Roboteq

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1. Getting the controller flags

The controller flags belong to the following three categories: 

• Controller status (FS)
• Motor status (FM)
• Fault flags (FF)

,and can be queried with the FS, FM and FF parameters respectively. Each fault corresponds to a specific bit of the status word with the following sequence: 

To check for a specific fault, the desired status word should be masked with the bit corresponding to the specific fault. For example, to read the loop error bit of the motor flags (FM) one should mask the FM with bit 3 (0b 00000100). A bitwise AND would be adequate to show if the specific fault is present.

Microbasic example: 

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2. VPM command

To troubleshoot motor or sensor problems, the Roboteq controller is equipped with a built-in function that allows the rotor to be rotated by supplying a low-frequency current without using the motor sensors.

The command syntax is the following:

!VPM cc nn

where cc is the channel and the nn is the number of electrical rotations. 

Please note that the VPM command uses the 'reference seek power' parameter to supply the required current to the motor. For the rotor to rotate properly, 'reference seek' should be set equal to the nominal motor current, and the motor must be unloaded.

Important Note

For the rotor to rotate properly, 'reference seek' should be set equal to the nominal motor current, and the motor must be unloaded.

The VPM command will supply a current of defined electrical cycles to the motor. If the number of electrical cycles is equal to the motor's pole pairs, then the rotor will perform exactly one rotation. Please note that this rotation will be evident prior to the gearbox. To determine the exact number of rotations after the gearbox, one should divide the number of electrical cycles by the gearbox ratio.

Example:

Let’s assume a motor with 5 pole pairs and a gearbox with a 9:1 ratio. Then, by sending a VPM command of 45 electrical cycles, the motor shaft should perform exactly one rotation after the gearbox.

!VPM 1 45

Observing a different result would imply that the pole pairs or the gearbox ratio have not been estimated correctly.

The VPM command is very helpful for troubleshooting sensor signals. The motor can be commanded to rotate for a specific number of cycles, and then the sensor signals can be logged for troubleshooting purposes.

The following considerations can be taken for the various motor sensors, when the rotor performs one full rotation (prior to the gearbox) : 

• Encoder sensors: The Encoder counts will be equal the Encoder resolution multiplied by 4 (due to the quadrature operation).
• Hall sensors: The Hall counts will be equal to the number of motor pole pairs multiplied by 6.
• Sin/Cos or Resolver sensors: The sensor’s output should perform one exact period. If the sensor has more than one poles, the number of periods will be proportional to the sensor poles.
• For SSI sensors, The number of counts will be equal to the sensor’s resolution. 

Please note that since by using the VPM command, the exact position of the rotor is not being controlled, there will be an accepted amount of error to the sensor values. An error of 5% is accepted in most of the cases.

Each phase of the motor is connected internally on the controller in a part of the power stage that is consisted by a top and bottom MOSFET. 

When a MOSFET fails, usually it gets shorted and this can be easily detected my measuring the MOSFETs body diode. The diode can be measured by using a multimeter in diode mode. By connecting the negative lead of the multimeter to the negative part of the diode and the positive lead of the multimeter to the positive part, one can measure the voltage drop across the diode. If the voltage drop is close to 0 V, then we can conclude that the MOSFET is failed. The expected voltage across A MOSFETs diode is around 0.4 V.

Important Note

                When measuring the controller MOSFETs the motor and power supply should be disconnected.
 

In total, the following MOSFET measurements can be taken for each channel. If any of the readings is below 0.1 V then the MOSFET can be considered shorted.

In drives featuring STO, the STT command can be used to assess the MOSFETs' health. First, the following command must be sent to run the MOSFET test:

!STT

Then, the test results can be queried with the following command:

?STT 1

A reply of 0 indicates that there is no MOSFET damage, while a 5 indicates that one or more motor drive MOSFETs are damaged.

A test script that can be used for checking the controller's MOSFETs can be found here.  

Where 'Par' is the parameter name, 'cc' is the channel, and 't' is the sampling time in milliseconds. Many parameters can be added to the same stream, starting with a question mark (?) and ending with an underscore (_).

The following example will stream the Ramped Command, Motor Power, Motor current, Motor speed and Fault Flags of channel 1, every 10 ms:

# c_/?RMP 1_?P 1_?A 1_?S 1_?FF 1_# 10

Multimeters are not sufficient for measuring motor resistance, which typically lies in the milliohm range, due to their limited accuracy. One way to approximate a motor's resistance accurately is by using a power supply with current-limiting capabilities. To do this, the power supply current should be set to a relatively low value, say 5 A. Then, two of the motor phases should be powered from the power supply. The power supply will regulate the motor voltage to limit the current to the configured value. Consequently, both the motor current and voltage will be known, enabling the calculation of motor resistance using Ohm's Law. Note that the calculated resistance will be the total resistance between the two phases (phase-to-phase), so to derive the phase resistance, this value should be divided by 2.

Consider the following example, where the power supply current is set to 5 A and the voltage is regulated to 0.2 V. Then the motor resistance can be calculated as follows: 

R=(V/I)/2 = (0.2/5)/2 = 20 mOhm

 A test script that can be used to check the Hall sensor's alignmet can be found here.