Eddy 感应涡流探针

This document describes the support for eddy current inductive probes in Klipper.

These probes detect the bed by measuring the resonant frequency of a coil within the sensor. The closer that coil is to a metal bed the higher the coil's resonant frequency. The frequency measurements can thus be used to estimate the distance between sensor and bed.

Probing mechanisms

Unlike traditional bed probes an eddy current sensor supports four different methods of probing: default, "scan", "rapid_scan", and "tap". The different probing methods are activated by passing a METHOD=xxx parameter to probe commands (for example, PROBE METHOD=tap). Each probing method has advantages and disadvantages as described below.

Default probing method

The default probing method behaves most like a traditional bed probe. The toolhead descends toward the bed until the sensor detects that it is near the bed and then several sensor measurements are taken at the halted position to estimate the distance between sensor and bed. This probing mechanism is activated by not specifying a METHOD parameter on probe type commands (eg, a bare PROBE command).

Advantages:

• It is the most general purpose probing method. It provides good precision with good flexibility.
• Can be used in many starting toolhead positions. It is necessary to ensure that the toolhead XY position places the sensor over the metal bed, but otherwise there is flexibility in the exact starting height.

Disadvantages:

• The probe results are subject to thermal drift. Distances reported by the probe correlate to distances measured during initial calibration (via PROBE_EDDY_CURRENT_CALIBRATE) and the results may be impacted if probing is run at a different temperature. Changes to the temperature of the bed, sensor coil, sensor electronics, or any metal near the sensor can all impact the results. The impact is small (think microns), but the acceptable precision for a bed probe is also small (again think microns). For best results, it is recommended to run the calibration and subsequent probes at a consistent temperature.

When to use:

This is the default probing method, and it is recommended for most probing actions. In particular, it is the recommended probe type for bed alignment tools such as QUAD_GANTRY_LEVEL, Z_TILT_ADJUST, SCREWS_TILT_CALCULATE, DELTA_CALIBRATE, and similar.

"scan" probing method

The "scan" probing method is similar to the default method, except the probe does not descend towards the bed. Instead, the probe gathers sensor measurements at the current Z position to estimate the distance between sensor and bed. It is useful for BED_MESH_CALIBRATE as the entire bed can be scanned with only horizontal movements.

Advantages:

• The Z position does not change during probing and there is less chance for Z stepper backlash (and similar) to impact measurements. This can be particularly useful when only relative Z height measurements are desired (eg, when using zero_reference_position with BED_MESH_CALIBRATE).
• A full bed scan may take less time than the default method.

Disadvantages:

• The bed must be nearly parallel to the printer XY rails and there must not be any large deviations in bed height. For acceptable results the bed scanning must be run with a low HORIZONTAL_MOVE_Z so that the sensor remains close to the bed during the entire bed scan. (The smaller the distance the more accurate the results.) In practice, this requires that the distance between nozzle and bed be no more than about a millimeter, and at these distances any notable bed deviations could result in a nozzle/bed collision during horizontal movement.
• The "scan" method has the same thermal drift disadvantages described for the default method. For best results, it is recommended to run the calibration and subsequent probes at a consistent temperature.

When to use:

The "scan" method is typically used during bed mesh calibration. It is recommended to always verify the bed is parallel to the printer XY rails prior to performing a bed scan. Depending on the printer hardware, one may use an automated tool utilizing the default probing method to verify the bed is parallel - for example: QUAD_GANTRY_LEVEL RETRY_TOLERANCE=0.250, Z_TILT_ADJUST RETRY_TOLERANCE=0.250, or SCREWS_TILT_CALCULATION MAX_TOLERANCE=0.250.

A bed mesh can then be run with something similar to BED_MESH_CALIBRATE METHOD=scan HORIZONTAL_MOVE_Z=1.

"rapid_scan" probing method

The "rapid_scan" probing method is very similar to the "scan" method, except the probe does not pause at each point to be measured. Instead, measurements taken during horizontal movement near each probing point are used to estimate the distance between sensor and bed.

Advantages:

• A "rapid_scan" full bed scan may be slightly faster than the "scan" method.
• Otherwise, it has the same advantages as the "scan" method.

