Yuhuan CNC Machine Tool Co., Ltd.

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Micro Internal Gear Rings of Dexterous Hands

This CNC broaching machine is purpose-built for the small-module internal gear rings used in the micro reducers of humanoid robot dexterous hands, and sits among the core upstream process equipment for humanoid robotics. The platform is typically a servo-driven vertical internal broaching machine that handles both soft broaching before heat treatment and hard broaching after it. Each dexterous-hand finger pairs a coreless (hollow-cup) motor with a micro planetary reducer, whose internal gear ring has an extremely small module — 0.15 is typical — and a bore of only about 5 mm. That gear ring is precisely the workpiece this machine is designed around.

Keywords

Precision grinding, intelligent manufacturing technology, integrated solutions

Classification

Others

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Typical Machining Parts

Equipment Highlights

灵巧手齿圈拼图

Workpieces

● Parts: thin-walled internal gear rings and internal splines for micro planetary reducers in dexterous hands

● Typical specifications: module 0.12–0.3, 30–60 teeth, bore diameter 4–10 mm; thin-walled and prone to distortion

● Materials: 40Cr, GCr15 and powder metallurgy; hard broaching after heat treatment cuts hardened parts at HRC 58–62 directly, eliminating the finishing grind

● Process advantage: a single form-cutting pass yields highly consistent tooth profile, pitch and roundness at a cycle time far shorter than gear shaping — well suited to high-volume production of micro gear rings

Core Equipment

The machine is an integrated mechanical-electrical, servo-driven vertical internal broaching machine in which the broaching motion is powered by a servo motor. Within its rated pulling force and working stroke it broaches through-holes of virtually any profile, with high productivity for batch and mass production.

For micro, thin-walled parts the design principle is low force, high precision: rated pulling force generally stays within 50 kN, the stroke is short, and dedicated precision fixtures locate the tiny workpiece. The machine switches between soft broaching before heat treatment and hard broaching after it, and can be fitted with a robotic loader for automated lines. The Yuhuan LJ51 series is one such platform, dedicated to micro gear rings and internal splines for humanoid robots.

Key Engineering Challenges

1. Micro broach manufacture — extremely small-module broaches, in HSS or carbide, carry very fine teeth that are difficult to grind; the tiny chips are hard to evacuate and readily scratch the tooth flanks.

2. Distortion control on thin walls — with minimal wall thickness, clamping and cutting forces easily produce ovality, so fixtures must provide floating location and low-stress clamping.

3. Tight accuracy targets — cumulative pitch error, profile error and surface roughness (Ra 0.4–0.8) directly govern backlash, lost motion and the tactile feel of the hand's joints.

4. Servo-controlled pulling force — micro parts tolerate no impact, so the servo system must run smoothly at low speed with closed-loop force feedback to prevent tooth chipping and tearing.

5. Cooling and lubrication — micro-volume, high-pressure broaching oil carries heat away, limits tooth wear and prevents burning of the minute tooth surfaces.

Process Route

A servo motor drives the screw through a planetary reducer; the screw nut carries the main slide up and down along the guideways to execute the broaching and return strokes. Semi-automatic cycle and setup modes let the machine handle different broaching methods.

One complete cycle: load the workpiece at the loading station → insert the broach manually → start broaching → main slide moves down into the cut → broaching complete → unload the part → initiate the return step → main slide travels back up → remove the broach, load the next workpiece and insert the broach again.

Typical Capability

Item	Specification
Module	0.12 – 0.3
Number of teeth	30 – 60
Bore diameter	4 – 10 mm
Workpiece hardness	Soft broaching before heat treatment; hard broaching at HRC 58–62 after
Tooth surface roughness	Ra 0.4 – 0.8
Rated pulling force	Up to 50 kN (precision broaching of micro parts)