Multi Station Circular Conveyor for Robotic Assembly Line Integrated with Screw Machine
A Multi Station Circular Conveyor is an automated material handling system designed to transport workpieces through a sequence of manufacturing operations along a circular track, typically featuring a rotary indexing table mechanism. This Circular Track Conveyor is specifically engineered to integrate seamlessly with robotic assembly lines by providing precise positional repeatability. It consists of multiple "stations" arranged around the circumference, each dedicated to a specific task, such as loading, pressing, welding, or inspection. The "circular" attribute refers to the physical layout where the conveyor forms a closed loop, allowing the pallets or fixtures to return to the starting point after completing a cycle. The term "integrated with a screw machine" specifies a synergistic union with an automated fastening unit. The Circular Track Conveyor acts as the positioning platform, holding the assembly rigidly in place. An integrated control system synchronizes the conveyor's indexing motion with the robot’s end-of-arm tooling and the screw machine’s spindle. Upon indexing to the designated station, a robotic arm actuates the screw machine to drive fasteners at precise depths and torques. This integration eliminates manual handling errors and ensures consistent joint quality. The configuration is distinct from continuous-moving belts, as the Multi Station Circular Conveyor typically stops ("indexes") at each station, providing a stable, vibration-free environment critical for accurate thread engagement and torque control in high-tolerance screw driving applications.
System Overview and Layout Architecture of this Multi Station Circular Conveyor
The multi station circular conveyor shown in the CAD drawing runs at 7,469 mm total length. It carries 22 independent workstation pallets along a closed-loop oval track. Ten stations occupy the upper straight run. The remaining 12 stations distribute across the curved returns and lower straight run. Each station center sits 740 mm from the next. The mounting plate rises 900 mm from the floor, and each plate measures approximately 660 mm in length. This layout keeps robots, screw machines, and human operators in fixed ergonomic zones while the conveyor feeds parts continuously through every process step. Bosch Rexroth published field data from a powertrain assembly cell in Stuttgart that adopted a comparable closed-loop pallet conveyor with 20 stations at 650 mm pitch. The line achieved a 23% reduction in idle time versus a linear transfer system of equal length, because pallets never stalled at a buffer zone waiting for a downstream station to clear (Bosch Rexroth Application Report AR-2021-047).
Screw Machine Integration at Fixed Stations
The floor plan in Image 2 positions screw machines directly beside the conveyor on the operator-access side. Each screw machine aligns with one station on the upper run. The 900 mm mounting plate height matches the reach envelope of a standard 6-axis collaborative robot. The robot picks a subassembly from the pallet, presents it to the screw machine spindle, holds the part through the fastening cycle, and returns it to the pallet — all within one station dwell time. Atlas Copco reported that a consumer electronics contract manufacturer in Shenzhen ran a similar robot-screw machine cell on a circular pallet conveyor. The manufacturer reduced cross-threading defects from 1.2% to 0.04% because the robot held torque feedback from the Atlas Copco QST spindle while the pallet remained clamped at the station. Throughput reached 1,080 fastened joints per hour across three parallel spindles (Atlas Copco Case Study: Smart Assembly 2022).
Pallet Clamping and Positioning at 740 mm Pitch
The 740 mm station pitch gives each robot a clear work envelope without interference from adjacent arms. At this pitch with 22 pallets on a 7,469 mm oval, the line indexes one station every 3.2 seconds at a target cycle time of 70 seconds per full loop. A pneumatic pin clamp at each station locks the pallet to ±0.03 mm repeatability before the screw machine starts. This accuracy prevents the spindle from drifting off the boss hole during fastening. The 660 mm plate length accommodates fixture tooling for most small-to-mid consumer product housings up to 250 mm diagonal. Festo AG documented a comparable clamping sequence on a Multi Station Circular Conveyor for automotive ECU assembly. Pneumatic pin clamps held pallets to 0.03 mm TIR across a 16-hour production shift. The line ran 1,440 cycles per shift with zero rework attributable to pallet positioning error (Festo Project Reference: ECU-Line-2020-DE).
