Brake configuration

In some cases, the motor is equipped with a mechanical brake which can be released by applying electrical voltage to the brake terminals.

Detailed description

The following diagram shows the steps for the release procedure:

A configurable voltage is applied to the positive terminal of motor brake (It is assumed that the negative terminal of the brake is connected to Ground).

Figure 1  -  Timing diagram

When the motion system has entered operation enabled, the specified “Brake pull voltage” will be automatically applied for a configurable amount of time designated as “Brake pull time”. After this time period, the second voltage level “Brake hold voltage” will be applied to the brake terminals permanently. The brake hold voltage can be set to a lower value to save energy.

Attention: Don’t set the hold voltage too low or you risk entering a marginally stable situation where any jerk can engage the brake.

Once the motion system leaves the state “operation enabled” the voltage is automatically dropped to Ground after the designated time “Brake engage delay” and the brake is mechanically activated.

Pin-brake strategy

A pin-brake is a special type of brake commonly used in light-weight robot joints. The brake usually consists of a solenoid linear actuator fixed to robot body and a notched wheel fixed to the rotating motor shaft.

Figure 2  -  Pin brake (illustration exemplary)

To release a pin-type brake, the motor must move slightly so that the pin can slide out. This is mainly required with hanging loads (e.g. robot arm) where gravity is producing a torque pressing the wheel notch against the actuator pin. The following method is implemented to ensure reliable pin-type brake operation.

Releasing the Pin brake in Different OP Modes

Diagnostic Mode

In Diagnostics Mode, the brake is controlled by the master itself using the `Brake Status` object (0x2004:7). So putting the drive in OP ENABLED state in diagnostics mode will not start the Pin brake release process. Brake will remain in the engaged position. But if the drive has a relative encoder with Index and QEI index is not known then enabling the drive in diagnostics mode will only internally trigger the Temporary offset detection. Brake will remain in the engaged position and no process to release the Pin brake will be initiated.

After the drive has been enabled, changing the brake status object to `DISENGAGE` will start releasing the pin brake.

Manual Release using Brake Status Object

Controlling the brake using the brake status object 0x2004:7 will trigger the brake release procedure only if the drive is in Diagnostic mode and OP ENABLED state.

If the drive is not in OP ENABLED state, then releasing the brake will only apply voltage on PIN (Phase D).

Timing diagram

Step 0

In this step, the variables related to the pin brake release are initialized. The motion polarity is also determined based on the phase's connection (object 0x2003:05). The open loop profiler is configured.

Step 1

The open loop profiler moves the motor in positive / negative direction, depending on the polarity.

Step 2

The motor´s movement is blocked in any direction and it starts moving in the opposite direction.

Step 3

If the motor has reached the target position, the pull voltage is applied for the duration specified by pull time. During the application of pull time, the motor does not move.

Step 4

Target position is set to the initial position of the rotor and the open loop profiler motor moves to the initial position.

Step 5

Control is enabled, the drive accepts Position / Velocity / Torque targets.

The brake controller raises the torque progressively until it reaches the maximum displacement threshold. If it reaches the maximum torque threshold first, it rises the torque again in the opposite direction. When the torque is high enough to compensate for gravity, the load is lifted until the position reaches the threshold value, the torque stays to a holding torque value and the brake will be disengaged. After the release delay, the brake voltage is driven to “Brake hold voltage” and Op Mode display is set to Op Mode. The controller is then enabled. To use the pin-brake mode please select the correct “Release strategy” in the brake configuration section in OBLAC Drives commissioning software, or via direct object dictionary access.

Note: The brake release is an open loop system. After the brake pull time it is assumed that releasing was successful and the hold voltage is applied.

Brake PWM switching frequency

The PWM switching frequency of the brake can be changed in object 0x2004:11 Brake options: Switching frequency.

• Enter the value 0 for 16 kHz

• Enter the value 1 for 32 kHz

• Enter the value 2 for 64 kHz

Custom brake modes

It is also possible to implement custom brake modes. For information please refer to Generic brake output voltage.

Parameters

Object ID	Name	Description
0x2004	Brake Release	All options that are required for brake release.