Disadvantages:

• The results of a "rapid_scan" may be less accurate than the "scan" method.
• Same disadvantages as "scan" probes (bed must be parallel and thermal drift).

When to use:

A "rapid_scan" may be useful when performing a large detailed bed mesh scan for diagnostic purposes. In this situation, the reduced scanning time may outweigh the possible loss of accuracy.

For normal printing, a bed mesh using the regular "scan" method is generally preferred for best accuracy and minimal additional probing time.

Once the bed is verified to be parallel to the XY rails then one can run a rapid bed mesh scan with something similar to BED_MESH_CALIBRATE METHOD=rapid_scan HORIZONTAL_MOVE_Z=1.

"tap" probing method

During "tap" probing, the toolhead descends until the nozzle makes contact with the bed, the nozzle is then lifted away from the bed, and sensor measurements during the lifting movement are analyzed to determine the location where the nozzle breaks contact with the bed.

Advantages:

• The probe results are determined by the actual point of contact between nozzle and bed instead of indirect measurements between sensor and bed. This can be particularly useful if one changes nozzles frequently, as the results will take into account the geometry of the current nozzle.
• A "tap" probe does not have the thermal drift issues associated with the other probing methods. The main probe calibration is not utilized during tap probes, and thus one does not need to track temperatures between initial calibration and subsequent probing.
• Axis "twist" inaccuracies are less of an issue during tap probes as there is no XY probe offset to compensate for. However, one must still ensure the toolhead XY position places both the nozzle and sensor above the bed prior to tap probing.

Disadvantages:

• One must ensure both the nozzle and bed are clean prior to tap probing. Any filament on the nozzle or debris on the bed may significantly skew the probe results.
• One must ensure that the nozzle is around 3-20mm away from the bed prior to starting each "tap" probe attempt. If the nozzle starts too close to the bed then contact may not be detected which could result in an uncontrolled nozzle/bed crash. If the nozzle starts very far from the bed then sensor measurements are not accurate and a tap attempt may fail or provide inaccurate results.
• The printer hardware must allow the nozzle to fully make contact with the bed. There must not be any limit switches or carriage stops that make contact prior to the nozzle contacting the bed.
• One must ensure that the nozzle temperature is not too high for the bed. A too high temperature could melt the PEI coatings on some beds, for example.

When to use:

A "tap" probe is often used as one step during a multi-step homing/leveling process to account for the current nozzle geometry and to reduce errors associated with thermal drift. For example, one might deploy a macro that homes, calls Z_TILT_ADJUST with default probe method, heats the printer to an intermediate temperature, cleans the nozzle by repeatedly wiping it over a brush, performs a "tap" probe, uses SET_KINEMATIC_POSITION with the tap results, runs BED_MESH_CALIBRATE while utilizing a zero_reference_position, and then brings the printer to normal printing temperature. The actual steps to utilize a "tap" probe depend heavily on the specific printer hardware.

A "tap" probe may be initiated with something like PROBE METHOD=tap.

Configuration

To configure an eddy current probe, start by declaring a probe_eddy_current config section in the printer.cfg file. It is recommended to set descend_z to 0.5mm. It is typical for the sensor to require an x_offset and y_offset. If these values are not known, one should estimate the values during initial calibration.

Then restart the printer and proceed to the following calibration steps.

Calibrating drive current

校准的第一步是确定传感器的适当 DRIVE_CURRENT。将打印机调至原位，并移动工具头，使传感器靠近床面中心并高出床面约 20 毫米。然后使用 LDC_CALIBRATE_DRIVE_CURRENT CHIP=<config_name> 命令。例如，如果配置部分名为[probe_eddy_current my_eddy_probe]，则应运行 LDC_CALIBRATE_DRIVE_CURRENT CHIP=my_eddy_probe。该命令应在几秒钟内完成。完成后，使用 SAVE_CONFIG 命令将结果保存到 printer.cfg 中，然后重新启动。

