FANUC α iS servo HRV calibration practice

FANUC α iS/β iS Series Servo Systems: A Complete Guide to HRV Control Optimization and Vibration Elimination

In modern high-precision CNC machining, the response speed and stability of the servo system directly determine the surface quality and machining efficiency of the parts. For engineers using FANUC α iS, α iF, and β iS series, they often feel at a loss when faced with hundreds of parameters in the servo parameter manual, multiple versions of HRV control (HRV1-HRV4), and complex vibration suppression functions. This article will be based on practical debugging experience to dismantle the complete process from parameter initialization, HRV control selection to mechanical resonance elimination and contour error compensation, helping you quickly locate and solve common problems in machine tool operation.

Quick initialization of servo parameters: avoiding the trap of "invalid parameters"

Parameter initialization is the cornerstone when replacing servo motors or conducting initial debugging. Many engineers often encounter alarms such as "SV0456 Invalid Current Control Cycle" or "SV0457 Invalid High Speed HRV Setting", which are fundamentally caused by conflicting control cycle settings or motor ID numbers that do not match the software version.

1.1 Key check items before initialization

Before starting, please make sure to confirm the following information:

NC models: such as 30i/31i/32i, 16i/18i, etc.

Servo motor model: such as α iS8/4000, pay attention to distinguishing between 200V and 400V drive versions.

Pulse encoder type: α iA1000 (absolute) or α iI1000 (incremental).

Whether to use a separate detector, such as a fully closed-loop grating ruler.

Mechanical transmission parameters: lead screw (mm/rev), detection unit (e.g. 0.001mm), command unit.

1.2 Key Points for Setting Core Parameters

The initialization process is usually carried out through the servo setting screen, and the following parameters are key to avoiding "illegal parameter" alarms:

Motor ID number (No.2020): must be strictly selected according to the manual. For example, for servo software 90D0/90E0, α iS8/4000 corresponds to ID number 285 (HRV2). Special note: For the 30i series, the ID number controlled by HRV2 should be specified; For series such as 16i, if the axis number is continuous, the HRV control type must be consistent.

Flexible feed gear (No.2084/2085): conversion between CMR and detection unit. For example, if the lead of the screw is 10mm, the detection unit is 1 μ m, the number of pulses required for one rotation of the motor is 10000, and the α i pulse encoder feedbacks 1000000 pulses per rotation, then FFG=10000/100000=1/100.

Full closed-loop setting: When using a serial output grating ruler, it is necessary to set No.1815 # 1=1 and calculate the number of flexible feed gears and position pulses. If the result exceeds 32767, the "Position Feedback Pulse Conversion Coefficient (No.2185)" should be used.

1.3 Quickly handle "illegal parameter" alarms

When the alarm displays "PRM" as 1, the error details can be viewed through diagnostic number 352 (16i series) or servo alarm screen (15i series). For example:

Alarm detail 23: If the number of position pulses exceeds 13100, it needs to be scaled 10 times through PLC0 (No. 2000 # 0).

Alarm detail 84: Speed proportional gain (PK2V) overflow, internal format can be changed by setting No.2200 # 6=1.

Alarm detail 10092: Invalid current control cycle. This usually means that HRV1 and HRV2 are mixed under the same servo CPU, or HRV1 is mistakenly set in the 30i series.

Deep Analysis of HRV Control: The Path to Advancement from HRV1 to HRV4

HRV (High Response Vector) control is the core of FANUC servo performance. Choosing the correct HRV version is the key to improving acceleration and deceleration characteristics and machining accuracy.

2.1 HRV2: A stable and reliable all-around foundation

For most standard machine tools, HRV2 is the most robust choice.

Features: Adopting a 125 μ s current control cycle, providing TCMD filters (mid frequency resonance cancellation), resonance cancellation filters (high frequency), and disturbance cancellation filters (low frequency).

Setting: After setting the motor ID number, set 2004 to 0X000011. If manual conversion from HRV1 is required, the current integral gain (PK1) needs to be multiplied by 0.8, and the current proportional gain (PK2) needs to be multiplied by 1.6.

2.2 HRV3: Performance multiplier for high-speed cutting

When higher loop gain is required in cutting feed, enable HRV3.

Enabling steps: Based on HRV2, set 2013 # 0=1. At the same time, it is recommended to enable No.2202 # 1 (cutting/fast moving speed loop gain switching).

Gain adjustment: During cutting, the speed loop gain will be amplified by parameter No.2335 (recommended 150% -200%), and the current loop gain will be amplified by No.2334 (recommended 150%).

Limitation: When using the 90B0/90B5 series software, the torque command in HRV3 mode will be automatically limited to 70% of the amplifier's maximum current. Therefore, it is more suitable for precision machining.

2.3 HRV4: The Ultimate Choice for Pursuing Extreme Accuracy (30i/31i Series)

For machine tools that require nanoscale interpolation and ultra-low latency, HRV4 is the only answer.