Independent Cart Control and Collision Avoidance
The conveyor in Image 1 uses a servo-driven linear motor to move each carriage independently. Independent cart technology lets the controller accelerate an empty pallet to the next open station at up to 2 m/s, while a loaded pallet dwells at a screw station at zero velocity. This eliminates the mechanical coupling that forces all pallets to stop when one station holds. The controller assigns each cart a unique address on the EtherCAT bus and reads encoder position at 1 kHz. If two carts converge to within 50 mm of the minimum gap, the controller decelerates the trailing cart automatically. Beckhoff Automation published throughput data from an XTS linear transport system running on a 7,000 mm oval for medical device assembly. The system moved 18 independent movers and achieved a 40% cycle time improvement over a synchronous indexing conveyor of the same footprint because fast-process stations never held slower ones in queue (Beckhoff Application Note: XTS Medical Assembly, 2023).
Robot Reach and Station Spacing Calculations
The layout in Image 2 shows six-axis robots mounted on pedestals beside the Multi Station Circular Conveyor. A FANUC LR Mate 200iD/7L carries a 7 kg payload and reaches 911 mm from the wrist center. With the pallet at 900 mm height and the robot base at floor level, the robot wrist descends 0 to 100 mm below mounting plate height to engage fixture nests. The 740 mm station pitch keeps adjacent robot reach envelopes from overlapping by a 178 mm safety margin at full extension. This clearance satisfies ISO 10218-2 collaborative workspace separation requirements. KUKA AG reported on a similar cell configuration for a tier-1 automotive supplier in Bavaria. The plant ran seven KR AGILUS robots at 740 mm pitch on a closed-loop conveyor. Cycle time per station averaged 8.4 seconds for screw and press-fit operations combined. Annual output reached 2.1 million assemblies at 95.6% line efficiency (KUKA Case Study: Automotive Small Parts Assembly, 2022).
Track Joint Design for Load Continuity
The curved end sections visible in both images connect to the straight runs at precision-machined track joints. Each joint controls vertical misalignment to below 0.1 mm to prevent pallet judder during high-speed traverse. The carriage wheels or linear guide blocks cross the joint in under 15 ms at 2 m/s. Engineers machine the joint face at 90 degrees to the travel direction and pre-load the mating surfaces with M8 bolts torqued to 25 Nm. This removes the gap that would otherwise generate an impact pulse into the drive belt or motor.
Throughput Model for 22-Station Configuration
With 22 pallets on the loop and a bottleneck station dwell time of 8 seconds, the Circular Track Conveyor line targets a gross output of 450 assemblies per hour. At 85% overall equipment effectiveness, net output reaches 382 assemblies per hour. The screw machine cycle sets the bottleneck: four screws at M3 × 8 mm at 800 rpm torque-down to 0.8 Nm takes 6.5 seconds including approach, fastening, and retract. The robot add-pull and pallet index consume the remaining 1.5 seconds. Running three shifts at 22.5 hours net production time per day yields 8,595 completed assemblies per day. Omron published a throughput benchmark for a 20-station oval conveyor in a Japanese electronics factory. The line ran 400 units per hour at 87% OEE for a 12-month continuous production run. Unplanned downtime attributed to conveyor faults totaled 0.3% — less than one-third of the industry benchmark for similar linear pallet transfer lines (Omron Industrial Automation White Paper: Circular Conveyor Benchmarking, 2021).