Calibrating Z heights

The second step in calibration is to correlate the sensor readings to the corresponding Z heights. Home the printer and navigate the toolhead so that the nozzle is near the center of the bed. Then run a PROBE_EDDY_CURRENT_CALIBRATE CHIP=my_eddy_probe command. Once the tool starts, follow the steps described at "the paper test" to determine the actual distance between the nozzle and bed at the given location. Once those steps are complete one can ACCEPT the position. The tool will then move the toolhead so that the sensor is above the point where the nozzle used to be and run a series of movements to correlate the sensor to Z positions. This will take a couple of minutes. After the tool completes it will output the sensor performance data:

probe_eddy_current: noise 0.000642mm, MAD_Hz=11.314 in 2525 queries
Total frequency range: 45000.012 Hz
z: 0.250 # noise 0.000200mm, MAD_Hz=11.000
z: 0.530 # noise 0.000300mm, MAD_Hz=12.000
z: 1.010 # noise 0.000400mm, MAD_Hz=14.000
z: 2.010 # noise 0.000600mm, MAD_Hz=12.000
z: 3.010 # noise 0.000700mm, MAD_Hz=9.000

issue a SAVE_CONFIG command to save the results to the printer.cfg and restart.

在第一次校准后最好验证 x_offset 和 y_offset 是否准确。请按照校准探针 X Y 偏移的步骤操作。如果修改了 x_offset 或 y_offset ，请务必在修改后运行 PROBE_EDDY_CURRENT_CALIBRATE 命令（如上所述）。

Note that eddy current sensors are susceptible to "thermal drift". That is, changes in temperature can result in changes in reported Z height. Changes in either the bed surface temperature or sensor hardware temperature can alter the results. Therefore, for best results the calibration done here and the subsequent probing that utilizes that calibration should be done at the same temperature.

Tap calibration

In order to utilize "tap" probing it is necessary to configure some parameters.

It must be possible to command the toolhead below the nominal plane of the bed. This is typically done by setting position_min: -1 in the [stepper_z] config section of the printer.cfg (or similar setting, such as minimum_z_position, depending on the kinematics). This is necessary to ensure the nozzle can be commanded to firmly contact the bed. This is also to ensure the nozzle makes contact with the bed before it would otherwise be commanded to start deceleration.

It is also necessary to configure a tap_threshold parameter. This parameter determines when downward toolhead movement during a "tap" probe should be halted. A value too large could result in a nozzle/bed contact not detected, which could result in the nozzle crashing uncontrollably into the bed. A value too small could result in a "tap" probe attempt halting before making contact with the bed, which could result in probing errors or inaccurate probe results.

The PROBE_EDDY_CURRENT_TAP_CALIBRATE command can be used to configure an appropriate tap_threshold value. This tool may be run after completing the main PROBE_EDDY_CURRENT_CALIBRATE calibration. Follow these steps to calibrate tap_threshold:

1. Verify that both the nozzle and bed are clean. Enable the printer, home the printer, move the toolhead to a position near the center of the bed, and make sure the nozzle is between 3 - 10 millimeters from the bed.
2. The next step involves commanding the nozzle to make contact with the bed. This process always has some risks, so be prepared to issue an emergency halt (M112) if the probing descent does not stop after contacting the bed. When ready issue the following command: PROBE_EDDY_CURRENT_TAP_CALIBRATE TAP=guess This command analyzes the data found during the main probe calibration to make an initial coarse guess for the tap_threshold value and it then performs the corresponding "tap" probe. Ideally the above command will cause the probe to descend until it hits the bed, lift away from the bed, and then report a valid probe result. If not, see the paragraphs at the end of this section to troubleshoot. If the attempt was successful then continue to the next step.
3. The next step is to run another tap probe with a "refined" threshold setting. The tool utilizes information gathered during a previous successful tap probe to determine this improved threshold. Make sure that the nozzle is near the center of the bed, that it is between 3 - 10mm above the bed, be ready to issue an emergency halt, and then run the following command: PROBE_EDDY_CURRENT_TAP_CALIBRATE TAP=refine Ideally this command will also succeed; if not, see the paragraphs at the end of this section to troubleshoot. If the attempt was successful then continue to the next step.
4. If probing with the refined threshold is successful then the next test is to verify that it is stable over multiple probe attempts. Make sure that the nozzle is near the center of the bed, that it is between 3 - 10mm above the bed, be ready to issue an emergency halt, and then run the following command: PROBE_EDDY_CURRENT_TAP_CALIBRATE TAP=verify This command will probe the bed five times in a row. Ideally the above command will also succeed; if not, see the paragraphs at the end of this section to troubleshoot. If the attempt was successful then continue to the next step.
5. If all of the above steps are successful then one can issue a SAVE_CONFIG command to save the "tap_threshold" parameter to the printer.cfg file. Calibration should now be complete.

