渦電流電感式探針

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

校準的第一步驟是為感測器找出合適的 DRIVE_CURRENT。將列印機歸零，並移動工具頭，使感測器位於列印床中央上方約 20mm 處；然後輸入指令 LDC_CALIBRATE_DRIVE_CURRENT CHIP=<配置名稱> 。舉例來說，若配置部分名為 [probe_eddy_current my_eddy_probe]，那則應輸入 LDC_CALIBRATE_DRIVE_CURRENT CHIP=my_eddy_probe。此指令應該會在幾秒內完成，然後輸入指令 SAVE_CONFIG 以將結果儲存到 printer.cfg 中並重新啟動。

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.

在初始校準完成後，最好依照探針X/Y偏移校準確認 x_offset 與 y_offset 是否準確。若要修改 x_offset 與 y_offset 數值，則須在變更後再次輸入指令 PROBE_EDDY_CURRENT_CALIBRATE（如上一段落所述）。

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.

熱飄移校準

就如所有電感式探針一樣，渦電流探針有顯著的熱飄移狀況。若渦電流探針的線圈上有溫度感測器，便能透過設定 [temperature_probe] 以取得線圈溫度並開啟軟體飄移補償。若要將溫度感測器與渦電流探針連結，[temperature_probe] 與 [probe_eddy_current] 部分必須使用相同的名稱，例如：

[probe_eddy_current my_probe]
# 渦電流探針設定...

[temperature_probe my_probe]
# 溫度感測器設定...

See the configuration reference for further details on how to configure a temperature_probe. It is advised to configure the calibration_position, calibration_extruder_temp, extruder_heating_z, and calibration_bed_temp options, as doing so will automate some of the steps outlined below. If the printer to be calibrated is enclosed, it is strongly recommended to set the max_validation_temp option to a value between 100 and 120.

渦電流探針的製造商可能會提供預設的飄移補償，可以將它手動添加到 [probe_eddy_current] 部分中的 drift_calibration 設定。若是沒有、或預設補償效果不佳，可以輸入 TEMPERATURE_PROBE_CALIBRATE 指令以使用 [temperature_probe] 功能中的手動校準流程。

在開始校準之前，使用者必須知道探針線圈可能達到的最高溫度，這個溫度會在 TEMPERATURE_PROBE_CALIBRATE 指令中作為 TARGET 。校準的目標是涵蓋最大的溫度範圍，因此應在列印機冷卻後開始；並在線圈達到最高溫度時結束。

在 [temperature_probe] 設定完成後，按照下列步驟執行熱飄移校準：

• 當 [temperature_probe] 設定且連結完成後，使用 PROBE_EDDY_CURRENT_CALIBRATE 指令開始校準探針，這會記錄熱飄移校準所需的過程溫度變化。
• 確保噴嘴乾淨且沒有耗材。
• 列印床、噴嘴、探針線圈在開始前應為冷卻狀態。
• 若沒有設定 [temperature_probe] 部分中的 calibration_position、calibration_extruder_temp、extruder_heating_z，則須執行下列步驟：
  • 將工具頭移動至列印床中央。Z 軸須距離列印床 30mm 以上。
  • 將噴頭加熱至熱床最大安全溫度以上，多數情況下 150\~170 度即可。加熱噴頭是為了避免在噴嘴在校準時發生熱膨脹。
  • 當噴頭達到穩定溫度之後，將 Z 軸移動至距離列印床約 1mm。
• 開始偏移校準。如果探針的名稱為 my_probe，且探針最高可達溫度為 80 度，那麼指令應為 TEMPERATURE_PROBE_CALIBRATE PROBE=my_probe TARGET=80。若有設定 calibration_position 與 extruder_heating_z，那工具頭會移動到指定的 XY 位置，並在到達指定溫度後移動到相應 Z 高度。
• 此流程需要手動探高。按照 A4 紙測試法執行手動探高再輸入 ACCEPT 指令。校準流程會取第一組樣本，然後將探針停在加熱位置。
• 沒有設定 calibration_bed_temp，請設定列印床加熱至最高安全溫度。反之，這步驟將會自動執行。
• 預設校準流程中，每 2 度會需執行一次手動探高，直至到達設定之 TARGET 。此溫度變化量可以在 TEMPERATURE_PROBE_CALIBRATE 中的 STEP 自訂。請小心設定 STEP 數值，太高的數值會導致樣本數量不足而使校準結果不佳。
• 校準過程中可使用下列額外指令：
  • TEMPERATURE_PROBE_NEXT 可在溫度到達設定差值前強制取樣。
  • TEMPERATURE_PROBE_COMPLETE 可在到達 TARGET 前提前結束校準。
  • ABORT 可停止校準並拋棄結果。
• 校準完成後，輸入 SAVE_CONFIG 指令以儲存飄移校準。

總而言之，上述的校準過程要比其它流程更複雜且耗時，需多次練習與嘗試才能取得最佳校準結果。

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.