash of the gearhead − accuracy of the screw − axial play of the nut results in a reduced service life. 22 Max. feed force (intermittent)
The “Technical Data” block contains generally applicable data on screw, nut and gearhead. These are independent of the gearhead reduction ratio. Length The data sheets show the screw drives with the standard lengths. Other lengths are available as an option in 5 mm steps up to a given maximum length. Please give detailed requirements for special lengths. Max. efficiency/mass inertia The values stated refer to the screw alone (without gearhead). The values with gearhead are given in the “Gearhead data” main data field. Nut Standard screw drives are supplied with a thread nut. Flange or cylinder nuts are also available as an option. See details with corresponding reference number on page 487. Bearing The output stage and the screw are supported by preloaded axial bearings. This means that the high axial forces can be absorbed directly by the gearhead without additional support.
1 23 2
4 5 6
The particular type of screw required must first be established before a screw drive can be designed. Every type of screw has different characteristics and a number of specific limits. These limits are taken into account in the technical data. Ball screw: − highly efficient − not self-locking − high load capacity Metric lead screw: − self-locking − low costs Trapezoidal lead screw: − same as metric lead screw − higher load capacity than metric lead screw Feed force For the calculation of the feed force acceleration and friction forces as well as gravity have to be taken into consideration. Exceeding the maximum permissible load must be avoided, as this damages the screw. The maximum permissible feed force is displayed for stan- dard screws. For longer screws, the permissible feed force can be limited by the critical compressive force of the screw. In this case, supporting the end of the screw may be necessary.
Limitation for ball screws
2500 500 1000 1500 2000 3000 3500 4000
GP 22 S supported GP 22 S not supported
GP 32 S supported GP 32 S not supported
Maximum stroke The maximum possible stroke depends on the length of the screw L [mm]. The length of the nut L N [mm] and the thickness of its mounting plate X [mm] must be taken into consideration. Stroke = L − (L N + X + stroke reserve + Opt. FLEX-GEAR- SPIN06)
Speed and feed velocity Feed velocity v L [mm/s] is linked to output speed n [rpm] by the lead p [mm]. p · n 60 In combination with the gearhead, the motor speed n mot [rpm] is: v L = n mot = p v L · 60 · i Where i is the gearhead reduction ratio and p the screw lead. The screw speed is limited by the resonance frequency of the screw and for ball screws additionally by the ball return system. In addition, the maximum permissible speed of the gearhead has to be considered. Screw length [mm] 450 550 650 150 250 350 0
Limitation for ball screws
2500 500 1000 1500 2000 3000 3500 4000
GP 22 S supported GP 22 S not supported
GP 32 S supported GP 32 S not supported
0
Mounting and safety instructions Using a ball screw with a flange nut, the mounting through a hole is only possible with the optional rec- tangular mounting flange. The ball screw nut may never be removed. As the balls are preloaded remounting would be impossible. The screw may never block during operation, as this could damage the screw nut or gearhead. Service life crucially depends on the precision with which the gear is fixed to the screw nut. Eccentricities and angle errors sometimes result in massive radial loading which must never exceed the given maximum value. Additional information can be found in the maxon online shop at the item under downloads.
Screw length [mm] 450 550 650
150 250 350
Max. speed at ball screws
Torque The required torque of the screw M a [mNm] is calcu- lated with the feed force F L [N] (load), the thread lead p [mm] and the efficiency of the screw η 1 . F L · p 2 · · η 1 In combination with the gearhead, the required motor torque M mot [mNm] is: M a = M mot = F a · p 2 · · i · η Where i is the gearhead reduction ratio and η the efficiency of the complete screw drive. Max. speed at ball screws
2500 500 1000 1500 2000 4500 3000 3500 4000 5000
GP 22 S supported GP 22 S not supported GP 32 S not supported
GP 32 S supported
0
450 550 650
150 250 350
Screw length [mm]
2500 500 1000 1500 2000 4500 3000 3500 4000 5000
GP 22 S supported GP 22 S not supported GP 32 S not supported
X
GP 32 S supported
L N
468 maxon screw drive
© 2024 maxon. All rights reserved. September edition. Subject to change.
0
450 550 650
150 250 350
Screw length [mm]
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