Features: Adopting a 62.5 μ s current control cycle and enabling extended HRV function (No.2300 # 0=1). It further squeezes DSP performance, but limits the number of axes that each servo card can control (usually reduced to 1 axis/DSP).

Setting: HRV4 and HRV3 cannot coexist. Set 2014 # 0=1 and ensure that the connected amplifier and detector (such as α i pulse encoder, RCN727, AT553) support high-speed communication.

Practical experience: In HRV4 mode, the observer parameters POK1 and POK2 need to be readjusted. For example, POK1 (No.2050) needs to be reduced from 956 to 264, and POK2 (No.2051) needs to be reduced from 510 to 35.

Systematic elimination scheme for mechanical vibration and resonance

Machine tool vibration is the main bottleneck that restricts spindle speed and machining surface quality. FANUC servo provides multi-stage filters to effectively solve resonance at the software level.

3.1 Micro vibration treatment in stopped state

High frequency micro vibrations occur when the motor stops, usually due to excessive proportional gain of the speed loop or mechanical backlash.

High frequency management function of speed loop (2017 # 7=1): Increase the calculation frequency of speed loop ratio and raise the oscillation threshold. However, please note that this feature will disable the observer function.

Variable proportional gain when stopped (2016 # 3=1): When the position error is less than the threshold (No.2119), the proportional gain of the speed loop in the stopped state is automatically reduced to 75% or 50% of the set value (in conjunction with No.2207 # 3).

N-pulse suppression (2003 # 4=1): For the "crawling" vibration caused by small friction, the No.2099 parameter is set to ignore the small feedback pulses in the proportional term of the speed loop.

3.2 Resonance elimination strategy during operation

Choose the appropriate filter based on the different resonance frequencies:

Mid low frequency resonance (50-150Hz): Use a disturbance cancellation filter (No.2223 # 0=1). Adjust No.2318 (gain) and No.2320 (inverse model gain), observe the frequency characteristics of the velocity loop, and suppress the amplitude.

High frequency resonance (200-400Hz): First, try the torque command filter (No.2067). The smaller the setting value, the lower the cutoff frequency (such as setting 2185 to correspond to 100Hz).

High frequency resonance (>400Hz): A resonance cancellation filter (No.2113, etc.) must be used. The manual provides four levels of filters, which can be set to center frequency (No.2113), attenuation bandwidth (No.2177), and damping (No.2359) respectively. Advanced technique: Activate the active resonance elimination filter (No.2270 # 3=1), and the system will automatically track resonance peaks that drift due to temperature or wear.

Improvement of contour accuracy: all-round compensation from arc to square angle

The ultimate goal of servo optimization is to make the actual trajectory infinitely approach the programming path. This requires a precise combination of feedforward and backlash acceleration.

4.1 Feedforward adjustment: Eliminating errors in arc radius

Traditional servos rely on position error drive, which can result in theoretical radius errors during arc interpolation.

Advanced Preview Feedforward (No.2092): The set value is usually 9700-10000 (corresponding to 97% -100%). Enable in conjunction with No. 2005 # 1=1. In theory, 100% feedforward can eliminate tracking errors, but considering the delay in the speed loop, it is generally set at 98% -99%.

Speed feedforward (No.2069): used to compensate for lag during acceleration and deceleration. Adjustment method: Observe through the 1/4 circular square shape of R5/F4000. If there is overcutting when entering the arc, increase the speed feedforward; If it protrudes, reduce the speed feedforward.

Feedforward timing adjustment (No.2095): When the arc appears elliptical, use this parameter to fine tune the phase. Positive values lead, negative values lag.

4.2 Quadrant protrusion compensation: two-stage reverse gap acceleration

When reversing the tangential axis of a circular arc, sharp peaks often appear due to friction and clearance.

First level acceleration (No.2048): Add a pulse to the speed command at the moment of commutation. Recommend an initial value of 100. Judgment criteria: If dents (overshoot) appear under low feed rate of F500, the value should be reduced; If there is still a protrusion, increase it.

Second level acceleration (No.2039): Used to compensate for the sustained frictional force after switching. Usually set to 100-500. Adjust the duration of action in conjunction with No.2082 (second level acceleration starting distance) and No.2089 (end magnification).

Adaptive function: Using No.2114 (acceleration ratio) and No.2338 (acceleration limit), the compensation amount is proportional to the arc acceleration. Optimization path: Adjust No.2048 at low feed rate; Adjust No.2114 at medium feed to eliminate medium speed bumps; Use No.2338 to limit the dents caused by overcompensation under high feed.

4.3 Static friction compensation: solving the problem of "crawling" startup

When the machine tool starts from a standstill and experiences sticking, use # 2005 # 7=1 to enable static friction compensation. Set the compensation amount through No.2072 and the stop judgment time through No.2073. It is worth noting that this function can be linked with the second level reverse gap acceleration to achieve a smooth transition at the moment of startup.