Kelude Crane Creep Speed Hoisting for Precision Installation
Kelude Overhead Crane Creep-Speed Hoisting Solution
A closed-loop variable-frequency retrofit solution for creep-speed hoisting, engineered for precision positioning and alignment tasks. Built around the Inovance MD500 series VFD (closed-loop vector control with PG card encoder feedback) and a Siemens S7-1200 PLC, it delivers continuously adjustable hoisting speeds from 0.5 to 12 m/min, a creep-speed range of 0.5–2 m/min, smooth S-curve acceleration/deceleration, and positioning accuracy of ±1–3 mm. The existing motor, gearbox, and brake are retained — only the speed control system and electric control cabinet are upgraded, with an on-site installation time of 3–5 days. Deployed on 68 overhead cranes across 22 companies in China, the solution has improved overall efficiency by approximately 45%.
Kelude Heavy Industry has officially launched its creep-speed hoisting solution for overhead cranes. Targeting applications with stringent speed and positioning requirements — such as die handling, engine assembly, precision equipment installation, and nuclear fuel handling — the solution employs closed-loop vector control with encoder speed feedback to bring hoisting speeds down from a conventional minimum of 1.5–3 m/min (two-speed) to 0.5 m/min, while substantially improving start/stop smoothness and positioning accuracy.
Data sources: Inovance MD500 series VFD application manual (No. 19001530-AQ, Rev. 10, March 2024, P.89 closed-loop vector control accuracy table, P.122 PG card wiring instructions); Omron E6B2-CWZ6C incremental encoder datasheet (CSM_E6B2-CWZ6C_DS_J_3_2, OMRON, 2023); Siemens S7-1200 motion control function manual (A5E04945111-AQ, 2024, P.56 S-curve parameter description); ISO 12480-1:1997 "Cranes — Safe use — Part 1: General" (P.14, Table A.1 acceleration limits); and Kelude's retrofit project database of 22 installations (January 2022 – June 2026, project nos. KL-MS-2022-001 through 022).
Core Technical Approach
The creep-speed solution upgrades the existing open-loop or stepped speed control to closed-loop vector variable-frequency drive with encoder speed feedback, while retaining the original hoisting motor (either wound-rotor or squirrel-cage asynchronous) and gearbox.
System configuration: Inovance MD500T series VFD (sized to match the existing motor's rated power — MD500T45GB-NA for motors up to 45 kW, MD500T75GB-NA above 45 kW; closed-loop vector speed control accuracy ±0.05%, per manual P.89, Table 6-1) + incremental encoder (Omron E6B2-CWZ6C, 1024 P/R resolution, A/B/Z three-phase differential output, max response frequency 100 kHz, per Omron CSM_E6B2-CWZ6C_DS_J_3_2 P.2 technical data sheet) + PG card (Inovance MD34PG01, ABZ differential input, max response frequency 500 kHz, per Inovance MD500 manual P.122, Table 7-2) + Siemens S7-1200 PLC (handles S-curve acceleration/deceleration, multi-speed or analog speed setpoints, and PROFINET communication). Speed control accuracy: ±0.05% of rated frequency (closed-loop vector mode); speed regulation range: 1:1000.
S-Curve Acceleration and Deceleration Control
Conventional overhead cranes use step-change speed setpoints (a fixed frequency applied directly to the VFD), which produces impact acceleration (Δa = 0.3–0.5 m/s²) at start and stop, causing significant load sway. The creep-speed solution implements S-curve acceleration/deceleration in the PLC program: acceleration ramps linearly from zero to a preset maximum (e.g., 0.1 m/s²), holds a constant-speed segment, then ramps linearly back to zero. The jerk is adjustable from 0.05 to 0.2 m/s³ throughout the profile (per ISO 12480-1:1997 "Cranes — Safe use — Part 1: General," Table A.1 recommended acceleration limits for load sway control: ≤0.1 m/s² for precision lifting, ≤0.3 m/s² for general lifting; and per the Siemens S7-1200 motion control manual, A5E04945111-AQ, 2024, P.57 example: a jerk of 0.1 m/s³ yields an S-curve acceleration time of approximately 3.5 seconds). In practice, S-curve acceleration time measures 2–3 seconds in standard mode and 4–6 seconds in precision mode, with load sway at start/stop kept to ≤±5 mm (versus ±30–50 mm with conventional step-change setpoints).
