Power assist wheelchair, power assist unit for wheelchair, control device for power assist wheelchair, control method for power assist wheelchair, program, and terminal

A power assist unit for a wheelchair, comprising:

• first and second wheels separated from each other in a vehicle width direction;
• a first electric motor that drives the first wheel;
• a first encoder that detects rotation of the first wheel;
• a second electric motor that drives the second wheel;
• a second encoder that detects rotation of the second wheel;
• and
• a control device that controls the first and second electric motors, wherein
• the control device includes:
• a vehicle speed calculation unit configured to calculate a vehicle speed;
• a predicted turning torque calculation unit configured to calculate a predicted turning torque value based upon a first manual torque value acting on the first wheel, a first motor torque value outputted by the first electric motor, a second manual torque value acting on the second wheel, and a second motor torque value outputted by the second electric motor;
• an actual turning torque calculation unit configured to calculate an actual turning torque value based upon a detection signal of the first encoder and a detection signal of the second encoder;
• a compensation turning torque calculation unit configured to calculate a compensation turning torque value for compensating for at least a part of a shortage or excess of the actual turning torque value with respect to the predicted turning torque value, wherein the compensation turning torque value is smaller when the vehicle speed is a first speed than when the vehicle speed is a second speed faster than the first speed;
• a first target current determination unit configured to determine a target current of the first electric motor based upon the first manual torque value and the compensation turning torque value;
• and
• a second target current determination unit configured to determine a target current of the second electric motor based upon the second manual torque value and the compensation turning torque value.

A control method for a power assist wheelchair including first and second wheels separated from each other in a vehicle width direction, a first electric motor that drives the first wheel, a first encoder that detects rotation of the first wheel, a second electric motor that drives the second wheel, and a second encoder that detects rotation of the second wheel, the control method comprising:

• calculating a vehicle speed;
• calculating a predicted turning torque value based upon a first manual torque value acting on the first wheel, a first motor torque value outputted by the first electric motor, a second manual torque value acting on the second wheel, and a second motor torque value outputted by the second electric motor;
• calculating an actual turning torque value based upon a detection signal of the first encoder and a detection signal of the second encoder;
• calculating a compensation turning torque value for compensating for at least a part of a shortage or excess of the actual turning torque value with respect to the predicted turning torque value, wherein the compensation turning torque value is smaller when the vehicle speed is a first speed than when the vehicle speed is a second speed faster than the first speed;
• determining a target current of the first electric motor based upon the first manual torque value and the compensation turning torque value;
• and
• determining a target current of the second electric motor based upon the second manual torque value and the compensation turning torque value.