If any of the steps above did not succeed then it may be necessary to troubleshoot and manually determine an appropriate tap_threshold. This is done by running commands of the form: PROBE METHOD=tap TAP_THRESHOLD=<value> Where <value> is a threshold to test.

In general, if a probe attempt halts before making contact with the bed, then this indicates that the provided TAP_THRESHOLD parameter is too low. Try increasing it by about 10% and retry. Similarly, if a probe attempt does not halt after making contact with the bed then it indicates that TAP_THRESHOLD is too high. Consider decreasing the attempted value in half.

If the automated calibration tool failed during the initial "guess" stage, then one can use the tap_threshold value reported by the tool as a starting point for manual attempts. Once a successful probe attempt is completed then one can return to the main steps described above starting at the "refine" stage.

Performing initial calibration when homing with probe

It is possible to use an eddy current probe to home a Z axis. To use this process, set the [stepper_z] config section endstop_pin to probe:z_virtual_endstop.

In order to home with an eddy probe it is necessary to first calibrate the probe via the PROBE_EDDY_CURRENT_CALIBRATE command. However, that command requires that the printer be homed first.

The following steps may be used to avoid this circular dependency for the very first calibration:

1. Define a [probe_eddy_current] config section in the printer.cfg file as described in the configuration section.
2. Make sure a force move section is defined and ensure its enable_force_move option is present and set to true.
3. Manually adjust the carriages so that the toolhead is near the center of the bed and roughly 20mm away from the bed. Issue LDC_CALIBRATE_DRIVE_CURRENT CHIP=<config_name> and SAVE_CONFIG commands as described in the calibrating drive current section.
4. Manually move the toolhead so that it is roughly 20mm away from the bed and home the printer's X and Y axes. This is typically done with a G28 X0 Y0 command. Command the toolhead X and Y position so that the toolhead is roughly over the center of the bed. This is typically done with a command like G1 X50 Y50 (using appropriate XY values for the printer).
5. Manually adjust the bed so that it is mostly flat relative to the toolhead XY carriages (if necessary). Manually adjust the Z carriage so that the nozzle is roughly 20mm from the bed and issue a SET_STEPPER_ENABLE STEPPER=stepper_z command. Issue a SET_KINEMATIC_POSITION Z=25 command followed by a PROBE_EDDY_CURRENT_CALIBRATE CHIP=my_eddy_probe command. Important - after issuing these commands the printer will be able to move in the Z direction, but it does not know the actual Z position. Care must be taken to avoid movement requests that may cause the toolhead to descend into the bed.
6. Complete the eddy probe calibration as described in the calibrating z heights section. Issue a SAVE_CONFIG command upon completion.

These steps are only needed to obtain an initial configuration. If one needs to rerun PROBE_EDDY_CURRENT_CALIBRATE in the future then the normal mechanism should be possible once this initial configuration is available.

温度漂移校准

像所有的感应探针一样，eddy 涡流探针会有很严重的温度偏移。如果eddy 涡流传感器线圈上的温度传感器上可以被配置为[temperature_probe] 去反馈线圈的温度并且启用软件温度偏移补偿。要将探针温度传感器与eddy 涡流传感器连接[temperature_probe] 的名字必须和[probe_eddy_current]一致。比如：

[probe_eddy_current my_probe]
# eddy 探针配置文件

[temperature_probe my_probe]
# 温度探针配置文件

参见配置参考以获取更多有关temperature_probe的信息。建议配置 calibration_position, calibration_extruder_temp, extruder_heating_z, 以及 calibration_bed_temp选项，因为这样可以自动化某些以下步骤。如果将被校准的打印机是封闭的，极度推荐将max_validation_temp选项设置到100和120之间。