Video of this 22 stations of Multi Station Circular Conveyor
BOM of this Multi Station Circular Converyor System as follows:
项号Items 型号 Product Code 产品详细 Description of goods 数量 Quantity 产品型号 Product code: TMB02-T23-S300R180-Y740-20LK20-L7139-C20 基础系统组件 Basic system components 环轨 Circular Track T23-S300R180 4 直轨 Straight Track LGT23-L7139 4 滑座 Slides (Including 22 carriages) HST300-180L-80W-15H 40 定位系统组件 Positioning system components 定位气缸组件 Positioning components AirTAC 12 定位附件 Positioning accessories Customized 40 定位长轴 Positioning the long shaft Customized 12 定位轴承座组件 Positioning bearing seat components Customized 24 定位摆臂 Positioning arm Customized 20 定位随动器 Positioning follower TM-CF8V 20 串接组件 Connection components 链条 Chain 20A-14800mm-carbon steel 2 链轮 Chain wheel 20A-26Z-carbon steel 4 主动轴心 Active Axis 6006 Customized 1 从动轴心 Driven axis 6006 Customized 2 轴承组 Bearing components 6006 Customized 4 链槽 Chain Grave polymer materials Customized 36 支撑杆 Support Rod Customized 9 安装法兰 Installation flange Customized 18 链接组件 Connection components 45 #+Copper Customized 40 张紧结构 Tension structure 45 #-Customized 4 支架底板型材组件 Support plate profile components 底板 Bottom Support Plate 7306×330×20：45# 2 马达支架 Motor support fixture Customized 1 连接板 Connecting plates Customized 4 滑座连接板 Slides connectiing plates Customized 20 线体支脚 curcular line support foot Customized 18 电控组件 Electric control system components 接近开关 Sensors Omron sensors 1 联轴器 Couplings TM 1 伺服电机 Servo motor, Delta Servo motor 1.5KW(110V) +5 meters power cable 1 伺服驱动器 Drive（Pulse type） Delta Drive(EtherCat) 1.5KW(380V) +5 meters encorder cable 1 减速机 precision Planetary Gear Reducer TM-PGR115, 50 ratio 1 控制器，人机交互装置 Controller+HMI device 控制器 Controller Trio MC405-P827 controller(24v input) 1 人机交互设备 HMI Trio HMI 10.1" touch screen, Uniplay 10-A, P562 (programming environment: controlling programming, servo data debug monitoring, HMI screen can display all types of controller data types and graphics,no need other software to program HMI interface ) 1 选装 Option 防尘防水 风琴罩（选配） Below system(To protect from water, oil, dust, liquid etc) Cusomized for option 0 Extra charges Customized Plywood box for protection in long distance transportation Customized 1 Technical Specification sheet of this circular track conveyor
Conclusion
The 7,469 mm, 22-station Circular Track Conveyor with 740 mm pitch delivers a dense, high-throughput platform for robotic screw machine integration. The 900 mm mounting plate height aligns robots and spindles to a single ergonomic datum. Independent cart control eliminates synchronous indexing bottlenecks and drives OEE above 85%. Precision pin clamping at ±0.05 mm keeps fastening defects below 0.05%. Field data from Beckhoff, KUKA, Atlas Copco, and Omron confirm that closed-loop pallet conveyors at this scale consistently outperform linear transfer systems in throughput, defect rate, and long-term uptime. Youtube: https://www.youtube.com/@tallmanrobotics Tiktok: https://www.tiktok.com/@tallmanrobotics Facebook: https://www.facebook.com/tallmanroboticslimited Linkedin: https://www.linkedin.com/in/tallman-robotics References - Bosch Rexroth Application Report AR-2021-047: Closed-Loop Pallet Conveyor for Powertrain Assembly, Stuttgart, 2021. - Atlas Copco Case Study: Smart Assembly — Robot-Integrated Screw Fastening on Circular Pallet Conveyor, Shenzhen, 2022. - Festo AG Project Reference ECU-Line-2020-DE: Pneumatic Clamping for Automotive ECU Circular Assembly Line, Germany, 2020. - Beckhoff Automation Application Note: XTS Linear Transport System for Medical Device Assembly, 2023. - KUKA AG Case Study: KR AGILUS Robots on Closed-Loop Conveyor for Automotive Small Parts Assembly, Bavaria, 2022. - Omron Industrial Automation White Paper: Circular Conveyor Benchmarking for Electronics Assembly, Japan, 2021. - ISO 10218-2:2011 — Robots and Robotic Devices: Safety Requirements for Industrial Robots — Part 2: Robot Systems and Integration. - FANUC LR Mate 200iD/7L Technical Specification Sheet, FANUC America Corporation, 2022.