Problems to get a pca9685 Board running

I am trying to get pico explorer running with a genneric pca9685 board.
I have flashed the Pimoroni firmware on the PIco. (Examples are running without Problem)
I wrote a Programm to test the pca9685 Programm, wich is working withe the normal-pico-firmware without problems:

from machine import Pin
import servo
from time import sleep_ms
from pimoroni_i2c import PimoroniI2C

# machine.I2C(id, *, scl, sda, freq=400000)
# SCL -> Pin(21)
# SDA -> Pin(20)
ID = 0
#_scl = Pin(1)
#_sda = Pin(0)
_scl = Pin(21)
_sda = Pin(20)
i2c = PimoroniI2C(sda=(20), scl=(21))
adr_room = i2c.scan()
for adr in adr_room:

servo_board = servo.Servos(i2c=i2c)

for _servo in range(16):
    _servo_board.position(index=servo, degrees=0)

for _servo in range(16):
    _servo_board.position(index=servo, degrees=90)
for _servo in range(16):
    _servo_board.position(index=servo, degrees=180)

When i am running this programm I am getting the error message:

Traceback (most recent call last):
File “”, line 22, in
AttributeError: ‘module’ object has no attribute ‘Servos’ looks like this:

from pca9685 import PCA9685
import math

class Servos:
    def __init__(self, i2c, address=0x40, freq=50, min_us=600, max_us=2400,
        self.period = 1000000 / freq
        self.min_duty = self._us2duty(min_us)
        self.max_duty = self._us2duty(max_us)
        self.degrees = degrees
        self.freq = freq
        self.pca9685 = PCA9685(i2c, address)

    def _us2duty(self, value):
        return int(4095 * value / self.period)

    def position(self, index, degrees=None, radians=None, us=None, duty=None):
        span = self.max_duty - self.min_duty
        if degrees is not None:
            print('Winkel einstellen')
            duty = self.min_duty + span * degrees / self.degrees
        elif radians is not None:
            duty = self.min_duty + span * radians / math.radians(self.degrees)
        elif us is not None:
            duty = self._us2duty(us)
        elif duty is not None:
            return self.pca9685.duty(index)
        duty = min(self.max_duty, max(self.min_duty, int(duty)))
        self.pca9685.duty(index, duty)

    def release(self, index):
        self.pca9685.duty(index, 0)

What is causing the problem?