Eddy probe的制造商提供了一些可以使用的校准预设可以手动添加到[probe_eddy_current]中到drift_calibration选项中。如果他们没提供预设的校准文件或者预设的校准文件不适用于你的系统，temperature_probe模块可以使用TEMPERATURE_PROBE_CALIBRATE`命令来进行手动校准。

在进行校准前，用户应该知道大概的探针线圈最大温度。这个温度应该被配置到TEMPERATURE_PROBE_CALIBRATE命令的TARGET选项中。校准的目的是尽量有一个最宽的温度范围，因此最好在打印机冷却后进行校准，并且在线圈到达最高温度的时候停止。

当[temperature_probe] 被配置后，可以使用以下步骤进行热偏移校准：

• 当 [temperature_probe] 被配置后应该使用PROBE_EDDY_CURRENT_CALIBRATE对探针校准。这会获取校准中的温度的变化，并且这对于温度偏移校准是非常有必要的。
• 确保喷头保持清洁并且没有多余的耗材残留。
• 热床，喷头，和探针线圈在校准前需要到达室温。
• 如果没配置[temperature_probe]中的calibration_position，calibration_extruder_temp和extruder_heating_z选项，则需要执行以下步骤：
  • 移动喷头到热床的中心。z轴高度应该至少高于热床30mm。
  • 加热挤出机温度到最大热床安全温度。150-170C 通常来说适用于绝大部分的配置。加热挤出机的目的是避免喷头在校准过程中的热膨胀。
  • 当挤出机到达设定温度，移动z下降到离热床1mm的位置。
• 开始漂移校准。如果探针名字是my_probe 并且最大探针温度可以到达80C，可以使用TEMPERATURE_PROBE_CALIBRATE PROBE=my_probe TARGET=80来进行校准。如果进行了配置，喷头的XY应该会移动到calibration_position 并且Z轴通过extruder_heating_z来调整。将挤出机加热到指定温度后，工具将会移动到calibration_position中指定的 Z 值。
• 程序将要求进行手动探测。使用纸张测试执行手动探头，然后使用 ACCEPT接受当前位置。校准程序将使用探针采集第一组采样，然后将探针停在加热位置。
• 如果calibration_bed_temp未被配置启动热床加热到最高安全温度。否则将自动执行此步骤。
• 在默认的校准流程中在到达 TARGET之前会每2C要求一次手动偏移探针校准。温度偏移量在校准中可以通过TEMPERATURE_PROBE_CALIBRATE 中的STEP来进行修改。注意在自定义STEP 的值的时候，特别高的值和太少的校准点回导致很差的校准结果。
• 在热偏移校准中，可以使用这些额外的gcode 命令：
  • TEMPERATURE_PROBE_NEXT可以到达指定温度之前强制创建一个新的采样点。
  • TEMPERATURE_PROBE_COMPLETE 可以在到达 TARGET 之前完成校准。
  • ABORT 可以用来结束校准或者取消结果。
• 当校准完成使用SAVE_CONFIG去保存温度偏移设置。

综上所述，与大多数其他程序相比，上述校准过程更具挑战性，也更耗时。它可能需要练习和多次尝试才能达到最佳校准效果。

Errors description

Possible homing errors and actionables:

• Sensor error
  • Check logs for detailed error
• Eddy I2C STATUS/DATA error.
  • Check loose wiring.
  • Try software I2C/decrease I2C rate
• Invalid read data
  • Same as I2C

Possible sensor errors and actionables:

• Frequency over valid hard range
  • Check frequency configuration
  • Hardware fault
• Frequency over valid soft range
  • Check frequency configuration
• Conversion Watchdog timeout
  • Hardware fault

Amplitude Low/High warning messages can mean:

• Sensor close to the bed
• Sensor far from the bed
• Higher temperature than was at the current calibration
• Capacitor missing

On some sensors, it is not possible to completely avoid amplitude warning indicator.

You can try to redo the LDC_CALIBRATE_DRIVE_CURRENT calibration at work temperature or increase reg_drive_current by 1-2 from the calibrated value.

Generally, it is like an engine check light. It may indicate an issue.