I. Core Classification Dimensions of Ball Screws
Ball screw types are mainly classified based on four core dimensions structural design accuracy grade lead characteristics and mounting configuration. Different classifications correspond to different performance characteristics and applicable scenarios to meet the diverse needs for precision load and efficiency in mechanical transmission.
II. Main Types of Ball Screws
1. Classification by Ball Circulation Method (Core Structural Differences)
Internal-circulation ball screws：Balls circulate inside the screw nut with the circulation path not exceeding the outer diameter of the nut. They have a compact structure and small radial size making them suitable for installation in space-constrained scenarios (such as precision machine tool spindles and small automation equipment). Their circulation components are mostly "reversers" (such as round and square reversers) which ensure smooth ball circulation and low operating noise but the manufacturing process is relatively complex and the cost is slightly higher.
Externally recirculating ball screws：Balls circulate through external circulation channels (such as cannulated and end-capped types) of the nut with part of the circulation path exposed outside the nut. They have a simple structure low manufacturing difficulty and low cost and can improve load-bearing capacity by increasing the number of balls making them suitable for medium and heavy-load transmission scenarios (such as CNC machine tool feed axes and heavy lifting platforms). However their radial size is larger and slight noise may occur at the connection between balls and the channel during operation with high-speed stability slightly inferior to that of internal-circulation types.
2. Classification by Accuracy Grade (Transmission Accuracy Differences)
Ball screw accuracy grades are usually divided according to international standards (such as ISO) or industry standards (such as JIS) with core measurement indicators including lead error travel deviation and radial runout. Common grades from low to high are as follows:
Grade C7 (General Accuracy)：The lead error is about 0.15-0.3mm/300mm suitable for transmission scenarios with low precision requirements (such as general conveying equipment and manual adjustment mechanisms).
Grade C5 (Medium Precision)：The lead error is about 0.08-0.15mm/300mm which can meet the needs of most automated equipment (such as general industrial robots and small CNC machine tools).
Grade C3 (High Precision)：The lead error is about 0.025-0.08mm/300mm suitable for precision transmission scenarios (such as precision grinders and semiconductor wafer handling equipment).
Grade C1/C0 (Ultra-High Precision)：The lead error is ≤0.025mm/300mm mainly used in cutting-edge precision fields (such as aerospace equipment and fine-tuning mechanisms of optical instruments) with strict manufacturing processes and high costs.
3. Classification by Lead Characteristics (Motion Efficiency Differences)
Fixed-Lead Ball Screws：The lead is a fixed value (such as 5mm 10mm 20mm) with a constant transmission ratio and a linear relationship between output speed and input speed. They are suitable for scenarios requiring stable and uniform speed transmission (such as assembly line conveying and general machine tool feeding) and are currently the most widely used type.
Variable-Lead Ball Screws：The lead changes with the direction of the screw axis (such as progressive variable lead and step-by-step variable lead) which can realize non-uniform speed transmission. They are used in mechanisms that need acceleration deceleration or displacement compensation (such as some special testing equipment and precision cam replacement mechanisms) with relatively niche application scenarios and high customization requirements.
4. Classification by Installation Method (Assembly Compatibility Differences)
Fixed-End Ball Screws (Both Ends Fixed)：Both ends of the screw are fixed by bearings (such as angular contact ball bearings) which can bear radial and axial loads with high rigidity and positioning accuracy. They are suitable for scenarios requiring high precision and rigidity (such as precision machining centers and coordinate measuring machines) and the pre-tension of the screw must be strictly controlled to offset thermal deformation.
Fixed-End and Free-End Ball Screws：One end of the screw is fixed and the other end is suspended with a simple structure and easy installation but low rigidity and limited axial load capacity. They are only suitable for short-stroke and low-load scenarios (such as small lifting platforms and light-load manual adjustment mechanisms).
Fixed-End and Supported-End Ball Screws：One end of the screw is fixed and the other end is supported by bearings (such as deep groove ball bearings) with rigidity between that of both-ends-fixed type and fixed-end-free-end type. They can bear a certain radial load and are suitable for medium-short stroke and medium-load scenarios (such as general automated production lines and small robot joints).