Method of controlling an electric motor of a tightening tool

A tightening tool controller comprising processing circuitry configured to control an electric motor of a tightening tool during a tightening operation by performing the following operations:

• a) controlling the electric motor to run at a first motor speed using a first motor speed setpoint value;
• b) obtaining a torque or motor current value of the electric motor;
• c) determining a second motor speed setpoint value lower than or equal to the first motor speed setpoint value, based on an efficiency of the tightening tool at the torque or motor current value and the first motor speed setpoint value;
• d) setting the second motor speed setpoint value as the first motor speed setpoint value;
• e) controlling the electric motor to run at a second motor speed using the first motor speed setpoint value after step d);
• and
• repeating steps b)-e) until a predetermined motor speed or torque has been reached,
• wherein the second motor speed setpoint value is within a speed range of at most 500 revolutions per minute from the first motor speed setpoint value, and
• wherein the efficiency is at most 20% from a highest possible efficiency in the speed range for the torque or motor current value.

A tightening tool system comprising:

• a tightening tool comprising an electric motor;
• and
• the tightening tool controller, configured to control the electric motor during a tightening operation by performing the following operations:
• a) controlling the electric motor to run at a first motor speed using a first motor speed setpoint value;
• b) obtaining a torque or motor current value of the electric motor;
• c) determining a second motor speed setpoint value lower than or equal to the first motor speed setpoint value, based on an efficiency of the tightening tool at the torque or motor current value and the first motor speed setpoint value;
• d) setting the second motor speed setpoint value as the first motor speed setpoint value;
• e) controlling the electric motor to run at a second motor speed using the first motor speed setpoint value after step d);
• and
• repeating steps b)-e) until a predetermined motor speed or torque has been reached
• wherein the second motor speed setpoint value is within a speed range of at most 500 revolutions per minute from the first motor speed setpoint value, and
• wherein the efficiency is at most 20% from a highest possible efficiency in the speed range for the torque or motor current value.