Application Scenarios and Configurations
The creep-speed solution is available in three standard configurations:
Retrofit Performance Results
Based on statistical data from 68 completed retrofit projects:
Case Studies
A precision machinery manufacturer upgraded two 20t QD Type double-girder overhead cranes (Project No. KL-MS-2025-015) in its assembly workshop. Originally equipped with two-speed motors (8m/min/2m/min), the cranes were used for lifting and positioning precision machine tool headstocks (8–12t each) during assembly. Before the retrofit: the 2m/min creep speed caused excessive impact during positioning, requiring two assembly workers to manually push and pull components into place. Each positioning cycle took 8–12 minutes, and impact-related headstock damage occurred 1–2 times per month, with repair costs averaging ¥3,000–8,000 per incident. After the retrofit (precision assembly version at ¥72,000 per crane × 2 = ¥144,000 total): the new 0.5m/min creep speed with S-curve starting delivers smooth, jerk-free motion, achieving positioning accuracy of ±1mm. Positioning time dropped to 2–3 minutes per cycle, and impact-related damage has been eliminated entirely. Annual savings: approximately ¥66,000 in avoided repair costs plus ¥82,000 in reduced assembly labor, totaling ¥148,000 per year—a payback period of roughly 11.7 months.
Technical Parameters: Before vs. After Retrofit
| Comparison Item | Retrofit Before(Two-Speed/Open Loop) | Retrofit After(Variable Frequency Drive (VFD)Closed-loop Creep Speed Micro-motion) |
|---|---|---|
| Minimum Lifting Speed | 1.5~3m/min(Two-Speed Low Speed Step) | 0.5m/min(≤0.1m/min Customized) |
| Speed control Mode | Stepped2~3Low Speed Step | Stepless0~12m/min Continuously Adjustable |
| speedcontrol accuracy | ±1Hz(Open Loop V/F) | ±0.05Hz(Closed-loop Vector+PG) |
| Positioning Accuracy | ±10~20mm | ±1~3mm |
| Start/Stop Sway Working radius | ±30~50mm | ≤±5mm(SCurve) |
| Single Positioning Time | 45~90s | 8~20s |
| Monthly Average Collision Incidents | 1~2times(Caused by Operational Impact) | 0times |
| Frequency Inverter / VFD | None | Inovance MD500Series Closed-loop Vector |
| Encoder | None | Omron E6B2-CWZ6C 1024P/R |
| Control Mode | Cam Controller/Contactor | S7-1200 PLC + SCurve |
| Already Retrofit Unit Count | — | 22Enterprises / 68units |
Related reading: Kelude Heavy Industry Crane Control Cabinet Smart Upgrade — From Relay Logic to Integrated PLC + VFD Retrofit, Crane VFD Speed Control System Selection & Commissioning: G120 / ACS880 / ATV930 Engineering Comparison
Frequently Asked Questions
Q: Is the creep speed solution suitable for all overhead cranes?
A: Yes. Any overhead crane whose hoisting mechanism uses an asynchronous motor + gearbox drive can be retrofitted with a variable-frequency speed control system to achieve creep speed operation. The 68 cranes already retrofitted cover LD Type (5–10 t, 22 units), LH Type (10–20 t, 18 units), and QD Type (16–100 t, 28 units). For high-speed cranes with a lifting height above 30 m or a lifting speed above 20 m/min, the creep speed mode is added as an auxiliary function without affecting the original high-speed performance.
Q: Will the retrofit affect the original lifting speed?
A: No. The system provides a two-mode switch between "fast" and "creep" speed, which the operator can toggle with one press on the HMI touchscreen or remote control. Fast mode maintains the original rated speed (e.g., 8 m/min), while creep mode engages S-curve micro-motion at 0.5–2 m/min. Capacity limitation and safety protection functions are identical in both modes.
Q: Where is the encoder mounted? Is the protection rating sufficient?
A: The incremental encoder is mounted via a flexible coupling on the non-drive end shaft extension of the hoisting motor (or on the gearbox high-speed shaft), protected by a stainless steel protective cover (IP65) with an aviation plug connection. The encoder signal cable uses double-shielded twisted pair (LAPP UNITRONIC LiYCY 4×0.34mm²), routed at least 300 mm away from the VFD power cable. Field data from deployed projects shows an encoder failure rate of less than 0.5 failures per year.
Q: Does the retrofit change the operation mode?
A: No. The operation mode remains unchanged — remote control, operator console, and floor operation box all continue to work as before. A new HMI touchscreen is added for switching between fast/creep modes, setting S-curve parameters (acceleration / jerk), and viewing real-time speed feedback. In creep mode, the hoist button on the remote control or operator console acts as an inching jog control (each press moves the load approximately 2–5 mm, depending on the speed setpoint), allowing precise load positioning. Operators can master the system with one hour of training.
